Biomedical subjects

Christian Cohade

Publications and source records attributed to Christian Cohade.

26 records · Page 2Linked to original sources

PubMed2003

Initial experience with oral contrast in PET/CT: phantom and clinical studies.

UNLABELLED: The aims of the study were to evaluate the effects of oral contrast on apparent tracer activity measured with PET/CT when using CT attenuation correction and to report our initial experience in the use of oral contrast with PET/CT. METHODS: Phantom studies with (18)F activity and saline bags or syringes filled with barium or gastrografin of varying densities were performed using a PET/CT scanner (CT attenuation correction). In the study, 91 clinical patients received dilute oral contrast and were evaluated by whole-body (18)F-FDG PET. RESULTS: A phantom experiment with CT contrast (1.3% weight/volume [w/v] barium) showed a "cold" area in the cold stomach whereas a phantom with high-density barium (98% w/v) showed an artifactual focus of intense "activity" in the cold stomach. In clinical studies, stomach and right colon were opacified by CT contrast. Maximal measured contrast density was 239 Hounsfield units. CONCLUSION: High-density barium causes overestimation of tissue (18)F-FDG concentration. Low-density barium does not cause significant artifacts and appears suitable for clinical use.

Administration, Oral↗

PubMed2003

"USA-Fat": prevalence is related to ambient outdoor temperature-evaluation with 18F-FDG PET/CT.

UNLABELLED: Increased (18)F-FDG activity in fatty tissue has previously been reported with PET/CT. We previously named this activity uptake in supraclavicular area fat ("USA-Fat"). We and others have speculated that this uptake exists in metabolically active brown adipose tissue (BAT). Such tissue might be expected to have varying metabolic activity depending on the ambient temperature. The purpose of this study was to evaluate the frequency of USA-Fat and its relationship to the outdoor temperature. METHODS: Between July 2001 and June 2002, 1,017 consecutive whole-body scans were obtained with a PET/CT scanner and (18)F-FDG for clinical patients. PET images were reviewed for the presence of USA-Fat. RESULTS: USA-Fat was observed in 68 scans obtained from 62 patients (51 female and 11 male). The incidence of USA-Fat was highest, at 13.7%, in January through March, while outside temperatures were low, and was significantly lower, at 4.1%, during the rest of the year. CONCLUSION: The incidence of USA-Fat is clearly increased during the cooler period of the year. This finding suggests that stimulation by cold temperatures increases the frequency with which USA-Fat occurs, supporting underlying BAT as the etiology for this activity.

Adipose Tissue↗

PubMed2003

Direct comparison of (18)F-FDG PET and PET/CT in patients with colorectal carcinoma.

UNLABELLED: The purpose of this study was to compare (18)F-FDG PET and PET/CT in a population of patients with colorectal cancer. METHODS: PET and PET/CT images from 45 patients (17 women, 28 men; mean age +/- SD, 60.8 +/- 11.1 y) with known colorectal cancer referred for PET from June to November 2001 were retrospectively reviewed. Images were acquired with a PET/CT scanner, and (68)Ge attenuation correction was applied. PET images and fused (68)Ge attenuation-corrected PET and CT images were independently and separately interpreted by a moderately experienced reader unaware of the clinical information. Certainty of lesion characterization was scored on a 5-point scale (0 = definitely benign, 1 = probably benign, 2 = equivocal, 3 = probably malignant, 4 = definitely malignant). Lesion location was scored on a 3-point scale (0 = uncertain, 1 = probable, 2 = definite). The presence or absence of tumor was subsequently assessed using all available clinical, pathologic, and follow-up information. Analysis was provided for lesions detected by both PET and PET/CT. RESULTS: The frequency of equivocal and probable lesion characterization was reduced by 50% (50 to 25) with PET/CT, in comparison with PET. The frequency of definite lesion characterization was increased by 30% (84 to 109) with PET/CT. The number of definite locations was increased by 25% (92 to 115) with PET/CT. Overall correct staging increased from 78% to 89% with PET/CT on a patient-by-patient analysis. CONCLUSION: PET/CT imaging increases the accuracy and certainty of locating lesions in colorectal cancer. More definitely normal and definitely abnormal lesions (and fewer probable and equivocal lesions) were identified with PET/CT than with PET alone. Staging and restaging accuracy improved from 78% to 89%.

Adult↗

PubMed2002

PET-CT localizes previously undetectable metastatic lesions in recurrent fallopian tube carcinoma.

BACKGROUND: Fallopian tube carcinoma is a rare malignancy that commonly recurs after initial surgical resection. New combined instrumentation with co-registered PET and CT is a new technique that combines functional and anatomic imaging to detect metastatic disease that may be difficult to detect with either modality alone. CASE: We present two cases of suspected fallopian tube carcinoma recurrence demonstrating the unique potential of combined PET-CT using 18F-fluoro-2-deoxyglucose (FDG). These cases demonstrate the unique capability to detect and localize metastatic disease when serum CA-125, laparoscopy, and CT scan alone were unable to detect recurrence. CONCLUSION: PET-CT with FDG may prove to be a sensitive and accurate method for detection of metastatic disease and may influence the clinical management of recurrent fallopian tube carcinoma.

Aged↗

PubMed2002

Quantitative evaluation of 2-deoxy-2-[18F] fluoro-D-glucose uptake in hepatic metastases with combined PET-CT: iterative reconstruction with CT attenuation correction versus filtered back projection with 68Germanium attenuation correction.

PURPOSE: Iterative reconstruction (IR) is a statistical reconstruction method that may be influenced by high background activity such as in the liver. Recently developed combined positron emission tomography (PET) and computerized tomography (CT) instrumentation utilizes CT attenuation correction that may also differ compared to 68Germanium (68Ge) segmented attenuation correction (IR SAC). Quantitative differences could affect the clinical interpretation of metastatic foci and subsequent response to therapy. The purpose of this study is to characterize potential quantitative differences specifically in hepatic metastases. PROCEDURES: Thirty-three metastatic liver lesions in 23 patients were evaluated. Whole-body 2-deoxy-2[18F]fluoro-D-glucose(FDG) PET images were obtained on a dedicated PET-CT device and reconstructed with IR and CT measured attenuation correction (IR CT MAC), IR and 68Ge segmented attenuation correction, and also with filtered back-projection and segmented attenuation correction (FBP SAC). Regions of interest over the liver lesions (L) and liver background (B) were drawn on FBP SAC images and superimposed on the co-registered IR CT MAC and IR SAC images for comparison. To identify the individual effects of IR and CT attenuation correction, IR SAC was first compared to FBP SAC, followed by a comparison of IR CT MAC and IR SAC. Differences were expressed as bias (%) and compared to FBP SAC. RESULTS: Compared to FBP SAC, IR SAC showed significantly lower liver lesion (mean bias -7.1%; P < 0.00001), significantly higher liver background (mean bias -3.5%; P = 0.005), and significantly lower L/B ratio (mean bias -10.1%; P < 0.00001). Compared to IR SAC, the IR CT MAC showed small but not statistically significant increases in liver lesion (mean bias 3.0%; P = 0.1) and liver background (mean bias 4.3%; P = 0.09), and no significant difference in L/B ratio (mean bias -1.3%; P = 0.5). The overall effect of IR CT MAC compared to FBP SAC was a significant decrease in liver lesion (mean bias -4.2%; P = 0.002), significant increase in liver background (mean bias 8.7%; P = 0.002), and significantly lower L/B (mean bias -11.1%; P < 0.00001) compared to FBP SAC. CONCLUSION: Compared to FBP, IR resulted in significantly lower mean hepatic tumor activity, higher mean liver background activity, and lower L/B activity, but these differences were modest. These differences were similarly seen in the CT corrected IR CT MAC when compared to FBP SAC. CT attenuation correction did not result in significant differences when compared to 68Ge correction. Although the differences in IR CT MAC were modest, consistent reconstruction methods are important to decrease the measurement variability and improve reproducibility.

Journal Article↗

PubMed2002

PET/CT: comparison of quantitative tracer uptake between germanium and CT transmission attenuation-corrected images.

UNLABELLED: In PET, transmission scanning for attenuation correction has most commonly been performed with an external positron-emitting radionuclide source, such as (68)Ge. More recently, combined PET/CT scanners have been developed in which the CT data can be used for both anatometabolic image formation and attenuation correction of the PET data. The purpose of this study was to assess the quantitative differences between CT-based and germanium-based attenuation-corrected PET images. METHODS: Twenty-eight patients with known or suspected cancer underwent whole-body (18)F-FDG PET/CT scanning for clinical diagnostic purposes. For each patient, attenuation maps were obtained from both the CT scan and the (68)Ge transmission data, and 2 different attenuation-corrected emission datasets were produced. Measured activity concentrations (both mean and maximum) from identical regions of interest in representative normal organs and in 36 pathologic foci of uptake were compared. RESULTS: CT-corrected emission images generally showed slightly higher radioactive concentration values than did germanium-corrected images (P < 0.01) for all lesions and all normal organs except the lung. Mean and maximum radioactivity concentrations were 4.3%-15.2% higher for CT-corrected images than for germanium-corrected images. Calculated radioactivity concentrations were significantly greater in osseous lesions than in nonosseous lesions (11.0% vs. 2.3%, P < 0.05, for mean value; 11.1% vs. 2.1%, P < 0.01, for maximum value). A weak positive correlation was observed between the CT Hounsfield units within the regions of interest and the percentage difference in apparent tracer activity in the CT-corrected images. CONCLUSION: Although quantitative radioactivity values are generally comparable between CT- and germanium-corrected emission PET images, CT-based attenuation correction produced radioactivity concentration values significantly higher than the germanium-based corrected values. These effects, especially in radiodense tissues, should be noted when using and comparing quantitative PET analyses from PET and PET/CT systems.

Algorithms↗

PubMedDate not supplied

PET scanning and measuring the impact of treatment.

Positron emission tomography (PET) scanning with F18-fluorodeoxyglucose or FDG is a becoming a standard method for tumor staging. The prediction and evaluation of therapy response are newer applications of FDG-PET. PET often offers an early readout of treatment efficacy and is an attractive alternative to conventional anatomic assessments of treatment response. This article reviews the methods available with PET to monitor therapy response. Disease specific applications of PET imaging are then reviewed. While FDG is the most commonly used radiotracer for PET, many other radioligands could be applied in the future.

Fluorodeoxyglucose F18↗

PubMedDate not supplied

PET-CT in recurrent ovarian cancer: initial observations.

Noninvasive diagnosis of early recurrence of ovarian cancer is challenging due to the small size of peritoneal metastases. Small-volume disease may not be evident at anatomic imaging in patients with elevated serum tumor markers. Functional imaging in the form of positron emission tomography (PET) can help identify patients with recurrent tumor. However, lesion localization for possible surgical treatment is difficult with PET alone. Combined functional-anatomic imaging with fused PET and computed tomographic (CT) scans is feasible and may improve disease detection by increasing radiologic sensitivity and specificity. PET and PET-CT have a potential role in evaluating patients for recurrent ovarian cancer, particularly those with negative CT or magnetic resonance imaging findings and rising tumor marker levels. Fused PET-CT scans obtained with combined scanners can help localize pathologic activity and differentiate this activity from physiologic radiotracer uptake. Combined functional-anatomic imaging can also increase diagnostic confidence at CT. Further study is needed to determine the possible benefits of lesion conspicuity at PET and anatomic localization at CT on fused PET-CT scans.

Aged↗