[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.

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

Introducción: el objetivo de este trabajo fue valorar la utilidad de la tomografía computarizada por emisión monofotónica (SPECT) periictal para localizar la región epileptógena (RE) en pacientes con crisis parciales complejas (CPC) del lóbulo temporal. Material y métodos: de forma retrospectiva se ha evaluado a 37 pacientes con CPC del lóbulo temporal a quienes se realizó una lobectomía temporal completa o selectiva. Para ello, se comparó la concordancia de la RE quirúrgica con los hallazgos de la resonancia magnética (RM), el videoelectroencefalograma (vídeo-EEG) y las SPECT cerebrales interictal y periictal. En segundo lugar, se valoró el valor predictivo positivo (VPP) de estas exploraciones en los 29 pacientes que presentaron un buen control de las crisis tras la cirugía. La SPECT se realizó tras la inyección de 740 MBq de 99mTc-HMPAO. Resultados: la concordancia de la RE quirúrgica con el vídeo-EEG, la RM, la SPECT icterictal y la SPECT periictal fue del 86% (32/37 pacientes), el 84% (31/37 pacientes), el 54% (20/37 pacientes) y el 86% (32/37 pacientes), respectivamente. En los 11 casos con RM y vídeo-EEG discordante o normal, la SPECT periictal fue decisivo en 8 (73%). En los 29 pacientes con evolución favorable tras la cirugía, el VPP del vídeo-EEG fue del 95% (27/29) y el de la RM y la SPECT periictal fue del 90% (26/29). Conclusiones: la concordancia de la RE quirúrgica con la SPECT periictal fue similar al del vídeo-EEG y la RM y tuvo el mismo VPP que la RM. Por ello, creemos que la SPECT periictal debe emplearse de forma sistemática en la evaluación prequirúrgica de la epilepsia del lóbulo temporal, especialmente cuando vídeo-EEG y RM son discordantes o normales(AU)

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(AU)

[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.

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

Objetivos: Estudiar el efecto de la dispersión de fotones en la cuantificación de los cambios relativos en estudios longitudinales de tomografía por emisión de positrones (PET) cerebral utilizando 18F-FDG. Material y métodos: Se utilizó un maniquí numérico de Zubal y se simularon dos estudios, uno de referencia (basal) y otro en el que había un aumento/disminución de la captación en una región situada en el córtex cingulado anterior. Para obtener los sinogramas se utilizó SimSET, un código Monte Carlo que permite la simulación de estudios de tomografía de emisión. Para evaluar el efecto de la dispersión se almacenaron en ficheros separados los fotones primarios que no sufren ningún tipo de interacción y los fotones dispersados después de producirse una o más interacciones. La reconstrucción se realizó utilizando un algoritmo iterativo basado en subconjuntos ordenados OSEM-2D. Se calcularon los cambios relativos de captación a partir de las imágenes reconstruidas con fotones totales (primarios y dispersados) y de las obtenidas únicamente con fotones primarios. Resultados: Se obtuvo una relación lineal entre los valores de cambio relativo calculados y los teóricos, tanto para imágenes con fotones totales como con fotones primarios. En el caso en el que se consideraron sólo fotones primarios la recuperación del cambio relativo fue del 91 % +- 0,5 %, mientras que la presencia de fotones dispersados produce una recuperación del 79 % +- 0,4 %. Conclusiones: Nuestros resultados muestran que la presencia de fotones dispersados producen una subestimación de los valores de captación relativa del 12 % +- 0,7 % y, en consecuencia, evidencian la importancia de la corrección de esta degradación para mejorar la exactitud de la cuantificación

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

Corrección de movimientos en estudios de SPECT cardíaco / Correction of movements in cardiac SPECT studies

Objetivos: El movimiento del paciente durante la adquisición de imágenes es causa frecuente de artefactos en estudios de SPECT miocárdica de perfusión. En este trabajo se propone un algoritmo para la corrección de movimientos longitudinales. Material y métodos: El método está basado en el cálculo de la correlación entre funciones unidimensionales obtenidas de proyecciones sucesivas, utilizando una ventana obtenida de forma automática para eliminar datos espúreos antes de calcular la correlación. El algoritmo fue evaluado sobre estudios obtenidos a partir de un maniquí cardíaco y sobre estudios correspondientes a diez pacientes, 7 de los cuales presentaban movimientos apreciables y 3 en los que no se apreciaba movimiento que se utilizaron como control. Resultados: En los estudios obtenidos con el maniquí, el error medio en el desplazamiento calculado utilizando la ventana propuesta fue inferior a 0,5 píxeles. Cuando se utilizaron ventanas de mayor tamaño los errores medios aumentaron hasta 2,8 píxeles. En los estudios de pacientes, el método consiguió reducir los movimientos observados en siete casos y mantuvo inalterados los tres controles. Cuando no se utilizó una ventana para restringir la correlación, 3 de los 7 casos que presentaban movimiento no mejoraron, e incluso uno de los controles, empeoró. Conclusiones: Los resultados obtenidos indican la utilidad del algoritmo y ponen de relieve la necesidad de utilizar una ventana para eliminar datos antes de calcular la correlación (AU)

Objectives: Patient movement during SPECT acquisition of images is a frequent cause of artefacts in myocardial perfusion SPECT studies. In this paper we propose an algorithm for the correction of longitudinal movements. Materials and methods: The method is based on the calculation of the correlation between unidimensional functions obtained from successive projections with a window obtained automatically to eliminate unwanted data points before calculating the correlation. The algorithm was assessed on studies obtained from a cardiac phantom and from those corresponding to ten patients. Seven of these patients had significant movement during SPECT acquisition and those corresponding to the other three studies, in which no movement was observed, were used as a control. Results: In the phantom studies obtained, the mean error of the calculated displacements was less than 0.5 pixels when the window proposed was employed. The error reached 2.8 pixels when the length of the window increased. In patient studies, the method succeeded in reducing the patient motion in all cases and the three control studies remained unchanged. When no window was used to limit the correlation, three out of the seven studies that originally presented movements did not improve and one control study got worse. Conclusion: The results obtained indicate the utility of the algorithm and demonstrate the need to window the data before calculating the correlation (AU)

[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.