Dynamic CT myocardial perfusion without image registration

Abstract

The aim of this study was to validate a motion-immune (MI) solution to dynamic CT myocardial perfusion measurement, in the presence of motion without image registration. The MI perfusion technique was retrospectively validated in six swine (37.3 ± 7.5 kg) with a motion-susceptible (MS) perfusion technique performed for comparison. In each swine, varying severities of stenoses were generated in the left anterior descending (LAD) coronary artery using a balloon under intracoronary adenosine stress, followed by contrast-enhanced imaging with 20 consecutive volume scans per stenosis. Two volume scans were then systematically selected from each acquisition for both MI and MS perfusion measurement, where the resulting LAD and left circumflex (LCx) measurements were compared to reference microsphere perfusion measurements using regression and diagnostic performance analysis. The MI (PMI) and microsphere (PMICRO) perfusion measurements were related through regression by PMI = 0.98 PMICRO + 0.03 (r = 0.97), while the MS (PMS) and microsphere (PMICRO) perfusion measurements were related by PMS = 0.62 PMICRO + 0.15 (r = 0.89). The accuracy of the MI and MS techniques in detecting functionally significant stenosis was 93% and 84%, respectively. The motion-immune (MI) perfusion technique provides accurate myocardial perfusion measurement in the presence of motion without image registration.

Low-dose quantitative CT myocardial flow measurement using a single volume scan: phantom and animal validation

“…With our approach, low-dose quantitative flow can be measured under rest and stress flow conditions with a RMSE of 0.49 mL∕ min ∕g and a RMSD of 0.48 mL∕ min ∕g if using a single volume scan, or with a RMSE of 0.42 mL∕ min ∕g and a RMSD of 0.42 mL∕ min ∕g if using an additional pre-contrast volume scan, as previously validated. 24 When considering the large dynamic range of microsphere flows assessed in this study ranging from 0.077 to 7.45 mL∕ min ∕g, the RMSE of 0.49 mL∕ min ∕g and RMSD of 0.48 mL∕ min ∕g constitute only 6.6% and 6.5% of the total measurement range, respectively, meaning the single-volume quantitative CT flow technique is diagnostically accurate and precise. Moreover, the single-volume quantitative CT flow technique demonstrates similar near-unity slope of agreement, minimal measurement offset, and excellent Pearson's correlation as compared to clinical gold standard 13 N-ammonia and 15 O-H 2 O PET flow.…”

“…Whereas our single-volume quantitative CT flow technique uses these image data within a single-compartment model to directly measure the total myocardial flow from the rate of contrast mass accumulation within the entire left ventricular myocardium, after which the per-voxel myocardial flow values are derived. With our approach, low-dose quantitative flow can be measured under rest and stress flow conditions with a RMSE of 0.49 mL/min/g and a RMSD of 0.48 mL/min/g if using a single volume scan, or with a RMSE of 0.42 mL/min/g and a RMSD of 0.42 mL/min/g if using an additional pre-contrast volume scan, as previously validated 24 . When considering the large dynamic range of microsphere flows assessed in this study ranging from 0.077 to 7.45 mL/min/g, the RMSE of 0.49 mL/min/g and RMSD of 0.48 mL/min/g constitute only 6.6% and 6.5% of the total measurement range, respectively, meaning the single-volume quantitative CT flow technique is diagnostically accurate and precise.…”

“…Eventually, a comprehensive cardiac CT protocol was built, which enabled low-dose, vessel-specific 31 , 32 rest flow combined with CCTA, stress flow, and CFR measurement using only four prospectively acquired volume scans–two for rest and two for stress 33 . Yet, the major translational limitations of this comprehensive technique were: (1) its reliance on a specialized timing protocol for optimal acquisition of the four volume scans necessary for rest flow, CCTA, and stress flow measurement 34 , 35 and (2) its reliance on image registration to combat the effects of motion artifact between said volume scans 24 . Hence, the single-volume quantitative CT flow technique was developed as a solution, where the pre-contrast myocardial attenuation is estimated from the bolus tracking data, rather than from a separate volume scan, in turn, enabling quantitative flow measurement using a simplified protocol no different than a standard CCTA 25 …”

“…A corresponding “virtual” summation of the pre-contrast myocardial attenuation values is then approximated by multiplying the average pre-contrast myocardial attenuation (from the first few bolus tracking samples) by the total number of myocardial voxels, n, within the above volume scan (HU¯tissue·n). Eliminating the need for and errors inherent to image registration, 24 this “virtual” summation acts as a pre-contrast volume scan and assumes that the pre-contrast myocardial tissue density is spatially homogenous, i.e., that no fibrofatty scar is present. Taken in difference, and divided by the integration time from Eq.…”

“…33 Yet, the major translational limitations of this comprehensive technique were: (1) its reliance on a specialized timing protocol for optimal acquisition of the four volume scans necessary for rest flow, CCTA, and stress flow measurement 34,35 and (2) its reliance on image registration to combat the effects of motion artifact between said volume scans. 24 Hence, the single-volume quantitative CT flow technique was developed as a solution, where the pre-contrast myocardial attenuation is estimated from the bolus tracking data, rather than from a separate volume scan, in turn, enabling quantitative flow measurement using a simplified protocol no different than a standard CCTA. 25 To the best of our knowledge, this work is the first of its kind to show that accurate quantitative myocardial flow in mL/min/g can be derived using dynamic bolus tracking data, a single contrast-enhanced volume scan, and a one-compartment first-pass-analysis model.…”