The distribution of FDG at PET examinations constitutes a relative mechanism: significant effects at activity quantification in patients with a high muscular uptake.
OBJECTIVE
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.


CONCLUSIONS
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.
Department of Radiology, Karolinska University Hospital Solna, 171 76 Stockholm, Sweden. henry.lindholm@karolinska.se
Henry
H
Lindholm
Ove
O
Johansson
Cathrine
C
Jonsson
Hans
H
Jacobsson
D000328:Adult; D000368:Aged; D001853:Bone Marrow / Q000000981:diagnostic imaging; D002648:Child; D015444:Exercise; D005260:Female; D019788:Fluorodeoxyglucose F18 / Q000493:pharmacokinetics*; D006801:Humans; D008099:Liver / Q000000981:diagnostic imaging; D008168:Lung / Q000000981:diagnostic imaging; D008297:Male; D008875:Middle Aged; D064847:Multimodal Imaging; D018482:Muscle, Skeletal / Q000000981:diagnostic imaging* / Q000502:physiology; D049268:Positron-Emission Tomography; D019275:Radiopharmaceuticals / Q000493:pharmacokinetics*; D013154:Spleen / Q000000981:diagnostic imaging; D014018:Tissue Distribution; D014057:Tomography, X-Ray Computed
D019275:Radiopharmaceuticals; D019788:Fluorodeoxyglucose F18