Computed tomographic (CT) imaging utilizing the x-ray technology was developed in the early 1970s, and has been used extensively for its ability to provide cross-sectional images of the body . There has been a rapid development of CT technology, particularly in the last 10 years, focused on cardiac imaging. The latest generation CT scanners, namely the multidetector CT (MDCT), provide excellent spatial resolution, and allow accurate high-resolution assessment of morphological detail of both ventricles [51-52]. Intravenous injection of a non-ionic contrast agent provides excellent contrast resolution with clear delineation of the ventricular endocardium. Multiple cardiac phases can be extracted, with animated movies of the beating heart made available for visual assessment of global and regional function. Quantitative determinations of ventricular mass, right and left ventricular volumes, and global ventricular function can be performed in a variety of cardiac pathologic states . CT is fast, easy to perform, and has good im age quality. Although images are acquired only in the axial plane, the acquisition of a 3-dimensional dataset allows reformatting in any desirable plane. For the above reasons CT is a clinically valuable, noninvasive tool for assessment of myocardial pathology.
Similar to MR imaging, CT imaging also has the capability to provide tissue characterization of the myocardium. Using CT, Dery et al.  were the first to demonstrate a dilated hypokinetic right ventricle with a markedly thin anterior wall and normal left-sided chambers in an elderly patient with ARVC/D and RV failure. The ability of conventional CT to detect intramyocardial fat in ARVC/D was first reported by Villa et al.  in a series of seven patients with ARVC/D; subsequently, Sotozono et al.  provided biopsy confirmation of CT findings. They also demonstrated the ability of CT imaging to provide excellent anatomic details of the RV and the LV in a patient with advanced ARVC/D. Since that time, there have been only a few investigators who have used CT to image ARVC/D.
CT Imaging Findings in ARVC/D
Hamada et al.  imaged four ARVC/D patients who had abnormalities on electrocardiography and angiography using electron bean CT (EBCT). With contrast enhanced volume mode scanning they were able to demonstrate morphologic abnormalities in ARVC/D: (a) abundant epicardial fat, (b) low attenuation trabeculations, (c) scalloping of RV free wall, and (d) intramyocardial fat deposits. Quantification of ventricular volumes was performed on cine mode scanning, which showed regional dysfunction and depressed global RV function respectively. Tada et al.  added ten more ARVC/D patients to the above series and compared electron beam CT findings in 16 age-matched, non-ARVC/D patients with RV dilation/ dysfunction with 13 control subjects. Intramyocar-dial fat was defined based on tissue attenuation values. The attenuation value for epicardial adipose tissue is approximately —65±10 Hounsfield units (HU), and 5 to -17 HU for intramyocardial fat, which is far less than that of myocardium. Using the above values, none of the control subjects, and no patient without ARVC/D showed any evidence of intramyocardial fat, or any other qualitative features of ARVC/D as described by Tada et al. . The frequencies of abundant epicardial fat, low-attenuation trabeculae, scalloping and intramyocar-
dial fat in this study were 86%, 71%, 79%, and 50% respectively. An important finding of this study was that the abnormal area on EBCT corresponded to the areas of abnormality on electroanatomic mapping, and was frequently larger than the elec-troanatomic maps.
Kimura et al.  studied 32 ARVC/D patients using contrast enhanced, nongated, single row detector helical CT. Similar to the findings of EBCT, they found intramyocardial fat, RV enlargement, hy-pertrophied trabeculations, and abundant epicardial fat in patients with ARVC/D. This study also provided radiologic and pathologic correlation in one autopsied heart with ARVC/D, illustrating the applicability of widely available helical CT in ARVC/D evaluation. There have been no reports on the use of multidetector CT in ARVC/D. We recently reviewed our experience with MDCT in 17 patients with ARVC/D . Thirteen out of the 17 patients (76%) had RV intramyocardial fat (76%). Two of these patients had both RV and LV intramyocardial fat (Fig. 15.9). ARVC/D patients had increased RV volumes and RVOT dilation (Fig. 15.10), which correlated well with MR imaging-derived volumes in the same patients. However, in two patients, ICD lead artifacts deteriorated the image quality. We also encountered misregistration during reformatting due to motion artifacts mainly caused by arrhythmias, precluding evaluation of wall motion.
Current Role of CT in ARVC/D
Most centers currently rely on MR imaging instead of CT imaging for evaluating patients with suspected ARVC/D mainly because the former technique is devoid of radiation. However, many patients who are diagnosed with ARVC/D receive implantable defibrillators for prevention of sudden death. CT is often used to assess RV structure and function for serial morphologic evaluation.
CT is also useful in the occasional patient who has frequent premature beats resulting in arrhythmic artifacts on MR imaging, and also in patients who are claustrophobic. An additional use of CT imaging is to assess the lung fields for evidence of sarcoidosis, which occasionally mimics ARVC/D .
MDCT radiation can be quite high, exceeding conventional angiography by a factor of two when performing retrospective gating . Thus, MDCT may not be ideal for screening for ARVC/D in young, first-degree relatives. The current temporal resolution of CT (approximately 150msec) is still suboptimal compared to MR imaging . Despite the above limitations, CT provides certain advantages over MR imaging in terms of consistency in image quality, scan time, operator dependency, etc. With increase in familiarity of radiologists with the use of helical CT for ARVC/D and with the advances in both the temporal and spatial resolution, CT imaging may play an important role both in the diagnosis and in the follow-up of patients with ARVC/D.
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