High-throughput, accurate Monte Carlo simulation on CPU hardware for PET applications.

Monte Carlo simulations (MCS) represent a fundamental approach to modelling the photon interactions in positron emission tomography (PET). A variety of PET-dedicated MCS tools are available to assist and improve PET imaging applications. Of these, GATE has evolved into one of the most popular software for PET MCS because of its accuracy and flexibility. However, simulations are extremely time-consuming. The use of graphics processing units (GPU) has been proposed as a solution to this, with reported acceleration factors about 400-800. These factors refer to GATE benchmarks performed on a single CPU core. Consequently, CPU-based MCS can also be easily accelerated by one order of magnitude or beyond when exploiting multi-threading on powerful CPUs. Thus, CPU-based implementations become competitive when further optimisations can be achieved. In this context, we have developed a novel, CPU-based software called the PET physics simulator (PPS), which combines several efficient methods to significantly boost the performance. PPS flexibly applies GEANT4 cross-sections as a pre-calculated database, thus obtaining results equivalent to GATE. This is demonstrated for an elaborated PET scanner with 3-layer block detectors. All code optimisations yield an acceleration factor of ≈20 (single core). Multi-threading on a high-end CPU workstation (96 cores) further accelerates the PPS by a factor of 80. This results in a total speed-up factor of ≈1600, which outperforms comparable GPU-based MCS by a factor of ≳2. Optionally, the proposed method of coincidence multiplexing can further enhance the throughput by an additional factor of ≈15. The combination of all optimisations corresponds to an acceleration factor of ≈24 000. In this way, the PPS can simulate complex PET detector systems with an effective throughput of 106photon pairs in less than 10 milliseconds.

Technical Note: GATE-RTion: a GATE/Geant4 release for clinical applications in scanned ion beam therapy.

PURPOSE: GATE-RTion is a validated version of GATE for clinical use in the field of light ion beam therapy. This paper describes the GATE-RTion project and illustrates its potential through clinical applications developed in three European centers delivering scanned proton and carbon ion treatments. METHODS: GATE-RTion is a collaborative framework provided by the OpenGATE collaboration. It contains a validated GATE release based on a specific Geant4 version, a set of tools to integrate GATE into a clinical environment and a network for clinical users. RESULTS: Three applications are presented: Proton radiography at the Centre Antoine Lacassagne (Nice, France); Independent dose calculation for proton therapy at the Christie NHS Foundation Trust (Manchester, UK); Independent dose calculation for protons and carbon ions at the MedAustron Ion Therapy center (Wiener Neustadt, Austria). CONCLUSIONS: GATE-RTion builds the bridge between researchers and clinical users from the OpenGATE collaboration in the field of Light Ion Beam Therapy. The applications presented in three European facilities using three completely different machines (three different vendors, cyclotron- and synchrotron-based systems, protons, and carbon ions) demonstrate the relevance and versatility of this project.

High performance volume-of-intersection projectors for 3D-PET image reconstruction based on polar symmetries and SIMD vectorisation.

For high-resolution, iterative 3D PET image reconstruction the efficient implementation of forward-backward projectors is essential to minimise the calculation time. Mathematically, the projectors are summarised as a system response matrix (SRM) whose elements define the contribution of image voxels to lines-of-response (LORs). In fact, the SRM easily comprises billions of non-zero matrix elements to evaluate the tremendous number of LORs as provided by state-of-the-art PET scanners. Hence, the performance of iterative algorithms, e.g. maximum-likelihood-expectation-maximisation (MLEM), suffers from severe computational problems due to the intensive memory access and huge number of floating point operations. Here, symmetries occupy a key role in terms of efficient implementation. They reduce the amount of independent SRM elements, thus allowing for a significant matrix compression according to the number of exploitable symmetries. With our previous work, the PET REconstruction Software TOolkit (PRESTO), very high compression factors (>300) are demonstrated by using specific non-Cartesian voxel patterns involving discrete polar symmetries. In this way, a pre-calculated memory-resident SRM using complex volume-of-intersection calculations can be achieved. However, our original ray-driven implementation suffers from addressing voxels, projection data and SRM elements in disfavoured memory access patterns. As a consequence, a rather limited numerical throughput is observed due to the massive waste of memory bandwidth and inefficient usage of cache respectively. In this work, an advantageous symmetry-driven evaluation of the forward-backward projectors is proposed to overcome these inefficiencies. The polar symmetries applied in PRESTO suggest a novel organisation of image data and LOR projection data in memory to enable an efficient single instruction multiple data vectorisation, i.e. simultaneous use of any SRM element for symmetric LORs. In addition, the calculation time is further reduced by using simultaneous multi-threading (SMT). A global speedup factor of 11 without SMT and above 100 with SMT has been achieved for the improved CPU-based implementation while obtaining equivalent numerical results.

Integration of FDG-PET/CT into external beam radiation therapy planning: technical aspects and recommendations on methodological approaches.

UNLABELLED: This work addresses the clinical adoption of FDG-PET/CT for image-guided radiation therapy planning (RTP). As such, important technical and methodological aspects of PET/CT-based RTP are reviewed and practical recommendations are given for routine patient management and clinical studies. First, recent developments in PET/CT hardware that are relevant to RTP are reviewed in the context of quality control and system calibration procedures that are mandatory for a reproducible adoption of PET/CT in RTP. Second, recommendations are provided on image acquisition and reconstruction to support the standardization of imaging protocols. A major prerequisite for routine RTP is a complete and secure data transfer to the actual planning system. Third, state-of-the-art tools for image fusion and co-registration are discussed briefly in the context of PET/CT imaging pre- and post-RTP. This includes a brief review of state-of-the-art image contouring algorithms relevant to PET/CT-guided RTP. Finally, practical aspects of clinical workflow and patient management, such as patient setup and requirements for staff training are emphasized. PET/CT-guided RTP mandates attention to logistical aspects, patient set-up and acquisition parameters as well as an in-depth appreciation of quality control and protocol standardization. CONCLUSION: Upon fulfilling the requirements to perform PET/CT for RTP, a new dimension of molecular imaging can be added to traditional morphological imaging. As a consequence, PET/CT imaging will support improved RTP and better patient care. This document serves as a guidance on practical and clinically validated instructions that are deemed useful to the staff involved in PET/CT-guided RTP.

GATE V6: a major enhancement of the GATE simulation platform enabling modelling of CT and radiotherapy.

GATE (Geant4 Application for Emission Tomography) is a Monte Carlo simulation platform developed by the OpenGATE collaboration since 2001 and first publicly released in 2004. Dedicated to the modelling of planar scintigraphy, single photon emission computed tomography (SPECT) and positron emission tomography (PET) acquisitions, this platform is widely used to assist PET and SPECT research. A recent extension of this platform, released by the OpenGATE collaboration as GATE V6, now also enables modelling of x-ray computed tomography and radiation therapy experiments. This paper presents an overview of the main additions and improvements implemented in GATE since the publication of the initial GATE paper (Jan et al 2004 Phys. Med. Biol. 49 4543-61). This includes new models available in GATE to simulate optical and hadronic processes, novelties in modelling tracer, organ or detector motion, new options for speeding up GATE simulations, examples illustrating the use of GATE V6 in radiotherapy applications and CT simulations, and preliminary results regarding the validation of GATE V6 for radiation therapy applications. Upon completion of extensive validation studies, GATE is expected to become a valuable tool for simulations involving both radiotherapy and imaging.

Multi-modality imaging of uveal melanomas using combined PET/CT, high-resolution PET and MR imaging.

UNLABELLED: We investigated the efficacy of combined FDG-PET/CT imaging for the diagnosis of small-size uveal melanomas and the feasibility of combining separate, high-resolution (HR) FDG-PET with MRI for its improved localization and detection. PATIENTS, METHODS: 3 patients with small-size uveal melanomas (0.2-1.5 ml) were imaged on a combined whole-body PET/CT, a HR brain-PET, and a 1.5 T MRI. Static, contrast-enhanced FDG-PET/CT imaging was performed of head and torso with CT contrast enhancement. HR PET imaging was performed in dynamic mode 0-180 min post-injection of FDG. MRI imaging was performed using a high-resolution small-loop-coil placed over the eye in question with T2-3D-TSE and T1-3D-SE with 18 ml Gd-contrast. Patients had their eyes shaded during the scans. Lesion visibility on high-resolution FDG-PET images was graded for confidence: 1: none, 2: suggestive, 3: clear. Mean tumour activity was calculated for summed image frames that resulted in confidence grades 2 and 3. Whole-body FDG-PET/CT images were reviewed for lesions. PET-MRI and PET/CT-MRI images of the head were co-registered for potentially improved lesion delineation. RESULTS: Whole-body FDG-PET/CT images of 3/3 patients were positive for uveal melanomas and negative for disseminated disease. HR FDG-PET was positive already in the early time frames. One patient exhibited rising tumour activity with increasing uptake time on FDG-PET. MRI images of the eye were co-registered successfully to FDG-PET/CT using a manual alignment approach. CONCLUSIONS: Small-size uveal melanomas can be detected with whole-body FDG-PET/CT. This feasibility study suggests the exploration of HR FDG-PET in order to provide additional diagnostic information on patients with uveal melanomas. First results support extended uptake times and high-sensitivity PET for improved tumour visibility. MRI/PET co-registration is feasible and provides correlated functional and anatomical information that may support alternative therapy regimens.

Linking retinotopic fMRI mapping and anatomical probability maps of human occipital areas V1 and V2.

Using functional MRI, we characterized field sign maps of the occipital cortex and created three-dimensional maps of these areas. By averaging the individual maps into group maps, probability maps of functionally defined V1 or V2 were determined and compared to anatomical probability maps of Brodmann areas BA17 and BA18 derived from cytoarchitectonic analysis (Amunts, K., Malikovic, A., Mohlberg, H., Schormann, T., Zilles, K., 2000. Brodmann's areas 17 and 18 brought into stereotaxic space-where and how variable? NeuroImage 11, 66-84). Comparison of areas BA17/V1 and BA18/V2 revealed good agreement of the anatomical and functional probability maps. Taking into account that our functional stimulation (due to constraints of the visual angle of stimulation achievable in the MR scanner) only identified parts of V1 and V2, for statistical evaluation of the spatial correlation of V1 and BA17, or V2 and BA18, respectively, the a priori measure kappa was calculated testing the hypothesis that a region can only be part of functionally defined V1 or V2 if it is also in anatomically defined BA17 or BA18, respectively. kappa = 1 means the hypothesis is fully true, kappa = 0 means functionally and anatomically defined visual areas are independent. When applying this measure to the probability maps, kappa was equal to 0.84 for both V1/BA17 and V2/BA18. The data thus show a good correspondence of functionally and anatomically derived segregations of early visual processing areas and serve as a basis for employing anatomical probability maps of V1 and V2 in group analyses to characterize functional activations of early visual processing areas.

Does PET/CT render software registration obsolete?

It was the success of software-based image registration that eventually led to the introduction of hardware-based concepts for image fusion, such as combined PET/CT tomographs. A prototype PET/CT was first presented in 1998, with various commercial designs to follow since 2000. PET/ CT is used primarily as a diagnostic modality in the field of extra-cerebral oncology imaging. The major advantage of combined imaging over retrospective software registration is the nearly identical position of the patient during both complementary examination, and therefore tomograms of identical parts of the body can be provided in spatially-corresponding slices. Despite the availability of hardware combinations of complementary imaging modalities software-based image registration, however, still inherits a major role in subsequent data processing, in particular when individual imaging modalities other than combined PET/CT are being used during patient workup. Furthermore, software is likely to become an important tool for the correction of residual motion-induced mis-registration within combined PET/CT data sets, and for follow-up studies involving, for example, CT, PET, and PET/CT. Therefore, flexible algorithms that utilize non-linear interpolation schemes implemented on fast computer systems are needed, and will continue to contribute to successful image registration and fusion in clinical practice.

GATE: a simulation toolkit for PET and SPECT.

Monte Carlo simulation is an essential tool in emission tomography that can assist in the design of new medical imaging devices, the optimization of acquisition protocols and the development or assessment of image reconstruction algorithms and correction techniques. GATE, the Geant4 Application for Tomographic Emission, encapsulates the Geant4 libraries to achieve a modular, versatile, scripted simulation toolkit adapted to the field of nuclear medicine. In particular, GATE allows the description of time-dependent phenomena such as source or detector movement, and source decay kinetics. This feature makes it possible to simulate time curves under realistic acquisition conditions and to test dynamic reconstruction algorithms. This paper gives a detailed description of the design and development of GATE by the OpenGATE collaboration, whose continuing objective is to improve, document and validate GATE by simulating commercially available imaging systems for PET and SPECT. Large effort is also invested in the ability and the flexibility to model novel detection systems or systems still under design. A public release of GATE licensed under the GNU Lesser General Public License can be downloaded at http:/www-lphe.epfl.ch/GATE/. Two benchmarks developed for PET and SPECT to test the installation of GATE and to serve as a tutorial for the users are presented. Extensive validation of the GATE simulation platform has been started, comparing simulations and measurements on commercially available acquisition systems. References to those results are listed. The future prospects towards the gridification of GATE and its extension to other domains such as dosimetry are also discussed.

A functional magnetic resonance imaging study of local/global processing with stimulus presentation in the peripheral visual hemifields.

When stimuli are presented in the left or right visual fields, hemispheric specialization for global and local processing in occipital areas is attenuated. Using functional magnetic resonance imaging, we investigated how this attenuation is compensated for when information must cross the corpus callosum to reach the areas specialized for global and local processing. We presented hierarchically nested letters (e.g. a large E made of smaller E's) to the right or the left visual hemifield while subjects fixated centrally. In half the trials, subjects indicated whether the global aspect and in the other half whether the local aspect of the stimulus matched a pre-specified target letter. Visual hemifield presentations showed the expected contralateral activations of occipital cortex. The main effects of locally or globally directed attention did not show any differential occipital activations, but the right anterior cingulate cortex was activated differentially during local processing. Region-of-interest-based analyses showed increased neural activity in left posterior occipital cortex during local processing when stimuli were presented in the left hemifield. During global processing with stimulus presentation to the right hemifield, the right posterior occipital cortex was activated. Activation of right anterior cingulate cortex during local processing is likely to reflect the suppression of global processing precedence in order to select correctly the local stimulus level. The activations in left (local) and right (global) occipital areas are likely to reflect the top-down augmentation of stimulus information that has been degraded by callosal crossing in order to access the hemisphere specialized for local or global processing.

Clinical and diagnostic value of preoperative MR mammography and FDG-PET in suspicious breast lesions.

Dynamic enhanced magnetic resonance (MR) mammography and fluorine-18 fluorodeoxyglucose positron emission tomography (FDG-PET) of the breast were directly compared preoperatively in suspicious breast lesions. Forty-two breast lesions in 40 patients were examined with a three-dimensional dynamic MR imaging series and FDG-PET. The MR and PET examinations were evaluated separately and the results were compared with the histological findings. The sensitivity and specificity of each method were calculated. The diagnostic value of both modalities as single diagnostic tool and in combination was investigated. Nineteen malignant and 23 benign breast lesions were proven histologically. Magnetic resonance mammography and FDG-PET showed a sensitivity of 89 and 63%, respectively. The specificity was 74 and 91%, respectively. The combination of both imaging methods decreased the not-required biopsies from 55 to 17%. Only one false-negative finding-a patient pre-treated with chemotherapy-was observed in both methods. The combination of MR mammography and FDG-PET can help to decrease biopsies of benign breast lesions. Because of their high cost, these modalities should only be used in problematic cases to either rule out or to demonstrate malignancy. The best diagnostic strategy is achieved using MR mammography first. If the diagnosis is still questionable, FDG-PET can be performed.

Relation between 1H MR spectroscopic imaging and regional cerebral glucose metabolism in Alzheimer's disease.

1 H Magnetic resonance spectroscopic imaging (MRSI) and positron emission tomography (PET) of (18) F-2-fluoro-2-deoxy-D-glucose (FDG) were performed in 18 patients with probable Alzheimer's disease (AD) and 3 normal controls. We measured the distribution and relative signal intensities of N-acetyl aspartate (NAA; a presumed neuronal marker), choline residues (Cho) representing cellular membrane compounds and of creatine-containing metabolites (Cr), and correlated these to regional cerebral glucose metabolism (rCMRGI) after coregistration of both imaging-techniques. The pattern of choline was significantly different between AD and normals (p < 0.01). RCMRGI was significantly related to Cho/Cr (r=-0.21, p<.05) and NAA/Cho quotients (r=0.35, p<.001). Our results suggest that in AD reduced neuronal energy performance and membrane abnormalities contribute to metabolic deterioration.

Estimation of regional cerebral blood flow levels in ischemia using [(15)O]water of [(11)C]flumazenil PET without arterial input function .

Determination of residual flow within the ischemic brain may be important in patients eligible for thrombolytic therapy. Conventional cerebral blood flow (CBF) quantification often cannot be achieved in these cases because arterial blood sampling required for the input function is prohibited. Quantitative CBF was measured in 20 patients with ischemic stroke using [(15)O]water and [(11)C]flumazenil PET with arterial blood sampling and compared with normalized nonquantified data of the same patients. For both comparisons, percentiles were derived, allowing the determination of a normalized blood flow level corresponding to an absolute CBF value below which 95% of all pixels are located. These normograms can be used to derive absolute CBF levels in milliliters per 100 g per minute from normalized data without the need for measuring an arterial input function.

Interictal hippocampal benzodiazepine receptors in temporal lobe epilepsy: comparison with coregistered hippocampal metabolism and volumetry.

The significance of benzodiazepine receptor (BZR) concentration in comparison with hippocampal metabolism and volumetry was assessed in 14 patients diagnosed with temporal lobe epilepsy (TLE) without hippocampal signal change on T2-weighted magnetic resonance imaging (MRI) scans. Focus lateralization was achieved by clinical, electroencephalographic and neuropsychological examinations. Three-dimensional positron emission tomography (PET) and MRI scans were coregistered for determination of hippocampal 11C-flumazenil (FMZ) binding, normalized to average cortical values for glucose metabolism (rCMRglc) and volume. The hippocampi were individually outlined on T1-weighted MRI. Volumes of interest (VOI) were used for calculation of asymmetries between clinically affected and unaffected sides. Eleven out of 14 TLE patients presented a significant reduction in hippocampal volume. In nine of these 11 patients hippocampal FMZ binding and in seven cases hippocampal CMRglc was also reduced. In two patients without hippocampal volume asymmetry FMZ binding was markedly reduced in the mesial temporal lobe appropriately to the clinically diagnosed side. In our study volumetry is therefore the most sensitive tool for the detection of hippocampal abnormality in TLE. However, in cases without hippocampal atrophy the reduction of FMZ may indicate functional impairment of BZR before neuronal loss becomes evident. Our results emphasize the complementary nature of these tests in TLE patients.

2[F]-fluoro-2-deoxy-D-glucose positron emission tomography is a sensitive tool for the detection of occult primary cancer (carcinoma of unknown primary syndrome) with head and neck lymph node manifestation.

BACKGROUND: The neck lymph nodes are a common site of metastases from carcinoma of unknown primary (CUP syndrome). 2[(18) F]-fluoro-2-deoxy-D-glucose positron emission tomography (18-FDG-PET) has been shown to be a sensitive tool for detecting primary malignant lesions as well as metastatic spread. We have prospectively investigated the sensitivity of 18-FDG-PET in detecting occult primary carcinomas with manifestation in the head and neck lymph nodes. METHODS: From May 1994 to July 1998, in 723 patients a cancer of the head and neck was diagnosed at the University of Cologne ENT outpatient clinic. The routinely performed staging procedures were chest radiography; full blood count; cervical and liver ultrasound; endoscopy of the nasopharynx, oropharynx, hypopharynx, larynx, and esophagus; and laboratory analyses. After the staging workup, in 27 of 723 patients (3.7%) CUP syndrome had to be presumed because the primary cancer could not be detected. In these patients 18-FDG-PET was performed, and images were reconstructed with a transmission-emission fusion technique. RESULTS: In 7 of 27 patients (26%) 18-FDG-PET revealed an unknown primary: in 2 a bronchial carcinoma, in 2 a nasopharyngeal carcinoma, in 1 a squamous cell carcinoma of the parotid gland, in 1 a squamous cell carcinoma of the hypopharynx, and in 1 a carcinoma of the tonsil. In 4 of 7 patients the occult primary tumor was removed surgically. In 8 of 27 patients therapeutic strategy was changed as a result of the 18-FDG-PET findings. CONCLUSION: 18-FDG-PET should be performed in all patients with CUP syndrome after conventional diagnostic workup fails to identify the primary.

Enhanced accuracy in differential diagnosis of radiation necrosis by positron emission tomography-magnetic resonance imaging coregistration: technical case report.

OBJECTIVE AND IMPORTANCE: To demonstrate the usefulness of positron emission tomography-magnetic resonance imaging (MRI) coregistration for differentiation of radiation necrosis and recurrent tumor in stereotactic planning. CLINICAL PRESENTATION: T1-weighted MRI scans of a 43-year-old woman revealed a contrast-enhancing lesion 4 years after open removal of a recurrent, right parieto-occipital Grade II oligodendroglioma and subsequent external radiation therapy. The suspected contrast-enhancing lesion revealed only moderate tracer uptake (1.3 times the uptake in the contralateral normal cortex) in a coregistered [11C]methionine positron emission tomographic scan. Approximately 15 mm posterior and mesial to the center of the contrast-enhancing lesion, however, an area of higher tracer uptake was found (1.8 times that of the contralateral normal cortex), which exhibited only very minor contrast enhancement on MRI. TECHNIQUE: The coregistered images were used for planning stereotactic serial biopsies, from the contrast-enhancing lesion as well as from the area with higher methionine uptake. Histological examination demonstrated that the contrast-enhancing lesion with low methionine uptake was necrotic tissue, and the nonenhancing area with high methionine uptake was recurrent tumor. CONCLUSION: High-resolution positron emission tomography and modern coregistration techniques allow differentiation of contrast enhancement and methionine uptake in irradiated brain tissue within small areas. High methionine uptake is typical for recurrent tumor tissue and can be differentiated from minor tracer accumulation resulting from disruption of the blood-brain barrier or macrophage activity within the necrotic area.

[Changes in regional cerebral perfusion in depression.SPECT monitoring of response to treatment]. / Regionale Funktionsstörung bei der Depression. Hirn-SPECT zur Verlaufskontrolle.

The objective of this study was to investigate the relationship between the effect of sleep deprivation, recovery and regional brain perfusion in patients with major depression. Regional cerebral blood flow was assessed by 99mTc-HMPAO-SPECT before and after sleep deprivation in fourteen medicated patients. Three of the patients underwent a follow-up measurement after clinical recovery and with an unchanged antidepressant medication. Before sleep deprivation the responding patients had a significantly higher anterior cingulate perfusion than the nonresponding patients, that normalized after sleep deprivation. Cingulate perfusion uniquely differentiated eventual treatment response from non-responders, as perfusion in no other region under study discriminated the two groups. At baseline all patients revealed hypoperfusion in the left prefrontal cortex when compared to the right side, which was not affected by sleep deprivation, whereas prefrontal hypoperfusion was reversible upon remission. These findings are in agreement with previous PET investigations and provide evidence for cingulate and prefrontal dysfunction associated with depression, that are reversible by successful treatment and may represent state markers.

Regional cerebral blood flow during temporal lobe seizures associated with ictal vomiting: an ictal SPECT study in two patients.

PURPOSE: Ictal vomiting represents a rare clinical manifestation during seizures originating from the temporal lobes of the nondominant hemisphere. The precise anatomic structures responsible for generation of ictal vomiting remain to be clarified. Ictal single photon emission computed tomography (SPECT), which allows one to visualize the three-dimensional dynamic changes of regional cerebral blood flow (rCBF) associated with the ongoing epileptic activity, should be useful to study the brain areas activated during ictal vomiting. METHODS: We performed ictal Tc-HMPAO SPECT scans in two patients with mesial temporal lobe epilepsy (MTLE) whose seizures were characterized by ictal retching and vomiting. MTLE was documented by typical clinical seizure semiology, interictal and ictal EEG findings, hippocampal atrophy on magnetic resonance imaging (MRI) scan, and a seizure-free outcome after selective amydalohippocampectomy. In both patients, seizures originated in the nondominant temporal lobe. We obtained accurate anatomic reference of rCBF changes visible on SPECT by a special coregistration technique of MRI and SPECT. We used ictal SPECT studies in 10 patients with MTLE who had seizures without ictal vomiting as controls. RESULTS: In the two patients with ictal vomiting, we found a significant hyperperfusion of the nondominant temporal lobe (inferior, medial, and lateral superior) and of the occipital region on ictal SPECT. In patients without ictal vomiting, on the contrary, these brain regions never were hyperperfused simultaneously. CONCLUSIONS: Ictal SPECT provides further evidence that activation of a complex cortical network, including the medial and lateral superior aspects of the temporal lobe, and maybe the occipital lobes, is responsible for the generation of ictal vomiting.

Preictal SPECT in temporal lobe epilepsy: regional cerebral blood flow is increased prior to electroencephalography-seizure onset.

UNLABELLED: Peri-ictal SPECT provides unique information on the dynamic changes in regional cerebral blood flow (rCBF) that occur during seizure evolution and, thus, could be useful in clarifying the poorly understood interplay of the interictal and ictal states in human focal epilepsy. The regional hyperperfusion observed on ictal SPECT is generally believed to be a consequence of electrical seizure activity. However, recent studies using invasive long-term cortical CBF monitoring have demonstrated that rCBF changes occur up to 20 min prior to ictal electroencephalography (EEG) onset. Because of apparent technical difficulties, no preictal SPECT studies have been reported so far. Therefore, we present our results on two patients with temporal lobe epilepsy in whom preictal SPECT scans were performed fortuitously under continuous video-EEG monitoring control. METHODS: Technetium-99m-hexamethyl propyleneamine oxime was injected 11 min (Patient 1) and 12 min (Patient 2) before clinical and EEG seizure onset, as documented from simultaneous video-EEG monitoring in two patients with temporal lobe epilepsy. We obtained accurate anatomical reference of CBF changes visible on SPECT by a special coregistration technique of MRI and SPECT. RESULTS: Whereas interictal SPECT showed a hypoperfusion of the temporal lobe ipsilateral to the seizure focus, on preictal SPECT, a significant increase in rCBF in the epileptic temporal lobe could be observed. These rCBF changes were not accompanied by any significant changes of the ongoing EEG. CONCLUSION: Our study provides evidence that rCBF is increased in the epileptic temporal lobe several minutes before EEG seizure onset. Thus, rCBF changes observed on peri-ictal SPECT scan cannot be considered a mere consequence of EEG seizure activity but may rather reflect a change in neuronal activity precipitating the transition from the interictal to the ictal state.