Subtraction of interictal from ictal single-photon emission computed tomography (SPECT) yields numerous foci that encompass a range of pixel values scattered in the brain. This preliminary study evaluated the significance of this range of values.
Subtraction images were obtained by registering, normalizing, and subtracting interictal from ictal SPECT for 13 patients. Pixel values of the resulting foci were divided into two groups: group I with 75-100% and group II with 50-75% of the maximal pixel value. Locations of these foci were determined, and concordance with surgical outcomes and scalp and invasive EEG findings was evaluated.
In 10 of 13 cases, group I foci showed good concordance with ictal scalp EEG. In addition, group I foci corresponded well to invasive EEG findings in nine of 10 cases. Group I foci had bilateral distributions in seven of 13 cases. In 10 of 13 cases, group I foci corresponded well to regions of surgical resection. Of these 10 patients, nine showed good concordance with scalp EEG, eight showed good invasive EEG concordance, and eight were seizure free after resection. Conversely, group II foci had good concordance with ictal scalp EEG in only five of 13 cases, and invasive EEG findings, in only five of 10 cases. Group II foci had bilateral distributions in 10 of 13 cases. All 10 cases underwent unilateral surgical resections, and all had good surgical outcomes. In six of 13 cases, group II foci showed concordance with surgical sites. Of these six foci, four had poor concordance with scalp EEG, one had poor concordance with invasive EEG, and five had good surgical outcomes. Sensitivity and specificity for seizure localization of Group I foci were 40% and 88% respectively while sensitivity and specificity of Group II foci were 20% and 79% respectively.
Our data demonstrate that foci with 75-100% of maximal pixel values show good concordance with seizure foci, whereas foci of 50-75% may not. Therefore stratifying ictal/interictal differences may improve the specificity and localizing value of subtraction SPECT.
"It has been shown that ictal SPECT is far more useful for correctly localizing seizure onset than interictal SPECT (Spencer et al., 1995; Devous et al., 1998; Kim et al., 2009). In addition, ictal–interictal SPECT difference imaging analysis yields better results than visual read of ictal SPECT alone (Zubal et al., 1995; O'Brien et al., 1998; Spanaki et al., 1999; Lee et al., 2000b; Koo et al., 2003). Another important determinant of the sensitivity and specificity of ictal SPECT is the time of tracer injection. "
[Show abstract][Hide abstract] ABSTRACT: Partial seizures produce increased cerebral blood flow in the region of seizure onset. These regional cerebral blood flow increases can be detected by single photon emission computed tomography (ictal SPECT), providing a useful clinical tool for seizure localization. However, when partial seizures secondarily generalize, there are often questions of interpretation since propagation of seizures could produce ambiguous results. Ictal SPECT from secondarily generalized seizures has not been thoroughly investigated. We analysed ictal SPECT from 59 secondarily generalized tonic-clonic seizures obtained during epilepsy surgery evaluation in 53 patients. Ictal versus baseline interictal SPECT difference analysis was performed using ISAS (http://spect.yale.edu). SPECT injection times were classified based on video/EEG review as either pre-generalization, during generalization or in the immediate post-ictal period. We found that in the pre-generalization and generalization phases, ictal SPECT showed significantly more regions of cerebral blood flow increases than in partial seizures without secondary generalization. This made identification of a single unambiguous region of seizure onset impossible 50% of the time with ictal SPECT in secondarily generalized seizures. However, cerebral blood flow increases on ictal SPECT correctly identified the hemisphere (left versus right) of seizure onset in 84% of cases. In addition, when a single unambiguous region of cerebral blood flow increase was seen on ictal SPECT, this was the correct localization 80% of the time. In agreement with findings from partial seizures without secondary generalization, cerebral blood flow increases in the post-ictal period and cerebral blood flow decreases during or following seizures were not useful for localizing seizure onset. Interestingly, however, cerebral blood flow hypoperfusion during the generalization phase (but not pre-generalization) was greater on the side opposite to seizure onset in 90% of patients. These findings suggest that, with appropriate cautious interpretation, ictal SPECT in secondarily generalized seizures can help localize the region of seizure onset.
". SISCOM and subtractive ictal PET (SIPCOM) [normalized images; depicted pixels with > 70 % of the maximal pixel value (for details see Koo et al. 2003)]; ictal fMRI (normalized images; activated voxels meet a significance threshold of p < 0.007 uncorrected at a voxel level); voxel-based morphometry (normalized GM concentration Z-score map) – area with GM increase greater than the mean of the controls + 4.5 SD is given in red (Colliot et al. 2006 "
[Show abstract][Hide abstract] ABSTRACT: The rationale for this case report is to assess the degree of congruency between the results of several advanced functional, metabolic, and structural neuroimaging techniques used in patients with MRI-negative focal epilepsy.
We investigated the presurgical evaluation and post-operative outcome of a patient with intractable, extratemporal epilepsy. Because the habitual seizures in this patient could be easily induced, six, advanced, neurodiagnostic techniques were successively applied (SISCOM, ictal FDG-PET, ictal fMRI, postictal diffusion-weighted imaging, voxel-based morphometry, and MRS imaging).
The findings for the neuroimaging methods investigated, within the left central region, were fairly congruent. Subsequent, invasive EEG recordings revealed a seizure-onset zone at the site where most of the neuroimaging had shown abnormal findings. The surgical removal of the epileptogenic zone, as defined by concordant neuroimaging and SEEG data, resulted in seizure-free postoperative outcome. Histopathological findings revealed mild focal cortical dysplasia.
Great efforts should be made to combine most of the advanced neuroimaging methods in the preoperative assessment of non-lesional epilepsy surgery candidates.
Epileptic disorders: international epilepsy journal with videotape 10/2006; 8(3):190-4. · 0.95 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: In pharmacoresistant partial epilepsy (PRPE) in children, functional cerebral imaging helps localizing the epileptogenic zone using SPECT (Single Photon Emission Computed Tomography) and PET (Positron Emission Tomography) and the functional motor and language cortex using functional MRI. Regarding SPECT, only ictal SPECT exhibits an acceptable sensitivity (80 p. 100), together with interictal SPECT and subtraction image processing. Regarding PET, sensitivity has not been validated yet compared with intracranial EEG, neither using 18FDG, nor using more recent tracers such as 11C-flumazénil or 11C-alpha-méthyl-tryptophane. However, both techniques are useful to decide the placement of the intracranial electrodes, particularly in cryptogenic cases or when preoperative data are discordant. Functional MRI for language is going to be validated compared with WADA test and to provide a very useful and non invasive alternative method to lateralize the language networks in children able to cooperate. FMRI also provides a unique opportunity to follow the post-lesional or post-surgery plasticity of these networks using repeated examinations in a same patient. Functional imaging techniques therefore provide a useful additional contribution in the presurgery work-up of PRPE in children.
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