To evaluate whether electrical admittance of intracellular water is applicable for monitoring filling of the heart, we determined the difference in intracellular water in the thorax (Thorax(ICW)), measured as the reciprocal value of the electrical impedance for the thorax at 1.5 and 100 kHz during lower body negative pressure (LBNP) in humans. Changes in Thorax(ICW) were compared with positron emission tomography-determined C(15)O-labeled erythrocytes over the heart. During -40 mmHg LBNP, the blood volume of the heart decreased by 21 +/- 3% as the erythrocyte volume was reduced by 20 +/- 2% and the plasma volume declined by 26 +/- 2% (P < 0.01; n = 8). Over the heart region, LBNP was also associated with a decrease in the technetium-labeled erythrocyte activity by 26 +/- 4% and, conversely, an increase over the lower leg by 92 +/- 5% (P < 0.01; n = 6). For 15 subjects, LBNP increased thoracic impedance by 3.3 +/- 0.3 Omega (1.5 kHz) and 3.0 +/- 0.4 Omega (100 kHz), whereas leg impedance decreased by 9.0 +/- 3.3 Omega (1.5 kHz) and 6.1 +/- 3 Omega (100 kHz; P < 0.01). Thorax(ICW) was reduced by 7.1 +/- 1.9 S. 10(-4) (P < 0.01) and intracellular water in the leg tended to increase (from 37.8 +/- 4.6 to 40.9 +/- 5.0 S. 10(-4); P = 0.08). The correlation between Thorax(ICW) and heart erythrocyte volume was 0.84 (P < 0.05). The results suggest that thoracic electrical admittance of intracellular water can be applied to evaluate changes in blood volume of the heart during LBNP in humans.
The diagnostic work-up in patients with fever of unknown origin (FUO) is often challenging and frequently includes nuclear medicine procedures. Whereas a role for leucocyte or granulocyte scintigraphy in FUO is generally accepted, a possible role of fluorine-18 fluorodeoxyglucose (FDG) positron emission tomography (PET) in these patients remains to be established. To study this, we compared prospectively, on a head-to-head basis, the diagnostic value of FDG-PET and indium-111 granulocyte scintigraphy in patients with FUO. Nineteen patients with FUO underwent both FDG-PET and (111)In-granulocyte scintigraphy within 1 week. FDG-PET scans and granulocyte scintigrams were reviewed by different doctors who were blinded to the result of the other investigation. The diagnostic values of FDG-PET and granulocyte scintigraphy were evaluated with regard to identification of a focal infectious/inflammatory or malignant cause of FUO. The sensitivity of granulocyte scintigraphy and FDG-PET were 71% [95% confidence interval (CI): 37-85%] and 50% (CI: 16-84%), respectively. The specificity of granulocyte scintigraphy was 92% (71-100%), which was significantly higher than that of FDG-PET, at 46% (34-62%). Positive and negative predictive values for granulocyte scintigraphy were both 85%. Positive and negative predictive values for FDG-PET were 30% and 67%, respectively. (111)In-granulocyte scintigraphy has a superior diagnostic performance compared to FDG-PET for detection of a localised infectious/inflammatory or neoplastic cause of FUO. The poorer performance of FDG-PET is in particular attributable to a high percentage of false positive scans, leading to low specificity.
With our present strategy of wide-field irradiation in patients with neck node metastases from a carcinoma of unknown primary, whole-body 18F-FDG PET had treatment-related implications in 24% (10 of 42) of the patients.
Correct staging is crucial for the management and prognosis of patients with malignant melanoma. The aim of this prospective study was to compare staging by whole-body positron emission tomography using fluorine-18 fluorodeoxyglucose (18F-FDG) with staging by conventional methods. Thirty-eight patients with malignant melanoma of clinical stage II (local recurrence, in-transit and regional lymph node metastases) or III (metastases to other sites than in stage II) were included in the study. The results of the PET scans were compared with those obtained by clinical examination, computed tomography, ultrasound, radiography, and liver function tests and histology or clinical follow-up. With 18F-FDG PET we found for all foci a sensitivity of 97% and a specificity of 56%, compared with 62% and 22%, respectively, when using routine methods. For intra-abdominal foci, the sensitivity and specificity were 100% for both 18F-FDG PET and routine methods. Corresponding figures for pulmonary/intrathoracic foci were 100% and 33%, respectively. Of the patients included in this study, 34% would not have been staged correctly by conventional methods alone. We conclude from this study that 18F-FDG PET is a sensitive method superior to conventional methods for detecting widespread metastases from malignant melanoma. Mutilating surgery of no benefit can thereby be avoided. 18F-FDG PET is useful as a supplement to clinical examination in melanoma staging.
Relapse occurs in 30% of patients with stage I non-seminomatous germ cell tumours (NSGCT) within 1 year after orchiectomy. Whole-body positron emission tomography with fluorine-18 fluorodeoxyglucose (FDG-PET) may detect small metastases when standard staging with computed tomography (CT) and tumour markers is negative. In this study, 46 patients underwent FDG-PET after staging with normal CT and tumour markers. To exclude diagnostic test bias and workup bias, all patients had routine follow-up with repeated CT and tumour marker evaluation, even though the initial FDG-PET was positive. Thirty-six patients have remained disease free with a median follow-up of 48 months (range 24-76). Ten patients (22%) suffered disease relapse after a median of 2 months (range 1-8), and of these, seven had a true positive initial PET with increased uptake of FDG indicating metastatic disease. There were three false negative and no false positive PET scans. The sensitivity, specificity and accuracy of PET were 70%, 100% and 93%, respectively. The sensitivity of detecting small retroperitoneal metastases was 88%. The negative and positive predictive values were 92% and 100%, respectively, whereas the negative predictive value of standard staging procedures was 78%. FDG-PET thus seems to be superior to conventional staging (P=0.06) in stage I NSGCT. This non-invasive method may improve the overall management of patients with NSGCT.
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