Chair of Renthenology and Radiology Medicomilitary Academy, Saint Petersburg, Russia
Progress in development of radioisotopic methods is conditioned first of all by appearance of new generations of diagnostic devices and radiopharmaceutical preparations, as well as mathematical methods of information processing. Creation of new methods of neurovisualization and improvement of existing ones have led to rise of numerous investigations. Each of them makes a contribution into understanding of pathogenesis of cerebral diseases and possesses some advantages over other methods.
The goal of the present study was preliminary analysis and generalization of results of using SPECT and combined PET/CT in neurosurgical practice.
SPECT-examination of brain was carried out with the E. Gam Variable Angle double-detector chamber (Siemens); a special headrest was used. This system allows to reconstruct an image at any angle and in axial, sagittal and frontal planes. Besides, one can get brain sections, which are similar to those, obtained in CT or MRI. It is of great practical importance, as there appears a possibility to superimpose SPECT images on corresponding CT or MRI sections and to get combined views of anatomic structures and functional indices. This superimposing, known as images fusion, is necessary for more exact topographic correlation of physiologic indices under study with these or those cerebral structures.
Radiopharmaceutical preparations, labeled with technetium-99 mTc, were used for brain examination. Pathologic formations were diagnosed with Technetril (Sestamibi) or Pentatech. Perfusion was studied with the help of examethazin-99 mTc (Ceretec). Despite individual peculiarities, these preparations have some common features: they penetrate through the blood-brain barrier quite well, spread within the brain in proportion to blood flow and stay within it during a period of time, which is sufficient for obtaining an image.
According to some data, SPECT is more sensitive method from the point of revealing focal ischemia in an early period of a transient ischemic attack, than CT.
Prognostication of an outcome with the help of SPECT is possible, when examination is carried out no later than 72 hours after stroke. Marked reduction of regional blood flow at an early period of stroke is an unfavorable prognostic sign. An area around a necrotic focus, characterized by decreased functional activity and preserved survivability of nerve cells (the so-called ischemic penumbra), is the main target of therapy and can be estimated with SPECT.
SPECT can be used successfully not only for estimation of ischemic disorders of cerebral circulation, but also hemodynamics, other vascular diseases and brain tumors. We used SPECT for examination of 22 cases; it allowed to diagnose different degrees of neoplasm malignancy.
PET has some additional diagnostic potentialities, though it has not become very popular and widespread in our country so far. The essence of this technology consists in registration of physiologic processes within tissue by means of tracking a small amount of isotopes with an ultra-short period of life. They are used for labeling substances, participating in a process under study. Energy consumption by cells is evaluated on the basis of glucose metabolism; its labeled analog, known as 18 F-desoxiglucose (DG), is used for estimation of neoplasm malignancy. One more radiopharmaceutical preparation (11 C-metionin), characterized by greater accumulation in cerebral tumors in comparison with normal tissue, can be used. This preparation possesses a wider diagnostic spectrum, than 18 F-DG and, thus, is more preferable in PET-diagnosis of cerebral tumors. Selective accumulation of 11 C-metionin in pathologic tissue permits to reveal small neoplastic nodes. Benign astrocytomas are characterized by a low index of 18 F-DG accumulation. Anaplastic astrocytomas have a moderate or high index of accumulation; one can watch partial fusion of foci of maximum accumulation. Glioblastomas are notable for a fused focus of preparation accumulation, characterized by a high index; it occupies more than a half of tumor volume, which contains areas of hypo-metabolic heterogeneity without regular outlines; it is conditioned by necrosis.
A new trend, being developed now, is immunoscintigraphy with labeled monoclonal antibodies (CEA-scan, Verluma) to a certain type of tumor and creation of radiopharmaceutical drugs on the basis of labeled peptides (NeoSpect).