Image Quality and Reconstruction Intervals of Dual-Source CT Coronary Angiography

Imaging of the vulnerable plaque: noninvasive and invasive techniques

In a large proportion of previously asymptomatic individuals, sudden coronary death or acute myocardial infarction occurs as the first manifestation of coronary atherosclerosis. Imaging of coronary atheromatous plaques has traditionally centered on assessing the degree of luminal stenosis. The angiographic techniques that are routinely used to identify stenotic atherosclerotic lesions are unable to identify high-risk plaques; plaques prone to rupture and cause a cardiovascular event. This is partly due to the fact that the majority of culprit lesions that produce acute cardiovascular syndromes are not severely stenotic, possibly due to significant positive remodeling and reduced protective collateral circulation as well as because the risk of plaque rupture is more closely related to plaque content than plaque size. Recently, the focus of new imaging techniques is to identify the high risk plaques; the "vulnerable plaques." In this review, we will refer to the noninvasive and invasive techniques that can detect the vulnerable plaque.

Dual-energy CT of the heart--principles and protocols

The introduction of coronary CT angiography (cCTA) has reinvigorated the debate whether management of patients with suspected coronary artery disease (CAD) should be primarily based on physiological versus anatomical testing. Anatomical testing (i.e., cCTA or invasive catheterization) enables direct visualization and grading of coronary artery stenoses but has shortcomings for gauging the hemodynamic significance of lesions for myocardial perfusion. Conversely, rest/stress myocardial perfusion imaging (MPI) has been extensively validated for assessing the clinical significance of CAD by demonstrating fixed or reversible perfusion defects but has only limited anatomical information. There is early evidence that contrast medium enhanced dual-energy cCTA (DECT) has potential for the comprehensive analysis of coronary artery morphology as well as changes in myocardial perfusion. DECT exploits the fact that tissues in the human body and iodine-based contrast media have unique absorption characteristics when penetrated with different X-ray energy levels, which enables mapping the iodine (and thus blood) distribution within the myocardium. The purpose of this communication is to describe the practical application of this emerging technology for the comprehensive diagnosis of coronary artery disease in the context of the currently used tomographic imaging modalities (cCTA, nuclear MPI, MR MPI).

Effect of dual-source cardiac computed tomography on patient radiation dose in a clinical setting: comparison to single-source imaging

BACKGROUND

Dual-source computed tomography (DSCT) was introduced with significant hardware and software changes compared with single-source CT (SSCT), resulting in improved temporal resolution (83 ms) and the potential for improved image quality. The effect of these changes on radiation dose requirements for coronary CT angiography in clinical practice has not been investigated.

OBJECTIVE

We evaluated patient radiation dose and image quality of electrocardiogram (ECG)-gated helical techniques, using DSCT compared with SSCT for clinical imaging of the coronary arteries.

METHODS

DSCT data from 160 patients were evaluated; 82 patients (DSCT group 1) were imaged with early software, and 78 patients (DSCT group 2) were imaged with a later software version. Patients imaged with SSCT (n = 124) were the control group. Effective radiation dose values were estimated for all patients. Image noise was measured, and image quality was evaluated on a 5-point scale.

RESULTS

Effective dose values for DSCT group 2 (11.7 +/- 4.0 mSv) were not different from those for SSCT group (10.9 +/- 2.9 mSv); the highest doses, 13.2 +/- 3.2 mSv, were recorded for DSCT group 1 (P < 0.001). A decrease in image noise was observed for DSCT compared with SSCT (P <or= 0.001) as was an increase in image quality (P < 0.01). With optimized DSCT imaging, lower dose values were associated with (1) shorter scan range, (2) lower maximum tube current, and (3) lower fraction of R-R interval receiving maximum tube current.

CONCLUSION

ECG-gated helical DSCT can provide images of the coronary arteries with improved image quality and decreased noise without an increase in radiation dose compared with SSCT in clinical patient groups.

Prevalence and morphology of coronary artery ectasia with dual-source CT coronary angiography

To assess the prevalence and morphological characteristics of coronary artery ectasia (CAE) with CT coronary angiography (CTCA) in comparison to conventional catheterangiography (CCA). Dual-source CTCA examinations from 677 consecutive patients (223 women; median age 57 years) were retrospectively evaluated by two blinded observers for the presence of CAE defined as a diameter enlargement > or = 1.5 times the diameter of adjacent normal coronary segments. Vessel diameters and contrast attenuation within and proximal to ectatic segments were measured. CCA was used to compare measurements obtained from CTCA with the coronary flow velocity by using the thrombolysis in myocardial infarction (TIMI) frame count. CTCA identified CAE in 20 of 677 (3%) patients. CCA was performed in ten of these patients. CAE diameter measurements with CTCA (10.0 +/- 5.4 mm) correlated significantly (r = 0.92, p < 0.001) with the CCA measurements (8.8 +/- 4.9 mm), but had higher diameters (levels of agreement: -1.0 to 3.4 mm). Contrast attenuation was significantly lower in the ectatic (343 +/- 63 HU) than in the proximal (394 +/- 60 HU) segments (p < 0.01). The attenuation difference significantly correlated with the CAE ratio (r = 0.67, p < 0.01) and the TIMI frame count (r = 0.58, p < 0.05). The prevalence of CAE in a population examined by CTCA is around 3%. Contrast attenuation measurements with CTCA correlate well with the flow alterations assessed with CCA.

Reference values for quantitative left ventricular and left atrial measurements in cardiac computed tomography

To assess reference values for left ventricular (LV) and left atrial (LA) dimensions, global LV function, and LV-myocardial mass for cardiac CT. We examined 120 subjects undergoing a coronary angiography using 64-slice and dual-source CT. All individuals had a low cardiovascular risk, normal ECG, negative biomarkers, and a normal cardiac CT examination. All subjects had a negative medical history of cardiovascular disease both on admission and at clinical 6-month follow-up. The following measurements were obtained: septal wall thickness (SWT), posterior wall thickness (PWT), LV inner diameter (LVID), LA anterior posterior diameter (LAD(sys)), end-systolic volume (ESV), and end-diastolic volume (EDV), LV-myocardial mass (LVMM). We found significant gender-related differences for all LV dimensions (SWT(sys), SWT(dia),PWT(sys),PWT(dia),LVID(sys),LVID(dia)). LAD(sys) showed no significant difference between males and females. Significant differences were found for global LV functional parameters including ESV, EDV, and SV, whereas no significant differences were found for the EF. LV-myocardial mass parameters showed significant gender-related differences. No significant correlation was found between any of these parameters and age. All data were transferred to percentile ranks. This study provides gender-related reference values and percentiles for LV and LA quantitative measurements for cardiac CT and should assist in interpreting results.

Image quality on dual-source computed-tomographic coronary angiography

Multi-detector CT reliably permits visualization of coronary arteries, but due to the occurrence of motion artefacts at heart rates >65 bpm caused by a temporal resolution of 165 ms, its utilisation has so far been limited to patients with a preferably low heart rate. We investigated the assessment of image quality on computed tomography of coronary arteries in a large series of patients without additional heart rate control using dual-source computed tomography (DSCT). DSCT (Siemens Somatom Definition, 83-ms temporal resolution) was performed in 165 consecutive patients (mean age 64 +/- 11.4 years) after injection of 60-80 ml of contrast. Data sets were reconstructed in 5% intervals of the cardiac cycle and evaluated by two readers in consensus concerning evaluability of the coronary arteries and presence of motion and beam-hardening artefacts using the AHA 16-segment coronary model. Mean heart rate during CT was 65 +/- 10.5 bpm; visualisation without artefacts was possible in 98.7% of 2,541 coronary segments. Only two segments were considered unevaluable due to cardiac motion; 30 segments were unassessable due to poor signal-to-noise ratio or coronary calcifications (both n = 15). Data reconstruction at 65-70% of the cardiac cycle provided for the best image quality. For heart rates >85 bpm, a systolic reconstruction at 45% revealed satisfactory results. Compared with earlier CT generations, DSCT provides for non-invasive coronary angiography with diagnostic image quality even at heart rates >65 bpm and thus may broaden the spectrum of patients that can be investigated non-invasively.

Low kilovoltage cardiac dual-source CT: attenuation, noise, and radiation dose

The purpose of this study was to investigate the effect of low kilovoltage dual-source computed tomography coronary angiography (CTCA) on qualitative and quantitative image quality parameters and radiation dose. Dual-source CTCA with retrospective ECG gating was performed in 80 consecutive patients of normal weight. Forty were examined with a standard protocol (120 kV/330mAs), 20 were examined at 100 kV/330mAs, and 20 at 100 kV/220mAs. Two blinded observers independently assessed image quality of each coronary segment and measured the image parameters noise, attenuation, and contrast-to-noise ratio (CNR). The effective radiation dose was calculated using CT dose volume index and the dose-length product. Diagnostic image quality was obtained in 99% of all coronary segments (1,127/1,140) without significant differences among the protocols. Image noise, attenuation, and CNR were significantly higher for 100 kV/330mAs (26 +/- 3 HU, 549 +/- 62 HU, 25.5 +/- 3.2; each P < 0.01) and 100 kV/220mAs (27 +/- 2 HU, 560 +/- 43 HU, 25.0 +/- 2.2; each P < 0.01) when compared to the 120-kV protocol (21 +/- 2 HU, 317 +/- 28 HU, 20.6 +/- 1.7). There was no significant difference between the two 100-kV protocols. Estimated effective radiation dose of the 120-kV protocol (8.9 +/- 1.2 mSv) was significantly higher than the 100 kV/330mAs (6.7 +/- 0.8 mSv, P < 0.01) or 100 kV/220mAs (4.4 +/- 0.6 mSv, P < 0.001) protocols. Dual-source CTCA with 100 kV is feasible in patients of normal weight, results in a diagnostic image quality with a higher CNR, and at the same time significantly reduces the radiation dose.

Identification of atherosclerotic lesion-prone sites through patient-specific simulation of low-density lipoprotein accumulation

We present a patient-specific model of low-density lipoprotein (LDL) transport from blood into arterial walls. To this end, the arterial endothelium is represented by a shear-stress dependent three-pore model taking into account blood plasma and LDL passage through the vesicular pathway, normal junctions and leaky junctions. We virtually remove atherosclerotic plaque from an in-vivo left coronary artery computed tomography (CT) dataset to obtain an approximation of the artery anatomy in its healthy state. By applying our model, we show that the location of the plaque in the diseased state corresponds to one of the two sites with predicted high LDL concentration in the healthy state. We further show that in the diseased state, the site with high LDL concentration has shifted distally, which is in agreement with the clinical observation that plaques generally grow in downstream direction.

Radiation dose estimates in dual-source computed tomography coronary angiography

The purpose of this study was to quantify radiation dose parameters of dual-source CT coronary angiography. Eighty patients underwent contrast-enhanced, retrospectively ECG-gated dual-source CT coronary angiography with heart rate-adapted ECG pulsing using two algorithms: In 40 patients, the tube current was reduced to 20% (A(min1)) of the normal tube current (A(max)) outside the pulsing window; in 40 patients tube current was reduced to 4% (A(min2)) of A(max). Mean CTDI(vol) in the A(min1) group was 45.1 +/- 3.6 mGy; the mean CTDI(vol) in the A(min2) group was 39.1 +/- 3.2 mGy, with CTDI(vol) in the A(min2) group being significantly reduced when compared to the A(min1) group (P < 0.001). A significant negative correlation was found between CTDI(vol) and heart rate in group A(min1) (r = -0.82, P < 0.001), whereas no correlation was found between CTDI(vol) and heart rate in group A(min2) (r = -0.066). Using the conversion coefficient for the chest, dual-source CT coronary angiography resulted in an estimated mean effective dose of 8.8 mSv in the A(min1) group and 7.8 mSv in the A(min2). Radiation exposure of dual-source CT coronary angiography using an ECG-pulsing protocol reducing the tube current to 20% significantly decreases with increasing heart rates, despite using wider pulsing windows at higher heart rates. When using a protocol with reduced tube current of 4%, the radiation dose is significantly lower, irrespective of the heart rate.