Optical coherence tomography: a novel technique for the study of tissue microcirculation.

Background: Three-dimensional (3D) observation techniques are useful for understanding organ microcirculation. Optical coherence tomography (OCT) is one of the 3-D imaging techniques and is increasingly applied for tissue microcirculatory studies. Objective: This article reviews the current and prospective usages of OCT in microcirculation. Methods: OCT is an optical technique to obtain tomographic images of highly scattering media like living tissues by means of coherence gating, whose spatial resolution is down to 10 μm. It is also capable of obtaining velocity profiles of blood flow by use of Doppler frequency shift (Doppler OCT). Results: The OCT technique has been applied for observation of microvessels in rat skin, hamster dorsal skin, rat brain etc. Small microvessels down to 20 μm have been detected with the aid of Doppler OCT. Doppler OCT also revealed that the blood flow in microvessels is a quasi-steady laminar flow. The OCT signal from the cerebral cortex was found to change following neural activation, probably reflecting the functional hyperemia. Conclusion: The OCT technique combined with Doppler OCT technique has a great potential for in vivo observation of 3-D structures of microvessels and blood flow distribution. Further OCT is expected to be a depth-dependent imaging tool for the study of brain function.

Low-Resolution Electromagnetic Tomography (LORETA) Source Imaging Compared with Structural Brain Imaging in Patients having Organic Brain Lesion / 신경정신의학

OBJECTIVES: Patients with organic brain lesion can produce unique slow waves (delta and theta) in the EEG. Basic assumption of this study was that the low resolution electro magnetic tomography (LORETA), an inverse source localization program, can provide functional images representing increased slow wave activity in these patients compared to normal subjects. METHODS: The current study was performed by 18 channels digital EEG for 10 patients whose organic deficit have been visually confirmed by CT or MRI. The source images of slow wave (1-7 Hz) frequency were produced by LORETA-key program. RESULTS: We found that in eight out of ten subjects, LORETA successfully found out the source regions which were very closely matched to their original brain lesions. However in two subjects whose organic brain lesions were too small (<1 cm) and located out of gray matter, we failed to find any increased slow wave activity compared with normal control. CONCLUSION: We can conclude that LORETA could be a useful method to provide functional imaging in patients with gray matter deficits in their brain. Its usefulness and limitations were discussed.

The Role of Functional Imaging Techniques in the Dementia / 대한핵의학회잡지

Evaluation of dementia in patients with early symptoms of cognitive decline is clinically challenging, but the need for early, accurate diagnosis has become more crucial, since several medication for the treatment of mild to moderate Alzheimer' disease are available. Many neurodegenerative diseases produce significant brain function alteration even when structural imaging (CT or MRI) reveal no specific abnormalities. The role of PET and SPECT brain imaging in the initial assessment and differential diagnosis of dementia is beginning to evolve rapidly and growing evidence indicates that appropriate incorporation of PET into the clinical work-up can improve diagnostic and prognostic accuracy with respect to Alzheimer's disease, the most common cause of dementia in the geriatric population. In the fast few years, studies comparing neuropathologic examination with PET have established reliable and consistent accuracy for diagnostic evaluations using PET - accuracies substantially exceeding those of comparable studies of diagnostic value of SPECT or of both modalities assessed side by side, or of clinical evaluations done without nuclear imaging. This review deals the role of functional brain imaging techniques in the evaluation of dementias and the role of nuclear neuroimaging in the early detection and diagnosis of Alzheimer's disease.

Neuropsiquiatra: pet y spect / Neuropsychiatrist: pet and spect

Functional brain imaging with PET and SPECT have a definitive and well established role in the investigation of a variety of conditions such as dementia, epilepsy and drug addiction. With these methods it is possible to detect early rCBF (regional Cerebral Blood Flow) changes seen in dementia (even before clinical symptoms) and differentiate Alzheimer's disease from other dementias by means of the rCBF pattern change. 18-F-FDG PET imaging is a useful tool in partial epilepsy because both rCBF and brain metabolism are compromised at the epileptogenic focus. During the seizure, rCBF dramatically increases locally. Using SPECT it is possible to locate such foci with 97% accuracy. In drug addiction, particularly with cocaine, functional imaging has proven to be very sensitive to detect brain flow and metabolism derangement early in the course of this condition. These findings are important in many ways: prognostic value, they are used as a powerful reinforcement tool and to monitor functional recovery with rehabilitation. There are many other conditions in which functional brain imaging is of importance such as acute stroke treatment assessment, trauma rehabilitation and in psychiatric and abnormal movement diseases specially with the development of receptor imaging.

Existen numerosas indicaciones claramente establecidas para el uso del SPECT y PET en patología neuro-psiquiátrica, particularmente en el estudio de demencias, epilepsia y adicción a drogas. Estos métodos permiten detectar precozmente (aun antes de las manifestaciones clínicas) cambios en la perfusión y metabolismo cerebral en pacientes con demencias. Es posible además diferenciar la enfermedad de Alzheimer de otras causas de demencia, analizando el patrón de la alteración neuro- funcional. En epilepsia parcial, tanto el metabolismo como la perfusión están alterados en el foco epileptogénico, lo que puede ser detectado con F-18FDG PET. Durante la crisis epiléptica, el flujo sanguíneo puede aumentar dramáticamente en el foco epileptogénico, lo que puede ser detectado con SPECT con 97% de certeza. En pacientes drogadictos, especialmente a la cocaína, estos métodos han demostrado ser muy sensibles para la detección precoz de cambios en el flujo y metabolismo cerebral, lo que es clínicamente importante en varios aspectos: 1) Tiene valor pronóstico (neuro-funcional), 2) Se puede usar para aumentar la adherencia a la terapia y 3) Permite evaluar objetivamente la recuperación funcional. Existen muchas otras indicaciones presentes y futuras, por ejemplo: en la monitorización de la revascularización en accidentes vasculares cerebrales agudos, rehabilitación post TEC, estudio de patología psiquiátrica y movimientos anormales especialmente con el desarrollo de radioligandos.