Effect of injection time on postictal SPET perfusion changes in medically refractory epilepsy

Single-photon emission tomography (SPET) brain imaging in epilepsy has become an increasingly important noninvasive tool in localizing the epileptogenic site. Ictal SPET demonstrates the highest localization sensitivity as compared with postictal and interictal SPET. While ictal SPET consistently reveals hyperperfusion at the epileptogenic site, postictal SPET reveals either hyper- or hypoperfusion depending on the timing of radiopharmaceutical injection. Much discussion in the literature exists about exactly when the transition from hyper- to hypoperfusion occurs at the epileptogenic site in postictal SPET. The systematic examination of two clinical variables – time of injection from seizure onset and offset – was useful in understanding postictal perfusion changes. Twenty-seven patients with medically refractory epilepsy receiving postictal and interictal SPET scans were studied. Quantitative SPET difference imaging was used to evaluate perfusion changes in relationship to injection time. Perfusion changes were found to reflect the time of injection in relation to seizure onset, but to be somewhat independent of seizure offset. Thus, the majority of patients (8/12, 67%) receiving postictal injections within 100 s after seizure onset demonstrated hyperperfusion, while all patients (15/15, 100%) receiving postictal injections more than 100 s after seizure onset showed hypoperfusion. The explanation of this phenomenon is unknown but the findings appear to parallel known changes in cerebral lactate levels. Received 8 March and in revised form 22 April 1999     

Effect of injection time on postictal SPET perfusion changes in medically refractory epilepsy.

Single-photon emission tomography (SPET) brain imaging in epilepsy has become an increasingly important noninvasive tool in localizing the epileptogenic site. Ictal SPET demonstrates the highest localization sensitivity as compared with postictal and interictal SPET. While ictal SPET consistently reveals hyperperfusion at the epileptogenic site, postictal SPET reveals either hyper- or hypoperfusion depending on the timing of radiopharmaceutical injection. Much discussion in the literature exists about exactly when the transition from hyper- to hypoperfusion occurs at the epileptogenic site in postictal SPET. The systematic examination of two clinical variables - time of injection from seizure onset and offset - was useful in understanding postictal perfusion changes. Twenty-seven patients with medically refractory epilepsy receiving postictal and interictal SPET scans were studied. Quantitative SPET difference imaging was used to evaluate perfusion changes in relationship to injection time. Perfusion changes were found to reflect the time of injection in relation to seizure onset, but to be somewhat independent of seizure offset. Thus, the majority of patients (8/12, 67%) receiving postictal injections within 100 s after seizure onset demonstrated hyperperfusion, while all patients (15/15, 100%) receiving postictal injections more than 100 s after seizure onset showed hypoperfusion. The explanation of this phenomenon is unknown but the findings appear to parallel known changes in cerebral lactate levels.     

Reproducibility of serial peri-ictal single-photon emission tomography difference images in epilepsy patients undergoing surgical resection

Peri-ictal single-photon emission tomography (SPET) difference images co-registered to magnetic resonance imaging (MRI) visualize regional cerebral blood flow (rCBF) changes and help localize the epileptogenic area in medically refractory epilepsy. Few reports have examined the reproducibility of SPET difference image results. Epilepsy patients having two peri-ictal and at least one interictal SPET scan who later underwent surgical resection were studied. Localization accuracy of peri-ictal SPET difference images results, interictal electroencephalography (EEG), and ictal EEG from the first (seizure 1) and second (seizure 2) seizure, as well as MRI and positron emission tomography (PET) findings, were compared using surgical resection site as the standard. Thirteen patients underwent surgical resection (11 temporal lobe and 2 extratemporal). SPET results from seizure 1 were localized to the surgical site in 12/13 (92%) patients, while SPET results from seizure 2 were localized in 13/13 (100%) patients. All other modalities were less accurate than the SPET results interictal EEG--seizure 1 6/13 (46%); ictal EEG--seizure 1 5/13 (38%); interictal intracranial EEG--seizure 2 4/9 (44%); ictal intracranial EEG--seizure 2 results 8/9 (89%); MRI 6/13 (46%); PET 9/13 (69%)[. SPET results were reproducible in 12/13 (92%) patients. SPET difference images calculated from two independent peri-ictal scans appear to be reproducible and accurately localize the epileptogenic area. While SPET difference images visualize many areas of rCBF change, the quantification of these results along with consideration of injection time improves the diagnostic interpretation of the results.     

Reproducibility of serial peri-ictal single-photon emission tomography difference images in epilepsy patients undergoing surgical resection

Peri-ictal single-photon emission tomography (SPET) difference images co-registered to magnetic resonance imaging (MRI) visualize regional cerebral blood flow (rCBF) changes and help localize the epileptogenic area in medically refractory epilepsy. Few reports have examined the reproducibility of SPET difference image results. Epilepsy patients having two peri-ictal and at least one interictal SPET scan who later underwent surgical resection were studied. Localization accuracy of peri-ictal SPET difference images results, interictal electroencephalography (EEG), and ictal EEG from the first (seizure 1) and second (seizure 2) seizure, as well as MRI and positron emission tomography (PET) findings, were compared using surgical resection site as the standard. Thirteen patients underwent surgical resection (11 temporal lobe and 2 extratemporal). SPET results from seizure 1 were localized to the surgical site in 12/13 (92%) patients, while SPET results from seizure 2 were localized in 13/13 (100%) patients. All other modalities were less accurate than the SPET results [interictal EEG – seizure 1 6/13 (46%); ictal EEG – seizure 1 5/13 (38%); interictal intracranial EEG – seizure 2 4/9 (44%); ictal intracranial EEG – seizure 2 results 8/9 (89%); MRI 6/13 (46%); PET 9/13 (69%)].SPET results were reproducible in 12/13 (92%) patients.SPET difference images calculated from two independent peri-ictal scans appear to be reproducible and accurately localize the epileptogenic area. While SPET difference images visualize many areas of rCBF change, the quantification of these results along with consideration of injection time improves the diagnostic interpretation of the results. Received 17 July and in revised form 27 September 1999     

Sensitivity and specificity of quantitative difference SPECT analysis in seizure localization.

True ictal SPECT can accurately demonstrate perfusion increases in the epileptogenic area but often requires dedicated personnel waiting at the bedside to accomplish the injection. We investigated the value of perfusion changes as measured by ictal or immediate postictal SPECT in localizing the epileptogenic region in refractory partial epilepsy. METHODS: Quantitative perfusion difference images were calculated by registering, normalizing and subtracting ictal (or immediate postictal) from interictal SPECT for 53 patients with refractory epilepsy. Perfusion difference SPECT results were compared with visually interpreted SPECT, scalp electroencephalography (EEG), MRI, PET and intracranial EEG. RESULTS: In 43 patients (81%), discrete areas of increased perfusion (with ictal injections) or decreased perfusion (with postictal injections) were noted. Interictal scalp EEG was localizing in 28 patients (53%), ictal scalp EEG was localizing in 35 patients (66%) and intracranial EEG was localizing in 22 patients (85%) (of 26 patients who underwent invasive study). MRI was localizing in 34 patients (64%), PET was localizing in 32 of 45 patients (71%), interictal SPECT was localizing in 26 patients (49%) and peri-ictal SPECT (visual interpretation) was localizing in 30 patients (57%). By comparison with an intracranial EEG standard of localization, SPECT subtraction analysis had 86% sensitivity and 75% specificity. CONCLUSION: Our data provide evidence that SPECT perfusion difference analysis has higher sensitivity and specificity than any other noninvasive localizing criterion and can localize epileptogenic regions with accuracy comparable with that of intracranial EEG. To obtain these results, one must apply knowledge of the timing of the ictal injection relative to seizure occurrence.     

Ictal brain SPET during seizures pharmacologically provoked with pentylenetetrazol: a new diagnostic procedure in drug-resistant epileptic patients

Functional brain imaging plays an important role in seizure focus localisation. However, truly ictal single-photon emission tomography (SPET) studies are not routinely performed owing to technical problems associated with the use of tracers and methodological and logistical difficulties. In this study we tried to resolve both of these issues by means of a new procedure: technetium-99m ethyl cysteinate dimer (ECD) brain SPET performed during seizures pharmacologically provoked with pentylenetetrazol, a well-known central and respiratory stimulant. We studied 33 drug-resistant epileptic patients. All patients underwent anamnestic evaluation, neuropsychological and psychodynamic assessment, magnetic resonance imaging, interictal and ictal video-EEG monitoring, and interictal and ictal SPET with (99m)Tc-ECD. In order to obtain truly ictal SPET, 65 mg of pentylenetetrazol was injected every 2 minutes and, immediately the seizure began, 740 MBq of (99m)Tc-ECD was injected. The scintigraphic findings were considered abnormal if a single area of hyperperfusion was present and corresponded to the site of a single area of hypoperfusion at interictal SPET: the "hypo-hyperperfusion" SPET pattern. In 27 of the 33 patients (82%), interictal-ictal SPET showed the hypo-hyperperfusion SPET pattern. Video-EEG showed a single epileptogenic zone in 21/33 patients (64%), and MRI showed anatomical lesions in 19/33 patients (57%). Twenty-two of the 27 patients with hypo-hyperperfusion SPET pattern underwent ablative or palliative surgery and were seizure-free at 3 years of follow-up. No adverse effects were noted during pharmacologically provoked seizure. It is concluded that ictal brain SPET performed during pharmacologically provoked seizure provides truly ictal images because (99m)Tc-ECD is injected immediately upon seizure onset. Using this feasible procedure it is possible to localise the focus, to avoid the limitations due to the unpredictability of seizures, to avoid pitfalls due to late injection, to avoid intracranial EEG recording and to minimise costs. The clinical value of our method is confirmed by the good outcome after 3 years of follow-up in those patients submitted to ablative or palliative surgery.     

Does technetium-99m bicisate image local brain metabolism in late ictal temporal lobe epilepsy?

Ictal increase in regional cerebral blood flow as judged by single-photon emission tomography (SPET) is a common phenomenon during focal epileptic seizures. Up to 2 min postictally, regional hyperperfusion is a consistent finding with technetium-99m hexamethylpropylene amine oxime (HMPAO) in temporal lobe epilepsy. A new ^99mTc-labelled lipophilic cerebral blood flow imaging agent, bicisate, has considerably longer radiochemical stability and yields better image quality than ^99mTc-HMPAO. In this report, we present the case of a 21-year-old female patient with temporal lobe complex partial seizures. Magnetic resonance imaging revealed right hippocampal sclerosis. A dose of 550 MBq of ^99mTc-bicisate was injected 35 s after the onset of a seizure during intracranial EEG-videotelemetry. At the moment of injection, subdural EEG demonstrated the beginning of late ictal discharges and postictal suppression in the right temporomesial areas. Late ictal SPET images showed marked right fronto-temporo-parietal hypoactivity. The interictal SPET study clearly showed right frontotemporal hypoactivity. These preliminary data suggest that ^99mTc-bicisate shows late ictal/early postictal hypoactivity which might represent the primary change in neuronal metabolism rather than the secondary change in cerebral blood flow. Correspondence to: J.T. Kuikka     

Regional differences between <Superscript>99m</Superscript>Tc-ECD and <Superscript>99m</Superscript>Tc-HMPAO SPET in perfusion changes with age and gender in healthy adults

A number of studies using single-photon emission tomography (SPET) have shown perfusion changes with age in several cortical and subcortical areas, which might distort the results of perfusion imaging studies of neuropsychiatric disorders. Technetium-99m labelled ethyl cysteinate dimer (ECD) and hexamethylpropylene amine oxime (HMPAO) are both used as markers of cerebral perfusion, but have different pharmacokinetics and retention patterns. The aim of this study was to determine whether age and gender effects on perfusion SPET differ depending on whether ^99mTc-HMPAO or ^99mTc-ECD is used. Forty-five subjects (20 male and 25 female, mean age 52.8±6.6 years) were assigned to ^99mTc-HMPAO SPET (HMPAO group), and 39 subjects (24 male and 15 female, mean age 52.6±6.7 years) to ^99mTc-ECD SPET (ECD group). SPET images were obtained about 10 min after intravenous injection of approximately 800 MBq ^99mTc-HMPAO or ^99mTc-ECD using the same SPET scanner. Three-dimensional volumetric magnetic resonance imaging was performed to as7sess morphological changes in the grey matter. All image processing and statistical analyses were performed using SPM99 software. An area in the right anterior frontal lobe showed an increase in perfusion with age only in the HMPAO group, whereas areas in the bilateral retrosplenial cortex showed decreases in perfusion with age only in the ECD group; neither group showed corresponding changes in the grey matter. The present study shows that different effects of age on perfusion are observed depending on whether ^99mTc-HMPAO and ^99mTc-ECD is used. This suggests that the results of perfusion SPET are differently confounded depending on the tracer used, and that perfusion SPET with these tracers has limitations when used in research on subtle perfusion changes.     

Visualization of posture-dependent cerebral blood flow in a patient with Takayasu's disease by means of 99mTc-HMPAO brain single photon emission tomography

A case of Takayasu's disease in a 22-year-old woman who complained of severe fainting attacks is presented. Bilateral obstruction of the cervical arteries was confirmed by digital subtraction angiography. Preoperative technetium-99m hexamethylpropylene amine oxime brain SPET in the sitting position showed bilateral hypoactivity in the temporoparietal areas. Subtraction brain SPET showed slightly increased activity in the lying position. The patient has had no fainting attacks since bypass surgery. Postoperative ^99mTc-HMPAO brain SPET in the sitting position showed normal activity except in the right temporoparietal area. This area was filled in the lying position. ^99mTc-HMPAO brain SPET is the only technique that can visualize the cerebral blood flow in any position, this capability deriving on the fact that the distribution of ^99mTc-HMPAO in the brain is fixed in the first 2–3 min following injection. The use of both sitting and lying ^99mTc-HMPAO brain SPET is very useful for detecting an abnormality (i.e. an inhomogeneous response due to the fall in perfusion pressure) that could not be seen if the cerebral blood flow were to be assessed only in the lying position. Correspondence to: K. Hayashida     

The usefulness of repeated ictal SPET for the localization of epileptogenic zones in intractable epilepsy

This study investigated whether repeated ictal single-photon emission tomography (SPET) is helpful in the localization of epileptogenic zones and whether it can provide information confirming that an area of increased perfusion is really the culprit epileptogenic lesion. Fifty-four repeated ictal SPET studies were performed in 24 patients with ambiguous or unexpected findings on the first ictal SPET study. These patients were enrolled from among 502 patients with intractable epilepsy in whom pre-operative localization of epileptogenic zones was attempted with a view to possible surgical resection. Video monitoring of ictal behaviour and EEGs was performed in all patients. Repeated ictal SPET was performed using technetium-99m hexamethylpropylene amine oxime (HMPAO) when there was no prominently hyperperfused area or when unexpected findings were obtained during the first study. Two ictal SPET studies were performed in 19 patients, three studies in four patients and four studies in one patient. The average delay between ictal onset and injection was 28 s for the first study and 22 s for the second, third and fourth studies. Using interictal SPET, ictal-interictal subtraction images were acquired and co-registered with the population magnetic resonance imaging (MRI) template. Invasive study and surgery were performed in 18 patients, and in these cases the surgical outcome was known. In the other six patients, epileptogenic foci were determined using MRI, positron emission tomography (PET) and ictal EEG findings. Two patients were found to have mesial temporal lobe epilepsy, two lateral temporal lobe epilepsy, eight frontal lobe epilepsy, three parietal lobe epilepsy and one occipital lobe epilepsy. The other eight had multifocal epilepsy. The first study was normal in 12 patients (group I) and indicated certain zones to be epileptogenic in the other 12 (group II). Among group I, the correct epileptogenic zone or lateralization was revealed at the repeated study in nine patients, while in the other three it was not. Among group II, six patients showed the same results at the second study, thus confirming that the initially identified zones were of epileptogenic significance. In the other six patients, different areas were identified on the first and second studies, and repeated ictal SPET corroborated multifocality of the ictal EEG findings in five. These results indicate that repeated ictal SPET is useful because it can yield new or additional information about the epileptogenic zones and can confirm that a region of interest is an epileptogenic zone or that the epilepsy is of multifocal origin.     

Motor stimulation response by technetium-99m hexamethylpropylene amine oxime split-dose method and single photon emission tomography

We applied the technetium-99m hexamethylpropylene amine oxime (^99mTc-HMPAO) split-dose method in order to evaluate the feasibility of assessing cerebral blood flow (CBF) changes with single photon emission tomography (SPET) during a motor activation task. Eleven normal subjects were studied using the Tomomatic 564 (Medimatic, DK). Five subjects were studied twice at rest and 6 subjects at rest and during a motor task performance (finger opposition movements). A total of 28 mCi of ^99mTc-HMPAO was injected in 2 doses with a 1:3 ratio. The first scan was obtained after injection of 7 mCi at rest in all subjects. The second scan was obtained a few minutes later, after injection of the remaining dose (21 mCi), under similar resting conditions or during a motor task performance. The mean brain uptake was proportional to the amount of tracer injected and to the acquisition time for both the first scan (5263±1266 counts × mCi × min) and the second (5034.4±966 counts × mCi × min). The grey/white matter ratio was 1.67±0.019 and 1.67±0.097 for the two scans, respectively. A three-way analysis of variance (ANOVA) for repeated measure showed no significant effects of side, slice and region of interest (ROI) on the CBF in the 5 subjects studied twice at rest, and the mean regional CBF change was –0.2%±5%. In the 6 subjects studied at rest and during motor activation, the image subtraction analysis showed a significant CBF increase in the primary motor cortex contralateral to the stimulated side (15%±7%, n=6) and medially in the supplementary motor area (22%±12%, n=4). Our results indicate that the split-dose method allows the detection of a local CBF response to motor activation using ^99mTc-HMPAO in a single imaging session. Correspondence to: P. Pantano     

Brain perfusion scintigraphy with99mTc-HMPAO or99mTc-ECD and123I-β-CIT single-photon emission tomography in dementia of the Alzheimer-type and diffuse Lewy body disease

Dementia of the Alzheimer-type (DAT) is characterized by progressive cognitive decline, variably combined with frontal lobe release signs, parkinsonian symptoms and myoclonus. The features of diffuse Lewy body disease (DLBD), the second most common cause of degenerative dementia, include progressive cognitive deterioration, often associated with levodopa-responsive parkinsonism, fluctuations of cognitive and motor functions, psychotic symptoms (visual and auditory hallucinations, depression), hypersensitivity to neuroleptics and orthostatic hypotension. A recent report suggests that positron emission tomography studies in patients with degenerative dementia may be useful in the differential diagnosis of DAT and DLBD. However, the diagnostic role of single-photon emission tomography (SPET) studies remains to be established. The aim of this study was therefore to evaluate regional cerebral perfusion [with either technetium-99m hexamethylpropylene amine oxime (^99mTc-HMPAO) or^99mTc-ethyl cysteinate dimer (^99mTc-ECD) SPET] and striatal dopamine transporter density [using iodine-123 2-carboxymethoxy-3-[4-iodophenyl]tropane (¹²³I--CIT) SPET] in patients with DAT and DLBD. Six patients with probable DAT and seven patients with probable DLBD were studied. Blinded qualitative assessment by four independent raters of^99mTc-HMPAO or^99mTc-ECD SPET studies revealed bilateral temporal and/or parietal hypoperfusion in all DAT patients. There was additional frontal hypoperfusion in two patients and occipital hypoperfusion in one patient. In the DLBD group, regional cerebral perfusion had a different pattern. In addition to temporoparietal hypoperfusion there was occipital hypoperfusion resembling a horseshoe defect in six of seven patients. In the DAT group, the mean 3-h striatal/cerebellar ratio of¹²³I--CIT binding was 2.5±0.4, with an increase to 5.5±1.1 18 h after tracer injection. In comparison, in the DLBD patients the mean 3-h striatal/cerebellar ratio of¹²³I--CIT binding was significantly reduced to 1.7±0.3, with a modest increase to 2.1±0.4 18 h after tracer injection (P<0.05, Scheffe test, ANOVA). These results suggest that^99mTc-HMPAO or^99mTc-ECD and¹²³I--CIT SPET may contribute to the differential diagnosis between DAT and DLBD, showing different perfusion patterns and more severe impairment of dopamine transporter function in DLBD than in DAT.     

“Schistotaxis” in cerebral blood flow on 99 mTc-HMPAO single-photon emission computed tomography during a seizure following a stroke

We describe a patient with seizures following a stroke in whom on ictal ^{99 m}Tc-HMPAO single-photon emission computed tomography demonstrated cerebral blood flow “schistotaxis”, i. e., focal hyperaemia corresponding to an epileptogenic focus together with an extensive hypoperfused area in the same hemisphere. This phenomenon may have been caused by haemodynamic alternation and a remote transneural effect during the seizures. Received: 13 January 2001/Accepted: 26 February 2001     

Regional cerebral blood flow single-photon emission tomography with 99mTc-HMPAO and the acetazolamide test in the evaluation of vascular and Alzheimer’s dementia

The diagnostic potential of technetium-99m hexamethylpropylene amine oxime (HMPAO) following systemic administration of the cerebral vasodilator acetazolamide (acetazolamide test) was evaluated by regional cerebral blood flow (rCBF) single-photon emission tomography (SPET) in patients with Alzheimer’s disease (AD) or vascular dementia (VD). An initial, high-resolution SPET study was performed with ^99mTc-HMPAO, and after 2 days the patients were re-evaluated with ^99mTc-HMPAO following systemic administration of acetazolamide. Reconstructed SPET slices were evaluated visually and semiquantitatively by a semi-automatic rCBF map method. When ^99mTc-HMPAO alone was used, bilateral hypoperfusion was found in the temporal and/or parietal regions in 33% (6/18) of the VD patients and in 70% (23/33) of the AD patients. The corresponding data obtained by quantitative evaluation were 41% (7/17) and 71% (15/21), respectively. The vascular reserve capacity, as determined with the acetazolamide test, was preserved visually in 22% (4/18) and quantitatively in 29% (5/17) of the VD patients, but in 73% (24/33) and 76% (16/21) of the AD patients. The differences in the perfusion patterns between the VD and AD patients were statistically significant (P<0.01, Fischer’s exact test). Of the VD patients with hypoperfusion (bilateral temporal and/or parietal), 4/6 (67%, visual evaluation) and 4/7 (57%, quantitative evaluation) had a decreased vascular reserve capacity as determined with the acetazolamide test. In the AD group of patients the corresponding results were 3/23 (13%) and 4/15 (27%). It is concluded that the acetazolamide test is promising in rCBF SPET to differentiate VD from AD. Received 1 August and in revised form 30 October 1998     

Role of brain perfusion single-photon emission tomography in traumatic head injury

This investigation examined the role of brain perfusion single-photon emission tomography (SPET) in traumatic head injury in 35 patients. The results were compared with those of X-ray computerized tomography (CT) and magnetic resonance imaging (MRI). CT and MRI detected brain contusions in seven patients, subarachnoid haemorrhage in one patient and both in nine patients. In 16 of the 17 subjects (94%), SPET with technetium-99m-hexamethylpropyleneamine oxime (Tc-HMPAO) revealed CT/MRI-negative abnormalities, such as hypoperfusion in the contre-coup region, frontal hypoperfusion related to personality change and cerebellar hypoperfusion associated with vertigo. In two patients presenting with diffuse axonal injury in the brainstem, hypoperfusion in the frontal cortex on the affected side was observed on SPET. SPET demonstrated hypoperfusion in the adjacent cortex, with no abnormality on either CT or MRI, in six of seven patients exhibiting acute epidural haematoma. SPET failed to provide additional information in two of five patients with acute subdural haematoma and in one of two patients displaying chronic subdural haematoma. In four of nine patients with post-traumatic amnesia, SPET detected hypoperfusion in the temporal lobe, with no abnormality on either CT or MRI. In five of eight patients with vertigo, SPET detected hypoperfusion in the morphologically normal cerebellum. In seven cases involving personality change, frontal hypoperfusion was observed in four; moreover, a markedly non-homogeneous pattern was evident in the remaining three. Overall, SPET afforded additional information in 26 patients (74%). CT possesses an advantage with respect to the detection of haemorrhagic lesions. MRI provides more precise information regarding contusions and axonal injury. Frequently, SPET may be the only examination to reveal perfusion abnormalities which are related to symptoms in the absence of other objective findings, such as post-traumatic amnesia, vertigo or personality change.     

A quantitative approach to technetium-99m ethyl cysteinate dimer: a comparison with technetium-99m hexamethylpropylene amine oxime

To develop non-invasive regional cerebral blood flow (rCBF) measurements using technetium-99m ethyl cysteinate dimer (^99mTc-ECD) and single-photon emission tomography (SPET), the same graphical analysis as was described in our previous reports using technetium-99m hexamethylpropylene amine oxime (^99mTc-HMPAO) was applied to time-activity data for the aortic arch and brain hemispheres after intravenous injection of^99mTc-ECD. Hemispherical brain perfusion indices (BPI) for^99mTc-ECD showed a highly significant correlation (n = 22,r = 0.935,P = 0.0001) with those for^99mTc-HMPAO in 11 patients who underwent both tracer studies. Using both linear regression line equations between^99mTc-ECD BPI and^99mTc-HMPAO BPI and between^99mTc-HMPAO BPI and mean cerebral blood flow (CBF) values obtained from a xenon-133 inhalation SPET method in a previous study,^99mTc-ECD BPI was converted to¹³³Xe CBF values (y = 2.60x + 19.8). Then raw SPET images of^99mTc-ECD were converted to rCBF maps using Lassen's correction algorithm. In this algorithm, the correction factor a was fixed to 1.5, 2.6 and infinite. In the comparison of rCBF values for^99mTc-ECD SPET with those for^99mTc-HMPAO SPET in 396 regions of interest in the aforementioned 11 patients, the fixed correction factor of 2.6 gave nearly the same rCBF values for^99mTc-ECD (50.1 ± 16.9 ml/100 g/min, mean ± SD) as for^99mTc-HMPAO (49.9 ± 17.3 ml/100 g/min). In conclusion, the same non-invasive method as has been used in^99mTc-HMPAO studies is applicable to a^99mTc-ECD study for the measurement of rCBF without any blood sampling.     

Cerebellar vascular response to acetazolamide in crossed cerebellar diaschisis: a comparison of99mTc-HMPAO single-photon emission tomography with15O-H2O positron emission tomography

Various observations on the cerebellar vasoreactivity in crossed cerebellar diaschisis (CCD) have previously been reported. The purpose of this study is to clarify the difference between oxygen-15 H₂O positon emission tomographic (PET) and technetium-99m hexamethylpropylene amine oxime (HMPAO) single-photon emission tomograph (SPET) findings in CCD and to evaluate the effect of the absolute values of the cerebellar blood flow as measured by¹⁵O-H₂O PET on the^99mTc-HMPAO SPET findings. The subjects comprised 15 patients with a supratentorial infarct and CCD. The cerebellar blood flow increased by about 40% at 5 and 20 min after acetazolamide i.v. on both the CCD and the non-CCD side, as measured by 150-1120 PET. The percentage differences in cerebellar blood flow between the CCD and the non-CCD side were –22.3%±5.7% in the resting state, –19.6%±6.4% at 5 min after acetazolamide i.v. and 21.5%±6.7% at 20 min after acetazolamide i.v., as measured by¹⁵O-H₂O PET, while they were –10.6%±5.5% in the resting state and –5.6%±5.1% at 5 min after acetazolamide i.v., as measured by^99mTc-HMPAO SPET. After Lassen's linearization correction, the latter two measurements were –16.2%±7.7% and –9.6%±8.9%, respectively. The effect of acetazolamide did not differ between the CCD and the non-CCD side in¹⁵O–H₂O PET, while a greater response on the CCD side was observed in^99mTc-HMPAO SPET, even after Lassen's linearization correction. It is concluded that acetazolamide HMPAO SPET may overestimate the cerebellar vascular response on the CCD side (or underestimate it on the non-CCD side).     

Ictal technetium-99m ethyl cysteinate dimer single-photon emission tomographic findings and propagation of epileptic seizure activity in patients with extratemporal epilepsies

Although ictal single-photon emission tomography (SPET) with technetium-99m ethyl cysteinate dimer (ECD) has a well-established role in the diagnostic evaluation of patients with temporal lobe epilepsy who are being considered for epilepsy surgery, its use in cases of extratemporal epilepsy is still limited. We investigated the influence of the propagation of extratemporal epileptic seizure activity on the regional increase in cerebral blood flow, which is usually associated with epileptic seizure activity. Forty-two consecutive patients with extratemporal epilepsies were prospectively evaluated. All patients underwent ictal SPET studies with simultaneous electroencephalography (EEG) and video recordings of habitual seizures and imaging studies including cranial magnetic resonance imaging and positron emission tomography with 2-[¹⁸F]-fluoro-2 deoxy-d-glucose. Propagation of epilptic seizure activity (PESA) was defined as the absence of hyperperfusion on ictal ECD SPET in the lobe of seizure onset, but its presence in another ipsilateral or contralateral lobe. Observers analysing the SPET images were not informed of the other results. PESA was observed in 8 of the 42 patients (19%) and was ipsilateral to the seizure onset in five (63%) of these eight patients. The time between clinical seizure onset and injection of the ECD tracer ranged from 14 to 61 s (mean 34 s). Seven patients (88%) with PESA had parieto-occipital epilepsy and one patient had a frontal epilepsy. PESA was statistically more frequent in patients with parieto-occipital lobe epilepsies (58%) than in the remaining extratemporal epilepsy syndromes (3%) (P<0.0002). These findings indicate that ictal SPET studies require simultaneous EEG-video recordings in patients with extratemporal epilepsies. PESA should be considered when interpreting ictal SPET studies in these patients. Patients with PESA are more likely to have parieto-occipital lobe epilepsy than seizure onset in other extratemporal regions. Received 14 August and in revised form 31 October 1997     

Visual and quantitative analysis of interictal SPECT with technetium-99m-HMPAO in temporal lobe epilepsy

Interictal 99mTc-HMPAO SPECT images were compared to ictal EEG localization in 51 patients with intractable temporal lobe epilepsy to determine their usefulness for preoperative seizure focus localization. Both quantified temporal lobe asymmetry and blinded visual detection of temporal lobe hypoperfusion were employed. Visual analysis detected ipsilateral hypoperfusion in 18 (39%) of the 46 patients with a unilateral focus and contralateral hypoperfusion in 3. None of the five patients with bitemporal foci had unilateral hypoperfusion. The positive predictive value of unilateral temporal lobe hypoperfusion was 86% (18/21). Quantified anterior temporal lobe asymmetry, greater than a previously derived normal range, correctly identified the focus in 22 (48%) but gave the wrong side in 5, resulting in a predictive value of 81%. The degree of asymmetry correlated inversely with age of seizure onset, but not with other clinical parameters, histology, or verbal and nonverbal memory. The usefulness of interictal 99mTc-HMPAO SPECT for pre-operative seizure focus localization is limited by low sensitivity when performed with a conventional rotating gamma camera. This suggests that ictal or immediate postictal imaging may be necessary for this purpose.     

Benzodiazepine receptors and cerebral blood flow in partial epilepsy

It was the aim of this study to compare benzodiazepine (Bz) receptor binding and cerebral perfusion in patients with partial epilepsy. Single photon emission tomography (SPET) studies with the flow-marker technetium 99m hexamethylpropylene amine oxine (^99mTc-HMPAO) and with the¹²³I-labelled Bz-receptor ligand Ro 16-0154 (¹²³I-Iomazenil) were performed in 12 patients with partial epilepsy, all with normal magnetic resonance imaging (MRI) and computed tomography (CT) scans. The SPET studies with¹²³I-Iomazenil were carried out 5 min and 2 h after injection. At 2 h the distribution of activity was very similar to the expected distribution of Bz-receptors in the human brain, known from positron emission tomography (PET) work and post-mortem studies. Early images showed a significantly higher tracer accumulation in the area of the basal ganglia, cerebellum, and naso-pharyngeal space. This finding is caused by non-specific binding and the contribution of the tracer in the blood pool in this phase. Also after 2 h p.i. of¹²³I-Iomazenil, 9 of the 12 patients showed a focal decrease of of Bz-receptor binding. Ten patients had focal flow abnormalities with^99mTc-HMPAO SPET. In 8 subjects impairment of flow was seen in sites of reduced¹²³I-Iomazenil uptake.¹²³I-Io-mazenil is suitable for Bz-receptor mapping. In this series of patients, Bz-receptor mapping with SPET seems to offer no advantage over^99mTc-HMPAO in the detection of epileptic foci. Offprint requests to: P. Bartenstein