Brain SPECT imaging using three different tracers in subacute cerebral infarction

Changes in synaptic density in the subacute phase after ischemic stroke: A 11C-UCB-J PET/MR study

Functional alterations after ischemic stroke have been described with Magnetic Resonance Imaging (MRI) and perfusion Positron Emission Tomography (PET), but no data on in vivo synaptic changes exist. Recently, imaging of synaptic density became available by targeting synaptic vesicle protein 2 A, a protein ubiquitously expressed in all presynaptic nerve terminals. We hypothesized that in subacute ischemic stroke loss of synaptic density can be evaluated with ¹¹C-UCB-J PET in the ischemic tissue and that alterations in synaptic density can be present in brain regions beyond the ischemic core. We recruited ischemic stroke patients to undergo ¹¹C-UCB-J PET/MR imaging 21 ± 8 days after stroke onset to investigate regional ¹¹C-UCB-J SUVR (standardized uptake value ratio). There was a decrease (but residual signal) of ¹¹C-UCB-J SUVR within the lesion of 16 stroke patients compared to 40 healthy controls (ratio_{lesion/controls} = 0.67 ± 0.28, p = 0.00023). Moreover, ¹¹C-UCB-J SUVR was lower in the non-lesioned tissue of the affected hemisphere compared to the unaffected hemisphere (ΔSUVR = -0.17, p = 0.0035). The contralesional cerebellar hemisphere showed a lower ¹¹C-UCB-J SUVR compared to the ipsilesional cerebellar hemisphere (ΔSUVR = -0.14, p = 0.0048). In 8 out of 16 patients, the asymmetry index suggested crossed cerebellar diaschisis. Future research is required to longitudinally study these changes in synaptic density and their association with outcome.

Nuclear medicine in cerebrovascular disease

Stroke and cerebrovascular diseases are major causes of mortality, morbidity, and disability. Nuclear Medicine, primarily via tomographic methods, has made significant contributions to the understanding of the hemodynamic and metabolic consequences of cerebrovascular diseases. In this review, the findings in acute, subacute, and chronic cerebrovascular diseases are described. Many of the pathophysiologic processes and consequences that follow stroke, including completed infarct core, adjacent penumbra, and diaschisis, have been investigated with Nuclear Medicine, and stroke outcome may be related to these phenomena. Additional topics included in this review are cerebrovascular reserve tests and multi-infarct dementia. Finally, Nuclear Medicine investigations of stroke recovery and cerebral plasticity appear to indicate that enhanced activity of preexisting networks, rather than substitution of function, represents the most important mechanism of improvement in chronic stroke rehabilitation.

Changes of brain perfusion after endovascular embolization of intracranial arteriovenous malformations visualized by 99mTc-ECD SPECT

OBJECTIVE

Published data describing scintigraphic evaluation of perfusion changes in patients with cerebral arteriovenous malformations (AVMs) after embolization are very scarce. The aim of our study was to evaluate these changes by using Tc-ethyl cysteinate dimer single photon emission computed tomography.

MATERIALS AND METHODS

The examinations were performed in 20 patients before and after the treatment. Voxel-based analysis was used for semiquantitative assessment of single photon emission computed tomography. Hypoperfusion in basal single photon emission computed tomography was diagnosed when asymmetry index was higher than 10% in a cluster volume (CV) greater than 10.0 ml. The change of perfusion between basal and control studies was considered significant when relative difference (RD) was higher than 10% in a CV greater than 10 ml.

RESULTS

Obliteration of AVMs was total or nearly total in 12 patients and partial in 8 patients, No serious complications were observed after the procedure. Before embolization hypoperfusion in the region of an AVM was seen in 17 cases, perfusion defects in areas distant from an AVM were found in 12 patients. After embolization, perfusion around an AVM deteriorated in 11 patients (CV=10.7-68.7 ml, mean 28.6+/-18.4, RD=14-26%, mean 17.8+/-4.5). Improvement was seen in three cases (CV=13.7-17.7 ml, mean 16+/-2, RD=16.5-20.1%, mean 18.2+/-1.8). Perfusion deterioration in areas distant from AVMs was found in nine cases, improvement in three cases.

CONCLUSION

The changes of perfusion caused by endovascular embolization of AVM can rely on both deterioration and improvement, and occur in the parenchyma surrounding the AVM and in the distant regions of the brain. Although deterioration of perfusion indicated that more frequent follow-up was necessary, it was not related with serious complications in our group of patients.

Brain single-photon emission CT physics principles

The basic principles of scintigraphy are reviewed and extended to 3D imaging. Single-photon emission computed tomography (SPECT) is a sensitive and specific 3D technique to monitor in vivo functional processes in both clinical and preclinical studies. SPECT/CT systems are becoming increasingly common and can provide accurately registered anatomic information as well. In general, SPECT is affected by low photon-collection efficiency, but in brain imaging, not all of the large FOV of clinical gamma cameras is needed: The use of fan- and cone-beam collimation trades off the unused FOV for increased sensitivity and resolution. The design of dedicated cameras aims at increased angular coverage and resolution by minimizing the distance from the patient. The corrections needed for quantitative imaging are challenging but can take advantage of the relative spatial uniformity of attenuation and scatter. Preclinical systems can provide submillimeter resolution in small animal brain imaging with workable sensitivity.

Scatter correction based on an artificial neural network for 99mTc and 123I dual-isotope SPECT in myocardial and brain imaging

The aim of this study was to elucidate the clinical usefulness of scatter correction with an artificial neural network (ANN) in 99mTc and 123I dual-isotope SPECT.

METHODS

Two algorithms for ANN scatter correction were tested: ANN-10 and ANN-3 employing 10 and 3 energy windows for data acquisition, respectively. Three patients underwent myocardial or brain SPECT with one of the following combinations of radiopharmaceuticals administered: 99mTc-tetrofosmin and 123I-metaiodobenzylguanidine (MIBG), 99mTc-methoxyisobutylisonitrile (MIBI) and 123I-beta-methyl-paraiodophenyl-pentadecanoic acid (BMIPP), or 99mTc-ethyl-cistainate dimmer (ECD) and 123I-iomazenil. The patients were also referred for single-isotope imaging incorporating conventional triple-energy window (TEW) scatter correction. Crosstalk- and scatter-corrected 99mTc- and 123I-SPECT images in dual-isotope acquisition with ANN were compared with those in single-isotope acquisition.

RESULTS

The ANN method well separated 123I and 99mTc primary photons. Although ANN-10 yielded images of poor quality, ANN-3 offered comparable image quality with the single-isotope scan without significant increase of acquisition time.

CONCLUSION

The proposed method is clinically useful because it provides various combinations of information without anatomical misregistration with one acquisition.

Evaluation of the pathophysiology of odontogenic maxillary sinusitis using bone scintigraphy

The inflammatory changes in the maxillary sinus mucosa and wall (mucosal and bony lesions) were evaluated to identify the pathophysiology of odontogenic maxillary sinusitis. Out of 80 patients who underwent CT, 32 patients were examined using single photon emission computerized tomography (SPECT) bone scintigraphy (bone SPECT) with 99mTc-hydroxymethylene-diphosphonate. Mucosal and bony lesions were evaluated morphologically on both images. SPECT data were used to assess the bone activity by calculating the count ratios of the causative alveolar process over the cervical vertebrae. The relationships with clinical symptoms, mucosal changes around the maxillary ostium (ostial lesions), and radiolucencies around the causal teeth (periapical lesions) were assessed. Bone SPECT showing the causal site was valuable for aiding a definitive diagnosis. Mucosal lesions tended to exceed bony lesions horizontally and vertically. Bony lesions tended to extend posteriorly and then anteriorly. The vertical extent of mucosal lesions and the horizontal and vertical extent of bony lesions were correlated with the presence of facial symptoms, ostial lesions, and periapical lesions. Bone activity was significantly correlated with the horizontal and vertical extent of mucosal lesions, horizontal extent of bony lesions, and presence of infraorbital symptoms, ostial lesions, and periapical lesions. Bone activity caused by alveolitis affects the pathophysiology of this disease.

Diagnostic value of spect bone scintigraphy for odontogenic maxillary sinusitis

PURPOSE

The aim of this study was to assess the diagnostic value of bone SPECT for odontogenic maxillary sinusitis and bone activity in the alveolar process to clarify the pathophysiologic nature of the disease.

MATERIALS AND METHODS

Computed tomography and bone SPECT with Tc-99m HMDP were performed in 28 patients with odontogenic maxillary sinusitis. Based on the findings of the computed tomographic images, the inflammatory changes in the maxillary sinus mucosa (mucosal lesions) were evaluated horizontally and vertically. For the initial diagnosis, visualization of the causative site by bone SPECT was compared with conventional radiographic and planar findings. SPECT data were used to assess bone activity by calculating the mean count ratios of the alveolar process over the cervical vertebrae. The relation of bone activity to the structure of the mucosal lesions, the presence of clinical symptoms, mucosal changes around the maxillary ostium (ostial lesions), and conventional radiolucent images around the causative teeth (periapical lesions) were assessed.

RESULTS

Identification of the causative site was sufficiently specific in bone SPECT images. Bone activity was significantly correlated with the structure of the mucosal lesions, both horizontally and vertically, and with the presence of infraorbital symptoms, ostial lesions, and periapical lesions.

CONCLUSIONS

It is important to view odontogenic maxillary sinusitis as a bone disease in which the bone activity associated with alveolar osteitis affects the pathophysiologic nature of the disease. Bone SPECT is valuable to make a more precise diagnosis, thereby allowing more appropriate treatment of the disease.