Clinical impact of fluorine-18 fluorodeoxyglucose positron emission tomography in cancer patients. A comparative study between dedicated camera and dual-head coincidence gamma camera.

AIM: Positron emission tomography (PET) using fluorine-18 fluorodeoxyglucose (FDG) can be performed using a dedicated PET scanner (PET-I) or a dual-head coincidence gamma camera (CGC-I). The aim of this study was to comparatively assess the impact of PET-I and CGC-I on clinical management in cancer patients. METHODS: From November 2000 to November 2002, PET-I and CGC-I were performed at an interval of 2 days in 151 patients with colorectal cancer (n=40), breast cancer (n=28), thyroid cancer (n=23), lung tumors (n=22), germ cell tumors (n=14), unknown primary cancer (n=7) and other cancers (n=17). PET-I and CGC-I were interpreted independently with knowledge of conventional imaging (CI). In June 2003, theoretical management, e.g. treatment modality/ies and treatment intent (curative or palliative), after CI, PET-I and CGC-I were stated during multidisciplinary sessions and were a posteriori considered as appropriate or inappropriate using pathological and follow-up data. RESULTS: The theoretical management proposed after PET-I and after CGC-I was similar in 112/151 (74%; 95% CI: 66-81%) patients. In 125 assessable patients, theoretical management after PET-I was appropriate in 86% (95% CI: 79-92%), significantly higher (P=0.0033) than after CGC-I (70%; 95% CI: 62-78%). Both proportions were also higher than after CI (46%; 95% CI: 37-56%), (P<0.0001). A similar trend for higher proportions of appropriate management after PET-I than after CGC-I was observed for each tumor localization. CONCLUSIONS: The clinical impact of PET-I is superior to that of CGC-I in a large series of cancer patients. Although CGC-I could be considered as an acceptable alternative, PET-I remains the standard and should preferably equip nuclear medicine departments.

Gallium-67 scintigraphy in lymphoma: is there a benefit of image fusion with computed tomography?

The usefulness and complementarity of gallium (67Ga) scintigraphy and computed tomography (CT) in the management of patients with lymphoma have been extensively demonstrated. Owing to a lack of anatomical landmarks and physiological distribution of the tracer, precise localisation of abnormalities on 67Ga scintigraphy can be difficult. As fusion imaging techniques between single-photon emission tomography (SPET) and CT have been developed recently, we investigated whether use of CT/67Ga SPET fusion imaging could help in the interpretation of 67Ga scintigraphy. From November 1999 to May 2001, 52 consecutive fusion studies were performed in 38 patients [22 patients with Hodgkin's disease (HD) and 16 patients with non-Hodgkin's lymphoma (NHL)] as part of pre-treatment staging (n=13), treatment evaluation (n=20) or evaluation of suspected recurrence (n=19). 67Ga scintigraphy was carried out 2 and 6 days following the injection of 185-220 MBq 67Ga citrate. On day 2, 67Ga SPET and CT were performed, focussing on the chest and/or the abdomen/pelvis. Data from each imaging method were co-registered using external markers. 67Ga scintigraphy and CT were initially interpreted independently by nuclear medicine physicians and radiologists. CT/67Ga SPET fusion studies were then jointly interpreted and both practitioners indicated when fusion provided additional information in comparison with CT and 67Ga SPET alone. Image fusion was considered to be of benefit in 12/52 (23%) studies which were performed for initial staging (n=4), treatment evaluation (n=4) or evaluation of suspected recurrence (n=4). In these cases, image fusion allowed either confirmation and/or localisation of pathological gallium uptake (n=10) or detection of lesions not visible on CT scan (n=2). Fusion was relevant for discrimination between osseous lesions and lymph node involvement adjacent to bone, especially in the thoracic and lumbar spine and pelvis. In the abdomen and pelvis, fusion helped to differentiate physiological bowel elimination from abnormal uptake, and assisted in precisely locating uptake in neighbouring viscera of the left hypochondrium, including the spleen, left liver lobe, coeliac area, stomach wall and even the splenic flexure. At the thoracic level, fusion also proved useful for demonstrating clearly the relationships of abnormal foci to the pleura, hepatic dome, mediastinum, ribs or thoracic spine. Clinical management was altered by fusion imaging in one patient (chemotherapy was given instead of radiotherapy) and was potentially affected in three other patients (in that, in conjunction with other factors, the results of fusion imaging had an influence on the decision regarding use of irradiation and especially the treatment volume). In conclusion, CT/67Ga SPET fusion imaging allowed precise localisation of gallium uptake and correct attribution to the involved viscera, thereby altering the diagnosis in 20%-25% of studies in comparison with CT and 67Ga SPET analyses alone. CT/67Ga SPET fusion therefore appears valuable in facilitating the interpretation of 67Ga scintigraphy and we recommend its use in patients with lymphoma when CT and 67Ga scintigraphy are planned.

Non-invasive grading of oligodendrogliomas: correlation between in vivo metabolic pattern and histopathology.

Several studies have shown that the prognosis of oligodendrogliomas is dependent on their histological grade. In order to identify a non-invasive method for the primary diagnosis and follow-up of these tumours, we investigated the relationship between their in vivo metabolism, assessed by positron emission tomography (PET), and their histological grade assessed at the same time. Forty-seven patients with histologically confirmed oligodendrogliomas were investigated. Conventional neuroradiological assessment by computed tomography and magnetic resonance imaging (MRI) was performed in all the patients. All the histology slices were reviewed by the same pathologist after referral from various pathology laboratories. The PET investigation included a carbon-1 methionine (11C-MET) uptake study and, in the majority of cases, a fluorine-18 fluorodeoxyglucose (18F-FDG) uptake study, in order to investigate at the same time both amino acid metabolism and glycolysis. The sampled tumour region of interest (ROI) was defined from the T1-weighted 3D MR scan matched with the PET scan. Tracer concentration in each voxel of the tumour ROI was divided by the mean concentration in an ROI of the same size located in the healthy brain tissue. For each tumour and each tracer, we characterized the metabolic pattern on the basis of the mean and the maximum tumour to healthy tissue concentration ratio, and also the standard deviation and range of the ratios, which indicate the degree of metabolic heterogeneity of the tumour. The histological criteria for differentiating between high- and low-grade tumours were those of the WHO and, partially, of the Sainte-Anne-Daumas-Duport classification. Highly significant differences between high- and low-grade oligodendrogliomas (Mann-Whitney test: P<0.0001) were observed for all the assessed parameters of 11C-MET uptake. On the other hand, the pattern of 18F-FDG uptake showed only moderate differences between the two tumour groups.

Steady-state captopril renography: continuous monitoring of the captopril-induced increase in 99mTc-MAG3 mean parenchymal transit time in renovascular hypertension.

Steady-state captopril renography (SSCR) is an original technique for assessing the captopril-induced increase in technetium-99m mercaptoacetyltriglycine (99mTc-MAG3) mean parenchymal transit time (MPTT) in kidneys affected with functional renal artery stenosis (RAS). The steady-state parenchymal activity achieved by constant infusion of 99mTc-MAG3 is directly linked to the MPTT of the radiopharmaceutical. This steady-state parenchymal activity was continuously monitored from 15 min before to 60 min after a single dose of captopril in order to detect possible disruption of the steady state. SSCR was performed in 11 hypertensive patients with unilateral RAS and in two with RAS of a solitary kidney before renal revascularization (RR). In four of these patients, an additional SSCR was performed after RR. Of the ten patients whose hypertension was cured or improved by RR, one presented an uninterpretable SSCR and six presented a positive SSCR on the affected side. Control SSCR performed in four of these six patients was bilaterally negative. SSCR was also bilaterally negative in the three patients who showed no blood pressure response to RR. These preliminary results tend to indicate that, in spite of the stability of pre- and post-captopril hydration and data acquisition conditions allowed by this steady-state technique, the sensitivity is lower than expected. However, the reason for the false-negative results does not seem to be inherent to SSCR.