Henry W. D. Yeung

Intensity of 18Fluorodeoxyglucose Uptake in Positron Emission Tomography Distinguishes Between Indolent and Aggressive Non-Hodgkin’s Lymphoma

PURPOSE (18)Fluorodeoxyglucose positron emission tomography (FDG PET) is widely used for the staging of lymphoma. We investigated whether the intensity of tumor FDG uptake could differentiate between indolent and aggressive disease. MATERIALS AND METHODS PET studies of 97 patients with non-Hodgkins lymphoma who were untreated or had relapsed and/or persistent disease and had not received treatment within the last 6 months were analyzed, and the highest standardized uptake value (SUV) per study was recorded. Correlations were made with histopathology. RESULTS FDG uptake was lower in indolent than in aggressive lymphoma for patients with new (SUV, 7.0 +/- 3.1 v 19.6 +/- 9.3; P < .01) and relapsed (SUV, 6.3 +/- 2.7 v 18.1 +/- 10.9; P = .04) disease. Despite overlap between indolent and aggressive disease in the low SUV range (indolent, 2.3 to 13.0; aggressive, 3.2 to 43.0), all cases of indolent lymphoma had an SUV <or= 13. A receiver operating characteristic (ROC) analysis demonstrated that the SUV distinguished reasonably well between aggressive and indolent disease (area under ROC curve, 84.7%), and an SUV > 10 excluded indolent lymphoma with a specificity of 81%. With a higher cutoff for the SUV, the specificity would have been higher. CONCLUSION FDG uptake is lower in indolent than in aggressive lymphoma. Patients with NHL and SUV > 10 have a high likelihood for aggressive disease. This information may be helpful if there is discordance between biopsy and clinical behavior.

PET/CT: a new imaging technology in nuclear medicine.

This review discusses the technical background of combined PET and CT and considers the clinical applications of PET/CT imaging. Questions addressed include: Is PET/CT superior to PET imaging alone? If so, in which patient populations and in what respect? Can PET/CT imaging affect patient management? Can PET/CT be practiced economically? While much work remains to be done, the available data clearly suggest that PET/CT decreases imaging time per patient and, even for the experienced reader, significantly reduces the number of equivocal PET interpretations. PET/CT also has the ability to improve accuracy of PET image interpretation and to affect clinical decision making, thereby improving patient management. The nuclear medicine community should approach this new technology with an open mind and focus on its clinical usefulness. The decision regarding whether PET/CT should be part of the equipment in a given nuclear medicine or radiology practice largely depends on the specific patient population. It is concluded that present skepticism concerning combined PET/CT will subside once critics of this new modality have had the opportunity to clearly see on images its many advantages compared with either PET alone or conventional image fusion approaches.

FDG-PET standardized uptake values in normal anatomical structures using iterative reconstruction segmented attenuation correction and filtered back-projection

Filtered back-projection (FBP) is the most commonly used reconstruction method for PET images, which are usually noisy. The iterative reconstruction segmented attenuation correction (IRSAC) algorithm improves image quality without reducing image resolution. The standardized uptake value (SUV) is the most clinically utilized quantitative parameter of [fluorine-18]fluoro-2-deoxy-D-glucose (FDG) accumulation. The objective of this study was to obtain a table of SUVs for several normal anatomical structures from both routinely used FBP and IRSAC reconstructed images and to compare the data obtained with both methods. Twenty whole-body PET scans performed in consecutive patients with proven or suspected non-small cell lung cancer were retrospectively analyzed. Images were processed using both IRSAC and FBP algorithms. Nonquantitative or gaussian filters were used to smooth the transmission scan when using FBP or IRSAC algorithms, respectively. A phantom study was performed to evaluate the effect of different filters on SUV. Maximum and average SUVs (SUVmax and SUVavg) were calculated in 28 normal anatomical structures and in one pathological site. The phantom study showed that the use of a nonquantitative smoothing filter in the transmission scan results in a less accurate quantification and in a 20% underestimation of the actual measurement. Most anatomical structures were identified in all patients using the IRSAC images. On average, SUVavg and SUVmax measured on IRSAC images using a gaussian filter in the transmission scan were respectively 20% and 8% higher than the SUVs calculated from conventional FBP images. Scatterplots of the data values showed an overall strong relationship between IRSAC and FBP SUVs. Individual scatterplots of each site demonstrated a weaker relationship for lower SUVs and for SUVmax than for higher SUVs and SUVavg. A set of reference values was obtained for SUVmax and SUVavg of normal anatomical structures, calculated with both IRSAC and FBP image reconstruction algorithms. The use of IRSAC and a gaussian filter for the transmission scan seems to give more accurate SUVs than are obtained from conventional FBP images using a nonquantitative filter for the transmission scan.

Extending Positron Emission Tomography Scan Utility to High-Risk Neuroblastoma: Fluorine-18 Fluorodeoxyglucose Positron Emission Tomography as Sole Imaging Modality in Follow-Up of Patients

PURPOSE Although positron emission tomography (PET) with fluorine-18 fluorodeoxyglucose ((18)F-FDG) has a major impact on the treatment of adult cancer, the reported experience with extracranial tumors of childhood is limited. We describe a role for PET in patients with neuroblastoma (NB). PATIENTS AND METHODS In 51 patients with high-risk NB, 92 PET scans were part of a staging evaluation that included iodine-123 or iodine-131 metaiodobenzylguanidine (MIBG) scan, bone scan, computed tomography (and/or magnetic resonance imaging), urine catecholamine measurements, and bone marrow (BM) examinations. The minimum number of tests sufficient to detect NB was determined. RESULTS Of 40 patients who were not in complete remission, only 1 (2.5%) had NB that would have been missed had a staging evaluation been limited to PET and BM studies, and 13 (32.5%) had NB detected by PET but not by BM and urine tests. PET was equal or superior to MIBG scans for identifying NB in soft tissue and extracranial skeletal structures, for revealing small lesions, and for delineating the extent and localizing sites of disease. In 36 evaluations of 22 patients with NB in soft tissue, PET failed to identify only two long-standing MIBG-negative abdominal masses. PET and MIBG scans showed more skeletal lesions than bone scans, but the normally high physiologic brain uptake of FDG blocked PET visualization of cranial vault lesions. Similar to MIBG, FDG skeletal uptake was diffusely increased with extensive or progressing BM disease but faint or absent with minimal or nonprogressing BM disease. CONCLUSION In the absence or after resolution of cranial vault lesions, and once the primary tumor is resected, PET and BM tests suffice for monitoring NB patients at high risk for progressive disease in soft tissue and bone/BM.

The majority of transformed lymphomas have high standardized uptake values (SUVs) on positron emission tomography (PET) scanning similar to diffuse large B-cell lymphoma (DLBCL)

BACKGROUND We previously correlated non-Hodgkins lymphoma (NHL) histology with (18)fluoro-2-deoxyglucose-positron emission tomography (FDG-PET) intensity: a standardized uptake value (SUV)>10 predicted aggressive lymphoma with >80% certainty and an SUV >13, with >90% certainty. PATIENTS AND METHODS To evaluate SUV in transformed lymphoma, we identified all FDG-PET scans for NHL at Memorial Sloan-Kettering Cancer 1999-2007 with (i) biopsy-proven transformation, (ii) no therapy 60 days before PET scan and (iii) FDG-PET scans no more than 60 days before or 90 days after transformation. RESULTS In 5 of 40 patients, the biopsy site was excised before PET; in two, only marrow was biopsied. In the remaining 33 patients, the SUV of the biopsy site ranged from 3 to 38, mean 14, median 12. Eighteen of 33 biopsies (55%) had an SUV>10 and 16 (48%)>13. The highest SUV in a transformed lymphoma PET scan (SUV(study-max)) ranged from 3.2 to 40, mean 15, median 12. Twenty-five of 40 patients (63%) presented with an SUV(study-max)>10 and 20 (50%)>13. CONCLUSIONS Like de novo aggressive lymphomas, the majority of transformations have a high SUV(study-max) for a given pretreatment staging study, although many do not have very high values. Transformation should be suspected in indolent lymphoma with high SUVs on FDG-PET. Biopsies should be directed to the site of greatest FDG avidity.

Incidental focal thyroid uptake on FDG positron emission tomographic scans may represent a second primary tumor.

Purpose This article discusses the value of incidental thyroid uptake of fluorodeoxyglucose (FDG) on whole-body positron emission tomography (PET) scans performed in patients with cancer. This issue has been reported diversely in the literature. Materials and Methods Whole-body PET scans of four patients with cancer (two of them women; age, 49 to 78 years) in whom focal thyroid uptake was visualized and subsequently correlated with thyroid carcinoma based on cytologic or histopathologic data were reviewed. The clinical outcomes of these patients were analyzed retrospectively. Maximum and average standardized uptake values (SUVs) of thyroid accumulation were recalculated in all patients. Results Two of the four patients referred for FDG PET scans had lung adenocarcinomas, one had prostrate carcinoma, and one had an unknown primary tumor. Focal thyroid uptake was visualized, with maximum and average SUVs ranging from 3.7 and 2.3 to 53 and 34, respectively. These findings were correlated with cytologic (two patients) or histopathologic data (two patients) that indicated thyroid carcinoma. In two patients, their treatment was changed and total thyroidectomy was performed; in one of them the SUVs of the focal thyroid accumulation (maximum and average values of 7.9 and 4.8, respectively) were less than the cutoff values for thyroid cancer noted in the literature. The clinical condition of the other two patients did not permit additional investigation or treatment for thyroid carcinoma. Conclusion Increased focal thyroid uptake on whole-body FDG PET scans should not be overlooked, even when it is not marked, and should prompt further investigation to rule out cancer.

FDG-PET in Esophageal Cancer: Incremental Value over Computed Tomography

OBJECTIVES: To evaluate the clinical utility of 18F-fluorodeoxyglucose positron emission tomography (FDG-PET) in patients with cancer (CA) of the esophagus, and its incremental value over computed tomography (CT) scan.METHODS: Positron emission tomography (PET) scan and CT scan reports of all patients with biopsy-proven CA esophagus from December 1995 to August 1998 were reviewed. PET images were acquired on a high-resolution dedicated PET scanner 45 minutes to 1 hour after intravenous injection of 370 MBq of fluorine-18-fluorodeoxyglucose (F-18-FDG). Emission images of the neck, chest, and abdomen were obtained, followed by transmission scans at selected sites.RESULTS: One hundred fifty-one scans were performed on 109 patients. The clinical indications were staging (67), follow-up evaluation after chemoradiation (66), and evaluation of possible recurrence after surgery (18). A final diagnosis was reached in 99 patients at 276 sites by histology (91.3%) or clinical follow-up of over 6 months (8.7%). FDG-PET scan showed a sensitivity of 80%, specificity of 95%, and accuracy of 86% compared with 68%, 81%, and 73% for CT. Of the 32 false negatives, 23 were perigastric or paraesophageal lymph nodes close to the primary, and 5 were peritoneal or pleural spread. PET detected 99% of the primary lesion (66 out of 67) with a mean standardized uptake value (SUV) of 11 (3.6 to 46). There was no apparent difference in 18F-fluorodeoxyglucose (FDG) uptake between squamous cell CA (N = 15, mean SUV 10.5), adenoCA (N = 48, mean SUV 11.2), and other cell types (N = 3, mean SUV 10.3). The one case where PET missed the primary lesion turned out to have a lesion measuring 0.4 cm in its maximum diameter. In 20 patients out of the 99 with confirmed diagnosis (20%), PET detected 24 confirmed lesions not seen on CT, and in 14 patients (14%) management was changed as a result of the PET finding.CONCLUSION: FDG-PET scan is more accurate than CT (86% vs. 73%; P = 0.0002) in the evaluation of patients with CA esophagus. It provides additional information over CT, impacting on management in 14% of patients.

Clinical value of combined positron emission tomography/computed tomography imaging in the interpretation of 2-deoxy-2-[F-18]fluoro-D-glucose-positron emission tomography studies in cancer patients.

BackgroundPositron emission tomography (PET)/computed tomography (CT) is a new imaging modality that provides exact coregistration of anatomic and metabolic data. We have investigated to what degree this new technique might affect the interpretation of PET images in a nonselected group of consecutive cancer patients, reflecting routine condition in a busy cancer center.MethodsWhole-body 2-deoxy-2-[F-18]fluoro-d-glucose (FDG)–PET and PET/CT fusion image sets were compared in 100 consecutive, nonselected patients: 21 with head and neck cancer, 39 with chest malignancies, and 40 with malignancies of the abdomen and pelvis. All studies were performed for primary staging or evaluation of therapy and were interpreted by two nuclear medicine physicians also trained in radiology. Areas of abnormal FDG uptake were identified on PET and graded as likely benign, equivocal, or likely malignant. Positron emission tomography/computed tomography fusion images were then made available, and the initial findings were amended if necessary.ResultsOne hundred sixty-six areas with abnormal FDG uptake were identified. Based on PET alone, 51 sites were considered equivocal for malignancy. With PET/CT, the number of equivocal lesions decreased to 24. This difference is more marked in the head and neck as well as the abdomen and pelvis. When the equivocal sites were included in the analysis and grouped with the malignant sites, positive predictive value (PPV) of PET/CT was 89% compared with 75% for PET (p = 0.04).ConclusionCombined PET/CT results in increased reader confidence and 53% fewer equivocal readings, as well as improved PPV compared with PET alone.

Differential metabolism and pharmacokinetics of L-[1-11C]-methionine and 2-[18F] fluoro-2-deoxy-D-glucose (FDG) in androgen independent prostate cancer

Metabolic imaging with positron emission tomography (PET) for the staging and monitoring of treatment response has important implications in clinical oncology. The choice of radiotracer is likely to be critically important. The objective of our study was to compare the pharmacokinetics of C-11-methionine with FDG in a group of androgen independent patients with metastatic prostate cancer, to determine the differential metabolism of the two tracers, and to determine the optimal time of imaging after injection in treated and untreated patients. A total of 29 dynamic scans (19 pretreatment and 10 posttreatment) were performed in 10 patients with progressive or new lesions on bone scans (index lesions). A total of 13 index lesions were identified in baseline scans. Patients were infused with 370 MBq C-11-methionine on the couch and 32 dynamic images acquired over 60 minutes. After at least 5 half-lives of C-11, patients were then dynamically imaged (15 frames) for 45 minutes with FDG. Index lesions demonstrated both C-11-methionine (13/13) and FDG uptake (12/13). The plateau of methionine uptake in tumor was reached by 10 minutes, and thereafter remained constant. FDG tumor uptake was slower and for some patients continued to rise beyond 45 minutes. The clearance of blood activity for C-11-methionine was more rapid than FDG and the plateau was 10 and 45 minutes respectively. In 5 patients scanned after therapy, 4 responded to treatment, which was reflected by a corresponding decrease in C-11-methionine and FDG tumor uptake. No change was observed in the relative shape of the uptake curves however, between the C-11-methionine and the FDG uptake, either in the 4 who responded to treatment or for one patient who did not respond. The SUV of C-11-methionine was significantly higher than for FDG (P <.008). Both C-11-methionine and FDG are taken up in index lesions in patients with progressive prostate cancer. The advantages of C-11-methionine over FDG are the higher tumor to blood ratio, the more rapid tumor uptake allowing earlier imaging, and a flatter plateau rendering lesion activity on whole body images more uniform and less susceptible to gradual change than FDG. This indicates the feasibility of whole body PET imaging with decay corrected C-11-methionine. Additional studies are planned to define optimal imaging times after different therapies in comparison to FDG and bone scans.

Incidental finding of focal FDG uptake in the bowel during PET/CT: CT features and correlation with histopathologic results

OBJECTIVE The purpose of this study was to identify and characterize the clinically significant lesions associated with incidental detection of focal uptake of (18)F-FDG in the bowel at PET/CT. MATERIALS AND METHODS Among 2,250 consecutively registered patients with various nongastrointestinal malignant diseases who underwent FDG PET/CT as part of their care, patients with the incidental finding of focal bowel uptake of FDG were included in the study. All patients underwent an endoscopic or surgical procedure for characterization of the lesions. The location, intensity of uptake, and appearance of the lesions on PET/CT images were recorded and compared with the endoscopic and surgical pathologic results. RESULTS Twenty-one of 25 foci of intense uptake in the bowel were associated with endoscopic or surgical abnormalities (positive predictive value, 84%). Seven lesions were malignant (two primary, five secondary); 13 were premalignant (nine tubovillous adenoma, four tubular adenoma); and one lesion was benign (hyperplastic polyp). Eleven lesions detected with endoscopy were not FDG avid, and all 11 were smaller than 1 cm in diameter. There was no statistically significant difference in the maximum standardized uptake values of the benign and malignant lesions. CONCLUSION The incidental finding of focal FDG uptake in the bowel justifies further investigation of these foci and should not be dismissed as physiologic uptake. Premalignant lesions, such as adenoma, are often found, and early treatment may prevent the development of carcinoma.