ABSTRACT
OBJECTIVE: SUVmax is often calculated at FDG PET examinations in systematic studies as well as at clinical examinations. Since SUVmax represents a very small portion of a lesion it may be questioned how statistically reliable the figure is. This was studied by assessing the repeatability of SUVmax between two FDG acquisitions acquired immediately upon each other in patients with chest lesions. METHODS: In 100 clinical patients with a known chest lesion, two identical 3 min PET registrations (PET1 and PET2, respectively) were initiated within 224±31 sec of each other. The difference in SUVmax between the lesion for the two PET scans (ΔSUVmax) was calculated and the uncertainty expressed as the coefficient of variation, CV (%). The correlation between ΔSUVmax and the lowest SUVmax from PET1 or PET2, the approximate metabolic lesion volume, the time from FDG injection to PET1 and the time between PET1 and PET2, respectively, was also assessed. RESULTS: In 56 patients SUVmax increased at the second acquisition and in 44 patients it decreased. Mean of SUVmax was 7.8±6.1 and 7.8±6.2 for PET1 and PET2, respectively. The mean percentage difference was 0.9±7.8. The difference was not significant (p=0.20). CV gave an uncertainty of 4.3% between the two measurements which is a strong indicator of equivalence. There was no correlation between ΔSUVmax and any of the assessed four parameters. The difference between the acquisitions, 0.9%, was much lower compared to the 3 previous published similar, but more restricted studies where the difference was 2.5-8.2%. CONCLUSION: From camera and computational perspectives, SUVmax is a stable parameter Conflict of interest:None declared.
ABSTRACT
BACKGROUND: At fluorodeoxyglucose/positron emission tomography (FDG/PET) examinations, a generally increased uptake of the skeletal muscles is sometimes encountered. As the tracer distribution constitutes a 'zero-sum-game', the uptake of lesions as well as of normal tissues is reduced in these patients. This has to be considered at calculation of standardised uptake values (SUVs), especially at longitudinal examinations in the same patient. In the current study, a possible similar influence on the FDG distribution by a high uptake of brown adipose tissue (BAT) was studied. METHODS: Twelve patients with strongly increased BAT uptake were examined twice with a mean of 5 days (study group). In six of these patients, there was at least one pathological lesion with increased uptake. The BAT uptake was normalised at the second examination after pretreatment with propranolol. SUVs of the pathological lesions and of the liver, spleen, lung, blood, skeletal muscles, bone marrow, gluteal fat, abdomen and heart were assessed. In order to control the effects of propranolol on normal organs/tissues, which could interfere with the findings, 25 age and gender matched normal controls were also studied (control subjects). RESULTS: In the study group, there was only a lower bone marrow uptake after propranolol administration. Comparing the study group with the control subjects, the bone marrow activity was higher at examination before propranolol treatment compared to the control subjects. There was also a higher uptake of the spleen in the study group before propranolol treatment compared to the control subjects. There were no differences between the study group after propranolol administration and the control subjects. CONCLUSIONS: The differences found are small and cannot be explained, why they could be random phenomena. Together with, there were no differences between the study group after propranolol administration and the control subjects; it is concluded that an effect on the FDG distribution in patients with a strong BAT uptake by can be disregarded in clinical praxis. This is important at longitudinal examinations of patients undergoing tailored tumour therapy and in contrast to examinations in patients with a generally increased uptake of the skeletal muscles which significantly affects the distribution of the radiopharmaceutical.
ABSTRACT
BACKGROUND: The influence of the blood glucose level on the tracer uptake of normal tissues at [18F]-2-fluoro-2-deoxy-d-glucose (FDG) positron emission tomography (PET) was retrospectively studied in examinations in clinical patients. METHODS: Five hundred examinations were evaluated in retrospect. The inclusion criteria were studies with a normal or near-normal FDG distribution. Patients who had been subjected to chemotherapy (including GSF treatment) or radiotherapy <4 weeks prior to the examination were excluded; we cannot exclude, however, that in a very few patients the available information might have been incomplete. Otherwise, patients were included regardless of concurrent diseases and/or therapy. In one evaluation, the mean standardized uptake value of the liver, spleen, lungs, peripheral blood, selected muscles and bone marrow of all 500 individuals was correlated to the blood glucose level. In another evaluation, a subgroup of 62 patients with increased blood glucose levels (≥7.0 mmol/l) was compared with another subgroup of 62 patients paired with regard to age and gender with blood glucose levels within normal range (≤6.0 mmol/l). RESULTS: There was a weak positive correlation between the blood glucose level and the muscular uptake of FDG, while there was no correlation with the tracer uptake of the liver, spleen, lungs, peripheral blood or bone marrow. The patient group with increased blood glucose levels showed a slightly, but significantly, higher muscular FDG uptake compared with the matched subgroup of patients with normal blood glucose levels. When comparing the other assessed tissues/organs, there were no differences between these two patient groups. CONCLUSIONS: The effect of hyperglycaemia at FDG PET on the studied normal tissues is restricted to a slightly increased muscular uptake. The effect of the blood glucose level on the blood activity at the time of examination is negligible.
ABSTRACT
PURPOSE: At (18)F-2-fluoro-2-deoxy-D-glucose (FDG) positron emission tomography (PET) examinations a high tracer uptake of the skeletal muscles is sometimes encountered which can lead to reduced uptake in pathological lesions. This was evaluated in retrospect in patients being recalled for a repeat examination after reducing the muscular uptake. METHODS: Ten patients with increased muscular tracer uptake were examined with FDG PET/CT on two occasions with a mean of 6 days. All patients showed at least one pathological lesion with increased tracer uptake. The muscular uptake was reduced at the second examination by informing the patient to refrain from physical activity together with pretreatment with diazepam. The maximum standardized uptake value (SUV(max)) of the pathological lesion and SUV(mean) of certain skeletal muscles, liver, spleen, lungs, blood and certain bone marrow portions were calculated. RESULTS: In all patients, the muscular uptake was reduced to a normal level at visual evaluation as well as at comparison of SUVs with 25 consecutive clinical patients exhibiting a normal FDG distribution (p < 0.001). The mean lesion SUV(max) increased from 2.4 to 3.7 (54 %) between the examinations (p < 0.05). All reference tissues/organs showed a significant increase of SUV at the second examination. Relating lesion SUV(max) to the activity of any of the reference tissues/organs there was no significant difference between the studies. CONCLUSION: The distribution of FDG constitutes a relative mechanism. This must be especially considered at longitudinal examinations in the same patient at therapy evaluations. In examinations with a somehow distorted general distribution of the activity, it may be more relevant to relate the lesion activity to a reference tissue/organ than relying on SUV assessments.
