Quantification of myocardial blood flow with (82)Rb: Validation with (15)O-water using time-of-flight and point-spread-function modeling

Abstract

Background: We quantified myocardial blood flow with (82)Rb PET using parameters of the generalized Renkin-Crone model estimated from (82)Rb and (15)O-water images reconstructed with time-of-flight and point spread function modeling. Previous estimates of rubidium extraction have used older-generation scanners without time-of-flight or point spread function modeling. We validated image-derived input functions with continuously collected arterial samples.

Methods: Nine healthy subjects were scanned at rest and under pharmacological stress on the Siemens Biograph mCT with (82)Rb and (15)O-water PET, undergoing arterial blood sampling with each scan. Image-derived input functions were estimated from the left ventricle cavity and corrected with tracer-specific population-based scale factors determined from arterial data. Kinetic parametric images were generated from the dynamic PET images by fitting the one-tissue compartment model to each voxel's time activity curve. Mean myocardial blood flow was determined from each subject's (15)O-water k 2 images. The parameters of the generalized Renkin-Crone model were estimated from these water-based flows and mean myocardial (82)Rb K 1 estimates.

Results: Image-derived input functions showed improved agreement with arterial measurements after a scale correction. The Renkin-Crone model fit (a = 0.77, b = 0.39) was similar to those previously published, though b was lower.

Conclusions: We have presented parameter estimates for the generalized Renkin-Crone model of extraction for (82)Rb PET using human (82)Rb and (15)O-water PET from high-resolution images using a state-of-the-art time-of-flight-capable scanner. These results provide a state-of-the-art methodology for myocardial blood flow measurement with (82)Rb PET.

Keywords: Image-derived input function; Myocardial blood flow; Rubidium-82 PET; TOF PET.

Fig. 1

a Example myocardium volume of interest (VOI), overlaid on a K ₁ image in horizontal long axis (HLA) and short axis (SA). b Example VOI for estimating image-derived right ventricle (blue) and left ventricle (red) TACs, overlaid on a composite image of three early ⁸²Rb frames

Fig. 2

Rate-pressure products (RPP) for ⁸²Rb scans versus ¹⁵O-water scans. The dashed line is the identity line. Rest RPP was measured immediately before scan start. Stress RPP is averaged over 4 min post-injection

Fig. 3

Arterial input functions (AIFs) and image-derived input functions (IDIFs) corrected using parameters estimated for these scans from a typical a ⁸²Rb scan and b ¹⁵O-water scan. In both cases, weighted-least-squares (WLS)-based scaling (green) and area-under-the-curve (AUC)-based scaling corrections are nearly identical. The two-parameter (partial-volume-corrected) PVC IDIFs were omitted from these plots, as they were virtually identical to the scale-corrected IDIFs (green, orange curves)

Fig. 4

Short-axis parametric images for one subject’s ¹⁵O-water and ⁸²Rb rest and stress scans, generated with different input functions. a K ₁ parametric images, b k ₂ parametric images, and c V _A parametric images. Background outside the heart has been omitted for display. AIF arterial sample-based input function, IDIF image-derived input function. Right ventricle spillover correction term (V _RV) not included

Fig. 5

a Comparison of mean myocardial ⁸²Rb K ₁ values using scale-corrected IDIFs vs. AIF. b Comparison of mean myocardial ¹⁵O-water k ₂ values. Parameters were estimated with the three-parameter model (omitting right ventricle spillover term). The solid lines and equations represent fits from Deming regression. The dashed line is the identity line. AIF arterial sample-based input function, IDIF image-derived input function

Fig. 6

Renkin-Crone model fit of K ₁ and myocardial blood flow from three-parameter kinetic model using scale-corrected image-derived input function. The dashed lines represent 95 % confidence interval of the regression line

Fig. 7

Comparison of this study’s Renkin-Crone model fit to published fits

Fig. 8

Bland-Altman plot comparing ¹⁵O-water myocardial blood flow (MBF) to ⁸²Rb MBF, using scaled image-derived input functions. Mean percent difference is −3.2 %. The dashed lines show 95 % confidence intervals