[Peri-ictal SPECT in temporal lobe epilepsy: post-surgical evaluation]. / SPECT periictal en la epilepsia del lóbulo temporal: valoración tras cirugía.

INTRODUCTION: our aim was to evaluate the usefulness of peri-ictal SPECT in localising the epileptogenic region (ER) in candidates for temporal lobectomy to treat medically refractory complex partial seizures (CPS). Interictal and ictal SPECT, MRI and video-EEG results were compared and the positive predictive value (PPV) was calculated in those patients with good surgical outcome. MATERIALS AND METHODS: 37 patients who had a minimum of 3 years follow-up after surgery were studied retrospectively. Pre-surgical evaluation had included video-EEG monitoring, MRI and interictal and ictal SPECT. These results were compared to the surgically treated ER and successful outcome confirmed by post-surgical clinical follow-up. 29/37 patients remained seizure-free in the post-surgical follow-up. Interictal and peri-ictal SPECT were performed using 740 MBq of 99mTc-HMPAO. Peri-ictal SPECT was ictal in 25 patients and postictal in 12. RESULTS: ER concordance with video-EEG and peri-ictal SPECT was 86% (32/37 patients). It was 84% (31/37) for MRI and 54% (20/37 patients) for interictal SPECT. Peri-ictal SPECT localised the ER in 8/11 patients with discordant MRI and video-EEG results. Ictal SPECT localised the ER in the correct temporal lobe in 23/25 patients (92% concordance). In the 29 patients with a good surgical outcome, the PPV of video-EEG was 95% (27/29) and it was 90% (26/29) for both MRI and peri-ictal SPECT. CONCLUSIONS: peri-ictal brain SPECT is well able to localize ER in patients with temporal lobe epilepsy. Periictal SPECT concordance with ER was as good as video-EEG and MRI and its PPV was as good as that of MRI. We strongly recommend its use in the pre-surgical evaluation of temporal lobe epilepsy, especially when MRI and EEG are discordant.

[Influence of photon scattering on the quantification of relative changes in longitudinal brain PET studies with 18F-FDG]. / Influencia de la dispersión de fotones en la cuantificación de cambios relativos en estudios longitudinales de PET cerebral con 18F-FDG.

AIM: To study the effect of photon scattering on the quantification of relative changes of 18F-FDG uptake in longitudinal brain PET studies. MATERIALS AND METHODS: Two studies from a numerical Zubal phantom were simulated. One of these was a basal reference study and the other was an activated study showing an increase or decrease in the uptake in a region of the anterior cingulated cortex. SimSET Monte Carlo code was used to simulate PET sinograms. Primary photons, which did not undergo interactions, and scattered photons, which underwent one or more interactions, were stored in separate files to assess the effect of scattering. Reconstruction was carried out using an iterative algorithm based on ordered subsets of projections (OSEM-2D). The relative changes in uptake were calculated from images reconstructed with all the photons (primary and scattered) and from images reconstructed with only primary photons. RESULTS: A linear relationship between the calculated and theoretical values was obtained both for the images reconstructed with all the photons and for those reconstructed with primary photons. Our findings show a relative change recovery of 79% +/- 0.4% for all photons and 91% +/- 0.5% for primary photons only. CONCLUSIONS: Our results highlight subestimation of relative changes of 12% +/- 0.7% when scattered photons are used. Thus the importance of correcting this degradation in order to improve quantification is shown.

[Determination of focal distance and convergence assessment in collimators with focalized geometry]. / Determinación de la distancia focal y evaluación de la convergencia en colimadores de geometría focalizada.

OBJECTIVE: A method to calculate intrinsic parameters of fan beam collimators is presented. This method allows us to determine focal length and to assess the convergence of the collimator on a single focus line. MATERIAL AND METHODS: Images of a radioactive source located successively in a series of known coordinate positions are acquired. To determine the focal distance, a method has been developed that minimizes the sum of the distances between the experimental image point and the theoretical ones. Collimator convergence was evaluated by the intersections between all the pairs of lines drawn between the source location and its experimental image point. RESULTS: The results found between the two collimators showed that the actual focal length deviates 1.5% from the real focal value and the nominal focal length. The results also indicate that the collimator holes do not converge on a single focal line but rather on a focal area, with average deviations in regards to the real focus being *x = 2.5 mm and *z = 7.1 mm. CONCLUSIONS: The errors in regards to the original values and the extension of the focal zone make it possible to conclude that the quality of the collimators used is acceptable.

Bone mineral density in two different socio-economic population groups.

We have studied the bone mineral density (BMD) of the lumbar spine in two healthy population groups in Spain with similar characteristics but with different socio-economic levels. BMD was measured in 1116 individuals of both sexes in two selected groups: (A) 832 volunteers in the urban Barcelona area and (B) 284 volunteers from a suburb with lower socio-economic level. Individuals of group A have greater spine BMD than group B. The maximum difference was found in the group between 20 to 39 years: 5% (P less than 0.001) in men and 3% (P less than 0.05) in women. The patterns of bone loss in both groups were similar in onset, rate and quantity, suggesting a possible developmental cause for this difference. Bone loss in women began before the menopause and increased considerably in the following years. The BMD values show that most people at advanced age from the low socio-economic group cross the fracture threshold earlier than the first group.