Feyzi Tamgac

In vitro and in vivo study of 99mTc-MIBI encapsulated in PEG-liposomes: a promising radiotracer for tumour imaging.

Abstract. Encapsulation of technetium-99m sestamibi (99mTc-MIBI) in polyethyleneglycol-liposomes (99mTc-MIBI-PEG-liposomes) could extend the duration of its circulation in blood and alter its biodistribution, enabling its concentration in tumours to be increased. An original method to encapsulate 99mTc-MIBI in PEG-liposomes is described. The 99mTc-MIBI-PEG-liposomes were compared with free 99mTc-MIBI with respect to (a) tumour availability (b) ability to distinguish between chemotherapy-sensitive and -resistant cells and (c) uptake ratio in tumour imaging. PEG-liposomal systems composed of distearoylphosphatidylcholine/cholesterol/PEG2000-distearoyl phosphatidylethanolamine and lissamine-rhodamine B-labelled liposomes were used. The encapsulation of 99mTc-MIBI in liposomes was achieved using the K+ diffusion potential method. We compared the uptake of free versus encapsulated 99mTc-MIBI by sensitive and resistant erythroleukaemia (K562) and breast tumour (MCF-7ras) cells. To assess the internalisation of these liposomes into cells, rhodamine B-labelled PEG-liposomes were used and visualised by fluorescence microscopy. Biodistribution and imaging characteristics of encapsulated and free radiotracer were determined in rats and tumour-bearing nude mice. The efficiency of 99mTc-MIBI encapsulation in PEG-liposomes was 50±5%. Use of 99mTc-MIBI-PEG-liposomes did not impair the ability of this tracer to distinguish between chemotherapy-sensitive and -resistant tumour cells; the percentage of radioactivity accumulated in the sensitive K562 cells was 1.24±0.04%, as compared with 0.41±0.04% in the resistant K562 cells. One hour post injection in rats, PEG-liposomes showed a ten times higher activity in blood than free 99mTc-MIBI, whereas activity of free 99mTc-MIBI in kidneys and bladder was markedly higher than that of encapsulated 99mTc-MIBI, indicating faster clearance of the free radiotracer. In the (MCF7-ras)-bearing nude mice, PEG-liposome uptake in tumour was two times that of free 99mTc-MIBI. Summarising, the 99mTc-MIBI-PEG-liposomes demonstrated a longer blood circulation time, enabled distinction between chemotherapy-sensitive and -resistant cells and improved tumour to background contrast in in vivo imaging. 99mTc-MIBI-PEG-liposomes therefore show promising potential for tumour imaging.

Dual-isotope myocardial imaging: feasibility, advantages and limitations

Two hundred and thirty-one patients underwent dual-isotope myocardial imaging (rest thallium-201 followed by stress technetium-99m sestamibi). The feasibility of the procedure was excellent: camera scheduling flexibility was improved and the duration of the procedure was less than that of a classical stress-redistribution procedure. Interpretation of defects due to image attenuation was facilitated by the different attenuation properties of 201Tl and 99mTc-sestamibi in 11 of 19 patients. 210Tl cross-over on 99mTc was found to be 15% ± 3% with doses of 201Tl and 99mTc-sestamibi of 3 and 10 mCi, respectively, and 7% ± 2% with doses of 3 and 20 mCi. This protocol should preferentially be reserved for patients with a history of myocardial infarction and/or a basal left ventricular dysfunction, in whom assessment of myocardial viability is of major interest. Extensive clinical validation of the dual-isotope procedure is required and optimal acquisition and reconstruction parameters should be established.

Non-matched images with 123I-IMP and 99mTc-bicisate single-photon emission tomography in the demonstration of focal hyperaemia during the subacute phase of an ischaemic stroke.

Focal hyperaemia is a fairly common phenomenon in the subacute phase of an ischaemic stroke. This has rarely been reported with iodine-123 iodoamphetamine (IMP) and has never been identified using technetium-99m bicisate (99mTc-ECD). In this report, we present the case of a patient suffering from a left cerebral posterior stroke. 123I-IMP single-photon emission tomography (SPET) images showed a large area of significantly increased IMP activity located in the left occipital region whereas 99mTc-bicisate SPET displayed hypoactivity in the same area.

Tc-99m HMDP imaging of a large chondrosarcoma of the knee

After multiple myeloma and osteogenic sarcoma, chondosarcoma is the third most common skeletal malignancy with known characteristics of cortical destruction and tumor necrosis. The median patient age is 45 years old. A large chondrosarcoma of the left knee in a 22-year-old man was identified on Tc-99m HMDP imaging.

Apport de l’imagerie au 18FDG dans la prise en charge du cancer du testicule

Resume Les cles du pronostic Le bilan d’extension initial et le diagnostic precoce des recidives conditionnent le pronostic et le traitement du cancer du testicule. Le bilan initial Il est difficile car les techniques traditionnelles n’identifient pas certaines localisations ganglionnaires. En outre, ces techniques sont peu specifiques car l’augmentation de taille d’un ganglion n’est pas synonyme d’envahissement. L’utilisation de la tomographie par emission de positons au 18FDG dans le bilan d’extension augmente l’exactitude diagnostique. Masses residuelles et recidives La persistance d’une masse ou une augmentation de son volume malgre une reponse favorable a la chimiotherapie pose un probleme particulier. Plusieurs etudes successives montrent l’interet de l’imagerie par 18FDG dans la caracterisation des masses residuelles. Dans le suivi des patients, l’imagerie par 18FDG du corps entier permet d’eviter la multiplication des examens et peut detecter les recidives avec une valeur diagnostique plus elevee que les autres modalites d’investigation.

Post-traumatic knee pain leading to the diagnosis of spondyloarthropathy.

The authors report a patient with persistent left knee pain after traumatic injury. The initial bone scan seemed to confirm a valgus stress knee injury. The final diagnosis, however, was focal inflammation of the knee ligaments (enthesopathy) related to ankylosing spondylitis. The diagnostic procedure and the results of other imaging modalities are presented. The bone scan findings are discussed.