Quantification of Myocardial Blood Flow in Absolute Terms Using 82Rb PET Imaging

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See related article, pp. 911-924One would perhaps be justified to remark that the title of this editorial only states the obvious and that its premise ought to be accepted by any reasonable reader, even if not particularly familiar with nuclear cardiology. Nevertheless, the paper to which the editorial refers, 1 describing good concordance but also substantial differences amongst three commercially available software packages to quantify LV perfusion and function from gated myocardial SPECT, offers us the opportunity to reflect on some of the specific reasons why those differences exist. As the authors describe in their comprehensive review of the published literature, a wealth of studies exists assessing the cross-correlation of the outputs of different quantitative gated SPECT algorithms, and the current study confirms previously reported findings, albeit in a larger population of 634 consecutive patients. Let us try to interpret and clarify those findings, while framing them in a more general context. DIFFERENT ALGORITHMS ARE BASED ON DIFFERENT COMPUTATIONAL TOOLS (AND WORKING ASSUMPTIONS)The specific software packages used by Alexiou et al are Emory University's Cardiac Toolbox (ECTb), 2Cedars-Sinai's Cardiac Suite (QGS/QPS), 3 and General Electric's Myovation. This writer is not aware of any published papers detailing the technical principles on which the Myovation software is based, but the other two algorithms and their differing characteristics have been well described in the literature. As far as measurement of global function is concerned, the ECTb performs a Fourier decomposition of the time-volume (T-V) curve that describes the LV cavity volume as a function of the cardiac cycle, then takes the first Fourier harmonic to estimate end-systolic (ES) and end-diastolic (ED) volumes-as a result, T-V curve estimates are less dependent on temporal sampling, and ejection fractions (EFs), EDVs and ESVs from 8-frame and 16-frame gated acquisitions will be relatively close in value. 2 In contrast, QGS/QPS measures the actual dynamic range of the T-V curve, which is directly proportional to the frequency of temporal sampling-in other words, 8-frame ESVs will be larger, EDVs smaller, and EFs lower compared to 16-frame gated acquisitions, with a substantially uniform difference of 3-4 EF points over the entire EF range. 4 With regard to myocardial thickening, the ECTb algorithm assumes a uniform myocardial thickness of 1 cm at ED, and increases it with a 1:1 relationship to the apparent myocardial ''brightening'' from ED to ES, since partial volume effect is fairly linear for the reconstructed spatial resolutions and myocardial thicknesses of interest. 2 QGS/QPS is also based, in part, on myocardial brightening, but uses phantom calibration to estimate ED thickness, and asymmetrical Gaussian fitting with a constant myocardial mass constraint to follow the endocardium and epicardium's location throughout the cardiac cycle. 3 As for perfusion quantification, aside from the different myocardial sampling techniques (hy...

Section: Good Cross-correlation Does Not Mean Interchangeability Of Rmentioning

confidence: 99%

Quantitative measurements of myocardial perfusion and function from SPECT (and PET) studies depend on the method used to perform those measurements

Germano

2018

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“…When highsensitivity, low dead-time list-mode scanners are available, infused activity can be 30 mCi (1,110 MBq) of 82 Rb or lower (Table 1). 3 Many of the systems in use today cannot be acquired at the high count rates necessary to perform the dynamic study in a 3D septa-retracted mode because of limitations on dead time. For these systems, it is necessary to acquire the dynamic study in the lower sensitivity 2D septa-extended mode.…”

Section: Optimizing the Protocolmentioning

confidence: 99%

“…7 In contrast, most SRM applications require the blood pool ROI be placed in the left atrium. 1,3 The location of these ROIs is crucial in obtaining accurate blood flow measurement, and technologists must be trained on appropriate processing techniques. 8 …”

Section: Processingmentioning

confidence: 99%

“…2 In a separate comparison of ten different 82 Rb flow quantitation programs and a constant activity infusion system, a high degree of correlation was observed between absolute flow and reserve values, as long as the same extraction model and input function model were used. 3 Given the small number of patients in each cohort, the current study from Klein et.al. (n=10 in the constant flow cohort), maintaining the quality of the data is essential for obtaining meaningful results.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Accurate myocardial blood flow measurements: Quality from start to finish is key to success

Case

2018

Overall repeatability and accuracy of myocardial blood flow measurements depend on the quality of the image data, the proper use of the quantitative software, and the training of clinical staff. Unlike most imaging tests, absolute blood flow measurements have the potential to provide accurate information beyond what is seen visually. This additive information has been shown to help identify multivessel disease, balanced ischemia, true normal studies, and quality control problems that may not be visible in the relative perfusion pattern. Absolute blood flow and flow reserve measurements have been shown to be useful and reproducible on a wide array of imaging systems, radiotracer delivery systems, and software approaches. Regardless of the technology or technique, these benefits can only be achieved when the quality of the study is sufficient and the clinical staff is properly trained on its implementation.

“…For example, in one of the largest studies by Nesterov et al, a multicenter study comparing all existing software packages (N = 10) for the quantification of Rb-82 PET myocardial perfusion imaging, the authors concluded that when using the identical kinetic model, software solutions might be interchangeable. 14 While most such studies focused on the comparison of software packages in patients that were assessed for coronary artery disease in a daily clinical routine manner, the present manuscript focused on a certain subpopulation with structural changes of the left ventricular geometry, namely patients suffering from hypertrophic cardiomyopathy. This disease entity is the most common genetic cardiovascular disease in the general population and is therefore of daily importance in a cardiovascular imaging center.…”

mentioning

confidence: 99%

Lost in quantification…: The influence of different software packages on flow quantification measures

Rischpler

Nekolla

2019

Over the last decades, non-invasive myocardial perfusion imaging has shown major improvements and has consolidated its role as a mainstay for the workup of coronary artery disease. 1 While the most often applied technique for myocardial perfusion imaging is still single-photon emission tomography (SPECT) imaging, positron emission tomography (PET) for myocardial perfusion imaging has gained growing importance and acceptance in clinical routine. Reasons for that development are-besides the persisting intermittent shortage of Technetium-99m-technical advantages such as reliable tracer uptake quantification, higher count sensitivity, higher temporal and spatial resolution of PET. 2 Furthermore, PET myocardial perfusion imaging gets along with a substantially lower radiation exposure to the patient due to different physical properties of PET radiotracers such as shorter half-life. 3 Last not least, the probably most important advantage of PET myocardial perfusion imaging is the potential for absolute quantification of myocardial blood flow, a technique which has first been described in the 80s. 4 The superior extraction fraction of PET perfusion tracers compared to Technetium-99m-labeled SPECT agents and the calculation of absolute measures of myocardial blood flow also are main reasons for the superior diagnostic accuracy of PET over SPECT. [5][6][7] However, absolute quantification of myocardial blood flow is not trivial and there are many factors that may have major impact on the calculated results. 8 As indicated before, the different available PET perfusion tracers also have different physical (half-life, positron range etc. of the respective radionuclide) and biochemical [extraction/retention fraction, excretion mechanism, accumulation (e.g., N-13 ammonia, Rubidium-82) vs diffusion (O-15 water) etc.] properties, which all have to be taken into account. Also, the protocol needs to be designed carefully: for example, the generation of an accurate input function, which is calculated from a small region of interest (ROI) in the left atrium, left ventricular cavity, or the aorta when the radiotracer passes the heart may be incorrectly assessed if the radiotracer is injected too fast (i.e., with a too high activity concentration) which may drive the scanner into saturation. 9 The ROI location for the estimation of the input function per se may also have a substantial effect on blood flow results. 10 Obviously, motion and subsequent misalignment between PET and CT data may cause erroneous estimation of the myocardial blood flow. 11 It goes without saying that different scanners with different properties (crystal material, 2D vs. 3D scanners, timeof-flight availability etc.) may result in different estimations of myocardial blood flow. 12 Another important factor that may have substantial impact on myocardial blood flow estimation is the choice of kinetic model, which has to be picked carefully and in dependence of different factors, e.g., the applied perfusion tracer. 13 Another important factor (also on the post-pro...