Elsevier

Journal of Nuclear Cardiology

Volume 29, Issue 6, December 2022, Pages 3443-3449
Journal of Nuclear Cardiology

Brief Report
Diagnostic performance of IQ·SPECT with high-speed scanning: A preliminary quality control study in obese patients

https://doi.org/10.1007/s12350-022-02928-3Get rights and content

Abstract

Background

IQ·SPECT is a recently introduced collimator design for myocardial perfusion imaging (MPI). Little data exist on use of this collimator type in obese patients, particularly Class 2 or 3 [body mass index (BMI) > 35 kg/m2].

Methods

Two consecutive rest–stress MPI scans were prospectively acquired using a conventional collimator and IQ·SPECT (acquisition times of 20 and 7 minutes, respectively) in 20 patients with a BMI of >30 kg/m2. Assigned by two blinded, independent readers, image quality (on a 5-point scale) and metrics of myocardial perfusion [summed stress score (SSS), summed rest score (SRS) and summed difference score (SDS)] were compared. Software-based left ventricular ejection fraction (EF) was also correlated.

Results

Mean BMI was 39.6 ± 7.6 kg/m2. Class 2 or 3 obesity was present in 12 patients (BMI, 44.1 ± 6.8 kg/m2). Gated/non-gated images from IQ·SPECT revealed fair to good quality scores (median ≥ 3.25), which were inferior to the conventional collimator (median ≥ 4.0; P ≤ 0.01). Significant correlative indices were achieved when comparing IQ·SPECT and conventional collimators for EF values (r = 0.86, P < 0.01), SSS (r = 0.75, P < 0.0001) and SRS (r = 0.60, P < 0.005), but not for SDS (r = 0.15).

Conclusion

IQ·SPECT was comparable to conventional SPECT in obese patients. The reduced acquisition time of IQ·SPECT may allow for improved throughput with no loss in diagnostic accuracy.

Introduction

Myocardial perfusion imaging (MPI) with single-photon emission computed tomography (SPECT) is associated with frequent soft tissue attenuation artifacts which may decrease image quality.1 The degree of soft tissue attenuation in myocardial SPECT has been previously associated with obesity.2 However, simple measures such as weight do not uniformly correlate with SPECT imaging accuracy and other patient-specific factors such as body habitus and body mass index (BMI) may be more important.2,3

Recent advances in collimator design have been introduced that may have implications for improving SPECT MPI image quality. A primary benefit of new collimator designs, such as the multi-pinhole and multifocal collimators, is increased detection of photons arising in the myocardium by the SPECT camera (i.e., increased detection efficiency).4,5 The recently introduced IQ·SPECT system (Siemens Healthineers, Erlangen, Germany) utilizes a multifocal collimator with a "fan-beam" arrangement of septa in the center of the field of view, and a near-parallel arrangement at the periphery.6 This arrangement has been shown to increase the detected photons from the myocardium by a factor of 2-4 while avoiding truncation artifacts elsewhere in the torso.6 With its “minimum dose, maximum speed”-concept, IQ·SPECT enables decreased imaging time compared with conventional SPECT using parallel-hole collimators (requiring 1/2 to as little as 1/8 amount of time), with similar image quality.7 Alternatively, the administered radiotracer dose may be reduced without sacrificing imaging quality.8

However, due to differences in collimator geometry, images reconstructed with IQ·SPECT are more dependent on proper patient positioning and attenuation artifacts may be less predictable compared to conventional methods.9 A previous study has noted no difference in IQ·SPECT vs. conventional SPECT imaging interpretation in obese patients (i.e., BMI > 30 kg/m2) vs. overweight patients (BMI < 30 kg/m2). Of note, mean BMI in this study population was 28.2 kg/m2, suggesting few, if any, patients with Class 3 (severe) obesity (BMI, >40 kg/m2) were included.8,10

The Centers for Disease Control and Prevention, has tabulated an increase in the age-adjusted prevalence of Class 3 obesity from 4.7% to 9.2% over the last 20 years in the United States.11 Not surprisingly, it is anticipated that 20.5 million individuals will be classified as severely obese by 2025, with an anticipated growth rate of 35% when compared to 2012.12 In light of this increasing trend, we undertook a prospective study to investigate the image quality of IQ·SPECT vs conventional SPECT in obese patients, specifically focusing on individuals with Class 2 (35 to < 40 kg/m2) or 3 obesity (> 40 kg/m2).

Section snippets

Methods

This prospective study was approved by the Johns Hopkins University School of Medicine Institutional Review Board and all subjects signed informed consent prior to participation (IRB00103256). 20 consecutive patients meeting all inclusion/exclusion criteria were enrolled in the study. Inclusion criteria were age between 18 and 80 years and BMI > 30 kg/m2. Patients were subdivided as having Class 1 (30 to < 35 kg/m2), Class 2 (35 to < 40 kg/m2), or Class 3 (> 40 kg/m2) obesity.11 Exclusion

Results

BMI for the study population was 39.6 ± 7.6 kg/m2. 8 individuals had Class 1 obesity, already presenting with a BMI at the upper limit of 33 ± 1.3 kg/m2. The remaining 12 subjects (BMI, 44.1 ± 6.8 kg/m2) met criteria for Class 2 (n = 5, 38.1 ± 1.8 kg/m2) or Class 3 obesity (n = 7, 48.3 ± 5.6 kg/m2; Table 1).

Discussion

In this prospective study of obese patients, high-speed IQ·SPECT imaging revealed comparable qualitative and quantitative diagnostic performance relative to conventional collimators. Thus, in obese subjects, the reduced acquisition time of IQ·SPECT may allow for higher throughput without sacrificing image quality. Of note, a substantial portion of our patients (60%) had a BMI > 35 kg/m2, supporting the notion that the derived findings also apply to individuals categorized with Class 2 or 3

Conclusions

In this head-to-head comparison of IQ·SPECT with a conventional collimator in obese patients (including those with severe obesity), revealed comparable performance for both quantitative and qualitative imaging parameters, even in individuals with Class 2 or 3 obesity. Given the increasing rise of such severely obese individuals with BMI > 35 kg/m2, the reduced acquisition time of IQ·SPECT may allow for higher throughput without sacrificing image quality.

New Knowledge Gained

Given the precipitous rise of severe obesity, nuclear cardiology laboratories can anticipate an increasing number of individuals presenting with a BMI of >35 kg/m2 at time. In the present prospective study enrolling obese and severely obese patients, high-speed IQ·SPECT demonstrated comparable performance relative to a conventional collimator. The reduced acquisition time of IQ·SPECT may allow for higher throughput without sacrificing image quality, even in obese or morbidly obese individuals.

Funding Statement

This work was supported by German Research Council (Deutsche Forschungsgemeinschaft, 453989101, TH, RAW) and through the Okayama University “RECTOR” Program (TH). A KAKENHI Grant (21K19450) has been provided for TH from the Japan Society for the Promotion of Science (JSPS).

Disclosure

None.

References (15)

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Rudolf A. Werner, Ricardo Bello Martinez, Mehrbod S. Javadi and Steven P. Rowe share equal contribution to this work.

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