Clinical impact of arrhythmias on gated SPECT cardiac myocardial perfusion and function assessment

Myocardial perfusion imaging with retrospective gating and integrated correction of attenuation, scatter, respiration, motion, and arrhythmia

BACKGROUND

Absolute quantitative myocardial perfusion SPECT requires addressing of aleatory and epistemic uncertainties in conjunction with providing image quality sufficient for lesion detection and characterization. Iterative reconstruction methods enable the mitigation of the root causes of image degradation. This study aimed to determine the feasibility of a new SPECT/CT method with integrated corrections attempting to enable absolute quantitative cardiac imaging (xSPECT Cardiac; xSC).

METHODS

We compared images of prototype xSC and conventional SPECT (Flash3DTM) acquired at rest from 56 patients aged 71 ± 12 y with suspected coronary heart disease. The xSC prototype comprised list-mode acquisitions with continuous rotation and subsequent iterative reconstructions with retrospective electrocardiography (ECG) gating. Besides accurate image formation modeling, patient-specific CT-based attenuation and energy window-based scatter correction, additionally we applied mitigation for patient and organ motion between views (inter-view), and within views (intra-view) for both the gated and ungated reconstruction. We then assessed image quality, semiquantitative regional values, and left ventricular function in the images.

RESULTS

The quality of all xSC images was acceptable for clinical purposes. A polar map showed more uniform distribution for xSC compared with Flash3D, while lower apical count and higher defect contrast of myocardial infarction (p = 0.0004) were observed on xSC images. Wall motion, 16-gate volume curve, and ejection fraction were at least acceptable, with indication of improvements. The clinical prospectively gated method rejected beats ≥20% in 6 patients, whereas retrospective gating used an average of 98% beats, excluding 2% of beats. We used the list-mode data to create a product equivalent prospectively gated dataset. The dataset showed that the xSC method generated 18% higher count data and images with less noise, with comparable functional variables of volume and LVEF (p = ns).

CONCLUSIONS

Quantitative myocardial perfusion imaging with the list-mode-based prototype xSPECT Cardiac is feasible, resulting in images of at least acceptable image quality.

The setting of heartbeat acceptance windows on gated myocardial perfusion single-photon emission computed tomography using CZT camera: effect of left ventricular functional parameters in patients with arrhythmia

OBJECTIVES

Consistently variable with several peaks in heart rate histogram (e.g. bigeminy and trigeminy) is one of the arrhythmia types. We investigated the effects of gating error by consistently variable patients on left ventricular (LV) functional with cadmium zinc telluride (CZT) camera. The purpose of this study is to evaluate LV functional parameters by setting different heartbeat acceptance windows on gated myocardial perfusion single-photon emission computed tomography (SPECT) (MPS) in consistently variable patients, using echocardiography (echo) as a reference.

MATERIALS AND METHODS

Sixteen consistently variable patients underwent the gated MPS using a D-SPECT. The MPS images were obtained by setting two different types of heartbeat acceptance windows. The heartbeat acceptance windows were set to include only one peak and two peaks of the maximum count peaks, respectively.

RESULTS

Mean end-diastolic volume, end-systolic volume and left ventricular ejection fraction (LVEF) were 112.7 mL, 62.2 mL and 51.3% for one peak, 114.5 mL, 66.1 mL and 47.1% for two peak, and 113.0 mL, 54.2 mL and 54.1% for echo, respectively. The mean differences between two peaks and echo in LVEF were larger than those of between one peak and echo.

CONCLUSION

Our study suggests that setting the heartbeat acceptance window of one peak was suitable for accurate measurement of LV function in consistently variable patients.

Imaging technology for myocardial perfusion single-photon emission computed tomography 2018 in Japan

AIM

Recently, nuclear cardiology has dramatically advanced by a new technology development such as the device, short-term acquisition system, image reconstruction algorithm and image analysis. Although these innovations have been gradually employed in routine examinations, we did not investigate the current use of image acquisition, image reconstruction, and image analysis with myocardial perfusion single-photon emission computed tomography (MPS). We investigated the current status of MPS imaging technology in Japan.

METHODS

We carried out a survey using a Web-based questionnaire system, the opening of which was announced via e-mail, and it was available on a website for 3 months. We collected data on the current use of MPS with ²⁰¹Tl and/or ^99mTc agents with respect to routine protocols, image acquisition, image reconstruction, and image analysis.

RESULTS

We received responses to the Web-based questionnaire from 178 and 174 people for ^99mTc and ²⁰¹Tl MPS, respectively. The routine protocols of MPS of stress-rest and rest-stress MPS on 1-day protocols with ^99mTc were 41.2% and 14.5%, respectively, and the rest-only scan response rate was 23.7%, whereas that of ²⁰¹Tl MPS was 65.9% with stress-rest MPS, 19.0% with rest-only MPS, and 10.9% with stress-rest MPS adding a rest scan 24 h after injection. The filtered back projection (FBP) method is most commonly used image reconstruction method, yielding 70.5% for ^99mTc MPS and 76.8% for ²⁰¹Tl MPS, including combined FBP and ordered subset expectation maximization method. The results for no-correction (NC) images were 49.2% with ^99mTc MPS and 55.2% with ²⁰¹Tl MPS including the response of NC and combined attenuation correction (AC) and scatter correction (SC) (i.e., ACSC) images. The AC or ACSC images of ^99mTc and ²⁰¹Tl were provided by 30-40% of the institutions surveyed.

CONCLUSIONS

We investigated the current status of MPS imaging technology in Japan, and found that although the use of various technical developments has been reported, some of these technologies have not been utilized effectively. Hence, we expect that nuclear medicine technology will be used more effectively to improve diagnosis.

The development and initial evaluation of a realistic simulated SPECT dataset with simultaneous respiratory and cardiac motion for gated myocardial perfusion SPECT

We developed a realistic simulation dataset for simultaneous respiratory and cardiac (R&C) gated SPECT/CT using the 4D NURBS-based Cardiac-Torso (NCAT) Phantom and Monte Carlo simulation methods, and evaluated it for a sample application study. The 4D NCAT phantom included realistic respiratory motion and beating heart motion based on respiratory gated CT and cardiac tagged MRI data of normal human subjects. To model the respiratory motion, a set of 24 separate 3D NCAT phantoms excluding the heart was generated over a respiratory cycle. The beating heart motion was modeled separately with 48 frames per cardiac cycle for each of the 24 respiratory phases. The resultant set of 24  ×  48 3D NCAT phantoms provides a realistic model of a normal human subject at different phases of combined R&C motions. An almost noise-free SPECT projection dataset for each of the 1152 3D NCAT phantoms was generated using Monte Carlo simulation techniques and the radioactivity uptake distribution of (99m)Tc sestamibi in different organs. By grouping and summing the separate projection datasets, separate or simultaneous R&C gated acquired data with different gating schemes could be simulated. In the initial evaluation, we combined the projection datasets into ungated, 6 respiratory-gates only, 8 cardiac-gates only, and combined 6 respiratory-gates & 8 cardiac-gates projection datasets. Each dataset was reconstructed using 3D OS-EM without and with attenuation correction using the averaged and respiratory-gated attenuation maps, and the resulting reconstructed images were compared. These results were used to demonstrate the effects of R&C motions and the reduction of image artifact due to R&C motions by gating and attenuation corrections. We concluded that the realistic 4D NCAT phantom and Monte Carlo simulated SPECT projection datasets with R&C motions are powerful tools in the study of the effects of R&C motions, as well as in the development of R&C gating schemes and motion correction methods for improved SPECT/CT imaging.

Erroneous cardiac ECG-gated PET list-mode trigger events can be retrospectively identified and replaced by an offline reprocessing approach: first results in rodents

The assessment of left ventricular function, wall motion and myocardial viability using electrocardiogram (ECG)-gated [(18)F]-FDG positron emission tomography (PET) is widely accepted in human and in preclinical small animal studies. The nonterminal and noninvasive approach permits repeated in vivo evaluations of the same animal, facilitating the assessment of temporal changes in disease or therapy response. Although well established, gated small animal PET studies can contain erroneous gating information, which may yield to blurred images and false estimation of functional parameters. In this work, we present quantitative and visual quality control (QC) methods to evaluate the accuracy of trigger events in PET list-mode and physiological data. Left ventricular functional analysis is performed to quantify the effect of gating errors on the end-systolic and end-diastolic volumes, and on the ejection fraction (EF). We aim to recover the cardiac functional parameters by the application of the commonly established heart rate filter approach using fixed ranges based on a standardized population. In addition, we propose a fully reprocessing approach which retrospectively replaces the gating information of the PET list-mode file with appropriate list-mode decoding and encoding software. The signal of a simultaneously acquired ECG is processed using standard MATLAB vector functions, which can be individually adapted to reliably detect the R-peaks. Finally, the new trigger events are inserted into the PET list-mode file. A population of 30 mice with various health statuses was analyzed and standard cardiac parameters such as mean heart rate (119 ms ± 11.8 ms) and mean heart rate variability (1.7 ms ± 3.4 ms) derived. These standard parameter ranges were taken into account in the QC methods to select a group of nine optimal gated and a group of eight sub-optimal gated [(18)F]-FDG PET scans of mice from our archive. From the list-mode files of the optimal gated group, we randomly deleted various fractions (5% to 60%) of contained trigger events to generate a corrupted group. The filter approach was capable to correct the corrupted group and yield functional parameters with no significant difference to the optimal gated group. We successfully demonstrated the potential of the fully reprocessing approach by applying it to the sub-optimal group, where the functional parameters were significantly improved after reprocessing (mean EF from 41% ± 16% to 60% ± 13%). When applied to the optimal gated group the fully reprocessing approach did not alter the functional parameters significantly (mean EF from 64% ± 8% to 64 ± 7%). This work presents methods to determine and quantify erroneous gating in small animal gated [(18)F]-FDG PET scans. We demonstrate the importance of a quality check for cardiac triggering contained in PET list-mode data and the benefit of optionally reprocessing the fully recorded physiological information to retrospectively modify or fully replace the cardiac triggering in PET list-mode data. We aim to provide a preliminary guideline of how to proceed in the presence of errors and demonstrate that offline reprocessing by filtering erroneous trigger events and retrospective gating by ECG processing is feasible. Future work will focus on the extension by additional QC methods, which may exploit the amplitude of trigger events and ECG signal by means of pattern recognition. Furthermore, we aim to transfer the proposed QC methods and the fully reprocessing approach to human myocardial PET/CT.

Outcome prediction in heart failure with atrial fibrillation: relative role of left ventricular ejection fraction and neurohormonal measures

BACKGROUND

Since atrial fibrillation (AF) impacts the measurement and interpretation of left ventricular ejection fraction (LVEF), we hypothesized that the outcome in heart failure (HF) with AF and LVEF ≤ 35% would be more strongly associated with neurohormonal measures than LVEF.

METHODS AND RESULTS

Cardiac adverse events [CAE; HF progression (HFP), life-threatening arrhythmia (ARR), and cardiac death (CD)] and all-cause mortality (ACM) were recorded prospectively in 954 patients with HF and LVEF ≤ 35%: 852 in sinus rhythm (SR) and 102 in AF. Cox proportional hazard models found that the univariate hazard ratios (HR) for LVEF and the first CAE (primary outcome), HFP, ARR, CD, and ACM were significant in SR (0.933, P < .001, 0.933, P < .001, 0.929, P < .001, 0.916, P < .001, 0.945, P = .001, respectively), but not in AF (1.002, P = .95, 1.060, P = .24, 0.922, P = .15, 0.885, P = .09, 0.932, P = .25). HRs for CAEs and ACM and one or more neurohormonal measures (iodine 123 m-iodobenzylguanidine cardiac parameters, B-type natriuretic peptide, and plasma norepinephrine) were significant in SR and AF. The multivariate models for the first CAE and HFP included neurohormonal measures and LVEF in SR and neurohormonal measures in AF.

CONCLUSIONS

In HF with LVEF ≤ 35% with AF, neurohormonal measures, but not LVEF, were related to outcomes.

On the importance of image gating for the assay of left ventricular mechanical dyssynchrony using SPECT

The potential of SPECT for quantifying left ventricular mechanical dyssynchrony is increasingly appreciated. We sought to examine the incidence and impact of image gating errors on this quantification and to test a possible solution for affected studies.

METHODS

First, to establish whether and how gating error alone could affect the measurement of dyssynchrony, we performed a prospective study in which patients with pacemakers were studied twice: during normal rhythm without gating error and with gating error caused by pacemaker-induced dysrhythmia. Second, to understand the pattern and magnitude of gating error during our typical imaging practice, we retrospectively examined studies from a separate cohort of 64 patients who were referred for dyssynchrony evaluation. Third, to understand whether studies with gating error could be repaired for the purpose of quantifying dyssynchrony, we tested a correction algorithm on the pacemaker-induced dysrhythmia image set to see whether it repaired this set so as to approximate the patients' normal rhythm image data. We subsequently applied this algorithm to the 64-patient cohort.

RESULTS

Pacemaker-induced gating error caused a spurious decrease in dyssynchrony magnitude. Among the 64-patient cohort, similar gating errors were common, and an inverse exponential relationship between gating-error magnitude and dyssynchrony magnitude was observed. The correction algorithm accurately repaired the pacemaker-induced dysrhythmia image set; when it was applied to the 64-patient cohort, the magnitude of the postcorrection increase in dyssynchrony magnitude was proportional to the magnitude of the gating error.

CONCLUSION

Gating errors cause a spurious reduction in SPECT assay of dyssynchrony magnitude. In our standard imaging practice, gating errors were common. Post hoc correction appears to be feasible.

Ventricular dyssynchrony assessed by gated myocardial perfusion SPECT using a geometrical approach: a feasibility study

PURPOSE

Left ventricular dyssynchrony may predict response to cardiac resynchronization therapy and may well predict adverse cardiac events. Recently, a geometrical approach for dyssynchrony analysis of myocardial perfusion scintigraphy (MPS) was introduced. In this study the feasibility of this geometrical method to detect dyssynchrony was assessed in a population with a normal MPS and in patients with documented ventricular dyssynchrony.

METHODS

For the normal population 80 patients (40 men and 40 women) with normal perfusion (summed stress score ≤2 and summed rest score ≤2) and function (left ventricular ejection fraction 55-80%) on MPS were selected; 24 heart failure patients with proven dyssynchrony on MRI were selected for comparison. All patients underwent a 2-day stress/rest MPS protocol. Perfusion, function and dyssynchrony parameters were obtained by the Corridor4DM software package (Version 6.1).

RESULTS

For the normal population time to peak motion was 42.8 ± 5.1% RR cycle, SD of time to peak motion was 3.5 ± 1.4% RR cycle and bandwidth was 18.2 ± 6.0% RR cycle. No significant gender-related differences or differences between rest and post-stress acquisition were found for the dyssynchrony parameters. Discrepancies between the normal and abnormal populations were most profound for the mean wall motion (p value <0.001), SD of time to peak motion (p value <0.001) and bandwidth (p value <0.001).

CONCLUSION

It is feasible to quantify ventricular dyssynchrony in MPS using the geometrical approach as implemented by Corridor4DM.

Interassay reproducibility of myocardial perfusion gated SPECT in patients with atrial fibrillation

AIM

The aim of this study was to assess interassay reproducibility of myocardial perfusion gated-SPECT for calculation of end-diastolic volume (EDV), end-systolic volume (ESV), and left ventricular ejection fraction (LVEF) in patients with atrial fibrillation (AF).

METHODS

One hundred and fifteen consecutive patients with AF from three participating hospitals (mean age 68.9 years, 39 women) were included in the study. All patients underwent two image gated acquisitions at rest with a 30 minute interval between them. Quantitative data were obtained using the QGS and ECT software algorithms.

RESULTS

Heart rate was similar in both studies: 74.94 +/- 15.2 vs 73.03 +/- 15.57. QGS yielded an LVEF of 54.4%/53.8%, an EDV of 100 mL/101.5 mL, and an ESV of 51 mL/52.3 mL; and ECT showed an LVEF of 63.6%/62.9%, an EDV of 125.8 mL/127.4 mL and ESV of 54.1 mL/56.3 mL. Correlation between the two acquisitions was high (>0.948) for both methods for LVEF, EDV and ESV. Regression and Bland-Altman graphics showed a good agreement between all parameters. Interassay variation coefficients for each method (QGS/ECT) were 5.29% vs 4.83% for LVEF, 4.94% vs 5.17% for EDV, and 9.94% vs 12.78% for ESV.

CONCLUSIONS

Interassay reproducibility of LVEF and EDV with gated-SPECT in patients with AF is good, whereas for ESV it is suboptimal, particularly when ESV is small.

Prognostic value of exercise echocardiography in patients with atrial fibrillation

AIMS

Non-invasive imaging techniques for the detection of coronary artery disease (CAD) may have technical problems in patients with atrial fibrillation (AF). Although the prognostic value of exercise echocardiography (ExEcho) has been well established in several subgroups of patients, it has not yet been specifically evaluated in these patients.

METHODS AND RESULTS

From a population of 8095 patients with known or suspected CAD referred for ExEcho, 419 had AF at the time of the tests. Ischaemia was defined as the development of new or worsening wall motion abnormalities with exercise. Endpoints were hard cardiac events (i.e. cardiac death or non-fatal myocardial infarction). Mean age was 68.4 +/- 8.5 years, and 256 patients (61.1%) were men. Ischaemia was detected in 92 patients (22%). Over a mean follow-up of 3.10 +/- 2.98 years, 59 hard cardiac events occurred. The 5-year hard cardiac event rate was 37.3% in patients with ischaemia, when compared with 14.5% in patients without ischaemia (P < 0.001). In multivariate analysis, ischaemia on ExEcho remained an independent predictor of hard cardiac events (hazard ratio 1.99, 95% confidence interval 1.06-3.74, P = 0.03), and also provided incremental value over clinical, resting echocardiographic and treadmill exercise data for the prediction of hard cardiac events (P = 0.04).

CONCLUSION

ExEcho provides significant prognostic information for predicting hard cardiac events in patients with AF.

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

OBJECTIVE

Algorithms 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 METHODS

We 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.

RESULTS

BP 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 (kappa=0.73; McNemar's 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.

CONCLUSION

MP 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.

The expanding role of left ventricular functional assessment using gated myocardial perfusion SPECT: the supporting actor is stealing the scene

BACKGROUND

Gating of single-photon emission computed tomography (SPECT) has significantly improved the reliability and diagnostic accuracy of myocardial perfusion imaging. The functional parameters derived from this technique, mainly left ventricular volumes and ejection fraction, have been demonstrated to be accurate and reproducible. They are able to increase the detection of severe and extensive coronary artery disease and show a significant incremental prognostic power over perfusion abnormalities. Therefore, the importance given to gated SPECT functional data has progressively grown.

DISCUSSION

This circumstance has further expanded the indications for myocardial perfusion imaging and strengthened its position among the different imaging modalities. Moreover, several studies show that the evaluation of ventricular function may have a leading part in justifying the execution of perfusion scintigraphy in various clinical conditions.

AIM

Aim of this review is to describe this evolution of gated SPECT functional assessment from a supporting rank with respect to perfusion, to a main actor position in the field of cardiac imaging.

Accuracy of radionuclide ventriculography assessed by magnetic resonance imaging in patients with abnormal left ventricles

BACKGROUND

We compared gated blood pool single photon emission computed tomography (SPECT) (GBPS), planar gated blood pool imaging (planar GBP), and cardiac magnetic resonance (CMR) measurements of left ventricular (LV) end-diastolic volume (EDV) and ejection fraction (EF) in patients with abnormal left ventricles.

METHODS AND RESULTS

LV functional parameters were measured for 40 subjects (age, 59 +/- 13 years; 85% male) by GBPS, planar GBP, and CMR. GBPS data were analyzed by use of count-threshold software (BP-SPECT) and surface gradient software (QBS). Limits of agreement with CMR for EF were -5% to +18%, -15% to +14%, and -15% to +16% for BP-SPECT, QBS, and planar GBP, respectively. However, limits of agreement with CMR for LV EDV were wide by both GBPS methods: -118 mL to +55 mL and -143 mL to +22 mL for BP-SPECT and QBS, respectively. Bland-Altman reproducibility limits for EF were -9% to +8%, -6% to +9%, and -7% to +7% by BP-SPECT, QBS, and planar GBP, respectively, and those for EDV were -46 mL to +48 mL and -31 mL to +35 mL by BP-SPECT and QBS, respectively.

CONCLUSION

GBPS LV EF measurements agree with measurements by CMR and are as reproducible as planar GBP measurements. However, wide limits of agreement of radionuclide versus CMR values suggest that caution must be applied in interpreting GBPS LV volume results, especially for patients with markedly abnormal left ventricles.

Prospective validation of a quantitative method for differentiating ischemic versus nonischemic cardiomyopathy by technetium-99m sestamibi myocardial perfusion single-photon emission computed tomography

BACKGROUND

Myocardial perfusion single-photon emission computed tomography (SPECT) permits assessment of stress perfusion and resting left ventricular (LV) function. Quantitative analysis of perfusion patterns among patients with LV dysfunction offers an opportunity for developing criteria to differentiate ischemic from nonischemic cardiomyopathy.

HYPOTHESIS

Quantitative assessment of SPECT may allow differentiation between ischemic and nonischemic cardiomyopathy.

METHODS

We evaluated 144 patients with LV ejection fraction < or =40%, divided into 63 patients with nonischemic and 81 with ischemic cardiomyopathy. Mean relative myocardial counts were obtained for regions drawn over defect and normal zones on rest and stress polar perfusion maps.

RESULTS

Multivariate logistic regression analysis of significant univariate SPECT predictors of ischemic cardiomyopathy revealed that the stress defect severity ratio (SDSR) was the best predictor of ischemic cardiomyopathy (p < 0.0001). By receiver operator characteristic (ROC) curve analysis, an SDSR of < or =45% optimized prediction of ischemic cardiomyopathy (sensitivity 81%, specificity 96%). An SDSR of < or =45% occurred in 65 of 81 (80%) patients with ischemic cardiomyopathy, but in only 3 of the 63 (4%) patients with nonischemic cardiomyopathy (p < 0.0001). Applying the < or =45% SDSR threshold to a prospective group of 89 patients yielded a somewhat lower sensitivity (60%), but retained high specificity (91%) for identifying ischemic cardiomyopathy (p = NS vs. retrospective group).

CONCLUSIONS

Presence of a severe and extensive stress perfusion defect is a hallmark of ischemic cardiomyopathy. By contrast, a mild stress perfusion defect (SDSR of >45%) is commonly present among patients with ischemic and nonischemic cardiomyopathy. An SDSR of < or =45% is a reproducible specific marker for identifying the presence of ischemic cardiomyopathy.

Quantitative single-photon emission computed tomography imaging

Over the past decade, quantitation of cardiac single-photon emission computed tomography (SPECT) data, once limited to perfusion assessment, has been extended to global and regional function assessment for both the left and the right ventricle, as well as to measurement of additional cardiac parameters of diagnostic and prognostic interest. A number of commercially available quantitative algorithms exist, based on different mathematic operators and with varying degrees of automation, that are capable of providing accurate and reproducible results. This article describes the many quantitative cardiac SPECT measurements available today, defining them in terms of validation, practical use, and limitations.

“W-shaped” volume curve with gated myocardial perfusion single photon emission computed tomography

OBJECTIVES

Gating errors (GEs) with ECG gated myocardial SPECT (G-SPECT) may occur irrespective of the presence or absence of arrhythmias. We evaluated the impact of GEs on both reconstructed tomograms and left ventricular ejection fraction (LVEF) derived from G-SPECT, and searched for clues to identify these errors.

METHODS

We studied 2 GE patients, 10 normal subjects (NLs), and 10 atrial fibrillation patients. Stress technetium-99m sestamibi G-SPECT was performed. Left ventricular (LV) contraction was evaluated in the beating slices. LVEF was calculated with G-SPECT using QGS (Cedars-Sinai, Los Angels) and p-FAST (Sapporo Medical University, Japan), and compared with that obtained by echocardiography (ECHO). LV volume curves were created by QGS and p-FAST. The heart rates (HRs) were calculated from the acquired images, and compared with their resting HRs. The mean count density of the myocardium was measured and time-activity curves were created.

RESULTS

In patients with GEs, bi-phasic LV contraction was demonstrated with fading-out towards end-diastole. G-SPECT underestimated LVEF compared to ECHO by 10% or more. The volume curves appeared "W-shaped." The HRs from the images were slower than the resting HRs. The count density decrement from frame #1 to #8 was larger than that of NLs. The time-activity curves were different in shape from those of NLs.

CONCLUSIONS

G-SPECT underestimates LVEF in patients with GEs. These errors can be identified with a combination of visual inspection of beating slices, time-volume curves, and time-activity curves. Monitoring the HR is a clue for anticipating and avoiding these errors.

Gated SPECT assessment of left ventricular function is sensitive to small patient motions and to low rates of triggering errors: a comparison with equilibrium radionuclide angiography

BACKGROUND

Patient displacements and errors in R-wave detection are the main causes of inaccurate acquisition for gated single photon emission computed tomography (SPECT) and equilibrium radionuclide angiography (RNA). This study aimed to compare the influences of both factors between gated SPECT and RNA determinations of left ventricular ejection fraction.

METHODS AND RESULTS

On gated SPECT and RNA acquisitions, recorded in 20 patients with coronary artery disease, we simulated the consequences of (1) 3-dimensional patient displacements of low (6.7 mm), moderate (13.4 mm), and high amplitude (20.1 mm) and (2) an erroneous triggering on T waves in 10% to 40% of recorded beats. Absolute values of left ventricular ejection fraction changes from baseline were higher with gated SPECT compared with RNA for patient displacements of low amplitude (5.0% +/- 3.8% vs 1.2% +/- 0.9%, P < .001) or moderate amplitude (10.0% +/- 6.2% vs 3.0% +/- 2.3%, P = .001) but not for patient displacements of high amplitude (12% +/- 9% vs 9% +/- 7%, P = not significant) and inaccurate triggering (for 20% T-wave triggering, 8.9% +/- 3.6% vs 7.9% +/- 3.0%; P = not significant).

CONCLUSION

Contrary to RNA, gated SPECT is vulnerable to small patient displacements, and thus, specific efforts might be useful for limiting this potential cause of erroneous results. Both techniques may be affected by low rates of triggering errors, suggesting that small acceptance windows on cycle length should be recommended not only for RNA but also for gated SPECT.

Feasibility of detecting cardiac torsion in myocardial perfusion gated SPECT data

BACKGROUND

The dynamic twisting component of cardiac motion is not accounted for by radionuclide techniques so that maps of perfusion and wall thickening are motion-blurred by torsion. This study examined whether torsion can be estimated from gated single photon emission computed tomography data and whether torsion corrections affect cardiac measurements.

METHODS AND RESULTS

Technetium 99m sestamibi myocardial perfusion gated tomograms were selected retrospectively for 52 patients who had x-ray contrast arteriograms: 12 with normal perfusion (group 1), 12 with abnormal perfusion (group 2), and 28 studied after angioplasty (group 3). The 8 gated perfusion maps were transformed by contrast normalization, the count minimums of which were tracked to quantify torsion. Measured torsion was used to correct maps of perfusion and wall thickening. Torsion was found to be visually detectable equally well in groups 1 and 2. Apical torsion was significantly greater for group 1 than groups 2 and 3 (15 degrees +/- 9 degrees vs 9 degrees +/- 15 degrees and 2 degrees +/- 12 degrees ) and was opposite in sign for patients with apical aneurysms (-4 degrees +/- 13 degrees ) and for patients after coronary artery bypass grafting (CABG) (-4 degrees +/- 15 degrees ). Maximum percent count differences were 10% +/- 16% between torsion-corrected versus uncorrected perfusion maps. The greatest wall thickening differences were seen for patients with left ventricular apical aneurysms and for patients after CABG versus group 1 (10% +/- 6% and 8% +/- 6% vs 3% +/- 1%, respectively).

CONCLUSIONS

It is feasible to detect cardiac torsion in the majority of Tc-99m sestamibi myocardial perfusion scans. Abnormal twisting patterns distinguished patients after CABG and those with left ventricular aneurysms from subjects with normal perfusion in a manner similar to magnetic resonance imaging observations.

Validation of SPECT equilibrium radionuclide angiographic right ventricular parameters by cardiac magnetic resonance imaging

BACKGROUND

Recent advances in the treatment of primary pulmonary hypertension (PPH), and in surgery to correct tetralogy of Fallot (TOF), have rekindled interest in evaluating right ventricular (RV) volume and ejection fraction (EF). The purpose of this investigation was to determine the accuracy of RV functional parameters assessed by single photon emission computed tomography (SPECT) equilibrium radionuclide angiography (ERNA).

METHODS AND RESULTS

Twenty-eight patients with PPH (n = 15) or TOF (n = 13) (aged 28 +/- 14 years; 57% male) were analyzed by means of SPECT ERNA algorithms that automatically identified mid-RV tomographic planes, generated regions isolating the right ventricle from other structures, and presented RV-segmented regions as a cinematic display. RV EF and volumes were computed and compared with values obtained by magnetic resonance imaging (MRI). Mean values were not different between SPECT ERNA and MRI for RV EF, end-diastolic volume, and end-systolic volume (42% +/- 11% vs 41% +/- 10%, 135 +/- 67 mL vs 139 +/- 91 mL, and 87 +/- 54 mL vs 85 +/- 61 mL, respectively; P = not significant for all comparisons). Significant linear correlation (P <.0001) was found between SPECT ERNA and MRI for RV EF, end-diastolic volume, and end-systolic volume (r = 0.85, r = 0.94, and r = 0.93, respectively). No statistically significant trends or biases for RV EF were found. Intraobserver and interobserver comparisons demonstrated good reproducibility. As expected, RV volume was significantly higher and RV EF was significantly lower for patients with PPH and TOF than were values for individuals at low likelihood for coronary artery disease or other cardiac disease.

CONCLUSIONS

SPECT ERNA provides accurate, reproducible assessment of RV volumes and EF and should prove useful in evaluating the magnitude of RV dysfunction in patients and in providing an objective means with which to assess the results of therapeutic interventions.