'A Test for the Masses': Understanding the Advantages of SPECT MPI and How Labs Can Make the Most of It

An interview with Saurabh Malhotra, MD, MPH, FASNC, Director of Advanced Cardiac Imaging at Cook County Health in Chicago, Illinois




THE DEBATE OVER WHICH MODALITY is optimal for cardiac imaging continues among those in nuclear cardiology and in cardiovascular imaging in general. While one must be cognizant of applying the appropriate test for a given patient, physicians now have several nuclear and non-nuclear imaging modalities to choose from.

As financial pressures facing healthcare continue to grow due to the COVID-19 pandemic, it is important that nuclear cardiology teams understand the value of the tools they currently have in place, such as the widely available single-photon emission computerized tomography (SPECT) myocardial perfusion imaging (MPI) technology, and how best to optimize it. There are various ways in which a nuclear cardiology lab can enhance the technology at hand by implementing novel imaging protocols and with hardware or software upgrades.

Dr. Malhotra discusses his perspective on the benefits of SPECT MPI:

1. It is an effective and viable choice
According to Dr. Malhotra, the value of SPECT MPI technology is crystal clear. “SPECT MPI is a test for the masses. It’s widely available, both from a technology standpoint and from an isotope standpoint,” he says. Based on 2019 Centers for Medicare & Medicaid Services Part B data, SPECT accounts for a majority of nuclear MPI scans. That’s no surprise, says Dr. Malhotra, given that positron emission tomography (PET) MPI is a newer modality and has not yet been adopted as widely. Most labs are presently configured and built for SPECT MPI, including access to isotopes and radiation safety. Existing SPECT MPI laboratories have the option of upgrading their technology in ways that allow for lab improvements in close to real time and still have a vision for long term quality improvement investments. Additionally, the elements of the SPECT MPI workflow are in place for most labs and institutions and can be tailored to a nuclear cardiology laboratory’s daily needs. Considering these factors, Dr. Malhotra says utilizing SPECT MPI can be a clear and efficient choice for many physician practices and imaging clinics.1
 
2. Patient outcomes are comparable
While newer non-nuclear imaging technologies and modalities, such as Fractional Flow Reserve derived from computed tomography (FFRCT), are commonly quoted2 to provide superior clinical data, clinical outcomes among patients have not been shown to be significantly different than SPECT MPI, says Dr. Malhotra. Therefore, Dr. Malhotra believes facilities should continue to have confidence in SPECT MPI.  A recent study concluded that there were no discernable differences in the ability of SPECT MPI with attenuation correction or PET MPI to diagnose angiographically significant CAD, with no differences in patients’ outcomes.3 (PET myocardial blood flow was not included as part of this protocol.) Dr. Malhotra also cautions considering FFRCT as the new “gold standard” as many may want to assume. He notes that FFRCT was developed in the background of exercise stress testing and SPECT MPI as gold standards. The inability to perform computed tomography (CT) among those with renal dysfunction limits the routine application of FFRCT. Additionally, a clinical algorithm combining SPECT MPI findings and appropriate use criteria has been recently shown to guide prognostication in over 12,000 patients with stable CAD. 4 This study further underscores the established prognostic value of SPECT MPI and innovative ways in which it can be incorporated into clinical practice.  


3. The ability to gather functional data from stress imaging
Pharmacologic stress MPI can be performed with both SPECT and PET techniques. Per Dr. Malhotra, the characteristics of SPECT radiopharmaceuticals allow for performance of exercise MPI, which is at this time difficult to perform with PET given the short tracer half-life. Exercise stress testing assesses a patient’s functional capacity, hemodynamic response and presence of any anginal symptoms7. Hemodynamic and electrocardiogram (ECG) data from exercise stress testing have both diagnostic and prognostic value, and supplements the information derived from MPI7. Dr. Malhotra also notes that, in patients with known coronary artery disease (CAD), exercise SPECT MPI is pivotal to understanding the efficacy of medical therapy.

 
4. Protocol flexibility aids lab throughput
Dr. Malhotra shares that a less widely known benefit of SPECT MPI is imaging during active chest pain. He states that injection of the tracer during chest pain has the diagnostic advantage of imaging myocardial perfusion during symptoms, which obviates the need for stress imaging to diagnose ischemia and allows for rapid image reporting and disposition. Such a protocol can be applied in the emergency department, especially during the current COVID-19 pandemic. Dr. Malhotra also notes the six-hour half-life of technetium-99m adds to the laboratory flexibility and reduction in overall costs related to a long hospital stay. This flexibility is enhanced by new cadmium zinc telluride (CZT) systems.
 
5. There are no contraindications
Dr. Malhotra mentions, unlike other imaging modalities, there are no known contraindications to performance of SPECT MPI.5 In comparison, cardiac computed tomography angiography (CCTA) is contraindicated in patients with chronic kidney disease who are not infrequently seen in contemporary clinical practice11. Additionally, Dr. Malhotra notes SPECT MPI does not require heart rate control, which is in contrast to CCTA, wherein the image quality can be significantly degraded when heart rate is not well controlled, which compromises angiographic diagnosis and also fractional flow assessment. In a recently published multicenter trial, approximately 11 percent of otherwise eligible patients were excluded as they could not undergo CCTA due to renal dysfunction. Similarly, renal dysfunction, presence of metal in the body and claustrophobia are contraindications to contrast-enhanced cardiac magnetic resonance, along with limited access to technology and expertise.6 Similarly, renal dysfunction, presence of metal in the body and claustrophobia are contraindications to contrast-enhanced cardiac magnetic resonance, along with limited access to technology and expertise.10  
 
Enhancing the diagnostic offerings of SPECT MPI
From the interview, it is Dr. Malhotra’s opinion that when considering the choice of nuclear cardiology modality, SPECT MPI is clinically appropriate, accurate and very accessible. Dr. Malhotra further states that when considering its own set of benefits and comparable patient outcomes, there’s clearly an immense value of the clinical application of this tried-and-true technology. 3 As SPECT MPI cardiology labs look to enhance their diagnostic offerings, Dr. Malhotra encourages nuclear cardiology teams to focus on improving what they already have and optimizing laboratory performance.
 
Dr. Malhotra offers two suggestions for how hospitals and imaging clinics could improve their existing SPECT MPI labs:

1. Upgrade software and hardware upgrades
Per Dr. Malhotra, laboratories with existing A-SPECT technology can improve image quality by upgrading their image reconstruction software to incorporate iterative reconstruction algorithms. Installation of hardware allowing for attenuation correction, either with a line-source technique or CT, will significantly enhance the image quality and improve the specificity of the SPECT MPI results8. The latter also allows for stress-first and stress-only imaging, which can improve laboratory throughput and reduces radiation exposure.
 
2. Invest in new gamma cameras
Dr. Malhotra recommends that laboratories aiming to replace older A-SPECT technology should strongly consider hybrid SPECT/CT systems or high-resolution CZT cameras. This is even more relevant now, given the significant financial constraints faced by numerous health systems that may not be able to afford more expensive technologies. He says hybrid SPECT/CT technology confers the additional advantage of assessment of coronary calcium score, which can be used by laboratories for better risk stratification, and a SPECT/CT system allows for accurate acquisition and interpretation of both planar and tomographic data, with the ability to co-localize true myocardial uptake from blood pool activity. Dr. Malhotra believes high-sensitivity CZT SPECT systems provide image resolution comparable to PET MPI, even among morbidly obese patients. CZT SPECT technology also enhances the ability of laboratories to provide improved patient-centered imaging – with lower radiation exposure (approaching that of PET MPI), ultra-fast imaging and enhanced application of low-dose stress-first and stress-only protocols.9
 
Disclaimer: The views and opinions expressed in this article are those of Dr. Saurabh Malhotra, MD, MPH, FASNC, Director of Advanced Cardiac Imaging at Cook County Health in Chicago, Illinois, and are based on his independent observations and judgements and do not necessarily reflect the policies, views or position of Cardinal Health. Any recommendations, analysis and or conclusions being provided are the opinions and conclusions of Dr. Malhotra. Cardinal Health does not warrant or guarantee the information provided is accurate, current or applicable for a particular use and accepts no responsibility or liability whatsoever.

For more information on radiopharmaceuticals, please visit Cardinal Health™ Nuclear & Precision Health Solutions.

References:
1.
Des Prez et al Journal of Nuclear Cardiology Cost-effectiveness of MPI November/December 2005
2. The American College of Cardiology, CCTA, FFR, and Perfusion PET for Ischemia Diagnosis, January 16, 2019
3. JACC: Cardiovascular Imaging, Volume 12, Issue 9, September 2019, Pages 1821-1831
4. Implementation of a Myocardial Perfusion Imaging Risk Algorithm to Inform Appropriate Downstream Invasive Testing and Treatment | Circulation: Cardiovascular Imaging (ahajournals.org)
5. Technetium TC 99M Sestamibi, medically reviewed by Drugs.com, December 1, 2020
6. The New England Journal of Medicine, Initial Invasive or Conservative Strategy for Stable Coronary Disease , April 9, 2020
7. Nuclear Medicine Stress Test, NCBI, May 2020,
8. Comparison of non-attenuation corrected and attenuation corrected myocardial perfusion SPECT, ScienceDirect, September 2016
9. Dedicated cardiac CZT SPECT is steadily moving to achieve its destiny, Journal of Nuclear Cardiology, July 2017
10. Magnetic Resonance Imaging Contraindications

 











SPECT MPI in a patient presenting with chest pain in the ED. Technetium-99m was injected during active chest pain, without stress, with gated SPECT being performed at 45 minutes after tracer injection. SPECT MPI shows, severe perfusion defect in the apex and the periapical region. This was consistent with a perfusion defect in the left anterior descending (LAD) coronary artery distribution, and severe mid LAD stenosis (purple arrow) was confirmed on a subsequent angiogram.

Source:  Saurabh Malhotra, MD, MPH, FASNC.














 

Saurabh Malhotra, MD, MPH, FASNC,
Director of Advanced Cardiac Imaging,
Cook County Health, Chicago, Illinois