In this case, the lung-to-heart ratio at stress and rest was 0.32 and 0.31, respectively. However, the lower limit of normal for lung-to-heart ratio has not been described. For Tc-99m sestamibi, the upper limit of normal for lung-to-heart ratio ranges from 0.42 to 0.56 ( 2). For 201-thallium, the reported upper limit of normal for lung-to-heart ratio ranges from 0.37 to 0.55 ( 2). The reason for this is that the lung-to-heart ratio is isotope-specific and also relies heavily on the time between injection of the radiotracer and acquisition of the image as well as the method of calculation ( 2). Unfortunately, there is a great deal of variation in the previously reported cutoff values for increased lung-to-heart ratio ( 2, 14). The lung-to-heart ratio has long been used as a method to quantify tracer uptake in the lungs ( 3, 4, 10, 11, 12). In our case, diffusely decreased tracer uptake in the lungs is a meaningful finding and may provide further insight into the patient's symptoms. However, to our knowledge, decreased tracer uptake in the lungs ("lucent lungs") has not been described in the literature. Diffusely increased tracer uptake in the lungs has been correlated with extent of coronary disease, left ventricular dysfunction, and also poor prognosis ( 1, 5, 10, 11, 12, 13). Focally increased tracer uptake in the lungs has been associated with malignant tumors, benign lesions, infiltrate, atelectasis, and granulomatous disease ( 1, 6, 7, 8, 9). Increased 201-thallium, Tc-99m sestamibi, and Tc-99m sestamibi uptake in the lungs has been described extensively in the literature ( 1, 2, 3, 4, 5). Dedicated cardiac cameras have a relatively narrow field of view, but general nuclear medicine cameras (with their larger field of view) allow visualization of additional structures above and below the diaphragm. 3).Īlthough myocardial perfusion SPECT imaging is used primarily to evaluate myocardial blood flow and function, careful inspection of the "rotating" planar images and tomographic images may yield important extracardiac findings ( 1, 2). The axial and coronal CT images demonstrated significant emphysema and large geographic areas of air trapping ( Fig. Correlation with prior noncontrast chest CT demonstrated hyperinflated lungs on the topogram ( Fig. The calculated lung-to-heart ratio was 0.32 at stress and 0.31 at rest. Review of the “rotating” planar images demonstrated "lucent" and hyperexpanded lung fields in both the stress and the rest acquisitions ( Fig. Images were processed with ordered subset expectation maximization (OSEM). All images were acquired on a GE Millenium MG with a dual 90-degree detector system using a 180-degree circular orbit and a low-energy, high-resolution collimator. The patient received 100 mg intravenous aminophylline for the chest pain, which subsequently resolved. The patient experienced chest pain however, there were no ST-segment changes during regadenoson administration. Due to the patient's inability to exercise, a standard regadenoson pharmacological stress test with 0.4 mg regadenoson was performed. A standard low-dose rest (9.3 mCi) / high-dose stress (36.4) Tc-99m sestamibi protocol was used. Her medical history included chronic obstructive pulmonary disease (COPD) and recent small bowel resection that was complicated by a myocardial infarction and an episode of atrial flutter. An 84-year-old female was referred for a single-day, gated, rest/stress, Tc-99m sestamibi myocardial perfusion imaging (MPI) study for evaluation of palpitations.
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