Importance of Tc-99m sulfur colloid liver-spleen scans performed before indium-111 labeled leukocyte imaging for localization of abdominal infection.

INTRODUCTION: The localization of intraabdominal abscesses is a difficult imaging problem in nuclear medicine, especially when the location of the abscess is in the area of the liver and spleen. The need for performing Tc-99m sulfur colloid liver-spleen scans before injecting indium-111 leukocytes for improved lesion detection and characterization versus performing In-111 leukocyte scans alone has been questioned in the literature MATERIALS AND METHODS: We present 3 patients with intraabdominal abscesses in the liver-spleen area, in which liver-spleen scans were performed before In-111 leukocyte scans. The findings of all were correlated with computed tomography and interventional procedures. RESULTS: In all patients, the Tc-99m liver-spleen scan helped for accurate recognition of the location of the abscess, correlated with computed tomography findings, and were helpful for intervention and exclusion of the other sources of infection. CONCLUSION: Data from these 3 patients reinforces the need for Tc-99m sulfur colloid liver-spleen scans before performing In-111 WBC scans for better localization and interventional treatment of intraabdominal abscesses.

Metastatic thyroid cancer occurring as an unknown primary lesion: the role of F-18 FDG positron emission tomography.

Thyroid cancer can appear as metastatic disease of an unknown primary origin, and fluorine-18 fluorodeoxyglucose (F-18 FDG) positron emission tomographic (PET) studies are helpful in the workup evaluation of these patients. The authors describe two patients who had metastatic disease from an unknown primary lesion. F-18 FDG PET studies played an important role in localizing the primary malignant site in the thyroid gland. The utility of F-18 FDG imaging in decreasing the number of procedures, cost, and inconvenience to patients is shown clearly in both cases.

Role of repeated F-18 fluorodeoxyglucose imaging in management of patients with bone and soft tissue sarcoma.

AIM OF THE STUDY: To assess the impact of repeated F-18 FDG studies on the management of patients with bone and soft tissue (B&S) sarcomas. MATERIAL AND METHODS: Twenty patients with B&S tissue tumors (11 M and 9 F age 17-72 years) had 52 F-18 FDG Dual Head Coincidence Imaging (DHCI) studies. 7 patients were followed for 6 months to 2 years clinically after removal of the primary tumor. Thirteen patients were evaluated for suspected recurrences. Patient's preparation, F-18 FDG injection and imaging procedure were done according to department protocol. Attenuation corrected images were interpreted visually by 3 trained physicians. Tumor to background ratios were calculated for all lesions. RESULTS: In 13 patients having both studies, baseline FDG and CT/MRI were concordant in 8 patients, FDG detected more lesions in 3 patients but it did not detect 4 metastatic pulmonary nodules in 2 patients. Follow up studies showed stable disease in 10 patients while 6 patients who showed worsening disease needed to change their chemotherapy. Surgery was avoided in 2 patients and 2 patients showed improved response. CONCLUSION: Repeated F-18 FDG DHCI examinations proved to have an impact on the clinical management of patients with malignant bone and soft tissue sarcoma. It helps to differentiate postoperative changes from local recurrence.

Attenuation-Correction Induced Artifact in F-18 FDG PET Imaging Following Total Knee Replacement.

Purpose: The clinical use of PET FDG in the work-up of patients with bone and soft tissue malignant tumors is rapidly increasing. The recognition of any source of artifact, therefore, is important to avoid interpretation pitfalls.Procedures: Two patients with complete knee joint replacement by metallic prosthesis in the course of their treatment for malignant bone and soft tissue sarcoma were evaluated by PET F-18 FDG imaging using a dual head coincidence gamma camera.Results: Both studies demonstrated in the attenuation-corrected images intense increase activity at the joint space between the metallic prosthetic surfaces at the level of the knee joint. No uptake, however, was noted in the same location on the non-attenuation-corrected images. Subsequent bone and thallium-201 scans confirmed the absence of tumor recurrence in the first patient. The second patient had multiple follow up F-18 FDG scans over a period of 16 months that show no changes from the baseline study.Conclusion: In the F-18 FDG PET images of patients with total knee metallic prosthesis, an intense activity tends to be seen in the joint space, only in the attenuation-corrected images. Such pattern of uptake is considered artifactual and should always be verified in the non-attenuated images.

The additive values of left ventricular function and extent of myocardium at risk to dipyridamole perfusion imaging for optimal risk stratification prior to vascular surgery.

Although the increased risk of cardiac complications in surgical patients with diminished left ventricular ejection fraction (LVEF) is well-established, this method has been supplanted in recent years by assessment of ischaemic burden using myocardial perfusion imaging (MPI). This study was conducted to determine if MPI and LVEF determination provide complementary or redundant information in preoperative evaluation of vascular surgery patients. A total of 101 patients were studied with dipyridamole MPI and radionuclide ventriculography before surgery. Single photon emission tomographic MPI images were scored for defect severity and categorized as either fixed or reflecting ischaemia. Resting left ventricular cavity was also categorized as normal or dilated. LVEF was subdivided into normal (> or = 50%) and abnormal (< 50%). Seventeen patients had cardiac events. Events were more frequent in patients with ischaemia, in patients with a LVEF < 50% and in those with dilated left ventricular chambers. The mean number of ischaemic segments was also higher in the cardiac event group. Higher event rates were seen when a combination of these factors was present. A history of myocardial infarct, congestive heart failure or coronary artery disease was also a significant predictor of subsequent events. Thus, both abnormal left ventricular function and extent of ischaemic myocardium have independent and complementary predictive power for cardiac events in vascular surgery patients.

The value and correlates of left ventricular cavity assessment in dipyridamole 201Tl SPET studies.

Left ventricular cavity (LVC) enlargement during SPET dipyridamole 201Tl myocardial perfusion imaging studies is a proven marker of severity of coronary artery disease. Nevertheless, the influence of the extent of myocardial infarct and ischaemia on the degree of LVC enlargement both at rest and with dipyridamole has not been clearly analysed. One hundred and one patients were studied by both dipyridamole myocardial perfusion imaging and radionuclide ventriculography within 1 week. The left ventricular ejection fraction (LVEF) was 57 +/- 9 in normal resting LVC patients (group I), 43 +/- 8 in mild LVC enlargement patients (group II) and 28 +/- 5 in moderate-to-severe LVC enlargement patients (group III). The number of fixed defects was increased in patients in group II and group III, but there was no significant differences in the number of ischaemic segments among groups. The number of ischaemic segments was much higher in patients with transient cavity dilatation than those without cavity change; nonetheless, both LVEF and the numbers of fixed segments were unchanged. The degree of LVC enlargement at rest strongly reflects the resting left ventricular systolic function as well as the extent of previous myocardial infarct. On the other hand, transient cavity dilatation during dipyridamole infusion can only reflect the extent of viable myocardium at risk.

Assessment of 99Tcm-tetrofosmin lung uptake: a modified method to avoid the contribution from high chest wall activity.

Evaluation of lung uptake during routine 99Tcm-tetrofosmin myocardial SPET (single photon emission tomography) studies may be hindered by substantial chest muscle uptake, particularly post-exercise. This study investigated this proposal and analysed the various components of chest activity that may add to the real lung uptake. Exercise SPET studies were performed on normal subjects using 99Tcm-tetrofosmin and compared with the results of 99Tcm-sestamibi and 201Tl studies. The chest to heart count ratio (CHR) was calculated from the anterior SPET projection and further subclassified into lung, anterior chest and posterior chest to heart ratios (LHR, AHR, PHR) from the left anterior oblique (LAO) projection. On post-exercise images, the 99Tcm-tetrofosmin CHR was significantly higher than that of 201Tl and 99Tcm-sestamibi. Both the 99Tcm-tetrofosmin AHR and PHR were higher than those of 201Tl and 99Tcm-sestamibi. However, the LHR was similar for all three radiopharmaceuticals. In contrast, the rest 99Tcm-tetrofosmin images differed little from the 201Tl and 99Tcm-sestamibi ones. Thus, 99Tcm-tetrofosmin lung uptake post-exercise should be interpreted with caution, as chest muscle uptake is higher than normal. A more accurate evaluation of 99Tcm-tetrofosmin lung uptake is achieved from the LAO projection, where the contribution from chest muscle counts is much less than in the routinely used anterior projection.

Technetium-99m-MIBI myocardial SPECT: supine versus right lateral imaging and comparison with coronary arteriography.

UNLABELLED: Myocardial perfusion SPECT using the prone position improves inferior wall counts and decreases motion problems as compared with the usual supine position. Nonetheless, it is not suitable for women. In addition, it is associated with artifactual anteroseptal defects and hot spots. METHODS: The right lateral (RL) position was evaluated instead of the prone position in 72 patients (26 women). RL imaging was performed immediately after the supine imaging during a routine 2-day 99mTc-sestamibi exercise protocol. The SPECT images were scored semiquantitatively by three physicians. Moreover, regional myocardial counts, as well as extent and severity of defects, were assessed by quantitative polar map analysis. RESULTS: All patients tolerated the RL position well and there was no significant patient movement in either position. Higher inferior myocardial counts per pixel were observed in the RL than in supine images. Inferior wall defects (especially mild ones) were more common in the supine than the RL images, whereas defects in other regions were not different. Quantitative analysis confirmed these findings. Analysis of 34 patients with recent coronary arteriography revealed an overall coronary artery disease (CAD) supine- and RL-imaging specificity of 50% and 75%, respectively, and the sensitivities of both were 93%. Right CAD sensitivity, specificity and normalcy rates for the supine position were 100%, 44% and 55%, whereas those of the RL position were 94%, 75% and 90%, respectively. CONCLUSION: The RL position improves CAD diagnostic accuracy, particularly right CAD, without significant artifacts in other myocardial regions. Unlike the prone position, the RL position is well tolerated by both women and men.