Original Article
Impact of Gd-153 scanning line source attenuation correction on downstream invasive testing

https://doi.org/10.1007/s12350-021-02565-2Get rights and content

Abstract

Background

Attenuation correction (AC) using hardware and software solutions has been shown to increase the specificity of SPECT MPI by decreasing false positive results and improving prognostic ability. Theoretically this should reduce downstream testing and unnecessary costs. We sought to assess the consequences of the use of Gd-153 scanning line source attenuation correction during SPECT myocardial perfusion imaging (MPI) on downstream invasive testing.

Methods

All patients who underwent a clinically indicated Tc-99m stress SPECT MPI study from 2013 to 2015 at five hospitals (2 with AC and 3 without) were retrospectively reviewed. Patient demographics, results of testing, subsequent coronary angiography within 3 months, and revascularization were recorded. The results of the MPI studies, downstream angiogram utilization, and results of angiography were compared and a propensity matched subgroup analysis was performed.

Results

A total of 9968 patients underwent SPECT MPI during the study time period (6106 performed with AC and 3862 without). Out of 3928 patients included in the propensity matched cohort, there was no difference in the proportion of abnormal MPI results between the two groups (31.5% vs 30.4%, P = 0.47), however, more patients underwent coronary angiography within 90 days in the AC group (10.6% vs 8.7%, P = 0.05). There was no significant difference in the proportion of patients with angiographically significant obstructive disease (53.4% vs 56.1%, P = 0.19), however, fewer patients in the AC group with obstructive coronary disease were revascularized (36.1% vs 46.8%, P = 0.04). The findings remained consistent after sub-group analysis in patients without known coronary disease.

Conclusion

The use of scanning line source AC did not meaningfully influence the rate of abnormal MPI results or downstream invasive testing in this cohort. The clinical utility of scanning line source AC may be limited to facilitating stress-first imaging protocols.

Introduction

Single photon emission computed tomography (SPECT) myocardial perfusion imaging (MPI) is a commonly used diagnostic test for the noninvasive evaluation of coronary artery disease. The accuracy of SPECT MPI is commonly compromised by the presence of soft tissue attenuation causing artifactual findings. Methods of reducing false positive results by the use of gated SPECT are limited, but more sophisticated methods of attenuation correction (AC) have increased both the sensitivity and specificity of SPECT MPI with the use of external-source gadolinium and low-dose computed tomography (CT). Most importantly, AC software and hardware have been shown to decrease false positives and improve the prognostic ability of the results.1

The published literature on the effects of AC is characterized by predominantly small studies (75-150 patients each) assessing the diagnostic accuracy of attenuation corrected SPECT MPI compared to the gold standard of invasive coronary angiography. A meta-analysis of 17 studies using both line source and CT AC found a small increase in sensitivity (80% to 84%), a larger increase in specificity (68% to 80%) and diagnostic odds ratio (9 to 22) when AC was used.2 Several other studies have investigated the change in prognostic power of MPI studies with and without AC.3, 4, 5 Most have found improved risk stratification with the use of AC with the summed stress score cutoffs shifted lower.3,4

However, attenuation correction technology comes at a significant cost and is not widely available as a result. The initial investment is substantial and the annual maintenance costs continue to add to the expenditure. As a result it has been reported that only 5% of installed SPECT systems have AC.6 The reported increased specificity should decrease false positive results and may reduce the need for downstream coronary angiography and potentially result in savings to the health care system. By decreasing unnecessary downstream testing and costs, the cost to benefit ratio of AC technology may be favorable. However, to our knowledge this has not yet been studied. We sought to assess the consequences of Gd-153 scanning line source attenuation correction utilization on downstream invasive testing.

Section snippets

Patient Selection

In a protocol approved by our institutional IRB, all patients who underwent a clinically indicated Tc-99m stress SPECT MPI study from 2013 to 2015 at five different hospitals (all within our healthcare network) were retrospectively reviewed. Two of the hospitals performed SPECT studies routinely with Gd-153 scanning line source AC equipped SPECT dual head conventional Na-I SPECT cameras and three of the hospitals utilized dual head conventional Na-I SPECT cameras without AC. The two hospitals

Results

A total of 9968 patients underwent SPECT MPI during the study time period with 6106 performed with AC and 3862 without AC (Table 1). The average age was 64.5 ± 13.0 years with 51.1% males and 31.4% having a previous history of CAD. The AC cohort was younger (63.6 ± 13.1 vs 66.1 ± 12.7, P < 0.0001) with a similar gender distribution and no difference in the proportion of patients with known CAD. There was a smaller proportion of patients with hypertension, high cholesterol, and smoking in the AC

Discussion

AC software and hardware have been shown to improve accuracy and the prognostic ability of SPECT myocardial perfusion, but at increased expense without commiserate increase in reimbursement. As a result this technology has not been routinely adopted in the community.12 The current study was designed to assess a clinically pertinent and economically relevant consequence of the use of AC on perfusion results and downstream coronary angiography utilization. Based on previous literature one would

Conclusions

The use of Gd-153 scanning line source AC did not affect the rate of abnormal MPI results or influence the utilization of downstream invasive testing. It is possible that the presence of an on-site invasive cardiac lab at a referral center may have significantly biased the patient population to a degree that propensity matching could not overcome. However, it must be considered that the clinical utility of scanning line source AC may be limited to facilitating stress-first imaging protocols.

New Knowledge Gained

Attenuation correction using hardware and software solutions has been shown to increase the specificity of SPECT MPI by decreasing false positive results and improving prognostic ability which should reduce downstream testing and unnecessary costs. A total of 9968 patients who underwent a clinically indicated Tc-99m stress SPECT MPI study from 2013 to 2015 at five hospitals (2 with AC and 3 without) were retrospectively reviewed for downstream coronary angiography within 3 months. Out of 3928

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Aditi Singhvi and Stephanie Suacier are co-first authors.

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