CAD is the most common type of cardiovascular disease and the main cause of mortality and morbidity. Radionuclide myocardial perfusion imaging can be used to determine the presence of CAD, give risk stratification and to guide management of patients with known disease [11, 12]. Single Photon Emission Computed Tomography (SPECT) MPI using 99mTc-Sestamibi (MIBI) is cost effective than any other diagnostic modalities and more accurate than exercise ECG in detecting myocardial ischemia. It can be used to evaluate myocardial viability before revascularization and following-up after revascularization such as coronary artery bypass graft or angioplasty [2–4]. MPI was confirmed to be highly effective in the diagnosis of CAD, with sensitivity of 85–95%, specificity of 75%, and a normalcy rate of 88% [2].
Stress images in SPECT may help determine the degree of inducible ischemia or viable myocardium. This viable myocardium will get advantage if the patient undergo revascularization [13].
According to European Association of Nuclear Medicine (EANM) guidelines, the exercise stress test is preferred than pharmacological stress. Exercise stress allows evaluation of imbalance between oxygen supply and demand due to impaired flow reserve. It can identify the ischemic area related to heart workload. Images should be acquired 30–60 minutes after injection to allow adequate hepatobiliary clearance [14]. Meanwhile, according to SNMMI guideline, stress imaging should be taken between 15–60 minutes post-tracer injection [15]. The acquisition time we used in this study was 30 minutes after tracer injection.
High liver, bowel or gastric tracer uptake can interfere interpretation of MPI, especially the inferior wall and lead to false positive interpretation in normal MPI. Although this phenomenon can be reduced using iterative reconstruction and attenuation correction, a high tracer uptake around the heart may disturb the myocardial tracer uptake evaluation [5, 6]. Some centers ask the patients to consume fatty meal between injection and imaging time to increase clearance of tracer from the liver and gallbladder. In patient with retrograde passage of tracer from duodenum to stomach or the tracer reach the transverse colon, this maneuver may be counterproductive [14].
In our department, the standard stress SPECT MPI protocol is to drink 500 mL milk after MIBI injection 30 minutes before acquisition. However, some patients complain of diarrhea and abdominal discomfort after drinking the milk. Fluid intake is also believed can be used to remove intestinal activity from the subdiaphragmatic area [14].
In this study, we asked subject to drink 500 mL milk for the first group, and 330 mL of water for the second group following MIBI injection. We exclude subject who have history of fluid restriction, consume pro-motility drug such as metoclopramide, because it can increase the gastrointestinal tracer uptake activity.
Our study showed that water was as good as milk in reducing the infra-cardiac tissue tracer uptake. This result was similar to a prospective study conducted by Hoffman et. al. Their study demonstrated that there was no difference between milk and water on MPI interpretation [16]. Several previous studies have been conducted to find a substitute for milk in MPI procedure. Hurwitz et. al. using milkshake and found that decreased in infra-cardiac tracer uptake was due to volume of stomach [17]. Boz et. al. gave normal meal and drink 200–300 mL water 10–15 minutes before imaging. They hypothesized that filled stomach will push the intestinal caudally and set apart intestinal from myocardium [18]. Hara et. al. used 100 mL of soda water in their study, and their results showed that the mean inferior wall to abdomen count ratio was significantly higher in the soda water group than control [19]. Thomas et. al. also found the same result on their study about the use of carbonated water in reduction of adjacent gastric activity [20].
All of those previous studies showed that soda water, milk, and water could be used to minimize the infra-cardiac tracer uptake which can interfere interpretation of SPECT MPI.
Our qualitative assessments showed that both water and milk reduced physiological infra-cardiac organ tracer uptake and no difference in semi-quantitative assessment or in interpretation of the MPI result. Therefore, for patients with history of lactose intolerant, they can drink water instead of milk to get high quality MPI result with more convenience.