and LI Ning2
(1)
Radiology Department, Capital Medical University Beijing You’an Hospital, Beijing, China, People’s Republic
(2)
Capital Medical University Beijing You’an Hospital, Beijing, China, People’s Republic
Abstract
Fluoroscopy has the advantage of being simple to operate, which is appropriate for body parts with good innate contrast. Chest fluoroscopy is favorable to observe lungs, heart and major blood vessels. Abdominal fluoroscopy is preferably applied to observe subdiaphragmatic free air and gastrointestinal obstruction. In addition, various contrast imaging and interventions are commonly performed with assistance of fluoroscopy.
9.1 Techniques of Conventional X-ray and Digital X-ray
9.1.1 Conventional X-ray Techniques
9.1.1.1 Fluoroscopy
Fluoroscopy has the advantage of being simple to operate, which is appropriate for body parts with good innate contrast. Chest fluoroscopy is favorable to observe lungs, heart and major blood vessels. Abdominal fluoroscopy is preferably applied to observe subdiaphragmatic free air and gastrointestinal obstruction. In addition, various contrast imaging and interventions are commonly performed with assistance of fluoroscopy.
In addition to simple operation, fluoroscopy also has advantages of facilitating diagnosis by showing morphological changes and dynamic activities of the organs from multiple perspectives. However, its disadvantages include unclear demonstrations of the imaging details, difficulty protection, exposure of the patients to large amount of radioactive rays and difficulty in keeping permanent records.
9.1.1.2 Conventional X-ray
The conventional X-ray is clinically the most common and basic diagnostic imaging method. It can be applied to any body parts and the X-ray film is clinically referred to as plain film.
The conventional X-ray has advantages of widely applicable body parts, high resolution in space destiny, clear demonstration of image details and being capable of keeping permanent records for convenient review and consultation. In addition, the exposure of the patients to radioactive rays is less than that by fluoroscopy. However, its demonstration areas are limited by the size of the film and dynamic activities of the organs cannot be demonstrated with conventional X-ray.
9.1.2 Digital X-ray Techniques
9.1.2.1 Computerized Radiography (CR)
Working Principles of CR
CR is a relatively mature technology in digitalizing X-ray plain film. It gives up films as the carrier of imaging data, but adopts imaging plate (IP) as the carrier of imaging data being readable by laser. The digital plain image of a body part is demonstrated by its exposure to X-ray and data readout processing.
Clinically Application of CR System
1.
Application in head-neck and osteoarticular system
CR is superior to traditional X-ray radiography in displaying bone structure, articular cartilage and soft tissue. The density resolution of CR image is significantly higher than that of the traditional X-ray film. In the semi-quantitative study of osteoporosis, CR is advantageous over the traditional screen-film system. CR system can clearly demonstrate the structure of auditory ossicle, vestibular and semicircular canal. It can also exactly display the bone destruction of nasal sinus wall.
2.
Application in chest
Generally, CR chest radiography is superior to traditional chest X-ray, especially in displaying the overlapping part of mediastinum and diaphragm. In addition, CR also has advantages in detecting pulmonary nodular diseases and displaying mediastinal structures including vascular system and trachea. However, in displaying interstitial and alveolar lesions, traditional chest X-ray is preferable to CR.
3.
Application in gastrointestinal and urinary systems
CR is better than traditional X-ray in displaying intestinal pneumatosis, pneumoperitoneum and calculus. In the double contrast examination of gastrointestinal tract, CR system is superior in displaying gastric area, minimal foci, mucosal folds and colonic innominate groove to traditional X-ray radiography. In the diagnostic examination of urinary system, CR has improved resolution to show the soft tissues and displays well urinary stones and small calcified foci.
4.
Others
In addition to above mentioned advantages, CR is also advantageous in displaying breast lesions and can be applied in pediatrics and angiography.
Advantages and Disadvantages of CR
CR system digitalizes the conventional X-ray data and optimizes the resolution of images to display better the inner structure of human body. The digitized data can be processed by computer techniques to improve the demonstrations. CR system also decreases the dosage of radioactive rays and realizes the digital storage, representation and transmission of X-ray data.
Meanwhile, CR system also has its disadvantages, namely poor temporal resolution which results in unfavorable dynamic displaying of organs and structures. In addition, its spatial resolution (displaying microstructures such as pulmonary markings) is poorer than traditional X-ray screen-film system. However, CR basically can facilitate the clinical diagnosis and its disadvantages can be compensated by adjusting the contrast.
9.1.2.2 Digital Radiography (DR)
Working Principles of DR
Based on the X-ray television system, DR transports analog video signals through sampling and analog to digit (A/D) transformation into computer to form digital matrix image.
DR can be performed by various ways, including cartridge, direct digital radiography and charge-coupled camera array.
Application of DR
The application range of DR is basically the same as that of CR.
Advantages and Disadvantages of DR
DR has advantages of high resolution, clear demonstration of image details, small dosage of radioactive rays and large exposure latitude. Being the same as CR, DR system also has advantages of post-processing images according to clinical requirement and direct access to images stored in transmission system, which greatly facilitates its clinical application, pedagogy and telemedicine.
9.2 Computerized Tomography (CT)
Computed tomography (CT) is invented and designed by Conmack Am and Hounsfield CN. Compared to traditional X-ray radiography, CT images are the real section images displaying the tissues density distribution of certain section of human body. Due to clear demonstrations, high density resolution and no interference from other tissues and structures, CT scanning significantly extends the range of physical examination and increases the detection rate of lesions and accuracy of diagnosis, which dramatically promotes the development of diagnostic imaging.
9.2.1 Basic Principles of CT Imaging
CT is to scan a body section with certain thickness by X-ray bundle. A detector receives X-ray attenuated values by human tissues from various directions of this section. The received values are then transmitted into a computer via analog to digit (A/D) transformation for computerized processing. The resulted tissue attenuation coefficient matrix of the scanned section is then via digit to analog (D/A) transformation to be shown on a screen with different grayness levels, namely a CT image.
According to the tissue components and density differences of examined body parts, the reconstruction of CT images should employ appropriate mathematical calculations, usually including standard algorithm, soft tissue algorithm and bone algorithm. Improper choice of algorithm would decrease the resolution of CT images.
9.2.2 Basic Concepts
9.2.2.1 Voxel and Pixel
A CT image presumably divides a body section with certain thickness into several small cubes in matrix arrangement, namely basic units. A CT value comprehensively represents the material density in a unit and these small units are called voxel. Being correspondent to voxel, a CT image is composed of lots of small units in matrix arrangement and these basic units of CT images are called pixel. Actually, pixel is the representation of voxel in images. Small pixel represents high resolution.
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