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(Radiographics. 1999;19:915-926.)
© RSNA, 1999

SCIENTIFIC EXHIBIT

SPECT and PET in the Evaluation of Coronary Artery Disease1

Hossein Jadvar, PhD, MD, 2, H. William Strauss, MD and George M. Segall, MD

1 From the Division of Nuclear Medicine, Department of Radiology, Stanford University School of Medicine, Stanford, Calif (H.J., H.W.S., G.M.S.), and the Nuclear Medicine Service, VA Palo Alto Health Care System, 3801 Miranda Ave, Palo Alto, CA 94305 (G.M.S.). Presented as a scientific exhibit at the 1997 RSNA scientific assembly. Received April 13, 1998; revision requested May 21 and received June 30; accepted July 1. Address reprint requests to G.M.S.


   Abstract
Top
 Abstract
INTRODUCTION
 BASIC PET PHYSICS AND...
 PET RADIOPHARMACEUTICALS FOR...
 DEFINITION OF TERMS
 PET OF MYOCARDIAL PERFUSION...
 IMAGING PROTOCOLS
 CONCLUSIONS
 References
 
Cardiac positron emission tomography (PET) is an accurate method for assessing myocardial perfusion and metabolism in the evaluation of coronary heart disease. PET allows more accurate detection of myocardial ischemia than single photon emission tomography (SPECT). In addition, PET has higher spatial resolution and allows attenuation correction and the quantification of various physiologic parameters. PET with 2-(fluorine-18) fluoro-2-deoxy-d-glucose is considered the standard of reference for predicting improvement in regional or global left ventricular function after revascularization by identifying hibernating viable myocardium that shows diminished perfusion and preserved metabolism. Other less commonly used clinical applications of cardiac PET include assessment of myocardial oxygen consumption and fatty acid metabolism. The use of PET in myocardial imaging is expected to increase in the near future with the regional distribution of positron-emitting radiotracers and the emergence of relatively low-cost PET systems.

Index Terms: Coronary vessels, diseases • Coronary vessels, emission CT (ECT), 54.12162, 54.12163 • Coronary vessels, radionuclide studies, 54.1217 • Myocardium, diseases • Myocardium, emission CT (ECT), 511.12162, 511.12163 • Myocardium, radionuclide studies, 54.1217


   INTRODUCTION
Top
 Abstract
 INTRODUCTION
BASIC PET PHYSICS AND...
 PET RADIOPHARMACEUTICALS FOR...
 DEFINITION OF TERMS
 PET OF MYOCARDIAL PERFUSION...
 IMAGING PROTOCOLS
 CONCLUSIONS
 References
 
The advantages of positron emission tomography (PET) over single photon emission tomography (SPECT) include higher spatial resolution and the ability to provide quantitative measurements of physiologic parameters. The use of PET in myocardial imaging is expected to increase in the near future with the regional distribution of positron-emitting radiotracers and the emergence of relatively low-cost PET systems.

In this article, we discuss basic PET physics and instrumentation and the radiopharmaceuticals commonly used in cardiac PET. We also define the terms most frequently used to describe the state of myocardium in coronary artery disease. In addition, we compare PET with more traditional single photon imaging methods in the assessment of myocardial perfusion and metabolism and describe the imaging protocols used at our institution.


   BASIC PET PHYSICS AND INSTRUMENTATION
Top
 Abstract
 INTRODUCTION
 BASIC PET PHYSICS AND...
PET RADIOPHARMACEUTICALS FOR...
 DEFINITION OF TERMS
 PET OF MYOCARDIAL PERFUSION...
 IMAGING PROTOCOLS
 CONCLUSIONS
 References
 
Table 1 shows the three positron-emitting radiotracers that are used for clinical cardiac PET. Positrons are released from the nuclei of unstable isotopes during radioactive decay. Positrons have the same mass as electrons but are positively charged. They travel a short distance in tissue before interacting with electrons. This interaction results in the "annihilation" of the electron-positron pair with the production of two 511-keV gamma rays that are emitted in opposite directions. PET scanners have a ring of detectors or two opposed detectors made of bismuth germanate or thallium-activated sodium iodide crystals. These detectors are designed to detect the two photons that are coincident. Coincidence events within a short time window (usually 5–20 nsec) are detected by a pair of opposed detectors (1). A filtered back projection or iterative reconstruction process is used to form emission images, which can be corrected for signal attenuation due to overlying tissue by acquiring transmission images with germanium-68 sources. The attenuation-corrected images are displayed in cardiac short-axis, vertical long-axis, and horizontal long-axis projections similar to those used in SPECT.


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  		TABLE 1. Radiopharmaceuticals Most Commonly Used in Cardiac PET
 
Dedicated PET cameras provide the highest spatial resolution. The initial capital cost remains significant but is declining. There has been an interest in developing hybrid cameras that allow imaging of both single photon and positron radiotracers. The use of gamma cameras equipped with ultra-high-energy collimators, thicker sodium iodide crystals, and extended energy range has been one approach in high-energy photon imaging. This technique detects the 511-keV photons as single events along the line of collimated emission. The detection efficiency at 511 keV ranges from 10% to 30% (depending on the thickness of the sodium iodide crystal) compared with 95% at 140 keV (2). Sensitivity and spatial resolution are substantially inferior to those of PET (3–5).

Another approach has been to implement coincidence detection circuitry in gamma cameras. These devices are designed to handle high count rates without collimation. The spatial resolution is considerably improved compared with collimated SPECT. A few such cameras are now commercially available at a lower cost than a standard PET camera, but they have not been fully evaluated clinically. Their use in PET is expected to increase if they prove to be diagnostically adequate. At our institution, PET is performed with an ECAT EXACT camera (CTI, Knoxville, Tenn) with a 16-cm field of view and an in-plane spatial resolution of 6 mm (full width at half maximum).


   PET RADIOPHARMACEUTICALS FOR CARDIAC STUDIES
Top
 Abstract
 INTRODUCTION
 BASIC PET PHYSICS AND...
 PET RADIOPHARMACEUTICALS FOR...
DEFINITION OF TERMS
 PET OF MYOCARDIAL PERFUSION...
 IMAGING PROTOCOLS
 CONCLUSIONS
 References
 
The most common radiotracers used in cardiac PET are ammonia (13NH3) and rubidium (82Rb) chloride for assessing myocardial perfusion and 2-(fluorine-18) fluoro-2-deoxy-d-glucose (FDG) for evaluating myocardial glucose metabolism (1). 13NH3 has a first-pass extraction of 80% and requires energy for myocardial uptake. As with SPECT myocardial perfusion agents, uptake is linear over a wide range of myocardial blood flow rates except at very high flow rates (6). Imaging with 13NH3 requires either an on-site cyclotron or proximity to a regional positron radiopharmaceutical source center.

82RbCl is a potassium analog that has a first-pass extraction of 65% and also requires energy for myocardial uptake (7). Repeat studies may be performed due to its very short half-life (Table 1). An advantage of 82RbCl over 13NH3 is that it is produced by a strontium-82/82Rb generator without the need for a costly cyclotron.

FDG is used in the evaluation of glucose utilization in ischemic myocardium with suppressed mitochondrial ß-oxidation of fatty acids (8,9). Ng et al (10) showed that insulin infusion in the fasting state reduced myocardial extraction of free fatty acids by 85% and stimulated myocardial uptake of both FDG and glucose. FDG uptake is heterogeneous in normal myocardium in the fasting state in diabetic patients as well as in patients with normal glucose tolerance (11–13). Increased FDG uptake is seen in ischemic tissue, whereas markedly reduced or absent uptake indicates scar (8). Oral glucose loading and continuous infusion of insulin, potassium, and glucose have been used to enhance myocardial FDG uptake. In a study by Knuuti et al (14), images obtained in nondiabetic patients after insulin infusion were of higher quality than those obtained after oral glucose loading. Ohtake et al (15) reported similar findings in patients with non–insulin-dependent diabetes. Some investigators have described insulin infusion as cumbersome for routine clinical use (5). Oral glucose loading and bolus injections of insulin have been suggested as possible alternatives (16).

Less commonly used PET radiotracers are carbon-11 acetate for assessing regional myocardial oxygen consumption, C-11 palmitate for measuring fatty acid metabolism, and oxygen-15 water for quantifying myocardial blood flow.


   DEFINITION OF TERMS
Top
 Abstract
 INTRODUCTION
 BASIC PET PHYSICS AND...
 PET RADIOPHARMACEUTICALS FOR...
 DEFINITION OF TERMS
PET OF MYOCARDIAL PERFUSION...
 IMAGING PROTOCOLS
 CONCLUSIONS
 References
 
Table 2 defines the terms that are commonly used to describe the state of myocardium in coronary artery disease. Ischemic myocardium is myocardium that is deprived of adequate coronary arterial blood flow in relation to metabolic demand. The blood supply may be sufficient at rest even in the presence of a significant stenosis (>50% narrowing of the luminal diameter). However, oxygen demand and removal of metabolic waste products is not adequate during periods of increased cardiac activity. Hypoxemia results in ST segment depression on an electrocardiogram, arrhythmia, angina, and regional or global impairment of ventricular function (17).


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  		TABLE 2. Terms Used to Describe the State of Myocardium in Coronary Artery Disease
 
Several methods are used to augment the sensitivity of myocardial perfusion imaging. Exercise on a treadmill or stationary bicycle is considered a standard means of increasing cardiac metabolic demand. Alternative methods are used in patients who cannot exercise adequately and include isometric hand-grip exercise, pharmacologic agents (eg, vasodilators [dipyridamole, adenosine], inotropes [dobutamine, arbutamine]), and transvenous or transesophageal atrial pacing.

Myocardial perfusion images acquired after injection of the radiotracer at peak stress are compared with images acquired at rest (Fig 1). Ischemic segments show stress-induced reversible (transient) perfusion abnormalities. Identification of these segments is one of the major objectives of stress-rest myocardial perfusion studies. Gated perfusion SPECT can be used to evaluate the presence, severity, and extent of myocardial ischemia as well as to provide functional data such as ejection fraction, regional wall motion, and wall thickening (18–20). The hemodynamic significance of stenoses detected with coronary arteriography can be evaluated with a myocardial perfusion study. Important prognostic information can also be obtained. Several studies have shown that normal findings at stress-rest myocardial perfusion imaging indicate that a patient has a very low (<1% per year) event rate (future cardiac death or nonfatal myocardial infarction) even when the stress electrocardiogram is markedly positive or significant angiographic lesions are present (21).



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  		Figure 1.  Normal myocardial perfusion in a 69-year-old man with coronary artery disease and bypass grafts to the left anterior descending and left circumflex coronary arteries. The patient was very active and had occasional chest pain with exertion. 13NH3 perfusion PET images obtained at rest (bottom row in each view) and following infusion of dipyridamole (top row in each view) demonstrate normal perfusion of the left ventricle. HLA = horizontal long axis, SA = short axis, VLA = vertical long axis.

 
Infarcted myocardium is myocardium that is irreversibly damaged with the histologic formation of scar (Fig 2). These myocardial segments appear as fixed perfusion abnormalities that are present on both rest and stress images. Fixed perfusion lesions do not always represent scar tissue, especially in the absence of correlative Q waves on the electrocardiogram. A fixed perfusion abnormality may also be due to severely reduced coronary arterial flow caused by a tight stenotic lesion.



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  		Figure 2a.  Myocardial infarct in a 48-year-old man with a history of anterior myocardial infarction and recurrent angina. HLA = horizontal long axis, SA = short axis, VLA = vertical long axis. (a) Tl-201 dipyridamole stress images (top row in each view) and redistribution images (bottom row in each view) show a large, severe perfusion lesion in the left anterior descending coronary artery territory (arrows). (b) FDG PET image shows a matching metabolic lesion (arrows), a finding that indicates a large myocardial infarct.

 


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  		Figure 2b.  Myocardial infarct in a 48-year-old man with a history of anterior myocardial infarction and recurrent angina. HLA = horizontal long axis, SA = short axis, VLA = vertical long axis. (a) Tl-201 dipyridamole stress images (top row in each view) and redistribution images (bottom row in each view) show a large, severe perfusion lesion in the left anterior descending coronary artery territory (arrows). (b) FDG PET image shows a matching metabolic lesion (arrows), a finding that indicates a large myocardial infarct.

 
Hibernating myocardium is myocardium that retains cellular integrity despite reduced perfusion but cannot sustain the high-energy requirements of contraction (22). Rest-redistribution or stress-redistribution-reinjection imaging protocols with Tl-201 attempt to distinguish infarcted myocardium from severely underperfused or hibernating myocardium (23–27). FDG PET is considered the standard of reference for detecting hibernating myocardium that may be amenable to revascularization (1,8,28–35). Studies have shown that left ventricular regional wall motion and ejection fraction improve after revascularization of hibernating myocardium (36–38). Accurate identification of patients with hibernating myocardium is important to avoid the high cost and morbidity of unnecessary interventions.

Tl-201 is commonly used in the assessment of viability (24,25). Tl-201 is taken up by the sodium-potassium adenosine triphosphate (Na-K ATPase) system with a first-pass extraction greater than 80% (19). The maximum single dose is 3–4 mCi (111–148 MBq). Tl-201 decays to mercury-201 by electron capture. The Hg-201 emits 68–83-keV x-ray photons that are used for imaging. Low photon energy results in more attenuation artifacts than higher photon energy (eg, with Tc-99m–labeled agents that have a photon energy of 140 keV). Tl-201 activity in the myocardium is dynamic. Ischemic zones clear at a slower rate than well-perfused regions. Ischemic tissues may appear to "fill in" with time or after delayed reinjection of Tl-201 in a phenomenon known as redistribution (19).

Saha et al (39) presented an excellent review of the various techniques for assessing myocardial viability. In the rest-redistribution method, Tl-201 is injected intravenously at rest and early SPECT images are obtained. Delayed SPECT is performed 4 hours and sometimes again 24 hours after injection. Necrotic myocardium will demonstrate perfusion defects on both early and delayed images. In contrast, hibernating myocardium shows redistribution of Tl-201 with defects on early images that fill in on delayed images. In the stress-redistribution-reinjection method, Tl-201 is injected at peak stress and early images are obtained. Delayed redistribution imaging is performed 4 hours after injection as in the rest-redistribution method. A second dose (1 mCi [37 MBq]) of Tl-201 is then injected, and additional images are obtained. Studies have shown that this technique may obviate 24-hour delayed imaging with up to one-half of the irreversible defects seen at delayed redistribution imaging demonstrating fill-in after reinjection (40).

Of the perfusion lesions that appear unchanged 4 hours after Tl-201 injection at peak stress, 21%–61% show redistribution at 24 hours (28). Similarly, 31%–49% of fixed lesions on stress–4-hour redistribution images show reversibility following reinjection of Tl-201 at rest (26). Sciagra et al (41) used a rest–4-hour redistribution Tl-201 SPECT protocol and found that the most valuable parameter for differentiating viable from nonviable myocardium was quantity of Tl-201 uptake in the delayed study. Uptake of more than 60% peak activity on the redistribution study had a sensitivity of 78% and a specificity of 58% in predicting functional recovery after revascularization. The Tl-201 activity level at early rest and the concept of reversibility were less important in identifying hibernating myocardium. The authors concluded that a single redistribution study performed 4 hours after Tl-201 injection at rest may be sufficient for assessing myocardial viability (41). The presence and extent of viable tissue can be underestimated with stress-redistribution-reinjection and rest-redistribution 24-hour-delayed imaging protocols. Pooled study results have demonstrated a cumulative positive predictive value (PPV) and negative predictive value (NPV) of 69% and 89%, respectively for regional functional improvement after revascularization with use of stress-redistribution-reinjection Tl-201 SPECT (23). The PPV and NPV for predicting functional improvement after revascularization with rest-redistribution Tl-201 SPECT are 69% and 92%, respectively (23). In contrast, the PPV and NPV for wall motion improvement with FDG PET are 76% and 92%, respectively (Table 3) (8).


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  		TABLE 3. PPV and NPV of FDG PET versus Tl-201 Imaging in the Assessment of Myocardial Viability and Functional Improvement after Revascularization
 
Studies have also shown functional improvement after revascularization in up to 25% of segments with fixed Tl-201 lesions at 24 hours and intact FDG metabolism (26,30). In one study, Tl-201 stress-redistribution-reinjection protocol was compared with Tl-201 rest-redistribution protocol and FDG PET for assessing viability. Segments that showed mild to moderate fixed perfusion abnormalities (15%–50% decrease compared with normal segments) were found to be viable in 89% of patients with the rest-redistribution protocol and in 98% of patients with FDG PET (42). In another study performed with use of FDG in combination with collimated SPECT, 95% of segments with FDG uptake had improved wall motion after revascularization (5). In contrast, 75% of segments without FDG uptake showed no improvement. The authors reported a sensitivity of 95%, a specificity of 75%, a PPV of 68%, and an NPV of 96% in predicting improvement in regional contractile function after revascularization.

Srinivasan et al (43) compared FDG PET and SPECT with high-energy collimators in the assessment of myocardial viability. Although FDG SPECT significantly increased the sensitivity for detection of viable myocardium (compared with Tl-201 SPECT) to 88% of the sensitivity attainable with dedicated PET, it also led to false-positive results (ie, viable tissue at SPECT but nonviable tissue at PET) in 27% of cases. Further studies comparing the new coincidence detection cameras with dedicated PET cameras are needed.

Studies have also compared FDG with Tc-99m sestamibi in the assessment of myocardial viability. One study found FDG uptake in 23% of severe resting sestamibi perfusion abnormalities (defined as 30%–50% of peak normalized counts) (44). The major discordance between findings obtained with FDG and sestamibi involved the inferior wall, which suggests that attenuation artifact may contribute significantly to the underestimation of viability with Tc-99m sestamibi (45). Therefore, FDG PET is considered the standard of reference for determining myocardial viability preoperatively (8,46).

Stunned myocardium is myocardium that displays contractile dysfunction despite normalization of perfusion and is caused by prior repetitive ischemic insults. It is often difficult to distinguish stunning from hibernation, which may coexist in the same myocardial region (23). Prolonged postischemic ventricular dysfunction may be present for up to 8 weeks after revascularization (47). Hibernating and stunned myocardium are examples of reversible ischemia-induced myocardial mechanical dysfunction.


   PET OF MYOCARDIAL PERFUSION AND METABOLISM
Top
 Abstract
 INTRODUCTION
 BASIC PET PHYSICS AND...
 PET RADIOPHARMACEUTICALS FOR...
 DEFINITION OF TERMS
 PET OF MYOCARDIAL PERFUSION...
IMAGING PROTOCOLS
 CONCLUSIONS
 References
 
PET has a high sensitivity (93%) and specificity (93%) for the detection of myocardial ischemia (Fig 3) (17,48). Several studies have compared perfusion imaging with PET and SPECT in the assessment of coronary artery disease. Wackers et al (17) presented a review of these studies. Stewart et al (49) found 82RbCl PET to be superior to T1-201 SPECT in terms of specificity (84% versus 53%) and predictive accuracy (85% versus 79%) (49). In a similar study, PET was found to be more accurate than SPECT, with a higher sensitivity (95% versus 79%), specificity (82% versus 76%), and predictive accuracy (92% versus 78%) (50). Tamaki et al (51) compared exercise Tl-201 SPECT and dipyridamole 13NH3 PET in 48 patients with coronary artery disease. The authors reported a sensitivity of 88% for PET and 81% for SPECT in the detection of stenoses greater than 50%. Table 4 shows the reported range of sensitivity and specificity for perfusion SPECT and PET in the detection of myocardial ischemia.



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  		Figure 3.  Myocardial ischemia in a 71-year-old man with a history of coronary artery disease, triple bypass surgery, and persistent angina postoperatively. 13NH3 rest perfusion images (bottom row in each view) and dipyridamole stress images (top row in each view) demonstrate a large, reversible perfusion abnormality in the anterior (short straight arrows), inferior (long straight arrows), and lateral (curved arrows) walls, findings that indicate ischemia in the territories of all three coronary arteries. The septum is relatively well perfused. HLA = horizontal long axis, SA = short axis, VLA = vertical long axis.

 

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  		TABLE 4. Sensitivity and Specificity of PET versus SPECT in the Detection of Myocardial Ischemia
 
Myocardial perfusion PET is particularly useful in reducing the number of false-positive SPECT scans due to attenuation correction. The higher sensitivity of PET can also be useful in the evaluation of coronary vascular reserve in view of negative SPECT results. MacIntyre et al (52) assessed outcome in patients with true-positive PET scans and false-negative Tl-201 SPECT scans and found that PET was more accurate than SPECT in predicting successful revascularization. Patterson et al (53) showed that perfusion PET is the most cost-effective diagnostic procedure in patients with a low to intermediate likelihood of coronary artery disease at pretesting (53). Gated perfusion PET may provide additional information regarding left ventricular regional and global function similar to gated perfusion SPECT (54).

PET can also be used to assess myocardial viability (33,51,55–58). Segments with reduced perfusion but normal or high FDG uptake (perfusion-metabolism mismatch) benefit from revascularization (Figs 4, 5) (36–38). Markedly reduced perfusion and metabolism identify segments that will not improve functionally after revascularization. Tillisch et al (59) found that a perfusion-metabolism mismatch had a PPV of 85% for functional improvement after revascularization, whereas a matched abnormality had an NPV of 92% for absence of functional improvement (59). In one study, the prognosis of patients with heart failure was compared for medical therapy versus revascularization. Medically treated patients with a mismatched pattern had a lower annual survival rate (50%) than did those with a matched pattern (82%). Moreover, patients with a mismatched pattern showed marked improvement in survival rate after revascularization (88%) compared with those with a matched pattern (50%) (60). Patients with large preoperative mismatched segments had greater functional improvement postoperatively than did patients with smaller segments (61). A possible limitation of FDG PET involves acute evolving myocardial infarction, which may display high myocardial FDG uptake (62). The exact mechanism for such a finding is unclear. In this clinical setting, other PET radiotracers (eg, C-11 acetate) may be useful in the assessment of oxidative metabolism.



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  		Figure 4.  Myocardial ischemia and infarct in a 49-year-old man with a history of myocardial infarction and recurrent angina. Coronary angiography showed 40% disease involvement of the left main artery, 100% stenoses of the proximal left anterior descending and right coronary arteries, and dyskinesis of the anteroapical and inferoapical walls. An echocardio-gram (not shown) demonstrated akinesis or dyskinesis of the distal one-third to one-half of the left ventricle. A PET scan was requested to evaluate for ischemia in the left anterior descending and right coronary arteries. 13NH3 rest perfusion images (top row in each view) and FDG metabolism images (bottom row in each view) (HLA = horizontal long axis, SA = short axis, VLA = vertical long axis) demonstrate little or no activity in the apex, a finding that confirms infarction (straight arrows). Reduced anterior wall perfusion with maintained glucose metabolism indicates ischemia of the anterior wall in the left anterior descending artery territory (curved arrow). The inferior wall also demonstrates good perfusion and glucose metabolism, a finding that indicates viable myocardium in the territory of the right coronary artery. The patient subsequently underwent triple bypass surgery (left internal mammary artery grafted to left anterior descending coronary artery, saphenous vein grafted to the first diagonal branch of the left anterior descending coronary artery and the marginal branch of the right coronary artery). Follow-up echocardiography showed mild improvement in overall left ventricular systolic function.

 


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  		Figure 5a.  Hibernating myocardium in an 81-year-old man with diabetes and angina. HLA = horizontal long axis, SA = short axis, VLA = vertical long axis. (a) Tl-201 dipyridamole stress images (top row in each view) and redistribution images (bottom row in each view) show a large, severe perfusion lesion in the right coronary artery territory (arrowheads). (b) FDG PET image shows normal glucose uptake throughout the left ventricular myocardium. The mismatched perfusion-metabolic lesion indicates hibernating "viable" myocardium in the inferior wall (arrows).

 


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  		Figure 5b.  Hibernating myocardium in an 81-year-old man with diabetes and angina. HLA = horizontal long axis, SA = short axis, VLA = vertical long axis. (a) Tl-201 dipyridamole stress images (top row in each view) and redistribution images (bottom row in each view) show a large, severe perfusion lesion in the right coronary artery territory (arrowheads). (b) FDG PET image shows normal glucose uptake throughout the left ventricular myocardium. The mismatched perfusion-metabolic lesion indicates hibernating "viable" myocardium in the inferior wall (arrows).

 

   IMAGING PROTOCOLS
Top
 Abstract
 INTRODUCTION
 BASIC PET PHYSICS AND...
 PET RADIOPHARMACEUTICALS FOR...
 DEFINITION OF TERMS
 PET OF MYOCARDIAL PERFUSION...
 IMAGING PROTOCOLS
CONCLUSIONS
 References
 
In this section, we describe imaging protocols used at our institution for cardiac PET.

FDG Myocardial Metabolism Imaging Protocol
Patients who undergo FDG myocardial metabolism imaging should fast for at least 4 hours prior to the study. Protocol for FDG myocardial metabolism imaging (used in patients with diabetes and in patients with normal glucose tolerance) is as follows:

  1. Check fasting blood glucose level with fingerstick measurement.
  2. Use sliding scale to determine regular insulin dose to be used to maintain hyperinsulinemic euglycemic condition. (a) If blood glucose level is less than 100 mg/dL, give 90 g of glucose orally, wait 1 hour, and inject two units of regular insulin and administer 10 mCi (370 MBq) of FDG intravenously. (b) If blood glucose level is between 100 and 150 mg/dL, inject five units of regular insulin and administer 10 mCi (370 MBq) of FDG intravenously. (c) If blood glucose level is between 150 and 200 mg/dL, inject 10 units of regular insulin and administer 10 mCi (370 MBq) of FDG intravenously. (d) If blood glucose level is greater than 200 mg/dL, inject 15 units of regular insulin and check blood glucose level with fingerstick 30 minutes later; use sliding scale for regular insulin dose and administer 10 mCi (370 MBq) of FDG intravenously.
  3. Acquire a rectilinear scan for positioning the patient so that a one-bed position scan of the chest includes the entire heart (~5 minutes total).
  4. Acquire a 5-minute transmission scan beginning 40 minutes after FDG injection for subsequent attenuation correction of the emission data.
  5. Acquire a 30-minute emission scan immediately following the transmission scan.
  6. Process the data and display the attenuation-corrected images in the cardiac axis projections (short axis, vertical long axis, horizontal long axis).
13NH3 Nongated Rest-Stress Myocardial Perfusion Imaging Protocol
Patients who undergo 13NH3 nongated rest-stress myocardial perfusion imaging should fast for 4–6 hours prior to the study. Furthermore, they should have had no caffeine for at least 24 hours and no theophylline for at least 48 hours. Protocol for 13NH3 nongated rest-stress myocardial perfusion imaging is as follows:

  1. Prepare the patient for a 12-lead electrocardiogram and blood pressure monitoring.
  2. Acquire a rectilinear scan for positioning the patient so that a one-bed position scan of the chest includes the entire heart (~5 minutes total).
  3. Acquire a 5-minute transmission scan.
  4. Inject 30 mCi (1,110 MBq) of 13NH3 intravenously and acquire a 15-minute emission scan beginning 5 minutes after radiotracer injection.
  5. Infuse dipyridamole intravenously at 0.142 mg/kg/min for 4 minutes.
  6. Inject 30 mCi (1,110 MBq) of 13NH3 intravenously 4 minutes after completion of dipyridamole infusion.
  7. Acquire a 15-minute emission scan 5 minutes after administration of radiotracer.
  8. (optional) Slowly administer 100 mg of aminophylline intravenously 5 minutes after injection of radiotracer to reverse the pharmacologic effect of dipyridamole.
  9. Process the data and display the attenuation-corrected images in the cardiac axis projections (short axis, vertical long axis, horizontal long axis).
13NH3 Rest Perfusion Imaging and FDG Myocardial Metabolism Imaging Protocol
Protocol for 13NH3 rest perfusion imaging and FDG myocardial metabolism imaging is as follows:

  1. Check fasting blood glucose level. If level is below 100 mg/dL, administer 90 g of glucose orally and wait 35 minutes before proceeding to the next step.
  2. Acquire a rectilinear scan for positioning the patient so that a one-bed position scan of the chest includes the entire heart (~5 minutes total).
  3. Inject 30 mCi (1,110 MBq) of 13NH3 intravenously and acquire a 15-minute emission scan 5 minutes after radiotracer injection.
  4. Inject 10 mCi (370 MBq) of FDG and regular insulin intravenously according to the schedule outlined earlier.
  5. Acquire a 5-minute transmission scan for attenuation correction beginning 30 minutes after FDG injection.
  6. Acquire a 30-minute emission scan of the same anatomic region.
  7. Process the data and display the attenuation-corrected images in the cardiac axis projections (short axis, vertical long axis, horizontal long axis) for both perfusion and metabolism images.
82RbCl Nongated Rest-Stress Myocardial Perfusion Imaging Protocol
Protocol for 82RbCl nongated rest-stress myocardial perfusion imaging (50) is as follows:

  1. Acquire a 5-minute transmission scan.
  2. Inject 40–60 mCi (1,480–2,220 MBq) of 82RbCl intravenously over 30–60 seconds.
  3. Acquire a 7-minute emission scan after a delay of 45–65 seconds.
  4. Infuse dipyridamole intravenously at 0.142 mg/kg/min for 4 minutes.
  5. Inject 40–60 mCi (1,480–2,220 MBq) of 82RbCl intravenously 4 minutes after completion of dipyridamole infusion.
  6. Acquire a 4-minute emission scan starting 45–65 seconds after administration of radiotracer.
  7. (optional) Slowly administer 100 mg of aminophylline intravenously 5 minutes after injection of radiotracer to reverse the pharmacologic effect of dipyridamole.
  8. Process the data and display the attenuation-corrected images in the cardiac axis projections (short axis, vertical long axis, horizontal long axis).

   CONCLUSIONS
Top
 Abstract
 INTRODUCTION
 BASIC PET PHYSICS AND...
 PET RADIOPHARMACEUTICALS FOR...
 DEFINITION OF TERMS
 PET OF MYOCARDIAL PERFUSION...
 IMAGING PROTOCOLS
 CONCLUSIONS
References
 
PET is highly accurate in detecting ischemic and infarcted myocardium. PET can also help reliably predict improvement in regional function after revascularization by identifying hibernating myocardium that shows diminished perfusion and preserved metabolism.


   Footnotes
 
2 Current address: Harvard Medical School Joint Program in Nuclear Medicine, Massachusetts General Hospital, Boston, Mass. Back

Abbreviations: FDG = 2-(fluorine-18) fluoro-2-deoxy-d-glucose NPV = negative predictive value PET = positron emission tomography PPV = positive predictive value SPECT = single photon emission computed tomography


   References
Top
 Abstract
 INTRODUCTION
 BASIC PET PHYSICS AND...
 PET RADIOPHARMACEUTICALS FOR...
 DEFINITION OF TERMS
 PET OF MYOCARDIAL PERFUSION...
 IMAGING PROTOCOLS
 CONCLUSIONS
 References
 

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