Coronary artery disease (CAD) remains the world’s leading cause of death with 16% of the world’s total death. According to World Health Organization, there were 2 to 8.9 million deaths in 2019.1 Prevention and early non-invasive diagnosis or early detection with high sensitivity and high specificity must be the priority to slow down the increasing death caused by CAD. SPECT-MPI using radiopharmaceutical 99mTc-Sestamibi can be used to diagnose and evaluate the prognostic value of CAD. It shows more cost effective than any other diagnostic modality, and more sensitive than exercise Electrocardiogram (ECG) in detecting myocardial ischemia. It has sensitivity 85–95%, and specificity 75%. The specificity can up to 94% if combine with ECG gated data.3–5 Stress images may help determine the degree of inducible ischemia or viable myocardium that are amenable to revascularization, evaluate myocardial viability before revascularization and following-up after revascularization such as coronary artery bypass graft or angioplasty.3–6
Physiological radioactivity uptake in the liver, bowel or stomach could interfere the interpretation of MPI. This phenomenon can be reduced by using iterative reconstruction and attenuation correction but a high tracer activity around the heart is still influence the evaluation of the myocardial.7, 8 Several methods to reduce the digestive activity have been described, such as filling the stomach with either solids or fluids9–11, increasing the gastrointestinal activity by using metoclopramide drug12, keeping the patient standing for several minutes after tracer injection13, or even ingesting iodinated contrast medium to absorb the emitted gamma-rays14. Prolonging the delay imaging between injection and image acquisition can lead to a significant decrease in the hepatic activity but also by increasing the activity in the bowel loops adjacent to the inferior wall of the heart.11, 12, 14
Patients should take fatty meal at time between injection and imaging to increase clearance of tracer from the liver and gallbladder as a standard protocol of MPI in some centers.2 Our department usually ask patients to drink milk to reduce physiological infra-cardiac organs uptake. However, some of patients are lactose intolerant, and caused diarrhea and abdominal discomfort. Data on Indonesian population showed that the prevalence of lactose malabsorption and intolerance are quite high, between 21–73%.15–17 Those patients will feel abdominal discomfort as well as diarrhea after MPI procedure, and sometimes disturb the MPI procedure.13 In this study we use water instead of milk, to minimize the infra-cardiac uptake that can interfere interpretation of SPECT MPI. Our previous study compares subjects in first group (drink 500 mL of milk) and second group (drink 330 mL of water) after doing physical stress MPI procedure with acquisition time 30 minutes after 99mTc-Sestamibi injection, showed that water was as good as milk in reducing the infra-cardiac tissue tracer uptake. In this study, 99mTc-Sestamibi was used as radiopharmaceutical for MPI. Since this radiopharmaceutical is a lipophilic agent, patients were advice to take solid fatty meal for breakfast on the day of MPI procedure.7, 8
Preparation before MPI procedure is important to get a good quality of images. Subjects should not take any food for at least 4 hours to prevent stress-induced gastric distress and minimize splanchnic blood distribution.18 Subjects must have no contraindications to perform exercise stress test using treadmill. Caffeine containing products must not be consumed for at least 12 hours prior MPI procedure, to avoid decrease vasodilatation respond from vasodilator stress agents, which will lead to reduce sensitivity in detecting myocardial ischemia. Subjects also suggested to stop β-blocker treatment for 24 hour and phosphodiesterase inhibitor for 24–48 hour before MPI procedure.19
Out of 35 subjects, 5 subjects were excluded because they didn't reach minimal target heart rate (85% maximal heart rate) and had contraindications to undergo the exercise test. Based on EANM/ESC guideline, patients are said to achieve maximum exercise stress test when they are able to reach ≥85% of their age-predicted maximum heart rate (maximal age–predicted heart rate = 220 – age).2
In accordance to conventional guideline, image acquisitions should be performed 15–60 minutes after tracer administration.19 Strauss, et al. said that image acquisitions with 99mTc based tracer should be performed after liver radioactivity has sufficiently cleared, this was usually between 15–30 minutes after tracer administration.20 While according to EANM/ESC guideline, image acquisitions should be begun at 30–60 minutes after tracer administration.2 In this study, MPI was done on 10 and 30 minutes following 99mTc-Sestamibi injection intravenously. Ten minutes acquisition time following injection of radiopharmaceutical based on the consideration that the time taken by patients between physical stress MPI, and imaging procedure was about 10 minutes. The 10 minutes image after radiopharmaceutical injection was considered as direct imaging, and 30 minutes image as control, based on EANM/ESC guideline, as an appropriate time for image acquisitions.2
All subjects were scanned in supine position with arms raised above the head and support the knees with pillow under the knees, shoulders and arms comfortably positioned in order to reduce movement and pain, particularly in older subjects, to make feel as comfortable as possible to minimize body motion as suggested by Dorbala, et al..19 Female subjects were imaged without bra, and used chest band to minimize breast attenuation and minimize motion. Chest band could also be used in male subjects to minimize body motion as suggested by Hesse B. et al..2
From the quantitative assessment results, we found that there was no significant difference TBR of heart to liver ratio between acquisition 10 and 30 minutes after radiopharmaceutical injection as seen in Fig. 2, with p-value = 0.15 (p > 0.05).