E. Gordon DePuey

Technical aspects of myocardial spect imaging with technetium-99m sestamibi

Most reports to date using single photon emission computed tomography (SPECT) with technetium-99m (Tc-99m) sestamibi have used acquisition parameters that were optimized for thallium-201. To fully utilize the superior imaging characteristics of Tc-99m sestamibi, there is a need to optimize the technical aspects of SPECT imaging for this agent. Performance can be enhanced through the careful selection of optimal radiopharmaceutical doses, imaging sequences, acquisition parameters, reconstruction filters, perfusion quantification methods and multidimensional methods for visualizing perfusion distribution. The current report describes theoretical considerations, phantom studies and preliminary patient results that have led to optimized protocols, developed at Emory University and Cedars-Sinai Medical Center, for same-day rest-stress studies, given existing instrumentation and recommended dose limits. The optimizations were designed to fit a low-dose-high-dose rest-stress same-day imaging protocol. A principal change in the acquisition parameters compared with previous Tc-99m sestamibi protocols is the use of a high-resolution collimator. The approach is being developed in both prone and supine positions. A new method for extracting a 3-dimensional myocardial count distribution has been developed that uses spherical coordinates to sample the apical region and cylindrical coordinates to sample the rest of the myocardium. New methods for visualizing the myocardial distribution in multiple dimensions are also described, with improved 2-dimensional, as well as 3- and 4-dimensional (3 dimensions plus time) displays. In the improved 2-dimensional display, distance-weighted and volume-weighted polar maps are used that appear to significantly improve the representation of defect location and defect extent, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

The value and practice of attenuation correction for myocardial perfusion SPECT imaging: A joint position statement from the American Society of Nuclear Cardiology and the Society of Nuclear Medicine

ConclusionDespite advancements in technologies, non-uniform soft tissue attenuation still affects the diagnostic accuracy of single photon emission computed tomography (SPECT) myocardial perfusion imaging. A variety of indirect measures have been used to reduce the impact of attenuation, most notably electrocardiography-gated SPECT imaging. However, all available techniques have limitations, making interpretation in the presence of attenuation difficult. The ultimate solution, similar to positron emission tomography imaging, is to use hardware/software algorithms to eliminate attenuation and provide images that are more uniform and easier to interpret. Several attenuation correction solutions are currently available and more will be available soon. The value of these solutions has been varied, particularly with clinical applications. Guidelines and standards clearly are necessary.In recognition of the importance of this issue, the American Society of Nuclear Cardiology and the Society of Nuclear Medicine convened a joint task force to develop a position statement on attenuation correction. It is being published concurrently in the Journal of Nuclear Cardiology and The Journal of Nuclear Medicine, a first for these societies.The purpose of this position statement is to clarify the role of attenuation correction in SPECT procedures, to provide guidelines for its clinical use, and to provide a basis for the evaluation of published validation. It is hoped that this position statement will provide an important and useful road map to the widespread adoption of attenuation correction into clinical practice.

Restenosis after transluminal coronary angioplasty detected with exercise-gated radionuclide ventriculography

Forty-one patients were evaluated with exercise-gated radionuclide ventriculography before and within 4 days after successful transluminal coronary angioplasty and 4 to 12 months later. Patients were subgrouped according to the degree of restenosis demonstrated angiographically at 4 to 12 months (Group I [n = 23]: less than or equal to 20%; Group II [n = 10]: greater than 20% but less than 50%; Group III [n = 8]: greater than or equal to 50%). Patients with abnormal findings on gated radionuclide ventriculography (less than 5 point increase in ejection fraction or wall motion deterioration) early after angioplasty were eventually found to have a greater degree of restenosis than were patients with normal findings (41.2 +/- 30.3 versus 19.0 +/- 25.4% restenosis, p less than 0.0001). The accuracy of abnormal radionuclide ventriculography in predicting 50% or greater restenosis was 73% immediately after angioplasty and 77% at the time of follow-up angiography. Gated radionuclide ventriculographic results were abnormal in 5% of Group I patients compared with 75% of Group III patients (p less than 0.01) early after angioplasty; at late follow-up, they were abnormal in 27% of Group I patients compared with 88% of Group III patients (p less than 0.01). Group I patients had a greater increase in ejection fraction than did Group III patients at early (+11.3 +/- 7.5 versus + 3.5 +/- 6.5 points, p less than 0.01) and late (+11.8 +/- 7.8 versus -1.9 +/- 8.7 points, p less than 0.0005) follow-up. It is concluded that gated radionuclide ventriculography is useful in predicting coronary restenosis after transluminal coronary angioplasty.

Traditional gamma cameras are preferred

Although the new solid-state dedicated cardiac cameras provide excellent spatial and energy resolution and allow for markedly reduced SPECT acquisition times and/or injected radiopharmaceutical activity, they have some distinct disadvantages compared to traditional sodium iodide SPECT cameras. They are expensive. Attenuation correction is not available. Cardio-focused collimation, advantageous to increase depth-dependent resolution and myocardial count density, accentuates diaphragmatic attenuation and scatter from subdiaphragmatic structures. Although supplemental prone imaging is therefore routinely advised, many patients cannot tolerate it. Moreover, very large patients cannot be accommodated in the solid-state camera gantries. Since data are acquired simultaneously with an arc of solid-state detectors around the chest, no temporally dependent “rotating” projection images are obtained. Therefore, patient motion can be neither detected nor corrected. In contrast, traditional sodium iodide SPECT cameras provide rotating projection images to allow technologists and physicians to detect and correct patient motion and to accurately detect the position of soft tissue attenuators and to anticipate associated artifacts. Very large patients are easily accommodated. Low-dose x-ray attenuation correction is widely available. Also, relatively inexpensive low-count density software is provided by many vendors, allowing shorter SPECT acquisition times and reduced injected activity approaching that achievable with solid-state cameras.

Impact of gating errors with electrocardiography gated myocardial perfusion SPECT

Case history and clinical course. A 72-year-old man with tongue carcinoma was admitted to undergo a surgical treatment. He was a smoker and had a complaint of shortness of breath. He was referred for stress testing so that he could be cleared for surgery. After the intravenous administration of 325 MBq technetium 99m sestamibi at rest and 1088 MBq during stress, single photon emission computed tomography (SPECT) of the heart was performed over 180° in 32 steps in a 64 64 matrix by use of a dual-head gamma camera (Optima; GE Medical Systems, Milwaukee, Wis) equipped with low-energy high-resolution collimators. Gated SPECT images with 8 frames per R-R interval were acquired 30 minutes after the stress completion. Filtered backprojection was used for image reconstruction. The baseline electrocardiogram showed normal sinus rhythm and tall T waves (Figure 1). The patient achieved more than 85% of his predicted maximal heart rate. He had no chest pain, and no ST-segment changes were detected. There was no patient motion during the acquisition. Perfusion was normal on both of the stress and rest images. The gated SPECT images revealed diffuse hypokinesis and no wall thickening. The time-volume curve (TVC) obtained by use of QGS software (Cedars-Sinai, Los Angeles, Calif) showed virtually a straight line (Figure 2). The left ventricular ejection fraction (LVEF) was calculated as 16.3% by QGS. However, normal wall motion was demonstrated subsequently by echocardiography, and LVEF was estimated to be 68%. The patient was considered to be at low risk for surgery and subsequently underwent the procedure without any perioperative events. Discussion. Myocardial perfusion SPECT plays an important role in assessing cardiac risk for noncardiac surgery. 1 Moreover, gating has improved diagnostic accuracy for detecting ischemia 2 nd has brought about an incremental predictive value for prognosis. 3 However, gating errors may occur with gated SPECT. These errors sometimes render the study suboptimal, especially for evaluation of wall motion, wall thickening, and calculation of LVEF. According to the reports of Nichols et al, left ventricular volumes and LVEFs are affected minimally by arrhythmias; however, wall thickening is more prone to be underestimated. Even if there are no arrhythmias, cardiac cycle variations may cause artifacts. With marked arrhythmias, gating errors may produce perfusion abnormalities. 4,6 In the present case, no arrhythmias or perfusion defects were detected. However, no significant contraction or thickening was demonstrated. A similar gating error has been reported for equilibrium radionuclide angiocardiography (ERNA). 7 With tall T waves, the R-T phase and T-R phase are regarded as two “cardiac cycles.” The first cardiac cycle, the R-T phase, consists of systole. The subsequent cardiac cycle, the T-R phase, consists predominantly of diastole. When the TVC is generated by summation of these phases, the R-T phase makes up the downsloping curve and the T-R phase makes up the upsloping curve. Because the R-T phase and T-R phase are regarded as identical cardiac cycles, the final TVC is produced essentially as a flat line (Figure 3A). Other potential errors also have been reported for ERNA. 7 First, with bigeminy or pulsus alter nans, the computer may erroneously select an R-R interval involving two entire cardiac cycles, detecting only the tallest R waves. When the original R wave is selected as a trigger, the TVC will show a “down-up” shape. If the premature beat or alternans beat appears before end systole of the original cycle, the TVC will be U-shaped. If it appears after end systole of the original cycle, the TVC will be W-shaped (Figure 3 B-1). If the premature beat or alternans beat is selected as a trigger, the TVC will be inverted (Figure 3 B-2). Second, if the T wave is tall and its amplitude is greater than the R wave, the T wave may trigger the electrocardiographic (ECG) gate. Although the gating interval will correspond in length to the R-R interval, the TVC will also be inverted (Figure 3C). From the Division of Nuclear Medicine, Department of Radiology, a

Myocardial perfusion SPECT horizontal motion artifact

Single photon emission computed tomography (SPECT) myocardial perfusion imaging is widely used for evaluation of patients with known or suspected coronary artery disease. It is an accurate and reliable diagnostic method for evaluation of myocardial perfusion with approximately 90% sensitivity and nearly 80% specificity. Patient motion is one of the most common sources of artifacts during SPECT study, which can lower the specificity of the SPECT study. We present a case of a patient who had significant myocardial perfusion defect due to horizontal motion which significantly improved after motion correction of the raw data.

Determination of Bone Mineral Content Medicine Using the Scintillation Camera

A method has been devised for measuring bone mineral content using a scintillation camera with X/V locator and multimode analyzer. The bone is immersed in water and exposed to a 1251 or 241Am source. Transmission of photons through the bone (In) and through water (In*) are recorded, employing the 10a-channel analyzer in profile mode. The sum of the natural logarithms of the ratio In*/In across the width of the bone defines a “mineral index” proportional to the bone mineral content. Correlation of mineral index to calcium content in 13 bone phantoms was 0.997 with 1251 and 0.979 using 241Am, with a precision of 2% over a two-month period.

Myocardial ischemia detection by expert system interpretation of thallium-201 tomograms

The accuracy of interpreting tomographic nuclear medicine images of the heart varies depending on the expertise of the diagnostician. This variability is a problem at some community hospitals or private imaging centers where expertise is limited due to the small number of studies performed. In order to standardize image interpretation at an expert’s level, we developed a totally automated rule-based expert system for interpreting three-dimensional myocardial perfusion distributions obtained from stress and delayed thallium-201 perfusion tomograms. The rules of the expert system determine the presence, location, and certainty of each fixed or reversible coronary lesion, combining certainty factors according to the MYCIN algorithm. Computer consultations were compared with interpretations of a human expert for a pilot group of 20 patients. The expert system interpreted myocardial perfusion distributions with artifacts, coronary territory overlap and multiple defects at a level approaching that of the human expert.

Effects of stress management training and dietary changes in treating ischemic heart disease

To evaluate the short-term effects of an intervention that consists of stress management training and dietary changes in patients with ischemic heart disease (IHD), we compared the cardiovascular status of 23 patients who received this intervention with a randomized control group of 23 patient who did not. After 24 days, patients in the experimental group demonstrated a 44% mean increase in duration of exercise, a 55% mean increase in total work performed, somewhat improved left ventricular regional wall motion during peak exercise, and a net change in the left ventricular ejection fraction from rest to maximum exercise of +6.4%. Also, we measured a 20.5% mean decrease in plasma cholesterol levels and a 91.0% mean reduction in frequency of anginal episodes. In this selected sample, short-term improvements in cardiovascular status seem to result from these adjuncts to conventional treatments of IHD.

Clinical standardization of the new dual cardiac probe.

A new mobile dual cardiac probe has been introduced for measurements of the left ventricular ejection fraction (LVEF). In 28 patients, correlation between LVEFs measured by the dual probe and biplane contrast ventriculography was 0.83. Central and peripheral injections yielded comparable curves, and the resultant LVEFs correlated well (R = 0.95). Correlation between LFEVs determined by the probe and by gated blood pool imaging in 43 patients was also 0.83. In 21 patients given three serial injections of 99mTc-albumin, the mean variation of the ejection fraction was 4.2 +/- 3.2%; however, reproducibility was unsatisfactory using 99mTc-sulfur colloid due to sequestration in hepatic background tissue.