Martine Klein

Added Value of SPECT/CT for Correlation of MIBG Scintigraphy and Diagnostic CT in Neuroblastoma and Pheochromocytoma

OBJECTIVE In pheochromocytoma and neuroblastoma, pathologic findings on metaiodobenzylguanidine (MIBG) scintigraphy (planar and SPECT) and on diagnostic CT are sometimes difficult to correlate. Furthermore, CT reading may be impaired by anatomic distortion after surgery or irradiation and if contrast agent is not injected. The present study evaluates the impact of SPECT/CT fusion images on correlation and image analysis of both techniques. MATERIALS AND METHODS Eleven patients, three adults (age range, 27-64 years) with pheochromocytoma and eight children (age range, 16-72 months) with neuroblastoma, underwent 15 (123)I-MIBG scintigraphy (whole body and SPECT/CT) and diagnostic CT during follow-up after treatment, with a time interval of 2 to 30 days (mean, 12 days) between MIBG scintigraphy and diagnostic CT. The diagnostic CT scans were read twice: blindly and with knowledge of the SPECT/CT findings. The scintigraphic and anatomic data were subsequently compared and were verified by clinical outcome. RESULTS Of 15 imaging studies, there were nine cases of discordance between SPECT/CT and diagnostic CT, whereas concordant findings of planar MIBG and diagnostic CT were observed in six studies. Overall, SPECT/CT provided additional information in eight of the 15 cases (53%) and in eight of nine discordant studies (89%). In one case of pheochromocytoma in which anatomy was distorted by previous surgery and contrast agent was not injected, SPECT/CT findings guided the diagnostic CT that had initially misinterpreted the right adrenal gland as the inferior vena cava. In three of 11 studies performed for neuroblastoma, SPECT/CT facilitated the diagnostic CT reading: in one study, a small paravertebral thickening was overlooked at blind CT reading and in another case, SPECT/CT localized and characterized a soft-tissue mass medial to the iliac bone, which was missed on diagnostic CT in an area of difficult differential anatomy (bowel loops and eventual involved lymph nodes). In the third case, SPECT/CT directed the diagnostic CT to the MIBG abnormality after multiple surgical procedures. In these four cases, MIBG SPECT/CT allowed for localization of the pathologic site that was difficult to visualize on diagnostic CT. In four additional neuroblastoma studies in which a residual mass was present on diagnostic CT, planar MIBG scintigraphy was negative. SPECT/CT, focused on the area of the diagnostic CT abnormality, showed no focal MIBG uptake, thus increasing the diagnostic certainty of remission. CONCLUSION In cases of equivocal diagnostic CT, SPECT/CT bridges the gap between MIBG scintigraphy and diagnostic CT, with guidance of the diagnostic CT and characterization of its findings. In this small series, MIBG SPECT/CT increased the diagnostic certainty in 89% of discordant studies.

SPECT attenuation artifacts in normal and overweight persons : Insights from a retrospective comparison of Rb-82 positron emission tomography and TI-201 SPECT myocardial perfusion imaging

Purpose Myocardial perfusion imaging can be performed using SPECT or positron emission tomography (PET). SPECT has lower specificity than PET, largely as a result of attenuation artifacts; however, it is more widely available. The authors describe a study of the effect of sex and body weight on the incidence of SPECT attenuation artifacts using a retrospective comparison of Tl-201 SPECT and Rb PET. Methods One hundred sixty-one persons (101 men, 60 women; 81 normal weight, 80 overweight) underwent Tl-201 SPECT and Rb PET. The incidence of observed perfusion defects was studied in territories of the three major coronary arteries. SPECT and PET results were also compared with those of angiography in a subset of 75 patients. Results One hundred fourteen defects were reported on Rb PET compared with 176 defects with Tl-201 SPECT. Excess Tl-201 SPECT defects occurred in male and female, normal-weight and overweight persons. The average specificity was 64% for Tl-201 SPECT and 84% for Rb PET, reflecting this difference. Conclusions Attenuation artifacts in Tl-201 SPECT occur frequently and are not confined to easily identifiable subgroups of patients. Therefore, measures to improve specificity of SPECT (e.g., prone or gated imaging) or alternative imaging techniques such as PET have potential advantages for everyone, not simply for obese patients and women with large breasts. In addition, awareness of the prevalence of SPECT attenuation artifacts, in both sexes and all weight categories, may contribute to improved accuracy of interpretation.

18F-Fluorodeoxyglucose-PET/CT Imaging of Lungs in Patients With Cystic Fibrosis

BACKGROUND Airway inflammation plays a critical role in the progression of cystic fibrosis (CF) lung disease, and in the destruction of airways and lung parenchyma. Current methods to assess CF lung disease (BAL, spirometry, and high-resolution CT scanning), do not always accurately reflect actual disease states. Fluorodeoxyglucose (FDG)-PET scanning has been used previously to image infection and inflammation. In this study, we assessed the use of (18)F-FDG PET/CT scanning to evaluate and monitor lung inflammation and/or infection in patients with CF. METHODS PET/CT scans were performed in 20 patients with CF (age range, 14 to 54 years); 7 of 20 patients underwent repeat PET/CT scans during and after acute exacerbations. The results were compared with clinical information and with images from eight control subjects with no known lung disease. RESULTS Foci of enhanced activity were observed on FDG-PET scans of patients with CF but not those of control subjects. Higher focal activity (standardized uptake value, > 3.0) was seen during disease exacerbation and infection. Coregistered CT scan images assisted in the localization of PET foci and showed corresponding CT scan findings, with many additional findings on CT scans that were not seen on PET scans. Foci seen on high-intensity PET scans during exacerbations disappeared after antibiotic therapy and the resolution of exacerbation, while corresponding CT scan findings remained unchanged. CONCLUSIONS PET/CT imaging demonstrated the presence of foci of enhanced uptake that may reflect active focal infectious or inflammatory processes in the lungs. These foci can be cleared with antibiotic therapy. Further studies are needed to validate these results and to determine whether FDG-PET/CT scanning can predict the nature/severity of disease in patients with CF.

11C-acetate PET/CT in bladder urothelial carcinoma: intraindividual comparison with 11C-choline.

Objective: We present a first study of the use of 11C-acetate (ACET) positron emission tomography (PET)/computed tomography (CT) in bladder urothelial carcinoma (UC) and an intraindividual comparison with 11C- choline (CHOL) PET/CT. Methods: Fourteen patients with biopsy-proven UC (11 T2, 3 T1 refractory to treatment) were prospectively evaluated before radical cystectomy and excision of pelvic lymph nodes (LNs), with ACET and CHOL PET/CT scans performed within 1 week. Image acquisition started 5 minutes after intravenous injection of 12 to 14 mCi for both tracers. Standardized uptake values (SUVs) and tumor-to-background ratios (TBR) were calculated for all tumor and nodal findings and correlated with histopathology and follow-up. Results: ACET and CHOL were taken up in all UCs, involved LNs, and prostate pathology. SUVs were on average slightly, nonsignificantly higher for CHOL uptake (SUV) in UCs and significantly higher for ACET in LNs. TBR was nonsignificantly higher with CHOL for UC and significantly higher for LNs. Conclusions: In this preliminary series, 11C-ACET and 11C-CHOL PET/CT showed equivalent results in the preoperative evaluation of UC. Both tracers have the potential to contribute to selecting patients who would benefit from combined treatment—neoadjuvant chemotherapy and surgery—by identifying pathologic LNs or from surgery only, thanks to their high negative predictive value for LN involvement.

Large Vessel (Takayasu's) Arteritis in a Patient With Myelodysplastic Syndrome: Is There a Common Pathogenesis?

Autoimmune phenomena may complicate the course of myelodysplastic syndromes (MDS) but large vessel arteritis is a rare event. We report a case of large vessel arteritis in a patient with MDS. A 62-year-old male presented with thrombocytopenia and was diagnosed with low-risk MDS, (<5% blasts in his bone marrow and a normal karyotype). Shortly thereafter he developed large vessel (Takayasus) arteritis (TA) that responded well to oral corticosteroid and methotrexate therapy. Ten months later the MDS transformed into acute myeloid leukemia (AML). After a successful induction course with cytarabine and daunorubicin he underwent allogeneic transplantation from a matched unrelated donor with reduced-intensity conditioning. The transplantation was complicated by systemic cytomegalovirus (CMV) disease and he died 6 weeks post transplantation. Takayasus arteritis is an uncommon form of vasculitis affecting primarily young women and is atypical for elderly males. Though autoimmune manifestations in MDS occur in 10%-18.5% of patients, usually large vessels are spared. In MDS, activated T cells are thought to mediate bone marrow failure via overproduction of proinflammatory cytokines that cause stem cell apoptosis. These T cells may also mediate the autoimmune phenomena in MDS. The prognostic significance of autoimmunity in the course of MDS is not yet determined. Some reports suggest worse prognosis. The case illustrates a possible association between MDS and large vessel vasculitis and suggests a possible relationship between the presence of autoimmune syndromes and the outcome of patients with MDS.

CD68 staining correlates with the size of residual mass but not with survival in classical Hodgkin lymphoma

Abstract The prognostic role of CD68 tumor-associated macrophages in classic Hodgkin lymphoma (cHL) remains controversial. We stained diagnostic biopsies and scored for CD68 using the PGM1 antibody among 98 consecutive patients with cHL from our center followed over a median of 45 months for progression-free survival (PFS). Among 79 patients we assessed interim and post-treatment positron emission tomography-computed tomography (PET-CT). Residual mass (RM) size was based on the greatest diameter of the largest mass seen in post-treatment imaging, and percent reduction was calculated by comparing RM size with its greatest pretreatment diameter. We found a significant association between CD68 positivity and absolute size of initial disease mass (p = 0.014) and residual mass at the end of therapy (p = 0.006) but no association was observed with interim PET-CT results or PFS. Our findings suggest that macrophages may influence tumor size by altering the microenvironment. This study does not support a prognostic role of CD68 positivity in predicting survival.

Tc-99m mercaptoacetyltriglycine clearance : Comparison of camera-assisted methods

Purpose To compare the accuracy of three camera-assisted methods for the measurement of Tc-99m mercaptoacetyltriglycine (MAG3) clearance. Materials and Methods MAG3 renal scintigraphy was performed in 21 adults with different degrees of renal function. Posterior views were obtained that included the heart and the kidneys in the camera field of view. The syringe for injection was imaged before and after injection. Blood samples were drawn 24 and 43 minutes after injection and plasma radioactivity was measured. Three camera-assisted techniques to measure MAG3 clearance were tested: 1) Biexponential fitting of the left ventricular curve, normalized to plasma activity at 24 minutes; 2) calculation of clearance by relating the integral of the plasma curve (normalized to plasma activity) to the kidney activity using the Rutland-Patlak space method; and 3) a regression equation measuring clearance from the percentage of the injected dose accumulating in the kidneys during the 1- to 2.5-minute period. The camera-assisted clearances were compared with the single-sample MAG3 clearances calculated using the Russell equation. Linear regression analysis was used to measure the correlation between the camera-based methods and the single-sample techniques. Results Correlation with r > 0.900 was found for all three techniques. The difference in correlation coefficients between the three methods was not significant; however, the regression line of method 3 was significantly closer to the line of identity (P = 0.005). Conclusion Method 3 most closely fits the line of identity and is probably the most practical because no blood sample is needed.

Gallium-67 scintigraphy as an aid in the detection of spinal epidural abscess

Gadolinium-enhanced MRI is considered the study of choice for diagnosing spinal epidural abscess (SEA). Most of such cases, however, are not suspected initially, and thus do not benefit from the procedure. A case of SEA is described in which positive Ga-67 scintigraphy shortly before onset of lower extremity dysfunction was instrumental in obtaining an emergency gadolinium-enhanced MRI and establishing the diagnosis.

Hybrid Imaging in Malignancies of the Urinary Tract, Prostate, and Testicular Cancers

The main urologic malignancies include renal, bladder, prostate, and testicular cancers. Although positron emission tomography (PET) and PET/computed tomography (CT) play an increasing role in diagnosis and staging of many primary and metastatic tumors, it has been slow to be implemented into oncologic urology. Most malignant tumors are characterized by enhanced glucose metabolism, resulting in increased 18F-FDG uptake, which can be imaged by PET. In urology, 18F-FDG is a suboptimal tracer due to its variable uptake in some urological tumors and due to its accumulation and excretion through the urinary tract, potentially masking kidney, bladder, and prostate tumors. Thus, other PET tracers are being investigated for urologic malignancies.

The use of external radioactive markers in scintimammography.

In Tc-99m MIBI scintimammography, the exact localization of foci of increased tracer uptake or the exact anatomic correlation of palpated breast masses with a scintigraphic finding is difficult. The authors describe three patients with known or possible malignant breast lesions for whom the use of external radioactive markers successfully helped to provide this information, thus improving the diagnostic accuracy and guiding decision-making in the patients’ treatment.