Technical and Personnel Requirements

Fig. 2.1

Comparison of 16-row (Panel A) and 64-row CT coronary angiography (Panel B) of the right coronary artery (curved multiplanar reformation) in a 61-year-old male patient. 64-row CT shows longer vessel segments, especially in the periphery (arrow). This enhanced performance can be explained by fewer motion artifacts (due to breathing, extrasystoles, or variations in the length of the cardiac cycle) and the better contrast between arteries and veins resulting from the faster scan and consequently better depiction of the arterial phase. The improved depiction of the arterial phase using 64-row CT is also demonstrated in Fig. 2.2. Panel B also illustrates the slightly higher image noise with 64-row CT, which can be compensated for by the better depiction of the arterial phase and the higher intravascular density. Ao aorta

Fig. 2.2

The improved depiction of the arterial phase using 64-row CT (Panel B) and even further using 320-row CT (Panel C) when compared with 16-row CT (Panel A) is illustrated by a double oblique coronal slice along the left ventricular outflow tract, with the aortic valve nicely depicted (Ao). In the craniocaudal direction, the density in the aorta and left ventricle shows less variation and decline when 64 simultaneous detector rows are used (Panel C) and almost no difference with 320-row CT acquired during a single heartbeat. Use of 64- and 320-row CT thus improves image quality and facilitates the application of automatic coronary vessel and cardiac function analysis tools

Fig. 2.3

Example illustrating the improved depiction of distal coronary artery branches using 64-row (Panel B) and 320-row CT (Panel C) in a 58-year-old female patient. Three-dimensional volume-rendered reconstructions of the left coronary artery with the left anterior descending (LAD) and left circumflex coronary artery (LCX) examined using 16-row (Panel A), 64-row (Panel B), and 320-row CT coronary angiography (Panel C). Note the improved depiction of smaller side branches with the 64-row (arrows in Panel B) and 320-row technology (arrows in Panel C) when compared with the same segments in 16-row CT (Panel A). Also, there is best depiction of the arterial phase (with less venous overlap, arrowheads in Panel C) using 320-row CT. Single-beat imaging using 320-row CT or second-generation dual-source CT with a fast prospective spiral also greatly reduces radiation exposure (Chap. 7). Ao aorta

Table 2.1

Typical characteristics of 16- and 64-row as well as single-heartbeat CT scanners

	16-row	64-row	Single heart beat CT^a
Slice collimation
Coronary arteries	0.5–0.75 mm	0.5–0.75 mm	0.5–0.6 mm
Coronary bypass grafts	0.5–1.25 mm	0.5–0.75 mm	0.5–0.6 mm
Gantry rotation time
Coronary angiography	0.4–0.6 s	0.27–0.4 s	0.28–0.35 s
Scan length
Coronary arteries	9–13 cm	Increase by 15%^b	9–13 cm
Coronary bypass grafts	12.5–22 cm	Increased by 5–10%	12.5–22 cm^c
Effective radiation dose
Coronary arteries	5–15 mSv	10–20 mSv^d	1–5 mSv
Coronary bypass grafts	10–30 mSv	20–40 mSv^d	2–10 mSv
Contrast-to-noise ratio
Coronary angiography	15–25	Similar	Similar
Vessel lengths free of motion
Coronary angiography		Improved by 10–30%^e	Further improvements expected
Breath-hold time ^f
Coronary arteries	25–30 s	8–12 s	3 s
Coronary bypass grafts	40–50 s	12–15 s	5 s
Contrast agent amount
Coronary arteries	90–130 ml	60–90 ml	40–70 ml
Coronary bypass grafts	130–160 ml	80–110 ml	50–80 ml

^a CT of the heart during a single beat can be performed using 320-row volume CT (Chap. 9a) and second- or third- generation dual-source CT with a fast spiral acquisition (Chap. 9b)

^b This increase is due to the larger overranging effect of 64-row CT, which in turn also increases radiation exposure by 15%

^c Bypass grafts are scanned with 320-row CT in two heartbeats and with dual-source CT in the caudocranial direction with the proximal parts of the bypass grafts covered during the next R-wave and early systole of the next beat

^d The values given here are for retrospectively acquired data. The increase in effective dose with 64-row CT can be explained by the larger overranging effect, the fact that scanning cannot be stopped as abruptly once the lower border of the heart has been reached because of the faster table speed, and the higher mA settings necessary (because of the increased scattered radiation and noise with 64-row CT). Using prospectively acquired data with 64-row CT, effective dose can be drastically reduced to below 5 mSv in nearly all patients with stable and low heart rates (<65 beats per minute). See Chap. 7

^e The increase in the visible vessel length free of motion that can be obtained for the three coronary arteries with 64-row CT scanners is approximately 10% for the left anterior descending, 20% for the left circumflex, and 30% for the right coronary. Most notably, in more than one-third of all cases, the length of the right coronary free of motion is increased by more than 5 cm when 64-row CT is used

^f This includes a 2–3 s wait period after the breathing command before scanning to assure normalization of heart rate after inspiration

Fig. 2.4

Arterial bypass graft (left internal mammary artery, LIMA), which extends all the way down to the LAD and was scanned in less than 15 s, using a 64-row CT scanner. With this technology, preoxygenation is no longer necessary for bypass imaging. With 16-row technology, the scanning took an average of 40–50 s, and preoxygenation was almost always required. Note that CT nicely depicts the distance between the sternum and coronary bypass graft, which can be of relevance if repeat cardiac surgery is considered. Bypass imaging time can be further shortened with 320-row CT and second-generation dual-source CT (Table 2.1)

List 2.1. Technical requirements for cardiac CT

CT scanner with at least 64 simultaneous rows

CT scanner with a gantry rotation time of below 400 ms

Adaptive multisegment reconstruction or dual- source CT

ECG for gating or triggering^a of acquisitions

Dual-head contrast agent injector for saline flush

Workstation with automatic curved multiplanar reformation and three-dimensional data segmentation and analysis capabilities

^a This refers to the acquisition method: retrospective (ECG gating) or prospective (ECG triggering). See Chap. 7 for details on radiation exposure reduction using ECG triggering

Temporal resolution can be significantly improved by using two simultaneous X-ray sources (dual-source CT, Siemens) and adaptive multisegment reconstruction (Toshiba, Philips, and GE). We believe that one of these two approaches should be implemented on cardiac CT scanners to reduce the influence of heart rate on image quality (List 2.1). In addition to these technical improvements, beta blocker administration should be used whenever possible to lower the heart rate to below approximately 60 beats per min, because slowing the heart rate to this level further improves both the image quality and the diagnostic accuracy (Chaps. 6

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