Contemporary Cardiac SPECT Imaging-Innovations and Best Practices: An Information Statement from the American Society of Nuclear Cardiology

This information statement from the American Society of Nuclear Cardiology highlights advances in cardiac SPECT imaging and supports the incorporation of new technology and techniques in laboratories performing nuclear cardiology procedures. The document focuses on the application of the latest imaging protocols and the utilization of newer hardware and software options to perform high quality, state-of-the-art SPECT nuclear cardiology procedures. Recommendations for best practices of cardiac SPECT imaging are discussed, highlighting what imaging laboratories should be doing as the standard of care in 2018 to achieve optimal results (based on the ASNC 2018 SPECT guideline [Dorbala et al., J Nucl Cardiol. 2018. https://doi.org/10.1007/s12350-018-1283-y ]).

Prognostic value of the cadmium-zinc-telluride camera: A comparison with a conventional (Anger) camera

BACKGROUND

New multipinhole cadmium-zinc-telluride (CZT) cameras allow for faster imaging and lower radiation doses for single photon emission computed tomography (SPECT) studies, but assessment of prognostic ability is necessary.

METHODS AND RESULTS

We collected data from all myocardial SPECT perfusion studies performed over 15 months at our institution, using either a CZT or conventional Anger camera. A Cox proportional hazards model was used to assess the relationship between camera type, imaging results, and either death or myocardial infarction (MI). Clinical variables including age, sex, body mass index (BMI), and historical risk factors were used for population description and model adjustments. We had 2,088 patients with a total of 69 deaths and 65 MIs (122 events altogether). A 3% increase in DDB (difference defect burden) represented a 12% increase in the risk of death or MI, whereas a 3% increase in rest defect burden or stress defect burden represented an 8% increase; these risks were the same for both cameras (P > .24, interaction tests).

CONCLUSIONS

The CZT camera has similar prognostic values for death and MI to conventional Anger cameras. This suggests that it may successfully be used to decrease patient dose.

Technical aspects of resolution recovery reconstruction

Technological advances in processing have allowed nuclear cardiology labs to increase efficiency as well as reduce radiation exposure to both patients and staff. With increased awareness on reduced radiation exposure, efficiency and quality resolution recovery reconstruction is a perfect fit for nuclear cardiology. Having a basic understanding of what is required as well as being aware of the potential pitfalls can provide some clarity on how to incorporate resolution recovery reconstruction into the existing workflow of a nuclear cardiology lab.

Prevalence and predictors of mechanical dyssynchrony as defined by phase analysis in patients with left ventricular dysfunction undergoing gated SPECT myocardial perfusion imaging

BACKGROUND

A novel method to quantify dyssynchrony using phase analysis of single-photon emission computed tomography (SPECT) myocardial perfusion imaging has been developed. We sought to determine the prevalence of SPECT-derived mechanical dyssynchrony, and we report clinical variables which predict mechanical dyssynchrony in patients with left ventricular dysfunction.

METHODS

We used a count-based Fourier analysis method to convert the regional myocardial counts from discrete frames per cardiac cycle into a continuous thickening function which allows resolution of the phase of the onset of myocardial contraction. The standard deviation of left ventricular phases (Phase SD) describes the regional phase dispersion as a measure of dyssynchrony. Significant dyssynchrony was defined as Phase SD ≥ 43°. 260 patients with left ventricular ejection fraction ≤ 35% were examined.

RESULTS

The prevalence of mechanical dyssynchrony in the entire cohort of patients studied was 52%. Univariate predictors of Phase SD were age (P = .03), black race (P = .0005), QRS duration, EF, EDV, summed stress score (SSS), and summed rest score (SRS) (all P = <.0001). Black race, male gender, QRS EF, and SRS were independent predictors of SPECT-based mechanical dyssynchrony.

CONCLUSIONS

Significant SPECT-based mechanical dyssynchrony is relatively common among patients with left ventricular dysfunction. In a population of patients with predominantly ischemic heart disease referred for SPECT, a reduced EF, increasing QRS duration, severity and extent of myocardial scar on SPECT imaging are independent predictors of mechanical dyssynchrony and may serve to identify patients for dyssynchrony screening.

Use of phase analysis of gated SPECT perfusion imaging to quantify dyssynchrony in patients with mild-to-moderate left ventricular dysfunction

BACKGROUND

CRT has been shown to be beneficial in the majority of patients with NYHA class III-IV symptoms, prolonged QRS duration, and an EF < or =35%. The use of imaging modalities to quantify dyssynchrony may help identify patients who may benefit from CRT, but do not meet current selection criteria. We hypothesize that patients with mild-to-moderate LV dysfunction have significant degrees of mechanical dyssynchrony.

METHODS

We compared phase analysis measures of mechanical dyssynchrony from gated SPECT imaging in patients with mild-to-moderate LV dysfunction (EF 35-50%, n = 93), with patients with severe LV dysfunction (EF < or = 35%, n = 167), and with normal controls (EF > or = 55%, n = 75). Furthermore, we evaluated the relationships between QRS duration and dyssynchrony and determined the prevalence of dyssynchrony in patients with mild-moderate LV dysfunction.

RESULTS

Patients with mild-moderate LV dysfunction have more dyssynchrony than normal controls (phase SD 37.7 degrees vs 8.8 degrees , P < .001 and bandwidth 113.5 degrees vs 28.7 degrees , P < .001), but less dyssynchrony than patients with severe LV dysfunction (phase SD 37.7 degrees vs 52.0 degrees , P < .001 and bandwidth 113.5 degrees vs 158.2 degrees , P < .001). In the cohort of patients with LV EF 35-50%, there were only weak correlations between QRS duration and dyssynchrony (phase SD, r = 0.28 and bandwidth, r = 0.20). There were 73 patients with LVEF 35-50% and QRS duration <120 milliseconds of which 21 (28.8%) had mechanical dyssynchrony. Overall, 37% of patients with mild-to-moderate LV dysfunction had significant degrees of mechanical dyssynchrony.

CONCLUSIONS

This is the largest reported study evaluating mechanical dyssynchrony in patients with mild-moderate LV dysfunction using phase analysis of gated SPECT imaging. In this study, approximately one-third of patients with mild-to-moderate LV dysfunction had significant LV mechanical dyssynchrony. With further study, phase analysis of gated SPECT imaging may help improve patient selection for CRT.

Prognostic validation of an algorithm to convert myocardial perfusion SPECT imaging data from a 12-segment model to a 17-segment model

BACKGROUND

A 17-segment model has become the standard for interpreting myocardial perfusion single-photon emission computed tomography (SPECT). Methods for converting pre-existing databases from 12-segment models to the 17-segment model are needed for ongoing prognostic studies.

METHODS AND RESULTS

To develop the conversion algorithm, 150 consecutive SPECT studies (82 abnormal) were read by both a 12-segment and the standard 17-segment models. Summed stress scores (SSSs) were calculated from a 17-segment model derived from the 12-segment data and compared to those of the standard 17-segment model. The effect of the conversion algorithm on prognostic data derived from the 12-segment model was evaluated in 25,876 patients from the Duke Nuclear Cardiology Database, including a sample of 3,205 patients with known covariates for adjusted analysis. The derived 17-segment SSS from the 12-segment model was highly correlated (R = 0.99) to the SSS from the standard 17-segment model. In both unadjusted and adjusted analysis, there was no difference in the prognostic information.

CONCLUSIONS

An algorithm for conversion of 12-segment perfusion scores to 17-segment scores has been developed which is highly correlated to visual interpretation by the 17-segment model with nearly identical prognostic information.

Evaluation of mechanical dyssynchrony and myocardial perfusion using phase analysis of gated SPECT imaging in patients with left ventricular dysfunction

BACKGROUND

Using phase analysis of gated single photon emission computed tomography (SPECT) imaging, we examined the relation between myocardial perfusion, degree of electrical dyssynchrony, and degree of SPECT-derived mechanical dyssynchrony in patients with left ventricular (LV) dysfunction.

METHODS AND RESULTS

We retrospectively examined 125 patients with LV dysfunction and ejection fraction of 35% or lower. Fourier analysis converts regional myocardial counts into a continuous thickening function, allowing resolution of phase of onset of myocardial thickening. The SD of LV phase distribution (phase SD) and histogram bandwidth describe LV phase dispersion as a measure of dyssynchrony. Heart failure (HF) patients with perfusion abnormalities have higher degrees of dyssynchrony measured by median phase SD (45.5 degrees vs 27.7 degrees, P < .0001) and bandwidth (117.0 degrees vs 73.0 degrees, P = .0006). HF patients with prolonged QRS durations have higher degrees of dyssynchrony measured by median phase SD (54.1 degrees vs 34.7 degrees, P < .0001) and bandwidth (136.5 degrees vs 99.0 degrees, P = .0005). Mild to moderate correlations exist between QRS duration and phase analysis indices of phase SD (r = 0.50) and bandwidth (r = 0.40). Mechanical dyssynchrony (phase SD >43 degrees) was 43.2%.

CONCLUSIONS

HF patients with perfusion abnormalities or prolonged QRS durations have higher degrees of mechanical dyssynchrony. Gated SPECT myocardial perfusion imaging can quantify myocardial function, perfusion, and dyssynchrony and may help in evaluating patients for cardiac resynchronization therapy.

Emerging role of myocardial perfusion imaging to evaluate patients for cardiac resynchronization therapy

Left ventricular (LV) dyssynchrony is an increasingly important consideration in the evaluation and management of patients with LV systolic dysfunction. Improvements in clinical status, LV remodeling, and survival have been demonstrated with the use of cardiac resynchronization therapy (CRT). The current selection criteria for patients who undergo CRT include the presence of severe LV dysfunction, significant heart failure symptoms, and electrical dyssynchrony on surface electrocardiography (wide QRS interval). However, up to 40% of patients who undergo CRT do not experience reductions in symptoms or LV functional improvement. Because electrical dyssynchrony is not synonymous with contractile or mechanical dyssynchrony, efforts have been made to more accurately quantify mechanical dyssynchrony in the hope of improving the selection of patients for CRT. These efforts have focused largely on echocardiographic measures of mechanical dyssynchrony. A novel method to quantify LV mechanical dyssynchrony has been developed using phase analysis of gated single photon-emission computed tomographic myocardial perfusion imaging. In conclusion, this report describes potential advantages, compared with other methods, of using myocardial perfusion imaging to evaluate patients for CRT; reviews the method of the phase analysis technique to quantify dyssynchrony; reviews the available evidence of its utility; and describes future directions in research.

Prediction of mortality in patients with coronary artery disease undergoing vasodilator stress testing: A comparison between 99mTc-tetrofosmin and 99mTc-sestamibi

PURPOSE

To compare the prognostic ability of the imaging agents 99mTc-sestamibi versus 99mTc-tetrofosmin to predict mortality outcomes in patients with documented coronary artery disease and undergoing vasodilator stress testing.

MATERIALS AND METHODS

The study included 2147 consecutive patients who underwent rest and stress single photon emission computed tomographic (SPECT) examination with either 99mTc-sestamibi (n=1128) or 99mTc-tetrofosmin (n=1019). Information relating to all-cause death and cardiovascular death was collected over a 4-year study period. Unadjusted Kaplan-Meier estimates were compared for the two imaging agents. Cox proportional hazard models were examined to determine the incremental contribution of SPECT sum stress score (SSS) and the imaging agent after adjusting for clinical and demographic characteristics. Additionally, the interaction between SSS and agent was examined to determine if the effect of SSS on prognosis was different for the two agents.

RESULTS

Vasodilator agents were used for stress testing in all patients who received 99mTc-tetrofosmin and 99mTc-sestamibi. Despite differences in patient risk factors Kaplan-Meier estimates were similar for the two groups of patients. Resulting P-values for differences between models for the end points of (1) death from any cause and (2) cardiovascular death showed that SSS combined with clinical index was significantly better than a model that adjusted for only baseline characteristics (P<0.0001 for both endpoints). The addition of imaging agent (99mTc-tetrofosmin or 99mTc-sestamibi) to the model containing both SSS and the clinical characteristics did not show further significant improvement (P=0.62, P=0.96 for death from any cause and cardiovascular death, respectively).

CONCLUSION

The type of clinically available 99mTc-labelled myocardial perfusion agents did not affect interpretation of results for prognostic assessment.

Myocardial perfusion changes in patients irradiated for left-sided breast cancer and correlation with coronary artery distribution

PURPOSE

To evaluate postradiation regional heart perfusion changes with single photon emission tomography (SPECT) myocardial perfusion imaging in 69 patients treated with tangential photon beams radiation therapy (RT) for left-sided breast cancer. To correlate SPECT changes with percent irradiated left ventricle (LV) volume and risk factors for coronary artery disease (CAD).

METHODS AND MATERIALS

Rest SPECT of the LV was acquired pre-RT and at 6-month intervals post-RT. The extent of defects (%) with a severity > 1.5 standard deviations below the mean was quantitatively analyzed for the distributions of the left anterior descending (LAD) artery, left circumflex (LCX) artery, and right coronary artery (RCA) based on computer assisted polar map reconstruction (i.e., bull's-eye-view). Changes in perfusion were correlated with percent irradiated LV receiving > 25 Gy (range 0-32%). Data on patient- and treatment-related factors were collected prospectively (e.g., cardiac premorbidity, risk factors for CAD, chemotherapy, and hormonal treatment).

RESULTS

In the LAD distribution, there were increased perfusion defects at 6 months (median 11%; interquartile range 2-23) compared with baseline (median 5%; interquartile range 1-14) (p < 0.001). There were no increases in perfusion defects in the LCX or RCA distributions. In multivariate analysis, the SPECT perfusion changes in the LAD distribution at 6 months were independently associated with percent irradiated LV (p < 0.001), hormonal therapy (p = 0.005), and pre-RT hypercholesterolemia (p = 0.006). The SPECT defects in the LAD distribution at 12 and 18 months were not statistically different from those at 6 months. The perfusion defects in the LAD distribution were limited essentially to the regions of irradiated myocardium.

CONCLUSION

Tangential photon beam RT in patients with left-sided breast cancer was associated with short-term SPECT defects in the vascular distribution corresponding to the radiation portals. Factors related to the extent of perfusion defects included the percent irradiated LV, hormonal treatment, and pre-RT hypercholesterolemia.