Andrew Van Tosh

Prognosis of a Normal Positron Emission Tomography 82Rb Myocardial Perfusion Imaging Study in Women with No History of Coronary Disease

Objectives: Myocardial perfusion imaging (MPI) with positron emission tomography (PET) has advantages over single-photon emission computerized tomography, particularly for women. This investigation was undertaken to define the prognosis of a normal stress PET MPI study in women. Methods:The cohort comprised 457 women evaluated for suspected coronary artery disease (CAD) who had normal pharmacologic stress 82Rb PET MPI. No patient had clinically evident CAD. Kaplan-Meier estimates were used to determine death and initial nonfatal cardiac event rates over 7 years. Log rank tests were used to assess the relationship between baseline cardiac risk and events during follow-up, and to contrast survival in the cohort with age- and gender-matched US census comparators. Results: During follow-up, there were 11 deaths (all nonischemic), 3 nonfatal myocardial infarctions, 3 percutaneous coronary interventions and 1 coronary artery bypass operation. Average risks of death and initial nonfatal cardiac events were 0.72 and 0.47% per year, respectively. Cardiac events were associated with a history of diabetes (p < 0.0003) and a family history of CAD (p < 0.05). Conclusion: A normal cardiac PET study is associated with a very low rate of future cardiac events. Women with diabetes and a strong family history of CAD are more likely to sustain events and require close surveillance for the development of coronary disease.

Prospects for advancing nuclear cardiology by means of new detector designs

In the March/April issue of the Journal, there is a fascinating article by Slomka et al 1 reporting advances in SPECT detector design and image reconstruction techniques. In this essay we shall outline briefly the physical principles that have made these innovations possible and explore ways in which diagnosing cardiac disease may be advanced with this new technology. First, it is useful to understand how it has become possible to improve Nuclear Cardiology image quality. Usually, for any given technology, such as Anger camera tomograms reconstructed by filtered backprojection, improving one property of an image causes degradation of other image properties; for instance, improving signal-to-noise ratio by applying a stronger spatial filter decreases image contrast and spatial resolution. 2 In order to achieve a genuine improvement in image quality it is necessary to replace an older technology with a newer one. One way to accomplish this is to replace filtered backprojection reconstruction approaches with more sophisticated iterative reconstruction algorithms; another approach is to replace the Anger cameras with superior data collecting devices. Ultimately, the reliability of scintigrams is inseparably connected to the amount of information associated with each detected gamma ray. Anger cameras consist of a single large NaI(Tl) crystal with a bank of many photomultiplier tubes and a collimator. Some of the recent improvements in image quality have come about by replacing the NaI(Tl) crystal with a solid state device, such as CZT and CSI(Tl) crystals, which provide considerably more information for each detected gamma ray. For instance, every time a 140 keV gamma ray scintillates in a NaI(Tl) crystal, it produces 5,600 light photons, which are converted to 700 photoelectrons, which then must be amplified in a photomultiplier tube to produce an electronic signal suitable for information processing. 3 The greatest factor contributing to Anger

Automated detection of left ventricular dyskinesis by gated blood pool SPECT.

ObejctiveThe ability to detect left ventricular (LV) apical dyskinesis, the hallmark of an aneurysm, is an important requirement of diagnostic cardiac imaging modalities that perform wall motion analysis. Our investigation assessed the ability of gated blood pool single-photon emission-computed tomography (GBPS) to automatically detect LV dyskinesis, using cardiac magnetic resonance (CMR) as the reference standard. Materials and methodsGBPS data were analyzed for 41 patients with congestive heart failure or cardiomyopathy and compared with ECG-gated TrueFISP CMR evaluations. An experienced nuclear cardiologist without the knowledge of quantitative GBPS or CMR results graded visual impressions of regional wall motion while examining cinematic playbacks of GBPS images. GBPS algorithms automatically isolated LV counts and computed regional phase (ϕ) values in each of 17 conventional American Heart Association LV segments. LV asynchrony was quantified by the two local measures: maximum apical ϕ difference (Δα), and standard deviation among apical phases (σα), and by the five global measures: ϕ histogram bandwidth (BWHistogram), ϕ histogram standard deviation (σHistogram), Z-scores, Entropy, and Synchrony. For CMR data, an expert manually drew endocardial LV outlines to measure regional wall motion in 17 LV segments. ResultsApical dyskinesis was present in nine patients. Among GBPS measurements, the method with the greatest accuracy for detecting dyskinesis was Δα (receiver operating characteristic area=95%). The only method with a sufficiently high κ statistic to represent ‘very good agreement’ with CMR was Δα, with κ=0.81. Δα was more sensitive in detecting dyskinesis than visual analysis (100 vs. 33%, P=0.01). ConclusionAutomatic GBPS computations accurately identified patients with LV dyskinesis, and detected dyskinesis more successfully than did visual analysis.

Relationships between blood pool and myocardial perfusion-gated SPECT global and regional left ventricular function measurements.

ObjectiveAlgorithms have been developed to quantify global and regional left ventricular (LV) function and asynchrony from myocardial perfusion (MP) and blood pool (BP)-gated single-photon emission computer-assisted tomography, but relationships between measurements from these two imaging modalities have not been documented. The objective of this investigation was to determine the degree to which automated BP and MP measurements agree with each other and are accurate, using cardiac magnetic resonance (CMR) as the reference standard. We also sought to determine the extent to which regions of abnormal phase correspond to segments exhibiting abnormal wall motion. Materials and methodsWe studied 20 patients with prior myocardial infarction (age 60±11 years; 95% males) who had BP, MP, and ECG-gated CMR data acquisitions. MP and BP measured parameters included global ejection fraction (EF) and volumes, regional contraction phases, and standard deviations and bandwidths of phase versus R-R histograms. CMR algorithms used manually drawn endocardial and epicardial contours to measure global and regional wall motion and wall thickening. Regional measurements were resampled for all three imaging modalities into 17 conventional LV territories. ResultsBP LV counts significantly exceeded MP counts with a ratio of 5.2 : 1. There were no differences among the three methods for global EFs or volumes (analysis of variance P = 0.86 and 0.94). MP and BP correlated equally well (P = 0.15) versus CMR for global EFs (MP: r=0.87 and BP: r=0.95) and volumes (r=0.91 for both). Phase histogram parameters correlated significantly for MP versus BP for phase standard deviation (r=0.79) and phase bandwidth (r=0.93). Detection of five patients with significantly extended phase bandwidth, indicative of asynchrony, showed ‘good agreement’ between MP and BP (κ=0.73; McNemars difference=0%, P=0.48). Abnormal regional BP EF predicted abnormal wall motion of specific LV segments (receiver-operating characteristic area=85±2%), and abnormal regional MP wall thickening predicted abnormal CMR wall thickening (receiver-operating characteristic area=87±3%). Abnormal MP phase was present in 25% of 67 dyssynergic segments and 64% of segments adjacent to dyssynergic segments, indicating that locations of phase abnormalities were more widely distributed in the LV than sites of depressed wall motion. ConclusionMP and BP measures of LV global and regional function agreed well with each other and with independent CMR measurements. MP and BP phase measurements suggested that phase abnormalities were more widespread than localized wall motion abnormalities.

ASNC Model Coverage Policy: Cardiac positron emission tomographic imaging

This document is intended as a model coverage policy for cardiac positron emission tomography (PET) imaging studies and delineates under which clinical situations such a study is indicated. This document examines a variety of patient clinical indications and symptoms which support the use of cardiac PET by cross-referencing the indication with the appropriate use criteria (AUC) for radionuclide studies developed by the American College of Cardiology (ACC)/American Society of Nuclear Cardiology (ASNC) in 2005 and subsequently revised in 2009. In addition, the use of cardiac PET in patients with the indications delineated in the policy is supported by references to an abundance of the literature in the provided scenarios. Finally, we have provided the International Classification of Diseases (ICD)-9 codes which correlate to each of the indications to demonstrate which codes, or ranges of codes, are appropriate for each clinical indication.

Ventricular asynchrony: A shift to the right?

Evaluation of ventricular function has been a focus of nuclear medicine since 1971, when Zaret et al demonstrated that abnormalities of left ventricular (LV) wall motion and ejection fraction (EF) could be determined by injection of Tc-99m human serum albumen and acquiring images at end-diastole and end-systole. Multi-gated equilibrium radionuclide ventriculography (RNV) and first-pass imaging further refined characterization of LV asynergy and performance. Clinical trials soon showed that noninvasively determined LVEF was a strong predictor of survival in a broad range of heart diseases. Further work demonstrated that synchronicity of LV contraction could be derived from RNV by Fourier analysis of pixel by pixel labeled RBC time-activity curves, assigning a phase to each pixel (percent of the R-R interval from 0 -360 ) to identify time of maximum contraction. Synchronicity has important effects on LV performance: patients with interor intra-ventricular asynchrony have lower LVEF relative to normal control subjects. Mechanisms for reduced ventricular performance resulting from dyssynchrony remain unclear, but Sweeney et al suggested early-contracting segments stretch and deform later-contracting ones, and vice versa, expending energy in the process, resulting in lower rate of pressure rise, lower developed pressure, prolonged ejection, and reduced EF. The most ubiquitous methods to measure asynchrony are by tissue doppler echocardiographic techniques, which use low frequency signals to measure myocardial wall deformation, and calculate strain, strain rate, delay in contraction of opposing LV walls (four basal LV segments on 4-chamber view), and dispersion of time to peak systolic contraction. Cardiac resynchronization therapies (CRT) were designed to improve LV synchronicity through optimally timed pacing (as determined by echo) of right ventricle (RV) and LV lateral walls. CRT promotes reverse remodeling, with improved EF and survival in heart failure patients. However, clinical response to CRT (defined hemodynamically or as decrease in NYHA CHF class) occurs in only two-thirds of patients, prompting efforts to identify variables that would prospectively predict a positive CRT response. Multicenter studies (‘‘Prospect’’ and ‘‘Rethinq’’ trials) demonstrated large variability in performance of echo parameters, and their failure to predict CRT response, which fostered the development of nuclear cardiology methods for dyssynchrony assessment. One nuclear approach to quantifying asynchrony used gated myocardial perfusion imaging (GMPI) SPECT data. Because of partial volume effects, myocardial wall thickening varies linearly with systolic counts, so that onset of mechanical contraction (OMC) in each LV myocardial pixel was defined as increase of systolic counts from baseline. Fourier analysis generated curves of OMC phase per pixel, plotted as frequency histograms, the standard deviation (SD) and bandwidth (BW) of which were quantified. A slightly different approach that imposes constant myocardial mass constraints was developed for Quantitative Gated SPECT (QGS) software, the BW and SD measurements of which successfully separated normal patients from those with LBBB. Correlations between phase parameters from GMPI SPECT and tissue Doppler were modest, Reprint requests: Andrew Van Tosh, Research Department, St. Francis Hospital-The Heart Center, Roslyn, NY; andrew.vantosh@chsli.org J Nucl Cardiol 2017:24;79–82. 1071-3581/

RIGHT TO LEFT VENTRICULAR APICAL CONTRACTION INTERVAL–A NEW INDEX OF VENTRICULAR DYSSYNCHRONY DERIVED FROM SPECT GATED BLOOD POOL RADIONUCLIDE VENTRICULOGRAPHY

34.00 Copyright 2016 American Society of Nuclear Cardiology.

Rotating and stationary SPECT system patient motion myocardial perfusion artifacts

Left ventricular dyssynchrony (LVD) is an important determinant of prognosis in heart failure (CHF) pts. and can be treated with biventricular pacing (BiV). Noninvasive imaging parameters have failed to predict clinical response to BiV. Phase analysis of SPECT radionuclide ventriculography (RNV) can

Pharmacologic stress myocardial perfusion imaging in patients with pulmonary hypertension: What do we know, and what remains to be learned?

Since the advent of gamma cameras to perform SPECT studies to assess myocardial perfusion, it has been recognized that patient motion during data acquisition can result in artifacts that can compromise the accuracy of visual and quantitative scan interpretation. Originally, all SPECT systems consisted of one or more Anger detectors that rotated about the patient, so that abrupt patient motion in the caudal direction (corresponding to the ‘‘z’’ direction in the paper by Salvadori et al.) produced image data at those projections that are inconsistent with the image counts acquired at other projections. Reconstruction algorithms that are provided with data that are inconsistent from one projection to another often produce artifactual regional decreases in apparent myocardial perfusion that are misinterpreted as genuine perfusion defects. In recent years, several SPECT systems have become available that are composed of stationary detectors, rather than rotating Anger detectors. For such systems, all detectors are presented with three-dimensional count distributions that project into multiple detectors in multiple directions simultaneously. So, gamma rays emanating from the heart of a patient who moves caudally will impinge on an entire set of detectors all at the same time. In terms of the image data to be handled by the reconstruction algorithms, this is not unlike PET data. This situation would constitute data that at some times are inconsistent with data at other times, but not data at some projections that are inconsistent with data at other projections. Consequently, the same patient executing the same abrupt caudal translation would still cause problems for reconstructing data acquired by a non-rotating system, but just not the same problems as for a rotating system. For a non-rotating SPECT system, a patient with normal myocardial uptake who moved in this way would add anterior wall counts while subtracting inferior wall counts to the reconstructed count volume, so that the entire configuration would be blurred and distorted in the z-direction. Recognizing the inherent differences that the same patient motion would produce in rotating and stationary systems, investigators have developed some approaches to dealing with potential motion problems in data acquired with CZT SPECT systems, specifically. Overall, one would expect more severe localized artifacts in the case of a rotating SPECT system, compared to which a nonrotating SPECT system would have image data more frequently degraded by image blurring. Thus, the effect of overt patient motion for a non-rotating SPECT system should be similar to the effect of abrupt patient motion on PET scans. Reduced accuracy of myocardial blood flow computations obtained by analyzing cardiac PET data acquired in patients with overt motion problems has been documented, for which optical flow methods have been devised to correct motion and restore myocardial blood flow accuracy. These correction techniques subsequently evolved to recognize the fact that PET cardiac counts do in fact move as the heart contracts, and to apply those corrections in order to both improve absolute myocardial perfusion quantitation and to quantify the motion of the heart itself in normal sinus rhythm. Thus, techniques invented to correct for motion problems in PET data evolved to provide the quantified physiologic parameters of regional wall motion and ejection fraction. Even in patients with no overt motion, Reprint requests: Kenneth J. Nichols, PhD, Division of Nuclear Medicine and Molecular Imaging, Northwell Health, 270-05 76th Avenue, New Hyde Park, NY 11040; knichols@northwell.edu J Nucl Cardiol 2019;26:1323–6. 1071-3581/

Advances in dual respiratory and ECG-gated SPECT imaging

34.00 Copyright 2018 American Society of Nuclear Cardiology.