[18F]FDG PET/CT for the assessment of the volume of the spleen.

BACKGROUND: The aim of this study was to report on the feasibility and accuracy of spleen volume determination on FDG PET/CT imaging using region growing and the CT part of the PET/CT examination as anatomical landmark (PET-CT based spleen volume method PBM) and volume summation of axial CT sections of the spleen as gold standard (true spleen volume (TSV). We also aimed to compare results obtained to the estimative methods (ESV). METHODS: Thirty-nine FDG PET/CT images taken from 32 patients (15 women, age range: 16-83 years) suffering from lymphoma, covering a wide range of spleen volumes based on visual CT assessment, in whom CT as well as FDG PET images revealed no focal spleen abnormalities were included for analysis. ESV1, ESV2 and PBM were determined on all examinations and compared to TSV. RESULTS: ESV1 volumes were significantly larger (median 668 cm3 [range: 121-4303 cm3] [P=0.0001]) and ESV2 volumes significantly smaller (median 424 cm3 [range: 84-2679 cm3] [P=0.0001]) when compared to TSV volumes (median 582 cm3 [range: 105-4847 cm3] which was not so for PBS volumes (median 540cm3 [range: 120-4560 cm3]). Time needed for TSV assessment (median: 17 min. [range: 6-65 min.]) was related to spleen volume (r=0.691 [P=0.0001]). The mean and standard deviation of the percentage spread (ESV1, ESV2, PBM-TSV/100%) around the mean (ESV1, ESV2, PBM+TSV/2) were respectively 18%±15.6% (ESV1 vs. TSV), -25%±15.6% (ESV2 vs. TSV) and -2.8%±12.3% (PBM vs. TSV). Mean SUVmax of the spleen was 4.8 SUV (SD: 2.6 SUV), mean percentage cut-off for region growing was 7.3% (sd: 5.8%). Spleen volumes defined by PBM correlated with their corresponding SUVmax value (r=0.469 [P=0.03]). Time needed for PBM measurements was between 2-3 min in all patients. CONCLUSION: Spleen volumes may be rapidly and accurately derived from the FDG PET part of the PET/CT examination through region growing and by using the CT part of the PET/CT examination as anatomical landmark for contour delineation. As opposed to ESV1 and ESV2, the PBM method does not suffer from a systematic bias and shows a smaller variation against the mean percentage difference. Combining functional and morphological data for spleen volume assessment is time-saving.

Standardized added metabolic activity (SAM): a partial volume independent marker of total lesion glycolysis in liver metastases.

PURPOSE: The standardized added metabolic activity (SAM) is a new marker of total lesion glycolysis that avoids partial volume effect (PVE) and thresholding. SAM is calculated by drawing a volume of interest (VOI(1)) around the tumour and a larger VOI (VOI(2)) around VOI(1). Subtracting the background activity in VOI(2)-VOI(1) from VOI(1) yields SAM. If VOI(1) is set at a reasonable distance from the tumour, PVE are avoided. Phantom and initial clinical validation data are presented. METHODS: Spheres of a Jaszczak phantom were filled with a 5.4, 3.64 and 2.0 times higher concentration relative to background activity and positron emission tomography (PET) data were acquired during 10 min. SAM of all spheres was expressed as a percentage of the expected value (the actual activity ratio minus 1). In 15 patients a 10-min list-mode acquisition PET study centred on their primary squamous cell carcinoma (PSCC) was performed and images of 1-10 min reconstructed. SAM1-9min values of PSCC were expressed as a percentage of SAM10min. Nineteen patients suffering from liver metastases treated with chemotherapy underwent PET/CT prior to (scan 1) and after 3-6 cycles of chemotherapy (scan 2). SAM and maximum standardized uptake values (SUV(max)) of the liver lesions on scan 1 (SAM1 and SUV(max)1) and the percentage reduction between both ΔSAM and ΔSUV(max) were related to Response Evaluation Criteria in Solid Tumors (RECIST) response. RESULTS: For the phantom acquisitions, the mean normalized SAM/sphere volume calculated was 94.9 % (SD 5.9 %) of the expected value. In the PSCC patients, the mean difference between SAM1min and SAM10min was only 4 % (SD 5 %). SUV(max)1min and SUV(max)10min proved to be not significantly different, but the variability was slightly larger than that of SAM (SD 6.4 %). SAM1 and ΔSAM values for responders versus non-responders were, respectively, 57 (SD 119) versus 297 (SD 625) for SAM1 (p = 0.2) and 99 % (SD 3 %) versus 32 % (SD 44 %) for ΔSAM (p = 0.001). SUV(max)1 and ΔSUV(max) values in responders versus non-responders were, respectively, 3.9 (SD 2.4) versus 6.3 (SD 3.1) for SUV(max)1 (p = 0.08) and 94 % (SD 17) versus 7 % (SD 40 %) for ΔSUV(max) (p = 0.0001). The AUC of ΔSAM and ΔSUV(max) were not significantly different on receiver-operating characteristic (ROC) analysis (AUC 1.0 and 0.99, respectively, p = 0.6). CONCLUSION: SAM is a promising parameter for tumour response assessment of liver metastases by means of (18)F-fluorodeoxyglucose PET.

Time-dependent changes in 18F-FDG activity in the thymus and bone marrow following combination chemotherapy in paediatric patients with lymphoma.

PURPOSE: To investigate the time-dependent changes in (18)F-FDG uptake by the thymus and marrow following combination chemotherapy for lymphoma in a paediatric study population. METHODS: Included in the study were 27 paediatric patients who were in complete metabolic remission after chemotherapy and who underwent off-therapy follow-up with serial whole-body PET-CT scans. A total of 142 PET-CT scans were recorded. (18)F-FDG uptake by the thymus and marrow was assessed both visually and semiquantitatively. Visual uptake was scored on the three-dimensional maximum intensity projection of the whole-body PET image according to a three-point scale. For the semiquantitative assessment, standard uptake values were measured. To find a pattern in the (18)F-FDG uptake by the thymus and marrow a moving average technique was applied. RESULTS: Our time series analysis indicated that the marrow activity was highest at cessation of chemotherapy and declined thereafter. During an off-chemotherapy period of on average 6 months, marrow activity decreased quickly. From 6 months onward, the activity declined more slowly. The posttherapy changes in (18)F-FDG uptake by the thymus were quite different from the changes in uptake by the marrow. The lowest thymic FDG uptake was found at cessation of chemotherapy. Thereafter, thymic activity steadily increased, reached a peak on average 10 months after therapy, and then slowly decreased. CONCLUSION: Knowledge of the time-dependent changes in metabolic activity in the thymus and marrow is important to avoid misinterpretation of increased (18)F-FDG uptake as disease in the off-therapy setting.

Interobserver reproducibility in reporting on renal cortical scintigraphy in children: a large collaborative study.

OBJECTIVE: To evaluate the interobserver reproducibility in reporting on technetium-99m (99mTc) dimercaptosuccinic acid (DMSA) scan in children. METHODS: Sixty 99mTc-DMSA scans, issued from three centres, were distributed by e-mail to nuclear medicine physicians from the five continents interested in paediatric nuclear medicine. Observers had to choose, for each kidney, among four answers: normal, abnormal, equivocal or poor quality. An additional question was the location of the lesion if any: upper part, mid part, lower part. The responses had to be returned by e-mail. RESULTS: Sixty-one observers, with an experience of approximately five or more 99mTc-DMSA/month, contributed to the study. Median agreement was 93%. The agreement was less than 80% in 29 kidneys (24%) but only in 13% (16 kidneys) was there disagreement between normality and abnormality, the remaining cases being related to 'equivocal' responses. Disagreement was mainly related to the following patterns: (i) normal variants: pear-shaped kidney, hypoactive poles contrasting with important parenchymal mass, triangular kidney, unusual shape of the columns of Bertin; (ii) congenital abnormalities: hydronephrosis, normal duplex kidney; (iii) small defects. CONCLUSION: Interobserver reproducibility can be considered as good among a wide number of observers from the five continents. Disagreement among observers could be reduced by taking the normal variants into account.

Pixel-by-pixel mean transit time without deconvolution.

BACKGROUND: Mean transit time (MTT) within a kidney is given by the integral of the renal activity on a well-corrected renogram between time zero and time t divided by the integral of the plasma activity between zero and t, providing that t is close to infinity. However, as the data acquisition of a renogram is finite, the MTT calculated using this approach might result in the underestimation of the true MTT. To evaluate the degree of this underestimation we conducted a simulation study. METHODS: One thousand renograms were created by convoluting various plasma curves obtained from patients with different renal clearance levels with simulated retentions curves having different shapes and mean transit times. RESULTS: For a 20 min renogram, the calculated MTT started to underestimate the MTT when the MTT was higher than 6 min. The longer the MTT, the greater was the underestimation. Up to a MTT value of 6 min, the error on the MTT estimation is negligible. CONCLUSION: As normal cortical transit is less than 2 min, this approach is used for patients to calculate pixel-to-pixel cortical mean transit time and to create a MTT parametric image without deconvolution.

Interobserver reproducibility in the interpretation of 99mTc-labelled white blood cell scintigraphic images.

OBJECTIVE: This study was performed to investigate the interobserver reproducibility of the interpretation of Tc-labelled white blood cell scans combined or not with other nuclear medicine procedures. METHODS: Twenty nuclear medicine physicians working in Belgium received clinical data and scintigraphic images from 10 patients suspected of suffering from various infectious diseases. They had to choose, for each patient, one answer among 'high probability', 'intermediate probability' and 'low probability' of infection. In a first step the level of agreement, defined as the highest percentage obtained among the three proposed answers, was calculated for each case; complete agreement was arbitrarily defined when 80% or more of the observers gave the same answer. In a second step, a numerical score was given for each answer and for each observer. The scores were defined as 0 for the 'low probability' answer, 1 for the 'intermediate probability' and 2 for the 'high probability' answer. The scores of each observer were summed up allowing obtaining of a cumulated score for each observer; observers were thereafter classified as a function of their own cumulated score. RESULTS: An agreement of 80% or more was observed only in three patients. The cumulated scores of the observers were between 4 and 16, demonstrating that some observers were more sensitive than others. CONCLUSION: Interobserver reproducibility in the interpretation of the white blood cell scan was poor; several factors could explain these results, the most frequent being both the poor specificity of the labelled white blood cell scan and different concepts in interpreting combined nuclear medicine procedures in several situations. As observers received the anonymized overall results, this study may have a favourable impact on continuing education in medical imaging.

Does regional brain perfusion correlate with eating disorder symptoms in anorexia and bulimia nervosa patients?

OBJECTIVE: Using single photon emission computed tomography (SPECT), we sought brain perfusion correlates of eating disorder symptoms in anorexia and bulimia nervosa patients. METHOD: We investigated 67 female eating disordered (ED) patients. Eating disorder symptoms were measured by the Eating Disorders Inventory (EDI). Determination of brain areas in which regional perfusion co-varied with drive for thinness, bulimia, body dissatisfaction, ineffectiveness, perfectionism, interpersonal distrust, interoceptive awareness and maturity fears was done by open explorative correlation analysis using Statistical Parametrical Mapping (SPM). RESULTS: A significant positive correlation between scores on body dissatisfaction and ineffectiveness, and brain perfusion in the prefrontal and parietal cortex was demonstrated. There were no correlations between other eating disorder symptoms and brain perfusion. CONCLUSION: Based on the finding of an association between regional brain flow and body dissatisfaction and ineffectiveness, we argue that neurobiological findings in ED patients may not only reflect emotional and behavioural factors but cognitive-evaluative features as well.

Differences of cortical 5-HT2A receptor binding index with SPECT in subtypes of anorexia nervosa: relationship with personality traits?

OBJECTIVE: Using single photon emission computed tomography and the 5-HT2A receptor antagonist, 123I-5-I-R91150, we explored differences in 5-HT2A binding index in anorexia nervosa patients with and without bulimic features. We also searched for associations between temperament dimensions and cortical 5-HT2) binding. METHOD: About 9 restrictive and 7 bulimic anorexia nervosa patients were examined and cortical 123I-5-I-R91150 binding index values were compared between the two subgroups. Open explorative correlation analysis was used to examine any relationships between binding index values and temperament scores, as assessed with the Temperament and Character Inventory. RESULTS: 5-HT2A binding index was significantly reduced in the parietal cortex in bulimic anorexia nervosa patients in comparison with restrictive anorectics. Further, a positive correlation was documented between reward dependence and parietal 5-HT2A binding index across patients in the two subgroups. DISCUSSION: Restrictive anorexia nervosa patients differ from binging/purging anorexia nervosa patients on the basis of a reduced parietal 5-HT2A binding index in the latter. We speculate that the finding of a positive correlation between parietal 5-HT2A binding and reward dependence might reflect an association between these two variables, at least in anorexia nervosa patients.

Checking the consistency of the two blood samples slope-intercept method for estimating GFR using the single blood sample formula in children.

BACKGROUND: The slope-intercept method is widely used for the determination of the plasma clearance of 51Cr-EDTA. When three or more plasma samples are used, the goodness-of-fit (r2) can be used as a measure of consistency of the samples. This parameter can not be used, however, if only two samples are available. PURPOSE: To evaluate whether the single-sample technique (SBS) can be used to check the consistency of the slope-intercept method using two blood samples (2BS) in children. METHODS: Simulated computer models of a mono-exponential curve were created in order to represent three children aged 3, 6 and 10 years, each with a large range of clearances values and three distribution volumes, respectively 20%, 25% and 30% of body weight. Errors were then introduced in the injected dose (errors from -50% to +50%) and on the 120 or 240 min blood sample (errors from -50% to +50%). The effects of these errors on the clearance measurement using 2BS and SBS methods were calculated and compared. RESULTS: The errors on the injected dose, the 120 min and 240 min plasma samples introduced errors in the same direction and with the same magnitude on both the SBS and 2BS clearance values. For that reason, the comparison between the SBS methods and the 2BS techniques has a low sensitivity in detecting an eventual error. Striking differences between the SBS method and the 2BS technique were only observed when considerable errors on the injected dose or plasma samples were introduced, particularly in case of a reduced clearance. The comparison between the SBS clearances calculated using the 120 min sample to that obtained using the 240 min samples is slightly more sensitive. However, this approach is also slightly less specific. A difference of more than 10 ml . min(-1). 1.73 m(-2) can be observed in the absence of an error. CONCLUSIONS: The use of the SBS for checking the consistency of the 2BS constitutes an insensitive approach to detect an eventual error in the injected dose or in the plasma samples. Obvious different results obtained by SBS and 2BS or between the SBS calculated using the 120 min and the 240 min samples suggest the presence of an error, but comparable results do not exclude erroneous measurement. Moreover, a difference of more than 10 ml . min(-1). 1.73 m(-2) can be observed in the absence of an error in the injected dose or in the plasma samples.

Validation of a resolution-independent method for the quantification of 123I-FP-CIT SPECT scans.

OBJECTIVE: To verify the applicability of a recently described resolution-independent method for the semi-quantification of 123I-FP-CIT scans. METHODS: Visual interpretation, 'conventional' and resolution-independent semi-quantification was performed on 60 123I-FP-CIT scans. Using ROC analysis, the results were compared to the final clinical diagnosis after a follow-up of at least 18 months. Sensitivity and specificity values were calculated and a cut-off value of the specific binding, which differentiated between normal and abnormal scans with high sensitivity and specificity, was given. RESULTS: Application of the resolution-independent method to a new set of 123I-FP-CIT SPECT data yielded a cut-off value of the specific striatal binding of 55 ml. Corresponding values of sensitivity and specificity were 95% and 72%, respectively. Further, based on the values of the area under the ROC curve and the 95% confidence interval of different semi-quantitative methods, the resolution-independent semi-quantification agreed best with the final clinical diagnosis. CONCLUSION: We found a similar value of the specific 123I-FP-CIT binding as the one previously described in the literature, which proved the validity of the resolution-independent method. Further, this method, among other 'conventional' semi-quantitative methods, agreed best with the final clinical diagnosis. For this reason we recommend its use to aid in the diagnostic process.

Mismatch of F-18 fluorodeoxyglucose (FDG) positron emission tomography (PET) and Tc-99m pertechnetate single photon emission computed tomography (SPECT) in a euthyroid multinodular goiter.

Imaging results of F-18 fluorodeoxyglucose (FDG) PET/CT scanning and Tc-99m pertechnetate scintigraphy of the thyroid gland are described and compared with pathology in a patient who was followed after left nephrectomy for renal cell carcinoma diagnosed 10 years earlier. On F-18 FDG PET/CT scanning, a multinodular struma with increased localized F-18 FDG uptake in 4 nodules was seen. Two nodules with increased glucose metabolism appeared normal on Tc-99m pertechnetate scintigraphy. Pathology indicated hyperplastic nodules. High focal F-18 FDG uptake was also seen in a lesion that corresponded with a "cold" nodule on Tc-99m pertechnetate scintigraphy, suggesting malignant disease. However, pathology revealed hyperplastic nodules with a background of aspecific lymphocytic thyroiditis. A fourth nodule with increased F-18 FDG uptake appeared mixed ("cold"/"hot") on Tc-99m pertechnetate scintigraphy. On pathology, a well-differentiated follicular carcinoma was found. These findings, in a single patient, illustrate the wide spectrum of matched and mismatched F-18 FDG and Tc-99m pertechnetate thyroid uptake along with their variable pathologic correlates.

Pediatric applications of renal nuclear medicine.

This review should be regarded as an opinion based on personal experience, clinical and experimental studies, and many discussions with colleagues. It covers the main radionuclide procedures for nephro-urological diseases in children. Glomerular filtration rate can be accurately determined using simplified 2- or 1-blood sample plasma clearance methods. Minor controversies related to the technical aspects of these methods concern principally some correction factors, the quality control, and the normal values in children. However, the main problem is the reluctance of the clinician to apply these methods, despite the accuracy and precision that are higher than with the traditional chemical methods. Interesting indications are early detection of renal impairment, hyperfiltration status, and monitoring of nephrotoxic drugs. Cortical scintigraphy is accepted as a highly sensitive technique for the detection of regional lesions. It accurately reflects the histological changes, and the interobserver reproducibility in reporting is high. Potential technical pitfalls should be recognized, such as the normal variants and the difficulty in differentiating acute lesions from permanent ones or acquired lesions from congenital ones. Although dimercaptosuccinic acid scintigraphy seems to play a minor role in the traditional approach to urinary tract infection, recent studies suggest that this examination might influence the treatment of the acute phase, the indication for chemoprophylaxis and micturating cystography, and the duration of follow-up. New technical developments have been applied recently to the renogram: tracers more appropriate to the young child, early injection of furosemide, late postmicturition and gravity-assisted images and, finally, more objective parameters of renal drainage. Pitfalls mainly are related to the interpretation of drainage on images and curves. Dilated uropathies represent the main indication of the renogram, but the impact of this technique on the management of the child is, in a great number of cases, still a matter of intense controversy. Direct and indirect radionuclide cystography are interesting alternatives to the radiograph technique and should be integrated into the process of diagnosis and follow-up of vesicoureteral reflux.

Serotonin transporter and dopamine transporter imaging in the canine brain.

The serotonergic and dopaminergic systems are involved in a wide range of emotional and behavioral aspects of animals and humans and are involved in many neuropsychiatric disorders. Selective serotonin (5-HT) reuptake inhibitors (SSRIs) are designed to block the 5-HT transporter (SERT), thereby increasing the available 5-HT in the brain. Functional imaging with specific SERT and dopamine transporter (DAT) ligands contributes to the study of the SSRI-transporter interaction. First, we evaluated the feasibility of a canine model in the study of the SERT and DAT with the radioligands [123I]-beta-CIT and [123I]-FP-CIT as well as single-photon emission computed tomography imaging. Second, we studied the effect of SSRIs (sertraline, citalopram and escitalopram) on the SERT and DAT in two dogs. The position of the canine model in the study of the SERT and DAT is discussed and compared with other animal models.

Post-test quality control for the single blood sample technique in glomerular filtration rate measurement in children.

BACKGROUND: While the value of the single blood sample (SBS) method for estimating 51Cr-EDTA plasma clearance has been repeatedly demonstrated, some nuclear medicine physicians are still reluctant to use it because of the lack of quality control parameters. PURPOSE: To present a post-test quality control procedure for the SBS technique in children. METHODS: In addition to the SBS clearance calculated using the specific paediatric SBS method, three artificial slope intercept (ASI) method clearances were calculated by assuming the distribution volume as, respectively, 20%, 25% and 30% of body weight. By dividing the injected activity by the distributional volume, the initial plasma concentrations (A0,30%, A0,25% and A0,20%) were calculated. Using these A0 values and the available single sample, ASI clearances were calculated by using the classical slope-intercept method. The working hypothesis of this approach was as follows. In the absence of significant errors, the three ASI clearance values should be close to that of the SBS method. This hypothesis has been tested using both simulated and patients' data. RESULTS: The results of the simulated study showed that an error in the injected dose produced variable differences between SBS and ASI clearances depending on the clearance values. The effect of an error on the plasma sample also varied as a function of the clearance values. The analysis of patient data revealed that the ASI approach allowed the identification of patients in whom the classical slope-intercept method suggested the presence of a possible error. CONCLUSION: A post-test quality control procedure for the SBS GFR measurement is presented. When the SBS clearance shows a difference with the ASI method (> 10 ml . min(-1) per 1.73 m2), the presence of an error is highly probable. A smaller difference, however, does not exclude erroneous data.

Correction factors after having neglected the first exponential in the estimation of chromium-51 EDTA clearance: a reappraisal.

The aim of the present work was to evaluate two classical formulae allowing the correction for having neglected the first exponential in the slope-intercept method used for the determination of EDTA clearance, namely the Chantler's linear correction formula (CH) and the Bröchner-Mortensen's quadratic correction formula (BM). First, a comparison study was performed with the two correction formulae, in order to predict the behavior of the calculated clearance, for various levels of renal function. Second, using data obtained from 47 adult patients with normal renal function, the results obtained with the two correction formulae have been compared to the reference technique, namely the biexponential fit. The results of the comparison study indicated that for clearance values lower than 120 ml/min, the results obtained using CH were systematically lower than those of BM, whereas for clearance values between 120 and 140 ml/min, the reverse was observed. The differences however, never exceeded 8 ml/min. The results were quite different when the clearance was higher than 140 ml/min, when the difference between CH and BM results increased rapidly, and the BM provided values systematically lower than CH. The clinical study showed that, in the range of normal clearance values, both CH and BM clearances were slightly lower than the results obtained by means of the reference technique. Based on these results, a new specifically designed validation study involving patients with high clearance values is mandatory to determine which of these two correction methods is more accurate, or to devise a better correction formula.

Blunted prefrontal perfusion in depressed patients performing the Tower of London task.

Impairment of cognition is common in depression, and many tasks on which depressed patients are impaired are sensitive to frontal lobe dysfunction. Performance on the Tower of London (TOL) task, which includes setting up and maintaining multiple subgoals at the same time, has been shown to depend on intact prefrontal cortices. Single photon emission computed tomography (SPECT) with 99mTc-ethyl cysteinate dimer was used to compare cognitive activation in nine depressed patients and nine normal controls during performance of the TOL task. Planning times and accuracy were measured as performance parameters, and functional imaging data were analysed with statistical parametric mapping (SPM99) to determine significant voxel-wise differences in activation between the two groups. During activation, depressed patients were as accurate as controls but differed in that they spent more thinking time. These findings agree with the results of neuropsychological studies. Compared with the normal controls, depressed patients were characterized by a blunted perfusion response in the right middle frontal cortex [Brodmann area (BA) 6] and the left superior frontal gyrus (BA 9), and by increased perfusion in the right superior temporal gyrus (BA 21) and the insular cortex (BA 13). This study shows that a SPECT activation procedure using the TOL task under classical test conditions is feasible in depressed patients.

Interobserver reproducibility in the interpretation of bone scans from patients suspected of having reflex sympathetic dystrophy.

OBJECTIVE: This work was undertaken to identify scintigraphic patterns obtained in patients suspected of having reflex sympathetic dystrophy (RSD), now often referred to as complex regional pain syndrome, whose interpretations could be difficult. METHODS: Ten patients had bone scans because of clinical suspicion of RSD in the lower legs. They were selected retrospectively to have a wide sample of scintigraphic patterns. The radionuclide images and a multiple-choice questionnaire were presented as a PowerPoint file that was sent electronically on the Internet to 54 Belgian nuclear medicine physicians. They had to determine whether the images were in favor of the diagnosis of RSD. RESULTS: Twenty-eight answers (52%) were received. There was near-complete interobserver agreement for perfectly normal scans, for scans showing diffuse uptake with enhancement of periarticular activity, and for scans showing only focal hyperactivity at the site of previous trauma. Results were more discordant when the hyperactivity was mild and when there was a diffuse hypoactivity, with or without focal hyperactivity. CONCLUSION: This study shows that using very simple methodology, it is possible to identify some scintigraphic patterns in which there is disagreement among observers and whose interpretations vary. As the results are returned to the participants, they can compare their own interpretations with those of their peers. This aspect could be useful in continuing education in medical imaging.

Comparison of cortical 5-HT2A receptor binding in bulimia nervosa patients and healthy volunteers.

OBJECTIVE: Bulimia nervosa has been associated with alterations in central serotonergic (5-HT) function. This study investigated iodine-labeled 4-amino-N-[1-[3-(4-fluorophenoxy) propyl]-4-methyl-4-piperidinyl]-5-iodo-2-methoxybenzamide ((123)I-5-I-R91150) binding to the 5-HT(2A) receptor in the brain by using single photon emission computed tomography in acutely ill bulimia nervosa patients. METHOD: Cortical (123)I-5-I-R91150 binding in 10 normal-weight patients with bulimia nervosa, purging type, was compared with that of 11 healthy volunteers. RESULTS: The 5-HT(2A) binding index of the bulimia nervosa patients, with and without correction for age, was not significantly different from that of the comparison group. CONCLUSIONS: As a group, acutely ill bulimia nervosa patients cannot be discriminated from healthy subjects on the basis of cortical (123)I-5-I-R91150 binding to the 5-HT(2A) receptor.

Influence of renal function on renal output efficiency.

UNLABELLED: The purpose of this study was to quantify the influence of renal function on output efficiency (OE) and to evaluate factors that may modify this effect. METHODS: Renograms were generated in a computer simulation model by convolution of plasma disappearance curves with artificially created retention functions. Ten plasma curves were derived from a database corresponding to renal clearances ranging from 33 to 405 mL/min. The created retention functions had 3 characteristics: (a) no output until the minimal transit time (MinTT) followed by a linear increase in transit time; (b) ratio of MinTT to mean transit time (MTT) equal to 0.3 or 0.8; and (c) MTT between 3 and 60 min, increasing with 1-min steps. For each of the 1,160 renograms generated, output efficiency at time (t), OE(t), was calculated at 20, 40, and 60 min. Mean and SD of OE(t) for all clearances were calculated for MTT values between 5 and 60 min, increasing with 5-min steps. RESULTS: For the same retention function, different clearances resulted in different values of OE(t). The degree of variability of OE(t) depended on several factors, including the value of t, the value of MTT, and the shape of the retention function, expressed as the MinTT-to-MTT ratio. For OE(20), OE(40), and OE(60), the respective maximum SDs were 5.4%, 6.6%, and 7.1% for retention functions with a MinTT-to-MTT ratio equal to 0.3, and 6.2%, 8.4%, and 9.4% for retention functions with a MinTT-to-MTT ratio equal to 0.8. CONCLUSION: OE is influenced by renal function. Care should be taken in establishing the cutoff values for obstruction, non-obstruction, and the nondiagnostic zone, since a change in overall clearance can cause as much as a 20% variation in OE.