1,720,976 research outputs found
The use of molecular sieves to simulate hot lesions in (18)F-fluorodeoxyglucose--positron emission tomography imaging
No full textEstimated radiation risk of cancer from medical imaging in haemodialysis patients.
No full textBACKGROUND: In recent years the widespread use of medical procedures increased the cumulative effective doses of ionizing radiation. Although many haemodialysis patients undergo multiple examinations with high radiation exposure, no data are available characterizing their attendant potential risks of cancer.
METHODS: The radiation exposures were obtained from a retrospective study of 159 consecutive haemodialysis patients with a follow-up duration ≥ 1 year. Effective dose and organ dose were estimated on an individual basis. Radiation risk was expressed as risk of exposure-induced death (REID) (%).
RESULTS: The 159 patients (101 males) were followed for a median of 2.7 years (mean 3.0 years). A total of 486 patient-years were available for follow-up. The mean age at study entry was 65.3 years. The mean cumulative organ doses were 103, 102, 100, 99, 77 and 58 mSv for kidneys, lung, stomach, liver, colon and bone marrow, respectively. On average, computed tomography, nuclear medicine and interventional radiology accounted for 90, 4.5 and 5.5% of organ doses, respectively. The average REID was 0.99% (i.e. odds 1 in 100) and the median REID was 0.45%. At univariate analysis, increasing age and presence of diabetes were independent predictors of lower REID, whilst patients eligible for kidney transplantation were exposed to a significantly higher REID. At multivariate analysis, younger age was an independent predictor of higher REID.
CONCLUSIONS: The excess cancer risk-attributable radiation exposure in haemodialysis patients is not negligible. Particular attention should be paid to younger patients and to patients who will undergo kidney transplantation
Minimum acceptable sensitivity of intraoperative gamma probes used for sentinel lymph node detection in melanoma patients
No full textThe aim of this study was to determine the suspension level for the sensitivity of an intraoperative scintillation gamma probe in the detection of the sentinel lymph node (SLN) in melanoma patients. Thirty-eight consecutive patients with melanoma were enrolled in the study during a 12-month period and underwent lymphatic scintigraphy after the peritumoral intradermal administration of about 14 MBq of (99m)Tc-nanocolloids. The SLNs were successfully removed during the surgical intervention about 4 h later. To identify and localize the SLN, a scintillation NaI(Tl) collimated probe was used. Predictably, the probe sensitivity decreased as the photopeak energy window was progressively narrowed, from 6.9 ± 0.7 counts per second (cps)/kBq (designated as the 'optimum,' or 'OPT,' sensitivity) to 2.5 ± 0.3 cps/kBq (LOW sensitivity) and to 1.4 ± 0.2 cps/kBq (VLOW sensitivity). Maximum lymph node count rates (cps) were determined for the foregoing energy windows prior to skin incision (PREOPT, PRELOW, PREVLOW, respectively) and in vivo after incision (INVOPT, INVLOW, INVVLOW). Forty-three SLNs were removed with a mean source-to-detector distance of 46 ± 24 mm (min 12 mm, max 92 mm). Four SLNs could not have been detected using PRELOW. This figure would have decreased to 34, with nine undetectable lymph nodes, with PREVLOW. One SLN could not have been identified using INVLOW and four could not have be identified using INVVLOW. In the clinical scenario of SLN detection in melanoma patients, a system sensitivity of 2.5 cps/kBq represents a suspension level, that is, a level under which the equipment must be suspended from clinical use and the poor performance must be investigated
Performance characteristics obtained for a new 3-dimensional lutetium oxyorthosilicate-based whole-body PET/CT scanner with the National Electrical Manufacturers Association NU 2-2001 standard
No full textThe effect of activity outside the field of view on image quality for a 3D LSO-based whole body PET/CT scanner
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Threshold segmentation for PET target volume delineation in radiation treatment planning: the role of target-to-background ratio and target size
No full textA multivariable approach was adopted to study the dependence of the percentage threshold [TH (%)] used to define the boundaries of F 18 -FDG positive tissue on emission scan duration (ESD) and activity at the start of acquisition (Aacq) for different target sizes and target-to-background (T/B) ratios. An anthropomorphic model, at least for counting rate characteristics, was used to study this dependence in conditions resembling the ones that can be encountered in the clinical studies. An annular ring of water bags of 3 cm thickness was fitted over an International Electrotechnical Commission (IEC) phantom in order to obtain counting rates similar to those found in average patients. The scatter fraction of the modified IEC phantom was similar to the mean scatter fraction measured on patients, with a similar scanner. A supplemental set of microhollow spheres was positioned inside the phantom. The NEMA NU 2-2001 scatter phantom was positioned at the end of the IEC phantom to approximate the clinical situation of having activity that extends beyond the scanner field of view. The phantoms were filled with a solution of water and F 18 (12 kBq/mL) and the spheres with various T/B ratios of 22.5, 10.3, and 3.6. Sequential imaging was performed to acquire PET images with varying background activity concentrations of about 12, 9, 6.4, 5.3, and 3.1 kBq/mL. The ESD was set to 60, 120, 180, and 240 s/bed. Data were fitted using two distinct multiple linear regression models for sphere ID≤10 mm and sphere ID>10 mm. The fittings of both models were good with an R2 of 0.86 in both cases. Neither ESD nor Aacq resulted as significant predictors of the TH (%). For sphere ID≤10 mm the target size was the most significant predictor of the TH (%), followed by the T/B ratio, while for sphere ID>10 mm the explanatory power of the target size and T/B ratio were reversed, the T/B ratio being now the most important predictor of the TH (%). Both the target size and T/B ratio play a major role in explaining the variance of the TH (%), throughout the whole range of target sizes and T/B ratios examined. Thus, algorithms aimed at automatic threshold segmentation should incorporate both variables with a relative weight which critically depends on target size. © 2008 American Association of Physicists in Medicine
Comparison of retrospective PET and MRI-DWI (PET/MRI-DWI) image fusion with PET/CT and MRI-DWI in detection of cervical and endometrial cancer lymph node metastases
No full textOBJECTIVES:
The aim of this study was to compare the accuracy of retrospective image fusion of PET/MRI-DWI with that of PET/CT and MRI-DWI alone in detecting metastatic lymph nodes in patients with cervical and endometrial carcinoma.
MATERIALS AND METHODS:
Twenty-seven patients with endometrial (n = 14) and cervical (n = 13) cancer who had undergone preoperative MRI-DWI and PET/CT for staging were retrospectively evaluated. The accuracy, sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of PET/CT, MRI-DWI, and PET/MRI-DWI image fusion were calculated on a per-patient basis and on a per-node basis. Histopathological and follow-up imaging results were used as the gold standard.
RESULTS:
On a per-patient basis PET/MRI-DWI had the same sensitivity (87.5 %), specificity (84.2 %), diagnostic accuracy (85.1 %), PPV (70 %), and NPV (94.1 %) as PET-CT, but on a per-node basis PET/MRI-DWI showed better sensitivity (89 vs 70.2 %), specificity (91.6 vs 90.5 %), diagnostic accuracy (91.2 vs 87 %), PPV (68.7 vs 60.4 %), and NPV (97.6 vs 93.6 %) than PET-CT. Comparison of the areas under the ROC curves for the detection of metastatic lymph nodes demonstrated a non-significant difference (p = 0.055) between PET/CT and fused PET/MRI-DWI.
CONCLUSION:
PET/MRI-DWI may be a valuable technique for N-staging patients with endometrial and cervical cancer, but more studies are needed to investigate its potential clinical utility
In vitro tests of electromagnetic interference of electromagnetic navigational bronchoscopy to implantable cardioverter defibrillators
No full textImpact of target-to-background ratio, target size, emission scan duration, and activity on physical figures of merit for a 3D LSO-based whole body PET/CT scanner
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