CT coronary angiography: coronary CT-flow quantification supplements morphological stenosis analysis

Quantitative hemodynamic assessment of stenotic below-the-knee arteries using spatio-temporal bolus tracking on 4D-CT angiography

BACKGROUND

Peripheral arterial disease (PAD) is a chronic occlusive disease that restricts blood flow in the lower limbs, causing partial or complete blockages of the blood flow. While digital subtraction angiography (DSA) has traditionally been the preferred method for assessing blood flow in the lower limbs, advancements in wide beam Computed Tomography (CT), allowing successive acquisition at high frame rate, might enable hemodynamic measurements.

PURPOSE

To quantify the arterial blood flow in stenotic below-the-knee (BTK) arteries. To this end, we propose a novel method for contrast bolus tracking and assessment of quantitative hemodynamic parameters in stenotic arteries using 4D-CT.

METHODS

Fifty patients with suspected PAD underwent 4D-CT angiography in addition to the clinical run-off computed tomography angiography (CTA). From these dynamic acquisitions, the BTK arteries were segmented and the region of maximum blood flow was extracted. Time attenuation curves (TAC) were estimated using 2D spatio-temporal B-spline regression, enforcing both spatial and temporal smoothness. From these curves, quantitative hemodynamic parameters, describing the shape of the propagating contrast bolus were automatically extracted. We evaluated the robustness of the proposed TAC fitting method with respect to interphase delay and imaging noise and compared it to commonly used approaches. Finally, to illustrate the potential value of 4D-CT, we assessed the correlation between the obtained hemodynamic parameters and the presence of PAD.

RESULTS

280 out of 292 arteries were successfully segmented, with failures mainly due to a delayed contrast arrival. The proposed method led to physiologically plausible hemodynamic parameters and was significantly more robust compared to 1D temporal regression. A significant correlation between the presence of proximal stenoses and several hemodynamic parameters was found.

CONCLUSIONS

The proposed method based on spatio-temporal bolus tracking was shown to lead to stable and physiologically plausible estimation of quantitative hemodynamic parameters, even in the case of stenotic arteries. These parameters may provide valuable information in the evaluation of PAD and contribute to its diagnosis.

Non-invasive coronary physiology based on computational analysis of intracoronary transluminal attenuation gradient

Invasive procedure is a prerequisite for studying coronary physiology. We established the measurement of non-invasive physiological parameters including coronary blood flow (CBF), flow velocity, and microvascular resistance using coronary computed tomography angiography (CCTA). Vessel-specific CBF was derived from transluminal attenuation flow encoding (TAFE) and then tested using three separate datasets consisted of computational simulation, human perfusion CT, and human CCTA. TAFE-derived CBF correlated well with measured vessel-specific myocardial blood flow and CBF. TAFE-derived CBF per myocardial mass consistently decreased with the progressive severity of stenosis, and it was found to better to detect significant stenosis than transluminal attenuation gradient (TAG). With the addition of vessel anatomy, TAFE-derived CBF could calculate flow velocity and microvascular resistance. The results of non-invasively acquired parameters according to the severity of stenosis were similar to those obtained through invasive physiology studies. Our study demonstrated that non-invasive comprehensive coronary physiology parameters can be derived from CCTA without any pre-specified condition or performing complex heavy computational processes. Our findings are expected to expand the clinical coverage of CCTA and coronary physiology.

Influence of scan technique on intracoronary transluminal attenuation gradient in coronary CT angiography using 128-slice dual source CT: multi-beat versus one-beat scan

The purpose of our study was to investigate the impact of temporal uniformity and adjustment by the contrast opacification enhancement in the aorta on the performance of transluminal attenuation gradient (TAG) for obstructive coronary artery disease. A total of 274 coronary arteries from 94 patients who underwent both multi- and single-beat scan using 128-slice scanner at the same time were enrolled. TAG and corrected coronary opacification (CCO) of both scan technique were compared against obstructive coronary arteries defined by diameter stenosis ≥50%. In per-vessel analysis, both TAG and CCO were slight but significantly different between multi- and single-beat scan in overall (-13.3 vs. -14.3 HU/10 mm; 0.31 vs. 0.38; p < 0.05, all). However, the difference was evident only in right coronary artery (p < 0.05) but not in left coronary arteries (p = NS). Correlation coefficient value are more than 0.8 for all coronary arteries (0.84) and each of the three vessels (RCA: 0.87, LAD: 0.84, LCX: 0.81) in TAG in single-beat versus multi-beat scans (p < 0.0001). Radiation exposure was significantly lower in single-beat scan compared to multi-beat scan (0.9 vs. 3.7 mSv, p < 0.001). TAGs of multi- and single beat scans well correlated each other in all coronary arteries and were not affected by temporal non-uniformity.