Usefulness of ictal and interictal 99mTc ethyl cysteinate dimer single photon emission computed tomography in patients with refractory partial epilepsy

Temporal Changes in Brain Perfusion in Neuronal Intranuclear Inclusion Disease

We herein report a patient with neuronal intranuclear inclusion disease (NIID) who presented with encephalitis-like episodes. A neurological examination revealed a disturbance of consciousness without any evidence of encephalitis or epilepsy on laboratory tests. Brain perfusion single-photon emission computed tomography revealed an elevated cerebral blood flow during the encephalitis-like episode and reduced cerebral blood flow in the chronic phase with clinical recovery. This report suggests that the cerebral blood flow of patients with NIID can change over the clinical course. Encephalitis-like episodes of NIID should thus be considered in the differential diagnosis of acute disturbance of consciousness.

Utility of SPECT Functional Neuroimaging of Pain

Functional neuroimaging modalities vary in spatial and temporal resolution. One major limitation of most functional neuroimaging modalities is that only neural activation taking place inside the scanner can be imaged. This limitation makes functional neuroimaging in many clinical scenarios extremely difficult or impossible. The most commonly used radiopharmaceutical in Single Photon Emission Tomography (SPECT) functional brain imaging is Technetium 99 m-labeled Ethyl Cysteinate Dimer (ECD). ECD is a lipophilic compound with unique pharmacodynamics. It crosses the blood brain barrier and has high first pass extraction by the neurons proportional to regional brain perfusion at the time of injection. It reaches peak activity in the brain 1 min after injection and is then slowly cleared from the brain following a biexponential mode. This allows for a practical imaging window of 1 or 2 h after injection. In other words, it freezes a snapshot of brain perfusion at the time of injection that is kept and can be imaged later. This unique feature allows for designing functional brain imaging studies that do not require the patient to be inside the scanner at the time of brain activation. Functional brain imaging during severe burn wound care is an example that has been extensively studied using this technique. Not only does SPECT allow for imaging of brain activity under extreme pain conditions in clinical settings, but it also allows for imaging of brain activity modulation in response to analgesic maneuvers whether pharmacologic or non-traditional such as using virtual reality analgesia. Together with its utility in extreme situations, SPECTS is also helpful in investigating brain activation under typical pain conditions such as experimental controlled pain and chronic pain syndromes.

Comparative analysis of MR imaging, Ictal SPECT and EEG in temporal lobe epilepsy: a prospective IAEA multi-center study

BACKGROUND AND PURPOSE

MR imaging, ictal single-photon emission CT (SPECT) and ictal EEG play important roles in the presurgical localization of epileptic foci. This multi-center study was established to investigate whether the complementary role of perfusion SPECT, MRI and EEG for presurgical localization of temporal lobe epilepsy could be confirmed in a prospective setting involving centers from India, Thailand, Italy and Argentina.

METHODS

We studied 74 patients who underwent interictal and ictal EEG, interictal and ictal SPECT and MRI before surgery of the temporal lobe. In all but three patients, histology was reported. The clinical outcome was assessed using Engel's classification. Sensitivity values of all imaging modalities were calculated, and the add-on value of SPECT was assessed.

RESULTS

Outcome (Engel's classification) in 74 patients was class I, 89%; class II, 7%; class III, 3%; and IV, 1%. Regarding the localization of seizure origin, sensitivity was 84% for ictal SPECT, 70% for ictal EEG, 86% for MRI, 55% for interictal SPECT and 40% for interictal EEG. Add-on value of ictal SPECT was shown by its ability to correctly localize 17/22 (77%) of the seizure foci missed by ictal EEG and 8/10 (80%) of the seizure foci not detected by MRI.

CONCLUSIONS

This prospective multi-center trial, involving centers from different parts of the world, confirms that ictal perfusion SPECT is an effective diagnostic modality for correctly identifying seizure origin in temporal lobe epilepsy, providing complementary information to ictal EEG and MRI.

Correct localization of epileptogenic focus with 1-123 iomazenil cerebral benzodiazepine receptor imaging: a case report of temporal lobe epilepsy with discordant ictal cerebral blood flow SPECT

A 26-year-old female with intractable epileptic seizures was studied with I-123 iomazenil cerebral benzodiazepine receptor, I-123 IMP inter-ictal and Tc-99m ECD ictal cerebral blood flow SPECT. The ictal cerebral blood flow SPECT indicated the location of the seizures to be in the left temporal lobe, where increased regional cerebral blood flow was noted in marked contrast to the inter-ictal SPECT. Ictal electroencephalograms (EEGs) recorded with scalp and sphenoidal electrodes also suggested the left temporal lobe as the location of the seizures. On I-123 iomazenil SPECT, however, decreased benzodiazepine receptor density was demonstrated in the right temporal lobe. MRI showed mild atrophy and abnormal signal intensity in the right temporal lobe. Ictal EEGs recorded with intracranial electrodes revealed that abnormal electrical activity of the brain always emerged from the right temporal lobe and then propagated to the contralateral side. Based on the findings of intracranial EEGs, partial resection of the right anterior temporal lobe including hippocampus was performed. After the surgery, no seizure occurred. Pathological examination of the surgical specimens revealed hippocampal sclerosis. This case suggested that cerebral benzodiazepine receptor imaging with I-123 iomazenil can be helpful for correct localization of epileptogenic foci.

Interictal patterns of cerebral glucose metabolism, perfusion, and magnetic field in mesial temporal lobe epilepsy

PURPOSE

To characterize the epileptogenic condition of patients with mesial temporal lobe epilepsy, the interictal patterns of glucose metabolism, perfusion, and magnetic field in the temporal lobe were evaluated by using [18F]fluorodeoxyglucose-positron emission tomography, [99mTc]-ethylcysteinate dimer-single photon emission computed tomography, and magnetoencephalography (MEG).

METHODS

Twenty-one patients with mesial temporal lobe epilepsy related to hippocampal sclerosis were studied. The ictal-onset area was located by continuous video-EEG monitoring. Quantitative analysis of glucose metabolism and perfusion in the temporal lobe was performed, and the cerebral magnetic field was evaluated to measure the equivalent current dipole (MEG-ECD).

RESULTS

Although hypometabolism and hypoperfusion in the temporal lobe were lateralized with the ictal-onset area in 16 (76.2%) and in 11 (52.4%) respectively, they were localized in diverse ways without any coupling. MEG-ECD was distributed in diverse ways unrelated to the ictal-onset area: ipsilateral medial temporal origin in five (23.8%), ipsilateral lateral temporal origin in two (9.5%), ipsilateral mixed (medial and lateral) temporal origin in six (28.6%), bilateral temporal origin in four (19.0%), and contralateral temporal origin in two (9.5%).

CONCLUSIONS

MEG-ECD was distributed in varied ways with the disorder and uncoupling of glucose metabolism and perfusion in the temporal lobe. These results may help resolve the clinical controversy over the possibility that the cortical irritative area generating the interictal epileptic discharge is distinct from the ictal-onset area, and also may have some functional implications in identifying different brain compartments in the generation of metabolic signals.

Superiority of HMPAO ictal SPECT to ECD ictal SPECT in localizing the epileptogenic zone

PURPOSE

We examined diagnostic performances of Tc-99m hexamethylpropylene amine oxime (HMPAO) and Tc-99m electron capture detection (ECD) ictal single-photon emission computed tomography (SPECT) to localize the epileptogenic zones in mesial temporal lobe epilepsy (TLE) and neocortical epilepsy (NE).

METHODS

Epileptogenic zones were identified by invasive EEG or surgical outcome. Ictal SPECT was performed with stabilized Tc-99m HMPAO (TLE, 17; NE, 23) and with Tc-99m ECD (TLE, 7; NE, 7). Single-blind visual interpretation was used to localize the epileptogenic zones. Asymmetric index was calculated. Subtraction ictal SPECT was coregistered to a magnetic resonance imaging (MRI) template.

RESULTS

In TLE, the sensitivity of Tc-99m HMPAO SPECT was 82% (14 of 17) and that of Tc-99m ECD SPECT was 71% (five of seven). The asymmetric index (AI; 25 +/- 10) of Tc-99m HMPAO SPECT was larger (p = 0.05) than the AI (13 +/- 13) of Tc-99m ECD SPECT in patients with TLE. In NE, the sensitivity of Tc-99m HMPAO SPECT was 70% (16 of 23), but that of Tc-99m ECD SPECT was 29% (two of seven). The AI (15 +/- 10) of Tc-99m HMPAO SPECT was significantly larger (p = 0.02) than the AI (4.8 +/- 6) of Tc-99m ECD SPECT in patients with NE. Subtraction ictal SPECT coregistered to MRI supported the visual assessment.

CONCLUSIONS

We concluded that the sensitivity of Tc-99m ECD ictal SPECT is similar to that of Tc-99m HMPAO ictal SPECT in TLE; however, ictal hyperperfusion was higher with the Tc-99m HMPAO SPECT. In patients with NE, Tc-99m HMPAO ictal SPECT also was superior to Tc-99m ECD ictal SPECT in sensitivity and degree of hyperperfusion.

Subtraction ictal SPECT coregistered to MRI for seizure focus localization in partial epilepsy

Peri-ictal single-photon emission computed tomography (SPECT) of the brain is increasingly used in localizing the seizure focus in presurgical evaluation of patients with partial epilepsy. However, traditional side-by-side visual interpretation of ictal and interictal SPECT films is hampered by differences in slice location and tracer activity. Precise correlation of the seizure focus with a high-quality image of the underlying brain anatomy can improve the physician's understanding of seizure neurophysiology and assist in surgical planning. Computer-based methods have been developed for aligning, normalizing, and subtracting digital ictal and interictal SPECT images of the patient's brain to produce a map of the blood flow changes occurring between the seizure and resting states. These maps are then aligned with a high-resolution magnetic resonance image (MRI) of the patient's brain anatomy and fused to identify anatomical regions involved in the seizure. The purpose of this article is to review the technical components and clinical implementation of subtraction ictal SPECT, as well as to discuss recent technological advances that could extend and improve the diagnostic and localizing capacity of this method.

Localization of the epileptogenic zone by ictal and interictal SPECT with 99mTc-ethyl cysteinate dimer in patients with medically refractory epilepsy

PURPOSE

To evaluate the accuracy, feasibility and clinical value of both ictal and interictal 99mTc-ethyl cysteinate dimer (ECD) single photon emission computed tomography (SPECT) in patients with medically refractory epilepsy.

METHODS

The study included 75 consecutive patients, 48 with temporal lobe epilepsy (TLE group), and 27 with extratemporal epilepsy (ExT group). The accuracy of SPECT was analyzed considering the final diagnosis reached by convergence of clinical, electrophysiologic, structural, pathologic and outcome data.

RESULTS

Ictal SPECT correctly identified the epileptogenic zone in 21 (91.3%) of 23 patients, whereas interictal SPECTs could correctly identify the epileptogenic zone in only 41 (62.1%) of 66 patients (chi2 = 5.56, df = 1, p < 0.05). Results were similar when the two study groups were analyzed separately. Moreover, ictal studies had significantly higher specificity (91.3 vs. 60.6%) and positive predictive value (91.3 vs. 66.2%) than interictal studies for the whole series of patients. Considering all tools used in the preoperative workup of these patients, ictal SPECT significantly contributed to the final topographic diagnosis in seven of 14 patients from TLE group and in six of nine patients from the ExT group. In these patients, ictal SPECT either obviated the need for invasive EEG or helped to define where to concentrate the efforts of invasive investigation.

CONCLUSIONS

These data demonstrate that ictal SPECT can be easily achieved by using 99mTc-ECD and can accurately localize the epileptogenic zone in both temporal and extratemporal epilepsies. Ictal ECD SPECT proved to be significantly more sensitive and specific than interictal ECD SPECT, and clinically useful in the definition of the epileptogenic zone.

Comparative study of 99mTc-ECD and 99mTc-HMPAO for peri-ictal SPECT: qualitative and quantitative analysis

OBJECTIVES

Most studies that clinically validated peri-ictal SPECT in intractable partial epilepsy had used technetium-99m-hexamethylpropylene amine oxime (99mTc-HMPAO or 99mTc-exametazime) as the radiopharmaceutical. Because of some theoretical advantages, technetium-99m-ethyl cysteinate diethylester (99mTc-ECD or 99mTc-bicisate) is increasingly being used instead. This study compares unstabilised 99Tc-HMPAO and 99mTc-ECD in the performance of peri-ictal SPECT in partial epilepsy.

METHODS

The injection timing and localisation rates in 49 consecutive patients with partial epilepsy who had peri-ictal injections with unstabilised 99mTc-HMPAO were compared with 49 consecutive patients who had peri-ictal injections with 99mTc-ECD. Quantitative cortical/subcortical and cortical/extracerebral uptake ratios were also compared. Subtraction SPECT coregistered to MRI (SISCOM) was performed in patients whose interictal SPECTS were available.

RESULTS

In the 99mTc-ECD patients, the latency from seizure commencement to injection was shorter (median 34 v 80 seconds, p<0.0001) and there was a lower rate of postictal injections (16.3% v 57.1%, p<0.0001). The cortical/extracerebral and cortical/subcortical uptake ratios were greater in the 99mTc-ECD images (median 5.0 v 3.6, and 2.5 v 2.2 respectively; both p<0.005), but the relative peri-ictal increase in uptake in the cortical focus did not differ significantly (median 37.0% v 37.0%; p>0.05). Blinded review of the SISCOM images were localising in a higher proportion of the 99mTc-ECD patients (40/45 (88.9%) v 25/37 (67.6%), p<0.05), and had a better concordance with EEG, MRI, and with the discharge diagnosis.

CONCLUSION

99mTc-ECD compares favourably with unstabilised 99mTc-HMPAO as a radiopharmaceutical for peri-ictal SPECT studies. Its use results in earlier injections and less frequent postictal injections than unstabilised 99mTc-HMPAO, thereby enhancing the sensitivity and the specificity of peri-ictal SPECT for the localisation of intractable partial epilepsy.

Neutral and stereospecific Tc-99m complexes: [99mTc]N-benzyl-3,4-di-(N-2-mercaptoethyl)-amino-pyrrolidines (P-BAT)

Technetium-99m-labeled radiopharmaceuticals are currently the most commonly used agents in nuclear medicine. To prepare binding site-specific small molecules containing a Tc-99m complexing core, it is important to consider a ligand system, which selectively forms only one stereoisomer. A novel series of bisaminoethanethiol (BAT) derivatives as a model system were prepared. Stereoisomers of N-benzyl-3,4-di(N-2-mercaptoethyl)-amino pyrrolidines (P-BAT): (3R,4R)-P-BAT (R,R-4) and (3,4)meso-P-BAT (8), the trans and meso isomer, respectively, as a chelating group were prepared successfully. The desired Tc-99m P-BAT complexes were obtained by using Sn(II)/glucoheptonate as the reducing agent for [99mTc]pertechnetate. As predicted, after complexation with [99mTc]Tc'O, the trans isomer, (3R,4R)-P-BAT (R,R-4), showed only one isomer; whereas the corresponding meso isomer, (3,4)meso-P-BAT (8), produced two distinctive complexes isolated readily by high performance liquid chromatography (HPLC). The [99mTc](R,S) meso-P-BAT (8) isomers showed a different lipophilicity (partition coefficient [P.C.] = 54.3 and 55.4 for peak A and peak B, respectively), as compared with that of the corresponding [99mTc](3R,4R)-P-BAT (R,R-4), trans isomer (P.C. = 163). Results of the biodistribution study in rats of these isomers show different heart and brain uptake, suggesting that the intrinsic differences in biodistribution are due to structural and stereospecific factors. Examples in this report confirm that it is possible to design stereospecific Tc-99m complexes based on the bisaminoethanethiol (N2S2, BAT) ligand system. Consideration on stereoselectivity of site-specific agents labeled with Tc-99m is likely an essential requirement on developing binding-site specific radiopharmaceuticals.

Emission tomography contribution to clinical neurology

The role of functional neuroimaging techniques in furthering the understanding of pathophysiological mechanisms of neurological diseases and in the assessment of neurological patients is increasingly important. Here, we review data mainly from emission tomography techniques, namely positron emission tomography (PET) and single photon emission computerized tomography (SPECT), that have helped elucidate the pathophysiology of a number of neurological diseases and have suggested strategies in the treatment of neurological patients. We also suggest possible future developments of functional neuroimaging applied to clinical populations and briefly touch on the emerging role of functional magnetic resonance imaging (fMRI) in clinical neurology and neurosurgery.

The current state of epilepsy surgery

Epilepsy surgery is an effective therapy for many patients with refractory partial seizures. The results of epilepsy surgery have improved with advances in the evaluation of patients for surgery and the care of patients during and after surgery. This review looks at recent innovations in imaging modalities to identify the candidates for surgery who will benefit most, to identify subtle pathology, to resect the epileptogenic focus more precisely, and to preserve functionally important cortex in order to achieve the best possible outcome. Patient selection and the identification and removal of the epileptogenic focus, in a safe manner, are crucial for good outcome.

Neuroimaging in the evaluation of children and adolescents with intractable epilepsy: II. Neuroimaging and pediatric epilepsy surgery

The costs of epilepsy encompass all aspects of life, including medical, educational, and psychosocial. Adults with intractable epilepsy who undergo epilepsy surgery and have seizure-free outcomes still have significant barriers in the attainment of improved quality of life. For this reason, there is increasing interest in the recognition of children and adolescents with intractable epilepsy who might be epilepsy surgery candidates. This is Part II of an article on the role of neuroimaging in the evaluation of children and adolescents with intractable epilepsy. Part I addressed the role of MRI in detecting the substrates of epilepsy (Pediatr Neurol 1997;17: 19-26); Part II elaborates on the selection process of pediatric patients who might benefit from epilepsy surgery. Although EEG remains the cornerstone of the evaluation process, MRI, SPECT, and PET can play a pivotal role in the identification of the underlying epileptogenic focus and minimize the need for invasive EEG monitoring. Magnetic resonance spectroscopy and magnetoencephalography are also innovative, noninvasive techniques which may aid in the localization of the epileptogenic focus. Functional MRI scans may soon replace invasive technologies in the identification of eloquent cortex that should not be a part of the surgical resection.