Clinical significance of discordant findings between pre-therapy (123)I and post-therapy (131)I whole body scan in patients with thyroid cancer.

Radioactive therapy with (131)I (RAI) is commonly used during the management of patients with differentiated thyroid cancer (DTC). The aim of this study was to determine the clinical significance of discordant findings between pre-RAI whole body scan (WBS) with (123)I and post-RAI WBS in the management of DTC. We retrospectively evaluated 342 individuals between 2002 and 2008 who had a diagnosis of DTC and underwent RAI. All had WBS one day before RAI and WBS one week after RAI. Patients were divided into 3 groups: 1) RAI-naive subjects without known distant metastatic disease (M1); 2) patients with history of prior RAI and persistent disease (except M1); and 3) patients with known M1. In Group 1 (n=311), 7% of patients (n=22) had discordant scans, but in only 4 of these cases did this represent true disease (3 unsuspected lung and 1 mediastinal node metastasis). In the remaining 18 patients, discordant findings corresponded to physiologic or other benign causes. In group 2 (n=23), 7 subjects (30%) had discordant findings and all of the discrepant sites consisted of loco-regional nodal disease in the neck/upper mediastinum (n=6) and M1 in lung (n=1). In group 3 (n=8), 5 patients (62%) showed discordant uptake in lung and bone which corresponded to the locations of known M1. A total of 12 patients with iodine-avid M1 were identified on post-RAI WBS (3.5% of entire cohort). Pre-RAI WBS was only concordant in 3 of these cases (25%). In conclusion, the significance of pre and post-RAI WBS is highly influenced by the clinical setting. Unsuspected distant metastatic disease is infrequent in RAI-naive patients without known M1, where most discordant findings are usually due to benign explanations, and represent false positive findings in this group. In contrast, in patients with history of previous RAI or known M1, discordant results likely correspond to true disease. In our study, pre-RAI scans showed a low yield to detect iodine-avid distant metastatic disease when compared to post-RAI scans.

Comparison of the myocardial blood flow response to regadenoson and dipyridamole: a quantitative analysis in patients referred for clinical 82Rb myocardial perfusion PET.

BACKGROUND: Regadenoson is a novel selective A2A adenosine receptor agonist, which is administered as an intravenous bolus at a fixed dose. It is currently not clear if the absolute flow increase in response to this fixed dose is a function of distribution volume in individual patients or if it is generally comparable to the previous standard agents dipyridamole or adenosine, which are dosed based on weight. We used quantitative analysis of clinical 82Rb PET/CT studies to obtain further insights. METHODS: A total of 104 subjects with normal clinical rest/stress 82Rb perfusion PET/CT were included in a retrospective analysis. To rule out confounding factors, none had evidence of prior cardiac disease, ischaemia or infarction, cardiomyopathy, diabetes with insulin use, calcium score>400, renal disease or other significant systemic disease. A group of 52 patients stressed with regadenoson were compared with a group of 52 patients stressed with dipyridamole before regadenoson became available. The groups were matched for clinical characteristics, risk factors and baseline haemodynamics. Myocardial blood flow (MBF) and myocardial flow reserve (MFR) were quantified using a previously validated retention model, after resampling of dynamic studies from list-mode 82Rb datasets. RESULTS: At rest, heart rate, blood pressure and MBF were comparable between the groups. Regadenoson resulted in a significantly higher heart rate (34±14 vs. 23±10 beats per minute increase from baseline; p<0.01) and rate-pressure product. Patients in the regadenoson group reported less severe symptoms and required less aminophylline. Stress MBF and MFR were not different between the groups (2.2±0.6 vs. 2.1±0.6 ml/min/g, p=0.39, and 2.9±0.8 vs. 2.8±0.7, p=0.31, respectively). In the regadenoson group, there was no correlation between stress flow or MFR and body weight or BMI. CONCLUSION: Despite its administration at a fixed dose, regadenoson results in an absolute increase in MBF which is comparable to that following dipyridamole administration and is independent of patient distribution volume. This further supports its usefulness as a clinical stress agent.

Measuring the "unmeasurable": assessment of bone marrow response to therapy using FDG-PET in patients with lymphoma.

RATIONALE AND OBJECTIVES: To determine if anatomically "nonmeasurable" disease in bone marrow (BM) is assessable for response to therapy by [(18)F]-2-fluoro-2-deoxy-D-glucose (FDG) positron emission tomography (PET)/computed tomography (CT). MATERIALS AND METHODS: FDG PET/CT images of 27 patients with lymphoma, FDG-avid bone marrow (BM) lesions, and >or=1 FDG-avid, tumor-involved lymph node (LN) at baseline were retrospectively reviewed. FDG uptake in target LNs and BM foci was determined pre- and posttherapy using the standardized uptake value corrected for lean body mass (SUL(mean)). Size of the same target LNs was measured pre- and posttherapy on CT. Percentage decreases of LN size and LN and BM SUL were calculated. Response was classified according to revised International Workshop Criteria (IWC) with and without modification for metabolic evaluation of BM and correlated to overall survival. Statistical analyses were performed using paired t-tests, Pearson correlation coefficients, and z-tests. RESULTS: LN size, LN SUL(mean), and BM SUL(mean) were significantly higher pre- versus posttherapy (2337 mm(2) +/- 1810 vs. 309 mm(2) +/- 323; 6.94 +/- 4.96 vs. 1.02 +/- 1.00; and 6.81 +/- 4.58 to 1.84 +/- 1.58, all P < .001, respectively). After therapy, significant correlation was found between percentage declines of LN size and SUL(mean) of LNs (r = 0.84, P < .001) or BM (r = 0.56, P = .002) and SUL(mean) of LN and BM (r = 0.76, P < .001). Including a metabolic assessment of BM correctly altered overall response assessment in 5/27 (19%) patients and better predicted overall survival than revised IWC. CONCLUSION: Anatomically "unmeasurable" BM infiltration with lymphoma behaves similarly to LN disease after therapy and is "measurable" by FDG PET/CT. FDG PET/CT is valuable for monitoring tumor response in "measurable" disease and BM, which was previously considered "unmeasurable" by anatomical imaging.

Detection of bone metastases using diffusion weighted magnetic resonance imaging: comparison with (11)C-methionine PET and bone scintigraphy.

PURPOSE: We evaluated the ability of diffusion-weighted imaging (DWI) to detect bone metastasis by comparing the results obtained using this modality with those obtained using (11)C-methionine (MET) positron emission tomography (PET) and bone scintigraphy. MATERIALS AND METHODS: This retrospective study involved 29 patients with bone metastasis. DWI was obtained using a single-shot echo planar imaging (EPI) sequence with fat suppression using a short inversion time inversion recovery sequence. The detection capabilities of DWI for bone metastases were compared with those of whole body MET PET (in 19 patients) and 99mTc-methylene diphosphonate bone scintigraphy (in 15 patients). RESULTS: Among the 19 patients who were diagnosed using DWI and PET, the PET identified 39 bone metastases, while the DWI identified 60 metastases out of 69 metastases revealed with conventional magnetic resonance imaging (MRI). Among the 15 patients who were diagnosed using DWI and bone scintigraphy, the bone scintigraphy identified 18 bone metastases, while the DWI identified 72 metastases out of 78 metastases revealed with conventional MRI. The overall bone metastasis detection rates were 56.5% for PET, 23.1% for bone scintigraphy and 92.3% for DWI. CONCLUSION: DWI is a very sensitive method for detecting bone metastasis and is superior to MET PET and bone scintigraphy in terms of its detection capabilities.

Assessment of interobserver reproducibility in quantitative 18F-FDG PET and CT measurements of tumor response to therapy.

UNLABELLED: Our goal was to estimate and compare across different readers the reproducibility of the (18)F-FDG PET standardized uptake value (SUV) and CT size measurements, and changes in those measurements, in malignant tumors before and after therapy. METHODS: Fifty-two tumors in 25 patients were evaluated on (18)F-FDG PET/CT scans. Maximum SUVs (SUV(bw) max) and CT size measurements were determined for each tumor independently on pre- and posttreatment scans by 8 different readers (4 PET, 4 CT) using routine nonautomated clinical methods. Percentage changes in SUV(bw) max and CT size between pre- and posttreatment scans were calculated. Interobserver reproducibility of SUV(bw) max, CT size, and changes in these values were described by intraclass correlation coefficients (ICCs) and estimates of variance. RESULTS: The ICC was higher for the pretreatment, posttreatment, and percentage change in SUV(bw) max than the ICC for the longest CT size and the 2-dimensional CT size (before treatment, 0.93, 0.72, and 0.61, respectively; after treatment, 0.91, 0.85, and 0.45, respectively; and percentage change, 0.94, 0.70, and 0.33, respectively). The variability of SUV(bw) max was significantly lower than the variability of the longest CT size and the 2-dimensional CT size (mean +/- SD before treatment, 6.3% +/- 14.2%, 16.2% +/- 17.8%, and 27.5% +/- 26.7%, respectively, P < or = 0.001; and after treatment, 18.4% +/- 26.8%, 35.1% +/- 47.5%, and 50.9% +/- 51.4%, respectively, P < or = 0.02). The variability of percentage change in SUV(bw) max (16.7% +/- 36.2%) was significantly lower than that for percentage change in the longest CT size (156.3% +/- 157.3%, P < or = 0.0001) and the 2-dimensional CT size (178.4% +/- 546.5%, P < 0.0001). CONCLUSION: The interobserver reproducibility of SUV(bw) max for both untreated and treated tumors and percentage change in SUV(bw) max are substantially higher than measurements of CT size and percentage change in CT size. Measurements of tumor metabolism by PET should be included in trials to assess response to therapy. Although PET reproducibility was high, the variability observed in analyses of identical image sets by 4 readers indicates that automated analytic tools to assess response might be helpful to further enhance reproducibility.

Diagnosis and differentiation of bronchioloalveolar carcinoma from adenocarcinoma with bronchioloalveolar components with metabolic and anatomic characteristics using PET/CT.

UNLABELLED: (18)F-FDG PET has been reported to have reduced sensitivity in detecting bronchioloalveolar carcinoma (BAC) versus lung cancers with other histologies. However, there are CT characteristics that are suggestive of BAC, and potentially these could be useful to refine diagnostic criteria so PET/CT can be more accurate in the diagnosis of BAC. We correlated tumor size and density obtained with CT and glucose metabolism obtained with (18)F-FDG PET in patients with BAC and adenocarcinoma with BAC components (Adeno+BAC) to determine the roles of both the anatomic and the functional components of the PET/CT examination in diagnosing this disease. Also, the correlation between tumor size and (18)F-FDG uptake or Hounsfield unit (HU) value was determined in these 2 groups. METHODS: This was a retrospective study on a consecutive series of 53 patients with 57 pathology-proven lesions (26 BAC, 31 Adeno+BAC) who underwent (18)F-FDG PET/CT scans. The standardized uptake value (SUV) and average HUs reported were obtained for the tumors. The tumor size, (18)F-FDG uptake, and HU values in both groups were compared. The correlation between metabolic (SUV) and CT (HU) characteristics for the lesions and tumor size was assessed using the Pearson correlation coefficient. RESULTS: A total of 26 lesions with pure BAC had a median SUVmax of 1.48 (range, 0.63-4.54). A total of 81% of patients with BAC (21/26 lesions) had SUVmax values of less than 2.5. Thirty-one lesions diagnosed as Adeno+BAC had a median SUVmax of 6.03 (range, 2.45-24) (P < 0.0001 vs. BAC). The mean SUVmax (1.77 +/- 0.99) of BAC was much lower than that of Adeno+BAC (6.55 +/- 4.33) (P < 0.0001). Maximum HU in BAC lesions (-111.96 +/- 123.92) was substantially lower than that in Adeno+BAC (82.03 +/- 33.77) lesions (P < 0.0001). The average maximum tumor dimension in the lung window was much smaller for BACs (17.63 +/- 5.5) than for Adeno+BACs (49.38 +/- 27.5) (P < 0.0001). A strong positive correlation between tumor size and HU was observed in the Adeno+BAC group (P = 0.0002). CONCLUSION: PET/CT can help differentiate between BAC and Adeno+BAC by using tumor size, CT density, and metabolic activity. Pure BAC exhibits smaller size, lower (18)F-FDG uptake, and lower tumor density than does Adeno+BAC. Many BACs have low SUVs (<2.0), but their low HU on CT aids in their proper identification.

Scalene muscle uptake: a potential pitfall in head and neck PET/CT.

PURPOSE: To describe increased 2-deoxy-2-[(18)F] fluoro-D-glucose (FDG) uptake in the scalene muscles in a large population of patients referred for evaluation with FDG positron emission tomography/computed tomography (PET/CT) imaging. METHODS: The study met criteria for institutional review board exemption. FDG PET/CT images from 410 patients (179 males; mean age 56.8 years, range 6-88) were retrospectively reviewed for the presence or absence of FDG uptake in the neck that corresponded to the scalene muscles on the concurrent CT scan. Medical records were reviewed and data including age, sex, smoking history, reason for referral, and history of obstructive airways disease, thoracotomy, and thoracic radiation were recorded and evaluated. RESULTS: One hundred and forty-seven of the 410 scans (36%) demonstrated increased FDG uptake on PET that corresponded to the scalene muscles on the CT scan. The uptake was most often bilateral, symmetrical, and linear (n = 117). Other patterns of scalene muscle uptake included unilateral and linear uptake (n = 27) and unilateral and focal uptake (n = 3). Scalene muscle uptake was more common in patients referred for evaluation of lung carcinomas compared to other types of tumors (52% vs. 32%, p = 0.05). CONCLUSION: Linear FDG uptake in scalene muscles is a commonly seen pattern on PET/CT. This finding should be recognized as a distinct entity and not misinterpreted on transverse images as metastatic disease.