[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.

Effect of background region of interest and time-interval selection on glomerular filtration ratio estimation by percentage dose uptake of (99m)Tc-DTPA in comparison with (51)Cr-EDTA clearance in healthy cats.

Evaluation of glomerular function is a useful part of the diagnostic approach in animals suspected of having renal disease. Time-interval and background region of interest (bg ROI) selection are determining factors when calculating the glomerular filtration ratio (GFR) based on percentage uptake of (99m)technetium-labelled diethylene triamine penta-acetic acid ((99m)Tc-DTPA). Therefore, three different time intervals (60-120 s, 120-180 s, 60-180 s) and three different bg ROIs (C-shape, caudolateral, cranial + caudal) were investigated. In addition, global GFRs based on percentage dose uptake of (99m)Tc-DTPA for the different time-intervals and bg ROIs were compared with the global GFR based on (51)chromium-ethylene diaminic tetra-acetic acid ((51)Cr-EDTA) plasma clearance in nine healthy European domestic shorthair cats. Paired Student's t-tests and linear regression analysis were used to analyse the data. Different time intervals seemed to cause significant variation (P <0.01) in absolute GFR values, regardless of the choice of bg ROI. Significant differences (P <0.01) between bg ROIs were only observed in the 120-180s time interval between the C-shape and cranial + caudal bg ROI, and between the caudolateral and cranial + caudal bg ROI. The caudolateral bg ROI in the 60-180 s time interval showed the highest correlation coefficient (r = 0.882) between (99m)Tc-DTPA and (51)Cr-EDTA, although a significant difference (P <0.05) was present between both techniques.

The optimal timing for imaging brain tumours and other brain lesions with 18F-labelled fluoromethylcholine: a dynamic positron emission tomography study.

PURPOSE: To determine the optimal timing for imaging brain tumours and other brain lesions with 18F-labelled fluoromethylcholine (18F-FCho) PET. MATERIALS AND METHODS: Dynamic PET imaging with 18F-FCho (acquisition time of 28 min) was performed in 24 patients with space-occupying lesions in the brain. On the coregistered PET and MRI, lesion-to-normal tissue uptake ratios (LNRs) were calculated. Time-activity curves (TACs) were generated on the basis of the LNRs. Changes in LNR over time were calculated on the basis of the linear part of the TAC (last 22 min of the acquisition). RESULTS: TACs for 18F-FCho in gliomas of different grading showed that, after a rapid uptake phase, the mean increase in LNR was 1.07 ± 0.93 for glioblastomas, -0.52 ± 1.56 for anaplastic astrocytomas, 0.04 ± 0.13 for grade 2 oligoastrocytomas and 0.37 in a case of a pilocytic astrocytoma. The average increase in LNR was 0.46 for a brain metastasis, 0.41 ± 0.69 for radiation-induced mass lesions and 1.07 for a tumefactive demyelinating lesion. In contrast, TACs for 18F-FCho in meningiomas showed that, after a rapid uptake phase, the average change in LNR was -5.25 ± 4.19 for typical meningiomas and -3.04 in a case of a mixed angiomatous and clear cell meningioma. CONCLUSION: On the basis of the TACs, PET imaging with 18F-FCho starting within minutes after the administration of the tracer is preferred for the detection of brain tumours and other brain lesions. If discrimination between meningioma and other brain tumours is of concern, both 'early' and 'late' PET imaging could be helpful.

Distribution patterns of 18F-labelled fluoromethylcholine in normal structures and tumors of the head: a PET/MRI evaluation.

PURPOSE: To evaluate the distribution of 18F-labelled fluoromethylcholine (FCho) in normal structures and tumors of the head region using positron emission tomography (PET) and magnetic resonance imaging. MATERIALS AND METHODS: We retrospectively reviewed the positron emission tomography, magnetic resonance imaging, and the coregistered images obtained in 17 patients with suspected high-grade gliomas. The accumulation of 18F-FCho in the normal structures and in brain lesions was visually and semiquantitatively assessed. A 4-point grading system was used for the visual analysis. A standardized uptake value (SUV) was used to quantify uptake. RESULTS: In the normal brain parenchyma, 18F-FCho uptake was faint (SUVmean, 0.15 ± 0.03 (SD)). Uptake was generally moderate in the choroid plexus (SUVmean, 0.82 ± 0.16), cavernous sinus (SUVmean, 0.87 ± 0.19), extraocular eye muscles (SUVmean, 1.10 ± 0.27), masticatory muscles (SUVmean, 0.99 ± 0.22), and bone marrow (SUVmean, 1.06 ± 0.26), whereas uptake was usually moderately intense in the pituitary gland (SUVmean, 1.90 ± 0.21). Uptake was variable in the lacrimal glands and the mucosa of the nasal cavity (for SUVmean of subgroups see text). Intense uptake was observed in the parotid glands (SUVmean, 3.27 ± 0.73). (Moderately) intense 18F-FCho uptake was observed in glioblastomas (range SUVmax, 2.26-6.37) and typical meningiomas (range SUVmax, 3.75-5.81). Uptake was globally faint in grade II and III gliomas (range SUVmax, 0.33-0.78). 18F-FCho uptake was also demonstrated in benign lesions, such as a tumefactive demyelinating brain lesion. CONCLUSIONS: 18F-FCho uptake was faint in the normal brain parenchyma and usually moderate in the choroid plexus, cavernous sinus, extraocular eye muscles, masticatory muscles, and bone marrow. Uptake in the pituitary gland was generally moderately intense, whereas uptake in the lacrimal glands and the mucosa of the nasal cavity was variable. Parotid glands had intense uptake. Also, uptake in glioblastomas and meningiomas was usually (moderately) intense, whereas uptake in grade II and III gliomas was globally faint. However, 18F-FCho uptake was not tumor specific.

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.

Tumor perfusion using first-pass F-18 FDG PET images.

Many reports in the literature have focused on FDG PET imaging at conventional (60 minutes after injection) or delayed (several hours after injection) intervals, which exploits increased glycolysis in tumors for diagnosis. However, in rapidly growing tumors, accelerated glycolysis is, among other factors, mediated by hypoxia and poor perfusion. Interestingly, first-pass (0-2 minutes after injection) FDG PET images were shown to provide an index of perfusion. Here, we illustrate that tracer uptake by various (parts of) tumors is discrepant between first-pass and conventional PET images, probably reflecting the direct control of glucose transporter overexpression by hypoxia, resulting from poor perfusion (Warburg's hypothesis).

Educational impact of discussing results among nuclear medicine physicians participating in interobserver reproducibility studies: our experience with I-123 FP-CIT SPECT.

OBJECTIVES: In nuclear medicine, reproducibility studies allow the assessment of the robustness of a technique. They could also be used in continuing education. This study evaluates this educational impact. METHODS: Two series of clinical data and I-123 fluoropropyl-carbomethoxy-iodophenyl-nortropane single photon emission tomography images from 12 patients were prepared before initiating the study. Each series covered similarly a wide spectrum of clinical situations and images. Nuclear medicine physicians having experience with I-123 fluoropropyl-carbomethoxy-iodophenyl-nortropane single photon emission tomography were recruited and assigned two similar groups regarding their level of experience and type of institutions from which they were issued. Clinical data and images were transmitted by e-mail. For each case, observers had to choose among three answers: normal, equivocal, and abnormal. Answers were returned anonymously. Before the second series was sent, observers from group A had a collegiate discussion on the results of the first series of cases. Observers from group B received the second series without any information regarding analysis of series 1. RESULTS: In group A, median agreement increased from 75% (series 1) to 100% (series 2); in group B it was 75% (series 1) and 87% (series 2). In group A, a 100% agreement was observed for four cases (series 1) and for eight cases (series 2). In group B, a 100% agreement was observed for four cases for both series. CONCLUSION: These preliminary results, obtained in a small sample of observers, suggest that participating and discussing results of interobserver reproducibility studies seems to have a positive educational impact and therefore improves interobserver reproducibility.

(99m)Tc-DMSA absolute and relative renal uptake in cats: procedure and normal values.

In this study we investigated the influence of technical factors (positioning, background (BG) correction and attenuation correction) on qualitative and quantitative (absolute (AU) and relative (RU) uptake) assessment of feline kidneys with (99m)technetium labelled dimercaptosuccinic acid ((99m)Tc-DMSA). Eleven healthy adult cats were included. Influence of BG and depth correction on quantitative assessment was evaluated. Depth correction was based on the geometric mean method (using dorsal and ventral images) and the use of two standards placed over each individual kidney. Visual evaluation showed superiority of dorsal and ventral over lateral positioning due to increased separation of the kidneys permitting region of interest (ROI) placement without overlap. No apparent influence of BG correction was found for RU. However, AU was systematically overestimated without BG correction. Depth correction did not seem to affect RU in most cases, however, in some cats the differences were not negligible. The values for AU without depth correction were lower compared to depth corrected values.

Can severely impaired cortical transit predict which children with pelvi-ureteric junction stenosis detected antenatally might benefit from pyeloplasty?

INTRODUCTION: Until recently, renogram, performed in children with pelvi-ureteric junction stenosis detected antenatally, has not been able to predict the probability of function improvement after surgery or the risk of function deterioration in case of conservative attitude. Recently, Schlotmann et al. have suggested that cortical transit might have this predictive role. The aim of this study, focused on those kidneys with severely impaired cortical transit, was to verify this statement. METHODS: All renograms performed in children during a 3-year period (n=729) were retrospectively reviewed and 19 pediatric patients were selected based on an antenatally detected unilateral pelvi-ureteric junction syndrome, the existence of at least two renograms during the follow-up and a severe cortical transit impairment, visually defined. Twenty-six pairs of data could be analyzed and allowed comparing preoperative and postoperative differential renal function (DRF), and the DRF changes during the conservative management. RESULTS: Among the 16 patients who underwent pyeloplasty, 10 showed a significant DRF improvement. Among the 10 patients with conservative follow-up, four showed a significant DRF deterioration. CONCLUSION: Severely impaired cortical transit seems to be a valuable marker of those patients who could benefit from a pyeloplasty, either because of the high probability of postoperative DRF improvement, or because of DRF deterioration in case of an conservative approach. However, a normal cortical transit, as defined in this study, does not exclude the risk of DRF deterioration. Alternatively, the design of this study does not allow excluding the fact that DRF might improve after pyeloplasty despite a normal cortical transit.

A simple test to determine the quality of your clinical PET images.

OBJECTIVE: The objective of the study was to present a simple method for comparing clinical PET images to a set of increasing quality images. Those different quality images were obtained by varying the activity concentration and the acquisition time. METHODS: Images of a Jaszczak phantom were acquired with scan times that were calculated with a spreadsheet application for a personal computer to obtain 500, 1000, 2000, 5000, 7000 and 9000 counts/4 mm(3) voxel. During a 10-h period, each scan was repeated with longer acquisition times to obtain the same number of counts in the reconstructed images, but with lower count rate. On the second day, the study was repeated, putting the phantom in a water bath to simulate larger patients. RESULTS: The quality of the images obtained with the phantom in water was worse than without, as expected. Phantom data demonstrated clearly the effect of higher counts on image quality. Good quality images were obtained with counts above 5000 counts/voxel. Patient data can be situated to the phantom image set by comparing the counts per voxel and the activity concentration. The counts per voxel in all the regions of interest on patient data, with the exception of the brain, were at sub-optimal level leading to decreased image quality. It is clear that better image quality can be achieved mainly by incrementing the scan time. Our PET system, however, allows doubling our standard injected activity to obtain more image counts without significant contrast loss. CONCLUSION: This simple test can be performed at any PET center to situate the quality of routine clinical PET images in comparison to the optimal possible for that system.

Interobserver reproducibility of the interpretation of I-123 FP-CIT single-photon emission computed tomography.

OBJECTIVES: I-123 ioflupane (FP-CIT) single-photon emission computed tomography is a recognized tool in the diagnosis of Parkinsonian syndromes. In practice, data interpretation relies on visual and semiquantitative analyses. Good interobserver reproducibility is a prerequisite before claiming the robustness of a technique. This study aimed at evaluating interobserver reproducibility of this approach. METHODS: Thirty nuclear medicine physicians participated in the study. Data included FP-CIT images and semiquantitative measurements of 12 cases, covering a wide spectrum of scintigraphic patterns and for which a 'true' clinical diagnosis based on long-term follow-up was available. Interobserver agreement was defined, for each case, as the highest percentage reached among the three proposed answers with complete agreement arbitrarily set at 80% or more. Variability in an individual observer's sensitivity to assess data as normal, equivocal or abnormal was scored using a three-point scale. RESULTS: Response rate was 99.7%. Among the three possible answers,'normal' accounted for 41.2% of the total, 'abnormal' for 49.8% and 'equivocal' for 8.1%. The mean interobserver agreement was 76% (range: 37-100%), with complete agreement being reached only in five cases. The interpretation proposed by most observers accorded to clinical diagnosis in 75% of the cases. Abnormalities of the central nervous system were encountered in all the cases with disagreement between the observer's interpretation and clinical diagnoses. An important variability in the observers' sensitivity was seen. CONCLUSION: In the particular setting of this preliminary study evaluating the reproducibility of FP-CIT single-photon emission computed tomography interpretation in a group of nuclear medicine physicians with various experiences, interobserver agreement was suboptimal. Collegial discussion and standardized interpretation criteria could contribute to an improved reproducibility.

Determination of optimal sampling times for a two blood sample clearance method using (51)Cr-EDTA in cats.

Estimation of the glomerular filtration rate (GFR) is a useful tool in the evaluation of kidney function in feline medicine. GFR can be determined by measuring the rate of tracer disappearance from the blood, and although these measurements are generally performed by multi-sampling techniques, simplified methods are more convenient in clinical practice. The optimal times for a simplified sampling strategy with two blood samples (2BS) for GFR measurement in cats using plasma (51)chromium ethylene diamine tetra-acetic acid ((51)Cr-EDTA) clearance were investigated. After intravenous administration of (51)Cr-EDTA, seven blood samples were obtained in 46 cats (19 euthyroid and 27 hyperthyroid cats, none with previously diagnosed chronic kidney disease (CKD)). The plasma clearance was then calculated from the seven point blood kinetics (7BS) and used for comparison to define the optimal sampling strategy by correlating different pairs of time points to the reference method. Mean GFR estimation for the reference method was 3.7+/-2.5 ml/min/kg (mean+/-standard deviation (SD)). Several pairs of sampling times were highly correlated with this reference method (r(2) > or = 0.980), with the best results when the first sample was taken 30 min after tracer injection and the second sample between 198 and 222 min after injection; or with the first sample at 36 min and the second at 234 or 240 min (r(2) for both combinations=0.984). Because of the similarity of GFR values obtained with the 2BS method in comparison to the values obtained with the 7BS reference method, the simplified method may offer an alternative for GFR estimation. Although a wide range of GFR values was found in the included group of cats, the applicability should be confirmed in cats suspected of renal disease and with confirmed CKD. Furthermore, although no indications of age-related effect were found in this study, a possible influence of age should be included in future studies.

F-18 FDG-PET in children: do we have enough counts?

PURPOSE: The aim of the study was to find out whether in [F]fluoro-2-deoxy-D-glucose positron emission tomography (F-18 FDG-PET) performed in children in our department, the number of counts were sufficiently high to guarantee optimal image quality. METHODS: Phantom data with negative and positive lesions were acquired with an increasing count density and the relationship between image quality and counts per voxel was analyzed. On PET images obtained in 28 children aged 4-17 years and using a standard administered activity of 6.5 MBq/kg with a minimum of 74 MBq, the maximum counts per voxel in 10 regions of interest were noted and compared with those obtained on phantoms. RESULTS: Phantom data showed clearly the effect of higher count on image quality. Moreover, when high counts were available, reconstruction could be done using 2 mm voxel size, which improved the quality of the images further. In children, the counts per voxel in all the regions of interest, with the exception of the brain, were at a level of suboptimal image quality. CONCLUSION: By following the official guidelines, the counts per voxel observed in children with our gadolinium oxyorthosilicate-PET system were lower than the minimal required to produce optimal quality images. More efficient PET systems or higher F-18 FDG dose or increasing the acquisition time or combination of these factors are needed to improve the image quality and lesion detection.

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.

The effect of acquisition time on visual and semi-quantitative analysis of F-18 FDG-PET studies in patients with head and neck cancer.

OBJECTIVE: To evaluate the impact of acquisition time on F-18 fluorodeoxyglucose positron emission tomography (PET) image quality, lesion detection rate, standard uptake and lesion volume measures. METHODS: In 17 consecutively referred head and neck cancer patients, a 10-min acquisition of the head and neck was performed in list mode after completion of a whole-body PET-computed tomography scan. For each patient, 0.5, 1, 2, 3, 5, 7 and 10-min PET images were reconstructed. Image quality was scored on a 5-point scale. Lesions were visually identified and lesion locations were compared between scans with various acquisition times. Standard uptake values (SUVs) and lesion volumes were automatically obtained and compared. RESULTS: Image quality was scored excellent/good for 10 and 7-min scans; moderate for 5 and 3-min scans and poor/very poor for 2, 1 and 0.5-min scans. Lesion detection rate did not differ between scans with shorter acquisition times and the reference. Similarly, SUVmax was not significantly different between images with various scan times and the reference, except for the 0.5-min PET image (Wilcoxon, P = 0.04). Overall, lesion volume increased significantly with longer scan time (Friedman, P<0.0001). For individual lesions, however, the effect of scan time on volume was quite variable. The variability was significantly larger for images with scan times below 3 min than for images with scan times of > or = 3 min. CONCLUSION: Despite poor image quality for scans with short acquisition times, the lesion detection rate was not adversely affected. Increased scan time resulted in an increase in lesion volumes. This finding is of particular interest if PET images are implemented in radiation oncology treatment planning.

Normal uptake of F-18 FDG in the testis as assessed by PET/CT in a pediatric study population.

OBJECTIVE: To investigate the correlation between the F-18 FDG uptake in the normal testis as assessed by PET-CT and patient age in a pediatric study population. METHODS: The study population consisted of 22 subjects aged between 9 and 17 years. For these subjects 42 PET-CT scans were available for analysis. The testis was identified on the CT images. Mean standard uptake values and testicular volume were calculated based on manually drawn regions-of-interest over the organ. The correlation between mean SUV and age as well as between testicular volume and age was calculated using Pearson's correlation coefficient. RESULTS: A strong and statistically significant positive correlation between F-18 FDG uptake in the testis and age was documented. The correlation coefficient was 0.406 in the analysis based on 42 PET-CT studies (p = 0.005). The correlation between tracer uptake and age was reassessed based on 22 PET-CT studies including the last recorded PET-CT scan per patient. The correlation coefficient was 0.409 (p = 0.05). In addition, based on 22 PET-CT scans, a strong and statistically significant positive correlation between testicular volume and age was documented (r = 0.67, p < 0.001). CONCLUSION: Whereas it was previously shown that in adult men there was a weak but statistically significant negative correlation between F-18 FDG uptake in the normal testis and age, we found a strong and statistically significant positive correlation in children and teenage boys.

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.