Optimizing quantitative myocardial perfusion by po

Authors: K Lance Gould

Publish Date: 2016/09/14

Volume: 24, Issue: 6, Pages: 1950-1954

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Abstract

KLG received internal funding from the Weatherhead PET Center for Preventing and Reversing Atherosclerosis and is the 510k applicant for CFR Quant K113754 and HeartSee K143664 software packages for cardiac positron emission tomography image processing and analysis including absolute flow quantificationIn the current issue Lassen et al1 studied the effect of respiratory gating on myocardial stress perfusion imaging using positron emission tomography with Rb82 in 48 patients randomized to adenosine or dipyridamole stress The dipyridamole group consisted of nonsmoking women without a family history of cardiovascular disease and with a mean age of 64 years The adenosine group consisted primarily of men 86 at a mean age of 57 years of whom 39 were current smokers and 48 had a family history of cardiovascular diseaseThe timebased respiratory gating method divides the respiratory signal into 8 timeequal bins determined by either the inspiratory or the expiratory peak The timebased binning is based on the assumption of a steady nonchanging respiratory rate and depth throughout the PET acquisition often characterizing resting conditions but not during stress image acquisition since pharmacologic stress agents differentially alter the respiratory patternThe authors conclude that patients undergoing adenosine stress showed a decrease in measured respiratory rate from initial to later scan phase measurements 124 ± 57 vs 56 ± 47 per minute p  0001 and had a lower frequency of successful respiratory gating compared to dipyridamole 47 vs 71 p = 012 As a result of the varying respiratory pattern with adenosine the adenosine imaging quality was inferior to dipyridamole although dipyridamole respiratory gating still remained unsatisfactory in 29 of dipyridamole cases If respiratory gating is considered for use in cardiac PET the authors recommend dipyridamole stress due to its more uniform respiration pattern than adenosine with resulting higher frequency of successful respiratory gating that however still remains unsatisfactory in 29 of dipyridamole casesThis carefully done study is practically important as an essentially “negative” by showing definitively that respiratory gating of PET perfusion images is not useful and may be worse than no respiratory gating due to physiologic varying respiratory rates particularly during adenosine stress but also to a significant extent with dipyridamole stress Thus the most important observation is physiology the variable respiratory patterns after adenosine with 53 failed respiratory gating and 29 failure for dipyridamole These observations preclude useful respiratory gating for PET myocardial perfusion for physiologic reasons unrelated to any systematic PET data that are not reportedIn addition to the systematic physiologic data the single figure of PET images with successful respiratory gating shows a substantial difference between the septal and lateral walls not present on images with no respiratory gating This regional discordance of relative myocardial uptake of Rb82 on one example raises the question of whether even “successful” respiratory gating causes artifacts as reported for misregistration of emission and CT transmission data for attenuation correction While the physiologic observations on respiratory variation during vasodilator stress are definitive its negative finding might be even stonger by quantifying the differences in relative myocardial uptake in absolute myocardial perfusion or CFR with and without respiratory gating since the study was done with PET imaging On the other hand the physiologic observation is so definitive that quantitative PET data might be superfluousWhile not likely to change the conclusion the patient selection for adenosine versus dipyridamole stress is a curious bias at odds with the meticulous objective methodology and data on respiratory variability No explanation is provided for using dipyridamole in women and primarily adenosine in men This striking difference is not likely random but appears to reflect some guidelines or practice pattern for the author’s PET protocols that are not reported However again the definitive physiologic data make this odd selection of subjects of little import

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