Patient-Centered Imaging: Advanced Protocoling and Stress-First SPECT

• By: admin
• On: 03/29/2021 10:15:52
• In: Membership

Protocoling Studies
In our nuclear cardiology lab, directed by ASNC Immediate Past President Sharmila Dorbala, MD, MPH, MASNC, all studies are protocoled by the nuclear cardiology fellow or general cardiology fellow rotating in the lab prior to the examination. Outpatient studies are protocoled at least 24 hours in advance, and emergency room and inpatient studies are protocoled prior to the patient coming down to the lab. Patients with suspected acute coronary syndrome, prior myocardial infarction (MI), a regional wall motional abnormality on transthoracic echocardiography, known ischemic cardiomyopathy referred for viability imaging, and/or prior abnormal myocardial perfusion imaging are protocoled to undergo rest-first imaging. The “default” for all other patients is stress-first imaging.
 
Stress Testing
Exercise stress testing is preferred given multiple advantages over pharmacological stress including obtaining functional and prognostic information. We discuss the utility of further investigation via coronary computed tomography angiography or invasive angiography with the referring provider in patients who have normal MPI, but an ischemic response to exercise with anginal symptoms, a reduction blood pressure with exercise, ischemic electrocardiographic changes, or ventricular tachycardia. In cases where the electrocardiogram (ECG) will not be interpretable (left bundle branch block (LBBB), pre-excitation, paced rhythm, etc.) or in patients who cannot exercise to an adequate workload, pharmacologic stress, typically vasodilator with regadenoson or adenosine (dobutamine is also used on a case-by-case basis except for patients with LBBB or paced ventricular rhythm) is performed.
 
SPECT Protocols
Our cadmium zinc telluride (CZT) cardiac imaging SPECT system is typically utilized for stress-first studies. If not available or not feasible, our SPECT/CT system is used. The dose of ^99mTechnetium sestamibi used is listed in Table 1. The timing of image acquisition is based on the mode of stress testing, with a shorter time between stress testing and image acquisition following exercise stress testing. Supine and upright images are obtained post-stress and scan time is ten minutes.
 
Table 1. Weight-Based ^99mTechnetium Dosing for Stress-First SPECT at Brigham and Women's Hospital (Boston, MA).

Patient Weight	99mTechnetium Dose
< 150 lbs.	6 mCi
150 – 200 lbs.	8 mCi
200 – 300 lbs.	10 mCi
≥ 300 lbs.	12 mCi

 
After scanning is complete, the images are processed and sent for review by the nuclear cardiology fellow. The fellow makes an assessment on image quality, and if rest imaging should be obtained. Criteria for normal stress-first images include homogenous perfusion, normal left ventricular size and volumes, normal left ventricular function with no regional wall motion abnormalities, and normal right ventricular uptake. All available data are reviewed to make an assessment, including ECG tracings and prior SPECT imaging if applicable. The fellow then reviews the images and his/her assessment and plan to defer or obtain rest imaging with the nuclear cardiology attending prior to completing the patient's visit or obtaining rest imaging. As per ASNC Guidelines, rest imaging is performed with approximately three times the stress dose of ^99mTechnetium (Figure 1).²
 
Figure 1. Schematic of One Day Stress-Rest Tc99m Imaging Protocol (per ASNC Guidelines). From Henzlova MJ et al. J Nucl Cardiol. Jun 2016;23(3):606-39.²



Advantages of Stress-First SPECT:
Stress-first imaging allows for the adherence to the as low as reasonably achievable (ALARA) goal, minimizing radiation exposure to the patient by eliminating the need for rest imaging provided the stress-first images are normal. This carries the same advantage for the nuclear medicine technologists in also reducing their radiation exposure. It also allows for a more streamlined experience for the patient. It is also a more efficient process as it reduces the patient's visit time and increases throughout for the lab. Costs are reduced by avoiding the use of a second radiotracer dose and additional scan time. Studies have shown that patients with normal stress-first SPECT studies have an excellent prognosis that is similar to patients with normal rest-stress studies.^{3, 4}
 
Important Considerations for Stress-First SPECT:
Performing a stress-first SPECT requires a physician to be readily available to interpret the stress-first imaging and decide on the need for rest imaging. Delays in this step can degrade the patient experience and lab efficiency. Suspected soft tissue attenuation often requires rest image acquisition if prior rest MPI is not available. Stress-first imaging in more than one position (upright/supine as we do in our own lab, or supine/prone) can eliminate some of these artifacts. Increased body mass index (BMI) is not a contraindication to stress-first imaging. However, images from patients with a high BMI are more vulnerable to soft tissue attenuation artifact and the increased dose needed for rest imaging may result in unacceptable radiation exposure for a one-day protocol. One solution in these situations is to plan a two-day strategy and give a higher dose for stress-first imaging on Day 1. If stress-first imaging is normal, Day 2 can be deferred. This will result in less radiation exposure for the patient compared to a rest-first protocol. Finally, CPT code 78451 (single study code) should be used for stress-only SPECT, while CPT code 78452 should be used for rest-stress or stress-rest SPECT.

Summary
Stress-first SPECT MPI remains a cornerstone in the assessment of patients with chest pain in the absence of acute coronary syndrome, regardless of their risk for coronary artery disease. A stress-first approach has the advantage of minimizing radiation exposure to both patients and team members, in addition to reducing costs and leading to more effective resource utilization. Advanced protocoling and a stress-first approach whenever appropriate are key to a patient-centered approach to SPECT MPI.

References
1. Depuey EG, Mahmarian JJ, Miller TD, et al. Patient-centered imaging. J Nucl Cardiol. Apr 2012;19(2):185-215. doi:10.1007/s12350-012-9523-z
2. Henzlova MJ, Duvall WL, Einstein AJ, Travin MI, Verberne HJ. ASNC imaging guidelines for SPECT nuclear cardiology procedures: Stress, protocols, and tracers. J Nucl Cardiol. Jun 2016;23(3):606-39. doi:10.1007/s12350-015-0387-x
3. Chang SM, Nabi F, Xu J, Raza U, Mahmarian JJ. Normal stress-only versus standard stress/rest myocardial perfusion imaging: similar patient mortality with reduced radiation exposure. J Am Coll Cardiol. Jan 2010;55(3):221-30. doi:10.1016/j.jacc.2009.09.022
4. Duvall WL, Wijetunga MN, Klein TM, et al. The prognosis of a normal stress-only Tc-99m myocardial perfusion imaging study. J Nucl Cardiol. Jun 2010;17(3):370-7. doi:10.1007/s12350-010-9210-x
 
 
 
Laura Murphy, MB BCh is an advanced fellow in the Cardiovascular Imaging Program at Brigham and Women's Hospital/Harvard Medical School in Boston, MA.


Sanjay Divakaran, MD is an associate physician in the Division of Cardiovascular Medicine and the Cardiovascular Imaging Program at Brigham and Women's Hospital/Harvard Medical School in Boston, MA. He is a member of the ASNC Social Media Task Force Committee and the Education Committee. He is also a member of the Entering Class of 2020 ASNC Leadership Development Program.