PET perfusion and vasodilator function after angioplasty for acute myocardial infarction.

UNLABELLED: The aims of this study were to validate invasive coronary Doppler flows against noninvasive PET assessments of myocardial perfusion and to examine the timing and degree of regional coronary vasodilator reserve recovery in patients who are successfully reperfused with primary angioplasty (PTCA) for acute myocardial infarction. METHODS: PTCA was performed in 21 consecutive patients with acute myocardial infarction; the final diameter stenosis was 25% +/- 7%. After restoration of TIMI Grade 3 flow, all patients underwent quantitative coronary angiography and distal Doppler coronary blood flow studies (basal and after adenosine-induced hyperemia) in the infarct and noninfarct vessels. Regional myocardial perfusion and vasodilator function were quantitated after intravenous adenosine infusion PET in all patients at 26 +/- 9 hr after acute PTCA. These were repeated in 17 patients 9 +/- 3 days later. RESULTS: Post-PTCA resting coronary flow was 35 +/- 15 ml/min in the infarct-related vessels and 50 +/- 24 ml/min during peak hyperemia (p < 0.05). Coronary flow reserve (CFR) was 1.48 +/- 0.34 and 2.08 +/- 0.62 in the infarct and noninfarct vessels, respectively (p < 0.001). Early (< 36 hr) PET myocardial perfusion reserves (MPR) in the infarct and noninfarct regions were 1.59 +/- 0.33 and 2.03 +/- 0.62 (p < 0.01). Doppler CFR and PET MPR were correlated in the infarct (r = 0.61, p < 0.01) and noninfarct (r = 0.77, p < 0.0001) regions. Follow-up PET studies demonstrated improved MPR in both infarct and noninfarct regions (1.93 +/- 0.52 versus 2.54 +/- 0.97, p < 0.01). The improvement in coronary vasodilator function from the time of acute PTCA to follow-up PET in the infarct region was significant (p = 0.005). CONCLUSION: After successful mechanical revascularization by PTCA after acute myocardial infarction, intracoronary Doppler blood flows and noninvasive PET regional myocardial perfusion are correlated within the wide range of reperfusion blood flows observed in patients with contrast angiographic TIMI Grade 3 flow. Serial PET studies demonstrated a trend towards continued improvement in the vasodilator response in infarct-related myocardial regions after the restoration of blood flow by PTCA. PET offers the potential for accurate noninvasive serial assessment of reperfusion blood flow after primary angioplasty for acute myocardial infarction.

Clinical outcome of patients evaluated with emergency centre myocardial perfusion SPET for unexplained chest pain.

The clinical outcome of 68 patients with unexplained chest pain triaged with emergency centre (EC) SPET myocardial perfusion imaging (MPI) was assessed at 9 month follow-up. Based on clinical presentation and EC-MPI, 63% (43/68) of patients were discharged from the EC; 84% (36/43) of these patients reported no further symptoms at follow-up. There were no adverse clinical events in patients with totally normal EC-MPI.

Cost-effectiveness of myocardial perfusion imaging with SPECT in the emergency department evaluation of patients with unexplained chest pain.

PURPOSE: To determine the cost-effectiveness of promptly performing myocardial perfusion (MP) imaging with single photon emission computed tomography (SPECT) in patients presenting to the emergency department with unexplained chest pain. MATERIALS AND METHODS: Fifty patients with unexplained chest pain underwent MP imaging with SPECT and technetium-99m sestamibi. The cardiologists' management plans before and after receipt of imaging findings were compared. Costs were determined from analysis of comparable admissions for the 6 months before the start of the study. RESULTS: The cardiologists' confidence in their clinical diagnosis significantly increased with use of MP imaging (P<.0001). MP imaging results altered management decisions in 34 patients. Twenty-nine patients were sent home on the basis of imaging findings. None of the patients with a normal MP image experienced a serious adverse cardiac event. The total savings to the hospital was $39,296, or $786 per patient. CONCLUSION: Performing MP imaging in patients with unexplained chest pain while in the emergency department is cost-effective.

Modified PIOPED criteria used in clinical practice.

UNLABELLED: To assess the use of modified PIOPED scintigraphic criteria for lung scan (V/Q) interpretation to detect pulmonary embolism (PE), we prospectively applied these criteria in suspected PE patients referred for V/Q from 9/1/92 to 2/7/94. PIOPED criteria were modified by placing a moderate segmental perfusion mismatch in the intermediate instead of low probability of PE category and using the "stripe sign." METHODS: Patients were studied by six-view V/Q imaging using 74 MBq (2 mCi) 99mTc-MAA followed by 148-370 MBq (4-10 mCi) 99mTc-DTPA aerosol, contrast pulmonary selective angiography and Doppler sonography with leg compression as needed. Patients underwent follow-up (mean 13.9 mo) to detect subsequent thromboembolic events. In this study group, 1000 patients were studied by V/Q followed by angiography in 133 patients. RESULTS: The distribution of V/Q-assigned PE probabilities was: high probability 5.7%, intermediate 17.4%, low 41.4% and normal 35.5%. Group A patients (133) underwent angiography, which resulted in the determination of a 27.1% PE prevalence. Group B patients (867) did not have angiograms; the clinical prevalence of PE was 7.5%. In the total study population, the positive predictive value of a high probability V/Q study for PE (10.1% prevalence) was 98.2%, intermediate probability V/Q study for PE was 24.1% and a low probability study for PE was only 0.5%. CONCLUSION: Modified PIOPED V/Q interpretation criteria afford better angioproven PE discrimination between intermediate (31.8% PE prevalence) and low (5.5% PE prevalence) probability V/Q results than reported for PIOPED intermediate (32.6% PE prevalence) and low (16.3% PE prevalence) probability V/Q interpretation criteria.

Quantitative myocardial SPECT for infarct sizing: feasibility of a multicenter trial evaluated using a cardiac phantom.

UNLABELLED: This study determined the feasibility of performing a multicenter trial using quantitative SPECT myocardial perfusion imaging in patients with acute myocardial infarction. The feasibility was assessed by a cardiac phantom. METHODS: Twenty-two gamma camera systems in 19 laboratories were evaluated. Each laboratory performed nine studies on the cardiac phantom and performed quality control tests of system uniformity, collimator quality and gantry alignment on their gamma camera system. Defects simulating "hypoperfused" myocardium of differing amounts were placed in the myocardium for eight of the nine studies. Measured defect size was compared to true defect size. RESULTS: A total of 198 studies from 22 systems were analyzed. Three studies were technically inadequate. For all 22 systems, the average correlation coefficient between true and measured defect size was 0.992 +/- 0.009, with a range from 1.00 to 0.97. Three systems were rejected due to slopes of the regression line outside the limits 1.00 +/- 0.10 and mean errors > 5% in estimating defect size. The remaining systems had a correlation coefficient of 0.995 + 0.008 with an average slope of 1.00 +/- 0.04 and an intercept of 0.11% +/- 1.57%. The mean error in estimating defect size was 2.08% +/- 0.69%. CONCLUSION: The small interlaboratory variation and the close correlation with true defect size observed in a cardiac phantom indicate the feasibility of quantitative myocardial SPECT as a useful tool in multicenter trials evaluating therapy in acute myocardial infarction. Preliminary objective testing is required, however, to identify systems with technical deficiencies.

Krukenberg tumor and lung metastases from colon carcinoma diagnosed with F-18 FDG PET.

The authors report a case of a patient with postsurgical colorectal carcinoma and metastatic disease to the ovaries (Krukenberg tumor), the lung, and the liver first revealed by F-18 FDG PET imaging. The value of PET in a patient with an unexplained rising CEA is cited.

Indium-111 OncoScint CR/OV and F-18 FDG in colorectal and ovarian carcinoma recurrences. Early observations.

Indium-111 satumomab pendetide (In-111 OncoScint) planar and SPECT imaging and F-18 FDG positron emission tomography (PET) have been found individually to be helpful in the detection of recurrent colorectal and ovarian cancer, but have not been compared. Twelve patients who were examined for recurrent colorectal or ovarian carcinoma underwent both In-111 OncoScint imaging and F-18 FDG PET imaging. All had normal or equivocal results of CT or MR studies. Tumor detection abilities were similar in most cases. However, Oncoscint demonstrated an advantage in the detection of carcinomatosis. PET demonstrated an advantage in detecting focal tumor recurrence in one case and, not unexpectedly, in detecting liver metastases. All positive nuclear studies for tumor were found to be true-positives at pathology (7 patients), or by diagnostic new CT changes (1 patient). Finally, unreported, bone marrow, bowel, and colostomy sites appear to be normal sites of localization of F-18 FDG 1 hour after injection.

Watershed ischemia demonstrated with acetazolamide enhanced Tc-99m HMPAO SPECT.

A 75-year-old man who had a small right parietal infarction 8 months earlier underwent baseline and acetazolamide enhanced Tc-99m hexamethylpropylene amineoxime brain SPECT imaging. The acetazolamide study demonstrated a bilaterally symmetric perfusion deficit posteriorly near the midline. The baseline study was essentially normal. This finding was felt to represent watershed ischemia at the junction of the anterior circulations (anterior cerebral and middle cerebral arteries) and the posterior circulation (posterior cerebral artery). Carotid arteriography subsequently demonstrated left subclavian steal syndrome with retrograde flow through the left vertebral artery.

Ventilation-perfusion scintigraphy in the PIOPED study. Part I. Data collection and tabulation.

The Prospective Investigation of Pulmonary Embolism Diagnosis (PIOPED) study of more than 700 patients is the largest existing study of the accuracy of lung scintigraphy in the diagnosis of acute pulmonary embolism. Perfusion scans were obtained in all patients and ventilation scans in almost all, using standardized techniques. Chest radiographs were obtained in all patients within 12 hr of the lung scan. Most patients underwent pulmonary arteriography. The images were interpreted according to a set of interpretive criteria which remained constant throughout the trial. A standardized, detailed description of each image set was derived by consensus of teams of two readers blinded to clinical and arteriographic findings. This communication reports the methods used to describe and categorize the ventilation-perfusion scintigrams obtained in patients who were enrolled in the PIOPED study. Scintigraphic technique is reviewed briefly, probability assessment is described and the scan description is reviewed in detail. The form used to describe the findings on ventilation-perfusion scans is reproduced. Use of this standardized description permits retrospective evaluation of the PIOPED interpretive criteria. In addition, it represents a rigorous approach to scan analysis which could facilitate application of formal interpretive schemes and enhance the reproducibility of lung scan interpretations in the clinical setting.

Ventilation-perfusion scintigraphy in the PIOPED study. Part II. Evaluation of the scintigraphic criteria and interpretations.

This article presents an evaluation of the criteria used for categorical interpretation of the ventilation-perfusion (V/Q) scans performed in the PIOPED study. In addition, the correlation of percent probability estimates with the actual frequency of pulmonary embolism (PE) is presented. Cases which met the PIOPED criteria for various diagnostic categories were selected by computerized search of the detailed scan descriptions that had been done as part of the study. The process by which the scans were described was detailed in Part I of this report. Most of the criteria appropriately categorized V/Q scans which satisfied them. However, we recommend that three criteria should be reconsidered: 1. A single moderate perfusion defect is appropriately categorized as intermediate, rather than as low probability. 2. Extensive matched V/Q abnormalities are appropriate for low probability, provided that the chest radiograph is clear. On the other hand, single-matched defects may be better categorized as intermediate probability. Although due to the small number of cases with this finding, no definite, statistically founded recommendation can be made. 3. Two segmental mismatches may not be the optimum threshold for high probability, and in some cases should be considered for intermediate probability. However, due to the small number of cases with this finding, no definite, statistically founded recommendation can be made. We suggest that the revised criteria resulting from these adjustments should now be used for the interpretation of V/Q scans.

Effects of alterations in systolic pressure on radionuclide measurements of left ventricular filling dynamics.

To determine the effects of steady-state left ventricular systolic pressure alterations on radionuclide measures of left ventricular filling dynamics, we studied 15 normal patients and 17 patients with nonischemic heart disease. Micromanometer left ventricular pressures and computer assisted forward gated radionuclide angiograms were acquired simultaneously. Right atrial pacing maintained heart rates constant during the baseline condition and methoxamine and nitroprusside infusions. Diastolic filling dynamics, peak filling rate and time to peak filling rate were calculated using a three harmonic Fourier analysis of the left ventricular time-activity curves. Left ventricular systolic pressure increased to 165 +/- 25 mmHg with methoxamine (p < 0.001) and decreased to 106 +/- 18 mmHg with nitroprusside (p < 0.001) from a baseline value of 133 +/- 16 mmHg. Radionuclide left ventricular filling dynamics did not change significantly. Thus, we conclude that radionuclide measurements of left ventricular filling dynamics are not affected by modest, steady-state alterations in left ventricular systolic pressure and can therefore be useful for the assessment of left ventricular diastolic function during interventions which may also affect left ventricular systolic pressure.

Ratio of hepatic arterial-to-portal venous blood flow--validation of radionuclide techniques in an animal model.

The ratio of hepatic arterial-to-portal venous blood flow can be determined from the analysis of a first-pass bolus through the liver by a number of techniques. This study examines the validity of four radiotracer techniques in an animal model. Thirty-four flow studies (3 mCi 99mTc-DTPA/study) were performed in seven anesthetized pigs. Images were acquired for 200 sec and time-activity curves were generated from lung, liver and kidney ROIs. These curves were analyzed using a slope-based (HPI), a height-based (mHAR) and two deconvolution-based methods employing exponential or gamma variate fits. There was an excellent correlation (r greater than 0.9) between results obtained with flow probes and the radiotracer techniques, with the exception of the HPI technique (r = 0.75). The mHAR and deconvolution techniques were inaccurate at very low and high arterial flows, due respectively to noise limitations and hemodynamic instability in the animal. Nevertheless, these techniques appear to be the most promising for routine clinical use.

Lung scanning in the diagnosis of pulmonary embolism: the emperor redressed.

Diagnosis and management of the patient with pulmonary embolism remains a vexing clinical problem. Emboli are often unsuspected clinically. Ventilation-perfusion (VQ) scintigraphy is known to miss some emboli found on pulmonary angiography. Some physicians recommend diagnostic approaches in which the lung scan plays a relatively minor role, and angiography is required for many patients. Major prospective studies recently have made available objective data for formulation and evaluation of diagnostic and therapeutic strategies. These data suggest that the lung scan is a better predictor of patient outcome than has been previously appreciated. The goal of V/Q scanning is not detection of pulmonary emboli per se, but rather the identification of patients at a high or low risk for future embolic events if they are not anticoagulated. Several studies have shown that some emboli found on angiography are clinically benign and, in the absence of persistent thrombosis of the lower extremities, do not require anticoagulation. Treatment trials and clinical follow-up studies have shown that although the V/Q scan is not always predictive of angiogram results, it is a reliable predictor of patient outcome. In the absence of deep vein thrombosis, the low-probability scan identifies a patient population not requiring anticoagulation. When combined with objective studies of the venous system, the ventilation-perfusion lung scan provides a guide to management in the great majority of patients. Pulmonary angiography is required only occasionally.