The circulatory system^* has two complex systems of intimately associated vessels. Through these vessels, fluid is transported throughout the body in a continuous, unidirectional flow. The major portion of the circulatory system transports blood and is called the blood-vascular system (Fig. 25-1). The minor portion, called the lymphatic system, collects fluid from the tissue spaces. This fluid is filtered throughout the lymphatic system, which conveys it back to the blood-vascular system. The fluid conveyed by the lymphatic system is called lymph. Together, the blood-vascular and lymphatic systems carry oxygen and nutritive material to the tissues. They also collect and transport carbon dioxide (CO₂) and other waste products of metabolism from the tissues to the organs of excretion: the skin, lungs, liver, and kidneys.

Fig. 25-1 Major arteries and veins: red, arterial; blue, venous; purple, portal.

Blood-Vascular System

The blood-vascular system consists of the heart, arteries, capillaries, and veins. The heart serves as a pumping mechanism to keep the blood in constant circulation throughout the vast system of blood vessels. Arteries convey the blood away from the heart. Veins convey the blood back toward the heart.

Two circuits of blood vessels branch out of the heart (Fig. 25-2). The first circuit is the arterial circuit or the systemic circulation, which carries oxygenated blood to the organs and tissues. Every organ has its own vascular circuit that arises from the trunk artery and leads back to the trunk vein for return to the heart. The systemic arteries branch out, treelike, from the aorta to all parts of the body. The arteries are usually named according to their location. The systemic veins usually lie parallel to their respective arteries and are given the same names.

Fig. 25-2 Pulmonary, systemic, and portal circulation: oxygenated (red), deoxygenated (blue), and nutrient-rich (purple) blood.

The second circuit is the pulmonary circulation, which takes blood to the lungs for CO₂ exchange and for the reoxygenation of the blood, which is carried back to the arterial systemic circulation. The pulmonary trunk arises from the right ventricle of the heart; passes superiorly and posteriorly for a distance of about 2 inches (5 cm); and then divides into two branches, the right and left pulmonary arteries. These vessels enter the root of the respective lung and, following the course of the bronchi, divide and subdivide to form a dense network of capillaries surrounding the alveoli of the lungs. Through the thin walls of the capillaries, the blood discharges CO₂ and absorbs oxygen from the air contained in the alveoli. The oxygenated blood passes onward through the pulmonary veins for return to the heart. In the pulmonary circulation, the deoxygenated blood is transported by the pulmonary arteries, and the oxygenated blood is transported by the pulmonary veins.

Two main trunk vessels arise from the heart. The first is the aorta for the systemic circulation: The arteries progressively diminish in size as they divide and subdivide along their course, finally ending in minute branches called arterioles. The arterioles divide to form the capillary vessels, and the branching process is then reversed: The capillaries unite to form venules, the beginning branches of the veins, which unite and reunite to form larger and larger vessels as they approach the heart. These venous structures empty into the right atrium, then into the right ventricle, and then into the second main trunk that arises from the heart—the pulmonary trunk, or the pulmonary circulation. The process of oxygen exchange is carried out in small venous structures and then in larger and larger pulmonary veins. The pulmonary veins join to form four large veins (two from each lung), which empty into the left atrium, then into the left ventricle, and then into the aorta, which starts the circulation again throughout the body.

The pathway of venous drainage from the abdominal viscera to the liver is called the portal system. In contrast to the systemic and pulmonary circuits, which begin and end at the heart, the portal system begins in the capillaries of the abdominal viscera and ends in the capillaries and sinusoids of the liver. The blood is filtered and then exits the liver via the hepatic venous system, which empties into the inferior vena cava just proximal to the right atrium.

The systemic veins are arranged in a superficial set and in a deep set with which the superficial veins communicate; both sets converge at a common trunk vein. The systemic veins end in two large vessels opening into the heart: The superior vena cava leads from the portion of the body above the diaphragm, and the inferior vena cava leads from below the level of the diaphragm.

The capillaries connect the arterioles and venules to form networks that pervade most organs and all other tissues supplied with blood. The capillary vessels have exceedingly thin walls through which the essential functions of the blood-vascular system take place: The blood constituents are filtered out, and the waste products of cell activity are absorbed. The exchange takes place through the medium of tissue fluid, which is derived from the blood plasma and is drained off by the lymphatic system for return to the blood-vascular system. The tissue fluid undergoes modification in the lymphatic system. As soon as this tissue fluid enters the lymphatic capillaries, it is called lymph.

The heart is the central organ of the blood-vascular system and functions solely as a pump to keep the blood in circulation. It is shaped like a cone and measures approximately 4¾ inches (12 cm) in length, 3½ inches (9 cm) in width, and 2½ inches (6 cm) in depth. The heart is situated obliquely in the central mediastinum, largely to the left of the midsagittal plane. The base of the heart is directed superiorly, posteriorly, and to the right. The apex of the heart rests on the diaphragm against the anterior chest wall and is directed anteriorly, inferiorly, and to the left.

The muscular wall of the heart is called the myocardium. Because of the force required to drive blood through the extensive systemic vessels, the myocardium is about three times as thick on the left side (the arterial side) as on the right (the venous side). The membrane that lines the interior of the heart is called the endocardium. The heart is enclosed in the double-walled pericardial sac. The exterior wall of this sac is fibrous. The thin, closely adherent membrane that covers the heart is referred to as the epicardium or, because it also serves as the serous inner wall of the pericardial sac, the visceral pericardium. The narrow, fluid-containing space between the two walls of the sac is called the pericardial cavity.

The heart is divided by a septa into right and left halves, with each half subdivided by a constriction into two cavities, or chambers. The two upper chambers are called atria, and each atrium consists of a principal cavity and a lesser cavity called the auricle. The two lower chambers of the heart are called ventricles. The opening between the right atrium and right ventricle is controlled by the right atrioventricular (tricuspid) valve, and the opening between the left atrium and left ventricle is controlled by the left atrioventricular (mitral or bicuspid) valve.

The atria and ventricles separately contract (systole) in pumping blood and relax or dilate (diastole) in receiving blood. The atria precede the ventricles in contraction; while the atria are in systole, the ventricles are in diastole. One phase of contraction (referred to as the heartbeat) and one phase of dilation are called the cardiac cycle. In the average adult, one cardiac cycle lasts 0.8 second. The heart rate, or number of pulsations per minute, varies, however, with size, age, and gender. Heart rate is faster in small persons, young individuals, and females. The heart rate is also increased with exercise, food, and emotional disturbances.

The atria function as receiving chambers. The superior and inferior venae cavae empty into the right atrium (Fig. 25-3); the two right and left pulmonary veins empty into the left atrium. The ventricles function as distributing chambers. The right side of the heart handles the venous, or deoxygenated, blood, and the left side handles the arterial, or oxygenated, blood. The left ventricle pumps oxygenated blood through the aortic valve into the aorta and the systemic circulation. The three major portions of the aorta are the ascending aorta, the aortic arch, and the descending aorta. The right ventricle pumps deoxygenated blood through the pulmonary valve into the pulmonary trunk and the pulmonary circulation.

Fig. 25-3 Heart and great vessels: deoxygenated blood flow (black arrows); oxygenated blood flow (white arrows).

Blood is supplied to the myocardium by the right and left coronary arteries. These vessels arise in the aortic sinus immediately superior to the aortic valve (Fig. 25-4). Most of the cardiac veins drain into the coronary sinus on the posterior aspect of the heart, and this sinus drains into the right atrium (Fig. 25-5).

Fig. 25-4 Anterior view of coronary arteries.

Fig. 25-5 Anterior view of coronary veins.

The ascending aorta arises from the superior portion of the left ventricle and passes superiorly and to the right for a short distance. It then arches posteriorly and to the left and descends along the left side of the vertebral column to the level of L4, where it divides into the right and left common iliac arteries. The common iliac arteries pass to the level of the lumbosacral junction, where each ends by dividing into the internal iliac, or hypogastric, artery and the external iliac artery. The internal iliac artery passes into the pelvis. The external iliac artery passes to a point about midway between the anterior superior iliac spine and pubic symphysis and then enters the upper thigh to become the common femoral artery.

The velocity of blood circulation varies with the rate and intensity of the heartbeat. Velocity also varies in the different portions of the circulatory system based on distance from the heart. The speed of blood flow is highest in the large arteries arising at or near the heart because these vessels receive the full force of each wave of blood pumped out of the heart. The arterial walls expand with the pressure from each wave. The walls then rhythmically recoil, gradually diminishing the pressure of the advancing wave from point to point, until the flow of blood is normally reduced to a steady, nonpulsating stream through the capillaries and veins. The beat, or contraction and expansion of an artery, may be felt with the fingers at several points and is called the pulse.

Complete circulation of the blood through the systemic and pulmonary circuits, from a given point and back again, requires about 23 seconds and an average of 27 heartbeats. In certain contrast examinations of the cardiovascular system, tests are conducted to determine the circulation time from the point of contrast medium injection to the site of interest.

Lymphatic System

The lymphatic system consists of an elaborate arrangement of closed vessels that collect fluid from the tissue spaces and transport it to the blood-vascular system. Almost all lymphatic vessels are arranged in two sets: (1) a superficial set that lies immediately under the skin and accompanies the superficial veins and (2) a deep set that accompanies the deep blood vessels and with which the superficial lymphatics communicate (Fig. 25-6). The lymphatic system lacks a pumping mechanism such as the heart of the bloodvascular system. The lymphatic vessels are richly supplied with valves to prevent backflow, and the movement of the lymph through the system is believed to be maintained largely by extrinsic pressure from the surrounding organs and muscles.

Fig. 25-6 Lymphatic system: green, superficial; black, deep.

The lymphatic system begins in complex networks of thin-walled, absorbent capillaries situated in the various organs and tissues. The capillaries unite to form larger vessels, which form networks and unite to become still larger vessels as they approach the terminal collecting trunks. The terminal trunks communicate with the blood-vascular system.

The lymphatic vessels are small in caliber and have delicate, transparent walls. Along their course the collecting vessels pass through one or more nodular structures called lymph nodes. The nodes occur singly but are usually arranged in chains or groups of 2 to 20. The nodes are situated so that they form strategically placed centers toward which the conducting vessels converge. The nodes vary from the size of a pinhead to the size of an almond or larger. They may be spherical, oval, or kidney-shaped. Each node has a hilum through which the arteries enter and veins and efferent lymph vessels emerge; the afferent lymph vessels do not enter at the hilum. In addition to the lymphatic capillaries, blood vessels, and supporting structures, each lymph node contains masses, or follicles, of lymphocytes that are arranged around its circumference and from which cords of cells extend through the medullary portion of the node.

Numerous conducting channels, here called afferent lymph vessels, enter the node opposite the hilum and break into wide capillaries that surround the lymph follicles and form a canal known as the peripheral or marginal lymph sinus. The network of capillaries continues into the medullary portion of the node, widens to form medullary sinuses, and then collects into several efferent lymph vessels that leave the node at the hilum. The conducting vessels may pass through several nodes along their course, each time undergoing the process of widening into sinuses. Lymphocytes—a variety of white blood cells formed in the lymph nodes—are added to the lymph while it is in the nodes. It is thought that most of the lymph is absorbed by the venous system from these nodes, and only a small portion of the lymph is passed on through the conducting vessels.

The absorption and interchange of tissue fluids and cells occur through the thin walls of the capillaries. The lymph passes from the beginning capillaries through the conducting vessels, which eventually empty their contents into terminal lymph trunks for conveyance to the blood-vascular system. The main terminal trunk of the lymphatic system is called the thoracic duct. The lower, dilated portion of the duct is known as the cisterna chyli. The thoracic duct receives lymphatic drainage from all parts of the body below the diaphragm and from the left half of the body above the diaphragm. The thoracic duct extends from the level of L2 to the base of the neck, where it ends by opening into the venous system at the junction of the left subclavian and internal jugular veins.

Three terminal collecting trunks—the right jugular, the subclavian, and the bronchomediastinal trunks—receive the lymphatic drainage from the right half of the body above the diaphragm. These vessels open into the right subclavian vein separately or occasionally after uniting to form a common trunk called the right lymphatic duct.

Lymphography is seldom performed in current practice because of the superior imaging capabilities of newer modalities such as magnetic resonance imaging (MRI) and computed tomography (CT) (Fig. 25-7). At present, it is primarily used to assess the clinical extent of lymphomas or to stage radiation treatment. Lymphography may also be indicated in patients who have clinical evidence of obstruction or other impairment of the lymphatic system. A more detailed description of lymphography is provided in previous editions of this text.

Fig. 25-7 Axial PET/CT of lymph nodes with lymphoma.

ANGIOGRAPHY

Definitions and Indications

Blood vessels are not normally visible on conventional radiography because no natural contrast exists between them and other soft tissues of the body. These vessels must be filled with a radiopaque contrast medium to delineate them for radiography. Angiography is a general term that describes the radiologic examination of vascular structures within the body after the introduction of an iodinated contrast medium or gas.

The visceral and peripheral angiography procedures identified in this chapter can be categorized generally as either arteriography or venography. Examinations are more precisely named for the specific blood vessel opacified and the method of injection.

Angiography is primarily used to identify the anatomy or pathologic process of blood vessels. Chronic cramping leg pain after physical exertion, a condition known as claudication, may prompt a physician to order an arteriogram of the lower limbs to determine whether atherosclerosis is diminishing the blood supply to the leg muscles. A stenosis or occlusion is commonly caused by atherosclerosis and is an indication for an arteriogram. Cerebral angiography is performed to detect and verify the existence and exact position of an intracranial vascular lesion such as an aneurysm. Although most angiographic examinations are performed to investigate anatomic variances, some evaluate the motion of the part. Other vascular examinations evaluate suspected tumors by opacifying the organ of concern; after a diagnosis is made, these lesions may be amendable to some type of intervention. Interventional radiology assists in the diagnosis of lesions and then is used to treat these lesions through an endovascular approach.

Historical Development

In January 1896, just 10 weeks after the announcement of Roentgen’s discovery, Haschek and Lindenthal announced that they had produced a radiograph showing the blood vessels of an amputated hand using Teichman’s mixture, a thick emulsion of chalk, as the contrast agent. This work heralded the beginning of angiography. The potential for this new type of examination to delineate vascular anatomy was immediately recognized. The advancement of angiography was hindered, however, by the lack of suitable contrast media and low-risk techniques to deliver the media to the desired location. By the 1920s, researchers were using sodium iodide as a contrast medium to produce lower limb studies comparable in quality to studies seen in modern angiography.

Limitations still existed. Until the 1950s, contrast medium was most commonly injected through a needle that punctured the vessel or through a ureteral catheter that passed into the body through a surgically exposed peripheral vessel. In 1952, shortly after the development of a flexible thin-walled catheter, Seldinger announced a percutaneous method of catheter introduction. The Seldinger technique eliminated the surgical risk, which exposed the vessel and tissues (see Fig. 25-16).

Fig. 25-16 Seldinger technique. A, The ideal puncture occurs in the femoral artery just below the inguinal ligament. B, Beveled compound needle containing an inner cannula pierces through the artery. C, Needle is withdrawn slowly until there is blood flow. D, The needle’s inner cannula is removed, and a flexible guidewire is inserted. E, Needle is removed; pressure fixes the wire and reduces hemorrhage. F, Catheter is slipped over the wire and into the artery. G, Guidewire is removed, leaving the catheter in the artery. (Modified Seldinger would puncture only here, on the anterior wall.)

Early angiograms consisted of single radiographs or the visualization of vessels by fluoroscopy. Because the advantage of serial imaging was recognized, cassette changers, roll film changers, cut film changers, and cine and serial spot-filming/digital devices were developed. Pumps to inject contrast media were also developed to allow more rapid and precise control of injection rates and volumes than were possible by hand. Early mechanical injectors were powered by pressurized gas, and the injection rate was a function of the pressure setting. Electrically powered automatic injectors were subsequently developed that allowed the injection rate to be precisely set.

Until the early 1990s, most angiograms recorded flowing contrast medium in a series of images that required rapid film changers or cinefluorography devices; however, presently digital subtraction angiography (DSA) systems are used almost exclusively. Although some institutions may still have rapid film changers, most often the filming technique is by DSA. The newer imaging equipment has much better image quality and can produce images at a rate of 30 frames per second. In addition, digital imaging is cost-effective because images are stored electronically, reducing the need for expensive film and film storage. Digital images can be archived and retrieved in seconds from within the institution or any network connection. DSA imaging provides the interventionalist with a variety of tools for image manipulation analysis and measurement.

Lower limb angiograms are now performed using specialized DSA imaging techniques such as bolus chasing or stepping DSA. These techniques involve motorized movement of the table or C-arm to follow contrast medium as it flows distally into the lower extremities.

Angiographic Studies

CONTRAST MEDIA

Opaque contrast medium containing organic iodine solutions is used in angiographic studies. Although usually tolerated, the injection of iodinated contrast medium may cause undesirable consequences. The contrast medium is subsequently filtered out of the bloodstream by the kidneys. It causes physiologic cardiovascular side effects, including peripheral vasodilation, blood pressure decrease, and cardiotoxicity. It may also produce nausea and an uncomfortable burning sensation in about 1 of 10 patients. Most significantly, the injection of iodinated contrast medium may invoke allergic reactions. These reactions may be minor (hives or slight difficulty in breathing) and require minimal treatment, or they may be severe and require immediate medical intervention. Severe reactions are characterized by a state of shock in which the patient exhibits shallow breathing and a high pulse rate and may lose consciousness. Historically, 1 of every 14,000 patients has a severe allergic reaction. The administration of contrast medium is one of the significant risks in angiography.

At the kilovolt (peak) (kVp) used in angiography, iodine is slightly more radiopaque, atom for atom, than lead. The iodine is incorporated into water-soluble molecules formed as triiodinated benzene rings. These molecules vary in exact composition. Some forms are organic salts that dissociate in solution and are ionic. The iodinated anion is diatrizoate iothalamate or ioxaglate. The radiolucent cation is meglumine, sodium, or a combination of both. These ionic forms yield two particles in solution for every three iodine atoms (a 3:2 ratio) and are six to eight times as osmolar as plasma.

Other triiodinated benzene rings are created as nonionic molecules. These forms have three iodine atoms on each particle in solution (a 3:1 ratio) because they do not dissociate and are only two to three times as osmolar as plasma. Studies indicate that these properties of nonionic contrast media result in decreased nephrotoxicity to the kidneys. Nonionic contrast media also cause fewer physiologic cardiovascular side effects, less intense sensations, and fewer allergic reactions.

Another form of contrast medium is a dimer, in which the two benzene rings are bonded together as the anion. Ionic contrast medium with a dimer results in six iodine atoms for every two particles in solution, which yields the same 3:1 ratio as a nonionic contrast medium. The ionic dimer has advantages over the ionic monomeric molecule, primarily by reducing osmolality, but it lacks some of the properties of the nonionic molecule. Nonionic contrast medium can also be found as a dimer, which yields a ratio of 6:1 because it does not dissociate into two particles, producing an osmolality similar to blood.

All forms of iodinated contrast media are available in various iodine concentrations. The agents of higher concentration are more opaque. Typically, 30% iodine concentrations are used for cerebral and limb arteriography, whereas 35% concentrations are used for visceral angiography. Peripheral venography may be performed with 30% or lower concentrations. Ionic agents of higher concentration and nonionic agents are more viscous and produce greater resistance in the catheter during injection.

Patients with a predisposition to allergic reaction may be pretreated with a regimen of antihistamines and steroids to help prevent anaphylactic reactions to contrast media. Patients who have a history of severe reaction to iodinated contrast medium or with compromised renal function may undergo procedures in which CO₂ is used as a contrast agent. CO₂ is less radiopaque than blood and appears as a negative or void in angiographic imaging. CO₂ is approved for use only below the diaphragm because the possibility of emboli is too great near the brain. CO₂ imaging is possible only in the DSA environment because it requires a narrow contrast window and the ability to stack or combine multiple images to provide a single image free of bubbles or fragmented vascular opacification. Specific kVp values should be employed to display the CO₂ optimally in contrast to the rest of the body.

INJECTION TECHNIQUES

Selective injection through a catheter involves placing the catheter within a vessel so that the vessel and its major branches are opacified. In a selective injection, the catheter tip is positioned into the orifice of a specific artery so that only that specific vessel is injected. This technique has the advantage of more densely opacifying the vessel and limiting the superimposition of other vessels.

A contrast medium may be injected by hand with a syringe but ideally should be injected by an automatic injector. The major advantage of automatic injectors is that a specific quantity of contrast medium can be injected during a predetermined period. Automatic injectors have controls to set the injection rate, injection volume, and maximum pressure. Another useful feature is a control to set a time interval during which the injector gradually achieves the set injection rate, which is the linear rise. This may prevent a catheter from being dislodged by whiplash.

Because the opacifying contrast medium is often carried away from the area of interest by blood flow, the injection and demonstration of opacified vessels usually occur simultaneously. The injector is often electronically connected to the rapid imaging equipment to coordinate the timing between the injector and the onset of imaging.

Digital Subtraction Angiographic Procedures

A DSA study begins with catheter placement performed in the same manner as for conventional angiography. Injection techniques vary, but typically similar rates and volumes are used as in cut film. An automatic pressure injector is used to ensure consistency of injection and to facilitate computer control of injection timing and image acquisition.

The intravascular catheter is positioned using conventional fluoroscopic apparatus and technique, and a suitable imaging position is selected. At this point, an image that does not have a large dynamic range should be established; no part of the image should be significantly brighter than the rest of the image. This image can be accomplished by proper positioning, but it often requires the use of compensating filters. The filters can be bags of saline or thin pieces of metal inserted in the imaging field to reduce the intensity of bright regions. Metal filters are often part of the collimator, and water or saline bags are placed directly on or adjacent to the patient. Some newer imaging systems have built-in compensating filters.

If proper placement of compensating filters is not performed, image quality is reduced significantly. Automatic controls in the system adjust the exposure factors so that the brightest part of the image is at that level. An unusually bright spot satisfies the automatic controls and causes the rest of the image to lie at significantly reduced levels, where the camera performance is worse. An alternative to proper filter placement is to adjust the automatic sensing region, similar to automatic exposure control (AEC) for conventional radiography, to exclude the bright region. This solution is less desirable than the use of compensating filters, and it is not always effective for some positions of the bright spot on the image. Proper positioning and technique are essential for high-quality imaging.

As the imaging sequence begins, an image that will be used as a subtraction mask (without contrast medium) is acquired, digitized, and stored in the digital memory. This mask image and those that follow are produced when the x-ray tube is energized and x-rays are produced, usually 1 to 30 exposures per second at 65 to 95 kVp and between 5 mAs and 1000 mAs. The radiation dose received by the patient for each image can be adjusted during installation. The dose may be reduced or the same as that used for a conventional radiograph. Images can be acquired at variable rates, from one image every 2 to 3 seconds up to 30 images per second.

The acquisition rate can also be varied during a run. Most commonly, images are acquired at a faster rate during the passage of iodine contrast medium through the arteries and then at a reduced rate in the venous phase, during which the blood flow is much slower. This procedure minimizes the radiation exposure to the patient but provides a sufficient number of images to show the clinical information. Each of these digitized images is electronically subtracted from the mask, and the subtraction image is amplified (contrast enhanced) and displayed in real time so that the subtraction images appear essentially instantaneously during the imaging procedure. The images are simultaneously stored on a digital disk.

Some DSA equipment allows the table or the image intensifier (II) or flat panel detector system to be moved during acquisition. The movement is permitted to “follow” the flow of iodine contrast material as it passes through the arteries. Sometimes called the “bolus chase” or “DSA stepping” method, this technique is particularly useful for evaluating the arteries in the pelvis and lower limb. Previously, several separate imaging sequences would be performed with the II or flat panel positioned in a different location for each sequence, but this method required an injection of iodine contrast material for each sequence. The bolus chase method requires only one injection of iodine, and the imaging sequence follows (or “chases”) the iodine as it flows down the limb. The imaging sequence may be preceded or followed by a duplicate sequence without iodine injection to enable subtraction. Occasionally, this method may need to be repeated because the contrast medium in one leg may flow faster than in the other.

Misregistration, a major problem in DSA, occurs when the mask and the images displaying the vessels filled with contrast medium do not exactly coincide. Misregistration is sometimes caused by voluntary movements of the patient, but it is also caused by involuntary movements such as bowel peristalsis or heart contractions. Preparing the patient by describing the sensations associated with injection of contrast medium and the importance of holding still can help eliminate voluntary movements. It is also important to have the patient suspend respiration during the procedure.

During the imaging procedure, the subtraction images appear on the display monitor (Fig. 25-8). Often a preliminary diagnosis can be made at this point or as the images are reviewed immediately after each exposure sequence. A formal reading session occurs after the patient study has been completed; the final diagnosis is made at that time.

Fig. 25-8 DSA image of common carotid artery showing stenosis (arrow) of internal carotid artery.

Some postprocessing is performed after each exposure sequence to improve visualization of the anatomy of interest or to correct misregistration. More involved postprocessing, including quantitative analysis, is performed after the patient study has been completed. The processed images are available on the computer monitor for review by the radiologist. Because the images are digital, it is possible to store them in a picture archive and communication system (PACS). PACS allows images to be archived in digital format on various computer devices, including magnetic tape and optical disk. The images also can be transmitted via a computer network throughout the hospital or to remote locations for consultation with an expert or the referring physician. As an alternative to digital storage and reading, hard copy images may be produced using a laser printer or multiformat camera, with several images appearing on each radiograph.

Fluoroscopy, cine, and DSA systems consist essentially of a flat panel digital detector containing the output phosphor similar to that of an image intensification system. In DSA, the fluoroscopic image is digitized into serial images that are stored by a computer. The computer subtracts an early image, the mask image (before contrast medium enters the vessel), from a later image (after the vessel opacifies) and displays the difference, or subtraction image, on the fluoroscopy monitor.

Imaging systems may be used either singly or in combination at right angles to obtain simultaneous frontal and lateral images of the vascular system under investigation with one injection of contrast medium. This arrangement of units is called a biplane imaging system (Fig. 25-9). When two image receptors operate together for simultaneous biplane imaging, exposures in both planes cannot be made at the same moment because scatter radiation would fog the opposite plane image. Yet biplane imagers must cycle exactly together so that synchronization can be electronically controlled. It is necessary to alternate the exposures in the two planes. The x-ray tubes in a biplane system must fire alternately to prevent exposure of the opposite II. In addition, the II that is not being exposed is “blanked” or is powered off for an instant so as not to receive any input from the opposite exposure. The difference in the alternating exposures is about 3 msec.

Fig. 25-9 Modern biplane digital angiography suite. (Courtesy GE Medical.)

Rapid serial radiographic imaging requires large focal-spot x-ray tubes capable of withstanding a high heat load. Magnification studies require fractional focus tubes with focal spot sizes of 0.1 to 0.3 mm. X-ray tubes may have to be specialized to satisfy these extreme demands. Rapid serial imaging also necessitates radiographic generators with high-power output. Because short exposure times are needed to compensate for all patient motion, the generators must be capable of producing high-milliampere output. The combination of high kilowatt–rated generators and rare earth film-screen technology significantly aids in decreasing the radiation dose to the patient while producing radiographs of improved quality, with the added advantage of prolonging the life of the high-powered generators and x-ray tubes.

A comprehensive angiography suite contains a great amount of equipment other than radiologic devices. Monitoring systems record patient electrocardiogram (ECG) data, blood pressure readings, and pulse oximetry. Emergency equipment includes resuscitation equipment (e.g., a defibrillator for the heart) and anesthesia apparatus. The cardiovascular and interventional technologist (CIT) must be familiar with the use of each piece of equipment (Fig. 25-10).

Fig. 25-10 Modern single-plane digital angiography suite. (Courtesy GE Medical.)

MAGNIFICATION

Magnification occurs intentionally and unintentionally in angiographic imaging sequences. DSA imaging allows different magnification levels by employing different focusing filters inside the image intensifier. This type of magnification can be increased by varying the distance of the image receptor. Intentional use of magnification can result in a significant increase in resolution of fine vessel recorded detail. Fractional focal spot tubes of 0.3 mm or less are necessary for direct radiographic magnification techniques. The selection of a fractional focal spot necessitates the use of low milliamperage. Short exposure time (1 to 200 msec) is necessary because the size and load capacity of the smaller focal spot.

The formula for manual magnification is:

The SID is the source–to–image-receptor distance, the SOD is the source-to-object distance, and the OID is the object–to–image-receptor distance. For a 2:1 magnification study using SID of 40 inches (101 cm), the focal spot and the image receptor are positioned 20 inches (50 cm) from the area of interest. A 3:1 magnification study using 40-inch (101-cm) SID is accomplished by placing the focal spot 13 inches (33 cm) from the area of interest and the image receptor 27 inches (68 cm) from the area of interest.

Unintentional magnification occurs when the area of interest cannot be placed in direct contact with the image receptor. This is particularly a problem in the biplane imaging sequence, in which the need to center the area of interest in the first plane may create some unavoidable distance of the body part to the image receptor in the second plane. Even in single-plane imaging, vascular structures are separated from the image receptor by some distance. The magnification that occurs as a result of these circumstances is frequently 20% to 25%. A 25% magnification occurs when a vessel within the body is 8 inches (20 cm) from the image receptor—OID of 8 inches (20 cm)—and SID is 40 inches (101 cm).

Angiographic images do not represent vessels at their actual size, and this must be taken into account when direct measurements are made from angiographic images. Increasing SID while maintaining OID can reduce unintentional magnification. Increasing SID may not be an option, however, if the increase in technical factors would exceed tube output capacity or exposure time maximum. When any measurement is necessary, the DSA postprocessing quantitative analysis programs require the angiographer to calibrate the system by measuring an object in the imaging field of known value. Some systems calibrate by using the known position of the table, the II or detector, and x-ray tube and the tube angulation.

THREE-DIMENSIONAL INTRAARTERIAL ANGIOGRAPHY

The latest diagnostic tool is threedimensional angiography. To acquire a three-dimensional model of a vascular structure, a C-arm is rotated around the region of interest (ROI) at speeds up to 60 degrees per second. The C-arm makes a preliminary sweep while mask images are acquired. Images are acquired at 7.5 to 30 frames per second. The C-arm returns to its initial position, and a second sweep is initiated. Just before the second sweep, contrast medium is injected to opacify the vascular anatomy. The second sweep matches mask images from the first sweep, producing a rotational subtracted DSA sequence. The DSA sequence is sent to a three-dimensional rendering computer where a three-dimensional model is constructed. This model provides an image that can be manipulated and analyzed. It has proved to be a valuable tool for interventional approaches and for evaluation before surgery. Various methods of vessel analysis are available with three-dimensional models. Aneurysm volume calculation, interior wall analysis, bone fusion, and device display all are possible (Figs. 25-11 and 25-12).

Fig. 25-11 Three-dimensional angiography provides for reconstruction of the vessels and the skeletal anatomy.

Fig. 25-12 Three-dimensional reconstruction of left internal carotid artery. Note the anterior communicating artery aneurysm (arrow).

Angiographic Supplies and Equipment

NEEDLES

Vascular access needles are necessary when performing percutaneous procedures. Needle size is based on the external diameter of the needle and is assigned a gauge size. To allow for appropriate guidewire matching, the internal diameter of the needle must be known. Vascular access needles come in different types, sizes, and lengths. The most commonly used access needle for adult cardiovascular procedures is an 18-gauge needle that is 2.75 inches (7 cm) long. This particular needle is compatible with a 0.035-inch guidewire, which is the most frequently used guidewire in cardiovascular procedures. Appropriate needle size is predicated on the type or size of guidewire needed, the size of the patient, and the targeted entry vessel. To decrease the chances of vascular complications, the smallest gauge needle that meets the above-mentioned criteria is used for vascular access. Access needles for pediatric patients come in smaller gauge sizes with shorter lengths (Fig. 25-13).

Fig. 25-13 Various needles used during catheterization.

The most widely used catheterization method is the Seldinger technique.¹ Seldinger described the method as puncture of both walls of the vessel (the anterior and posterior walls). The modified Seldinger technique allows for puncture of the anterior wall only and has become the preferred method. The steps of the technique are described in Fig. 25-16. The procedure is performed under sterile conditions. The catheterization site is suitably cleaned and surgically draped. The patient is given local anesthesia at the catheterization site. With this percutaneous technique, the arteriotomy or venotomy is no larger than the catheter itself, so hemorrhage is minimized. Patients can usually resume normal activity within 24 hours after the examination. In some diagnostic angiographic studies, the procedure can be performed in the early morning, and the patient may be discharged later that same day. Most often, an uncomplicated interventional procedure may be performed, and the patient recovers in an ambulatory care area and is discharged home usually within 24 hours. The risk of infection is less than in surgical procedures because the vessel and tissues are not exposed.

After a catheter is introduced into the blood-vascular system, it can be maneuvered by pushing, pulling, and turning the part of the catheter still outside the patient so that the part of the catheter inside the patient travels to a specific location. A wire is sometimes positioned inside the catheter to help manipulate and guide the catheter to the desired location. When the wire is removed from the catheter, the catheter is infused with sterile solution, most commonly heparinized saline, to help prevent clot formation. Infusing the catheter and assisting the physician in the catheterization process may be the responsibility of the CIT.

When the examination is complete, the catheter is removed. Pressure is applied to the site until complete hemostasis is achieved, but blood flow through the vessel is maintained. The patient is placed on complete bed rest and observed for the development of bleeding or hematoma. Newer closure devices, which close the vessel percutaneously, can also be used to close the puncture site.

When peripheral artery sites are unavailable, a catheter may sometimes be introduced into the aorta using the translumbar aortic approach. For this technique, the patient is positioned prone, and a special catheter introducer system is inserted percutaneously through the posterolateral aspect of the back and directed superiorly so that the catheter enters the aorta around the T11-12 level.

Catheters are produced in various forms, each with a particular advantage in shape, maneuverability or torque, and maximum injection rate (Fig. 25-17). Angiographic catheters are made of pliable plastic that allows them to straighten for insertion over the guidewire, also called a wire guide. They normally resume their original shape after the guidewire is withdrawn. It usually requires manipulation from the angiographer to resume its original shape, however. Catheters with a predetermined design or shape are maneuvered into the origins of vessels for selective injections. They may have only an end hole, or they may have multiple side holes. Some catheters have multiple side holes to facilitate high injection rates but are used only in large vascular structures for flush injections. A pigtail catheter is a special multiple–side hole catheter that allows higher volumes of contrast medium to be injected with less whiplash effect, causing less damage to the vessel being injected.

Fig. 25-17 Selected catheter shapes used for angiography. (Courtesy Cook, Inc., Bloomington, IN.)

Common angiographic catheters range in size from 4 Fr (0.05 inch) to 7 Fr (0.09 inch), although smaller or larger sizes may be used. Most angiographic catheters have inner lumens that allow them to be inserted over guidewires ranging from 0.032 to 0.038 inch in diameter.

Patient Care

Before the initiation of an angiographic procedure, it is appropriate to explain the process and the potential complications to the patient. Written consent is obtained after an explanation. Potential complications include a vasovagal reaction; stroke; heart attack; death; infection; bleeding at the puncture site; nerve, blood vessel, or tissue damage; and an allergic reaction to the contrast medium. Bleeding at the puncture site is usually easily controlled with pressure to the site. Blood vessel and tissue damage may require a surgical procedure. A vasovagal reaction is characterized by sweating and nausea caused by a decrease in blood pressure. The patient’s legs should be elevated, and intravenous (IV) fluids may be administered to help restore blood pressure. Minor allergic reactions to iodinated contrast media, such as hives and congestion, are usually controlled with medications and may not require treatment. Severe allergic reactions may result in shock, which is characterized by shallow breathing, high pulse rate, and possibly loss of consciousness. Angiography is performed only if the benefits of the examination outweigh the risks.

Patients are usually restricted to clear liquid intake and routine medications before undergoing angiography. Adequate hydration from liquid intake may minimize kidney damage caused by iodinated contrast media. Solid food intake is restricted to reduce the risk of aspiration related to nausea. Contraindications to angiography are determined by physicians and include previous severe allergic reaction to iodinated contrast media, severely impaired renal function, impaired blood clotting factors, and inability to undergo a surgical procedure or general anesthesia.

Because the risks of general anesthesia are greater than the risks associated with most angiographic procedures, conscious sedation may be used for the procedure. Thoughtful communication from the CIT and physician calms and reassures the patient. The CIT or physician should warn the patient about the sensations caused by the contrast medium and the noise produced by the imaging equipment. This information also reduces the patient’s anxiety and helps ensure a good radiographic series with no patient motion.

Preparation of Examining Room

The angiography suite and every item in it should be scrupulously clean. The room should be fully prepared, with every item needed or likely to be needed on hand before the patient is admitted. Cleanliness and advance preparation are of vital importance in procedures that must be carried out under aseptic conditions. The CIT should observe the following guidelines in preparing the room:

• Check the angiographic equipment and all working parts of the equipment, and adjust the controls for the exposure technique to be employed.

• Have restraining bands available for application in combative patients.

• Adapt immobilization of the head (by suitable strapping) to the type of equipment employed.

• Ensure patient information is entered correctly on aquisition equipment.

The sterile and nonsterile items required for introduction of the contrast medium vary according to the method of injection. The supplies specified by the interventionalist for each procedure should be listed in the angiographic procedure book. Sterile trays or packs, set up to specifications, can usually be obtained from the central sterile supply room. Otherwise, it is the responsibility of a qualified member of the interventional team to prepare them. Extra sterile supplies should always be on hand in case of a complication. Preparation of the room includes having life-support and emergency equipment immediately available.

Radiation Protection

As in all radiographic examinations, the patient is protected by filtration totaling not less than 2.5 mm of aluminum, by sharp restriction of the beam of radiation to the area being examined, and by avoidance of repeat exposures. In angiography, each repeated exposure necessitates repeated injection of the contrast material. For this reason, only skilled and specifically educated CITs should be assigned to participate in these examinations. Gonadal shielding should be available and used when it would not interfere with the examination.

Angiography suites should be designed to allow observation of the patient at all times and provide adequate protection to the physician and radiology personnel. These goals are usually accomplished with leaded glass observation windows.

Angiography Team

The angiography team consists of the physician (usually an interventional radiologist); the CIT; and other specialists, such as an anesthetist or a nurse. The CIT assists in performing procedures that require sterile technique. Other duties may include operating monitoring devices, emergency equipment, and radiographic equipment. Instruction in patient care techniques and sterile procedure is included in the basic preparation of the CIT.

Angiography in the Future

Visceral and peripheral angiography is a dynamic area that challenges angiographers to keep abreast of new techniques and equipment. New diagnostic modalities that reduce or eliminate irradiation may be developed and may replace many current angiographic procedures. Some diagnostic information can be obtained only through conventional angiographic methods, however. Consequently, angiography will continue to be used to examine vasculature and, through therapeutic procedures, to provide beneficial treatment. Noninvasive imaging techniques, such as ultrasound, magnetic resonance angiography, and CT angiography, are being used more often. These less invasive procedures may eliminate some diagnostic angiographic procedures, but at the present time, therapeutic procedures continue.

AORTOGRAPHY

The most satisfactory visualization of the aorta is achieved by placing a multihole catheter into the aorta at the desired level, using the modified Seldinger technique. Aortography is usually performed with the patient in the supine position for simultaneous frontal and lateral imaging, with the central ray perpendicular to the imaging system. For introduction of a translumbar aortic catheter, the patient must be in the prone position.

Thoracic Aortography

Thoracic aortography may be performed to rule out an aortic aneurysm or to evaluate congenital or postsurgical conditions. The examination is also used in patients with aortic dissection. Biplane imaging is recommended so that anteroposterior (AP) or posteroanterior (PA) and lateral projections can be obtained with one injection of contrast medium. The CIT observes the following guidelines:

• For lateral projections, move the patient’s arms superiorly so that they do not appear in the image.

• For best results, increase lateral SID, usually to 60 inches (152 cm), so that magnification is reduced.

• If biplane equipment is unavailable, use a single-plane 45-degree right posterior oblique (RPO) or left anterior oblique (LAO) body position, which often produces an adequate study of the aorta.

• For all projections, direct the perpendicular central ray to the center of the chest at the level of T7. The entire thoracic aorta should be visualized, including the proximal brachiocephalic, carotid, and subclavian vessels. The contrast medium is injected at rates ranging from 25 to 35 mL/sec for a total volume of 50 to 70 mL.

• Make the exposure at the end of suspended inspiration (Fig. 25-18).

Fig. 25-18 AP thoracic aorta that also shows right and left coronary arteries.

Abdominal Aortography

Abdominal aortography may be performed to evaluate abdominal aortic aneurysm (AAA), occlusion, or atherosclerotic disease. Simultaneous AP and lateral projections are recommended. The CIT observes the following guidelines:

• For the lateral projection, move the patient’s arms superiorly so that they are out of the image field.

• Usually, collimate the field in the AP aspect of the lateral projection.

• Direct the perpendicular central ray at the level of L2 so that the aorta is visualized from the diaphragm to the aortic bifurcation. The AP projection shows best the renal artery origins, the aortic bifurcation, and the course and general condition of all abdominal visceral branches. The lateral projection best shows the origins of the celiac and superior mesenteric arteries because these vessels arise from the anterior abdominal aorta.

• Make the exposure at the end of suspended expiration (Figs. 25-19 and 25-20).

Fig. 25-19 AP abdominal aorta.

Fig. 25-20 Lateral abdominal aorta.

Pulmonary Arteriography

Under fluoroscopic control, a catheter is passed from a peripheral vein through the vena cava and right side of the heart and into the pulmonary arteries. This technique is usually employed for a selective injection, and the examination is primarily performed for the evaluation of pulmonary embolic disease (Fig. 25-21). Pulmonary angiography has widely been replaced with pulmonary CT angiography because it provides superior imaging.

Fig. 25-21 Right pulmonary artery.

Selective Abdominal Visceral Arteriography

Abdominal visceral arteriographic studies (Fig. 25-22) are usually performed to visualize tumor vascularity or to rule out atherosclerotic disease, thrombosis, occlusion, and bleeding. An appropriately shaped catheter is introduced, usually from a transfemoral artery puncture, and advanced into the orifice of the desired artery. The CIT observes the following steps: