Hybrid SPECT-CT and PET-CT imaging of differentiated thyroid carcinoma.

Hybrid imaging modalities such as radioiodine single photon emission CT with integrated CT ((131)I SPECT-CT) and 2-(fluorine-18)-fluoro-2-deoxy-D-glucose positron emission tomography with integrated CT (FDG PET-CT) allow the rapid and efficient fusion of functional and anatomic images, and provide diagnostic information that may influence management decisions in patients with differentiated thyroid carcinoma (DTC). Diagnostic localisation and therapy of these tumours are dependent upon their capacity to concentrate radioiodine ((131)I) via uptake through the sodium-iodide symporter and retention within the tumour. The prognosis for most patients with DTC is favourable, although controversy exists regarding the role of post-operative (131)I therapy in patients at low-risk for disease. Accurate identification of functional thyroid tissue (benign or malignant) using diagnostic (131)I planar scintigraphy complemented by SPECT-CT imaging enables the completion of post-operative staging and patient risk stratification prior to (131)I therapy administration. In patients with non-iodine-avid tumours (negative (131)I scan but elevated thyroglobulin indicative of persistent or recurrent disease), FDG PET-CT is used to identify tumours with enhanced glucose metabolism and to localise the source of thyroglobulin production. The CT component of this hybrid technology provides anatomic localisation of activity and allows CT-based attenuation correction of PET images. Images from 15 patients illustrate the applications of (131)I SPECT-CT and FDG PET-CT.

Recovery of muscles of old rats after hindlimb immobilisation by external fixation is impaired compared with those of young rats.

The right hindlimbs of 24-month-old female Wistar rats were immobilised for 4weeks using external fixation of the knee joint. In a further group, after the external fixation was removed, the rats were allowed to remobilise for an additional 4weeks. Hindlimb immobilisation for 4weeks caused a 32-42% reduction in wet weights of the hindlimb muscles of the rats as compared to those of the contralateral non-immobilised legs. After 4weeks of remobilisation the hindlimb muscles had not returned to the "control" weights. Biochemical changes in the gastrocnemius muscle resulting from the external fixation showed greatly elevated acid phosphatase activities (33.2%) and markedly reduced creatine phosphokinase activities (17.2%), which did not recover to preimmobilisation values after 4weeks of remobilisation. Light and transmission electron microscopy showed that remobilisation for 4weeks (after external fixation) resulted in only partial morphological restoration of the damage to the muscles in these aged rats. A comparison of similar hindlimb external fixation and remobilisation in young (6months old) rats showed that remobilisation caused a substantial recovery in biochemical parameters in both age groups, with the muscles of the young group (but not the old group) often reaching almost complete recovery accompanied by morphological restoration. We conclude that the net gain in the recovery period of biochemical and morphological parameters is significantly greater in the young rats compared to the old rats indicating that muscle metabolism and capacity for recovery from disuse atrophy is impaired with ageing.

Capacity for recovery and possible mechanisms in immobilization atrophy of young and old animals.

The effect of limb immobilization on muscle wasting and recovery of young and old rats was studied. Limb immobilization caused rapid and pronounced muscle weight loss, which was overcome efficiently in the muscles of young animals. However, muscles of old animals did not recover as well, indicating that muscle turnover (degradation and synthesis of proteins) is slower in old muscles than in young ones. The mechanisms of muscle wasting due to immobilization may involve two stages, the fast phase employing calcium-dependent proteolysis and the slower phase recruiting the lysosomal and ubiquitin-proteosome systems. The slow phase most probably involves the penetration of white cells between the muscle fibers and involves the secretion of cytokines that mediate a cascade of intracellular events, which culminates in muscle protein degradation. Thus, it was shown in our study and in other similar reports that through the influence of TNF-alpha and an increase in oxidative stress, there is marked activation of transcription factor NF-kappaB, which in turn induces many proteins to carry the signals that eventually result in protein breakdown. Because protein turnover was shown to slow down with age, it will be of great interest to study these events in aging muscles and to try to ascertain the specific events that make protein breakdown in aged muscles different from that in young ones.

Muscle recovery after immobilisation by external fixation.

We immobilised the right hindlimbs of six-month-old female Wistar rats for four weeks using a biplanar external fixation bridging the knee. The untreated left limbs served as a control group. An additional group of rats was allowed to recover for four weeks after removal of the frame. Immobilisation caused reduction in the wet weights of approximately 50% in the gastrocnemius, quadriceps, soleus and plantaris muscles; this was not restored completely after remobilisation. There was an increase in the activity of acid phosphatase of approximately 85% in the gastrocnemius and quadriceps muscles whereas that of creatine phosphokinase was reduced by about 40%. These values returned to nearly normal after remobilisation. Histological and ultrastructural examination showed a marked myopathy of the gastrocnemius muscle after immobilisation although the morphology was largely restored after remobilisation. We conclude that after four weeks of remobilisation, hind-limb muscles do not return to preimmobilisation weights, although biochemical activities and ultrastructural appearance are largely restored.