Contrast timing optimization of a two-volume dynamic CT pulmonary perfusion technique

Abstract

The purpose of this study is to develop and validate an optimal timing protocol for a low-radiation-dose CT pulmonary perfusion technique using only two volume scans. A total of 24 swine (48.5 ± 14.3 kg) underwent contrast-enhanced dynamic CT. Multiple contrast injections were made under different pulmonary perfusion conditions, resulting in a total of 141 complete pulmonary arterial input functions (AIFs). Using all the AIF curves, an optimal contrast timing protocol was developed for a first-pass, two-volume dynamic CT perfusion technique (one at the base and the other at the peak of AIF curve). A subset of swine was used to validate the prospective two-volume pulmonary perfusion technique. The prospective two-volume perfusion measurements were quantitatively compared to the previously validated retrospective perfusion measurements with t-test, linear regression, and Bland–Altman analysis. As a result, the pulmonary artery time-to-peak ($${T}_{PA}$$ T PA ) was related to one-half of the contrast injection duration ($$\frac{{T}_{Inj}}{2}$$ T Inj 2 ) by $${T}_{PA}=1.01\frac{{T}_{Inj}}{2}+1.01$$ T PA = 1.01 T Inj 2 + 1.01 (r = 0.95). The prospective two-volume perfusion measurements (PPRO) were related to the retrospective measurements (PRETRO) by PPRO = 0.87PRETRO + 0.56 (r = 0.88). The CT dose index and size-specific dose estimate of the two-volume CT technique were estimated to be 28.4 and 47.0 mGy, respectively. The optimal timing protocol can enable an accurate, low-radiation-dose two-volume dynamic CT perfusion technique.

A patient-specific timing protocol for improved CT pulmonary angiography

“…For the simulated prospective CTPA acquisitions, the was calculated to be 9.4 mGy, and the SSDE was estimated to be 17.8 mGy. The cardiac output for each acquisition was estimated by the whole-lung blood flow using a well-established CT pulmonary perfusion measurement [ 25 , 28 ]. The overall cardiac output was in a range of 1.4–5.1 L/min.…”

“…Specifically, given a short injection time (< 15 s) and a fast injection rate (> 4ml/s), the shape of the arterial input function curve is approximately normally distributed prior to the recirculation [7] . Hence, the time-to-peak delay ( ) can be linearly related to one-half of the total injection time ( ) plus a constant dispersion delay ( ) that describes the degree of contrast dispersion occurring between the venous injection site and vessel or organ of interest [25] . The estimated constant dispersion delay for pulmonary artery and descending aorta have been reported to be 1s and 2s, respectively [ 25 , 29 ].…”

“…Hence, the time-to-peak delay ( ) can be linearly related to one-half of the total injection time ( ) plus a constant dispersion delay ( ) that describes the degree of contrast dispersion occurring between the venous injection site and vessel or organ of interest [25] . The estimated constant dispersion delay for pulmonary artery and descending aorta have been reported to be 1s and 2s, respectively [ 25 , 29 ].…”

“…For patient-specific protocol (group C), the CTPA ‘acquisition’ occurred after a patient-specific delay time that was estimated using one-half of contrast injection duration and a constant dispersion delay ( Fig. 1 b) [ 18 , 25 ]. Specifically, given a fast injection rate and short injection duration, the contrast bolus would be diluted into a gaussian distribution, where the maximal enhancement located at the center of the contrast pass curve and such time-to-peak delay can be related to one-half of contrast injection duration.…”

“…Hence, the purpose of this preclinical swine study was to assess the objective and subjective image quality of CTPA with a patient-specific delay time between bolus tracking trigger and image acquisition as compared to a standard fixed delay time, using 20 volume scans acquired for CTPA as the reference standard. The patient-specific delay time was determined by one-half of contrast injection duration plus a constant dispersion delay [25] . The central hypothesis was that the patient-specific delay time can yield images with higher contrast-to-noise ratio and better diagnostic image quality as compared to the standard protocol with a fixed delay time.…”