Dynamic CT perfusion measurement in a cardiac phantom

Abstract

Widespread clinical implementation of dynamic CT myocardial perfusion has been hampered by its limited accuracy and high radiation dose. The purpose of this study was to evaluate the accuracy and radiation dose reduction of a dynamic CT myocardial perfusion technique based on first pass analysis (FPA). To test the FPA technique, a pulsatile pump was used to generate known perfusion rates in a range of 0.96-2.49 mL/min/g. All the known perfusion rates were determined using an ultrasonic flow probe and the known mass of the perfusion volume. FPA and maximum slope model (MSM) perfusion rates were measured using volume scans acquired from a 320-slice CT scanner, and then compared to the known perfusion rates. The measured perfusion using FPA (P(FPA)), with two volume scans, and the maximum slope model (P(MSM)) were related to known perfusion (P(K)) by P(FPA) = 0.91P(K) + 0.06 (r = 0.98) and P(MSM) = 0.25P(K) - 0.02 (r = 0.96), respectively. The standard error of estimate for the FPA technique, using two volume scans, and the MSM was 0.14 and 0.30 mL/min/g, respectively. The estimated radiation dose required for the FPA technique with two volume scans and the MSM was 2.6 and 11.7-17.5 mSv, respectively. Therefore, the FPA technique can yield accurate perfusion measurements using as few as two volume scans, corresponding to approximately a factor of four reductions in radiation dose as compared with the currently available MSM. In conclusion, the results of the study indicate that the FPA technique can make accurate dynamic CT perfusion measurements over a range of clinically relevant perfusion rates, while substantially reducing radiation dose, as compared to currently available dynamic CT perfusion techniques.

Functional Assessment of Coronary Artery Disease Using Whole-Heart Dynamic Computed Tomographic Perfusion

“…Based on a recent study, a correlation of at least r = 0.76 was expected between relative perfusion and reference standard FFR measurement 18 . However, as indicated by our previous work 28 , the FPA technique improves perfusion measurement correlation. Therefore, given a significance level of 0.05 and a power of 0.80, a sample size of 15 independent measurements was projected to adequately power the study.…”

“…As previously described 26–28 , our technique assumes that contrast material does not exit the myocardial tissue VOI over the measurement time. However, by dramatically increasing the size of that VOI to encompass the entire coronary perfusion territory distal to a stenosis, while also reducing the time necessary to measure perfusion, the problem of contrast material loss from the VOI over the measurement time is eliminated, i.e., the problem of perfusion underestimation 19 is solved.…”

“…As previously reported 28 , only two volume scans, denoted as V1 and V2 in Figure 2, are necessary for perfusion measurement with our FPA technique. V1 is used for dynamic CT perfusion measurement and is the first volume scan after the AIF exceeds 180 HU, while V2 is used for both dynamic CT perfusion measurement and CT angiography and is the first volume scan after the AIF reaches its peak.…”

“…By definition, the compartmental perfusion (P FPA ) is proportional to the mass of contrast material that accumulates in the compartment per unit time (dM C /dt), divided by the incoming contrast concentration (C in ) and compartment tissue mass (M T ), prior to significant contrast exit. Using cardiac CT data, dM C /dt may be derived from the change in integrated Hounsfield Units (HU) within the compartment, while C in may be estimated from the arterial input function (AIF) 28 .…”

“…The FPA technique can accurately measure absolute perfusion 28 . However, for the purposes of this study, absolute perfusion measurement could not be validated against FFR as FFR is a relative metric.…”