RESUMEN
Idiopathic intracranial hypertension (IIH) is characterized by increased ICP without evidence for intracranial mass lesion. Although the pathogenesis remains unknown, some association was found with intracranial venous thrombosis. To our knowledge, the extracranial venous drainage was not systematically evaluated in these patients. This study compared extracranial cerebral venous outflow in eight IIH patients and eight control subjects using magnetic resonance (MR) Venography and flow measurements. In addition, the study identified extracranial factors that affect cerebral venous drainage. In six of the IIH patients, either complete or partial functional obstruction of the internal jugular veins (IJVs) coupled with increased venous outflow through secondary venous channels was documented. On average, a four-fold increase in mean venous flow rate through the epidural and/or vertebral veins was measured in IIH patients compared with the healthy subjects. In one of the healthy subjects, intracranial venous outflow was studied also during external compression of the IJVs. Over 40% of the venous outflow through the IJVs shifted to the epidural veins and intracranial pressure, measured noninvasively by MRI, increased from 7.5 to 13 mmHg. Findings from this study suggest that increased ICP in some IIH patients could be associated with increased extracranial resistance to cerebral venous outflow.
Asunto(s)
Encéfalo/irrigación sanguínea , Venas Cerebrales/fisiopatología , Circulación Cerebrovascular , Flebografía , Postura , Seudotumor Cerebral/diagnóstico , Seudotumor Cerebral/fisiopatología , Adulto , Velocidad del Flujo Sanguíneo , Encéfalo/patología , Medicina Basada en la Evidencia , Femenino , Humanos , Presión Intracraneal , Imagen por Resonancia Magnética , MasculinoRESUMEN
Postural related changes in cerebral hemodynamics and hydrodynamics were studied using Magnetic Resonance Imaging (MRI) measurements of cerebral blood flow and cerebrospinal fluid (CSF) flow dynamics. Ten healthy volunteers (mean age 29 +/- 7) were studied in supine and upright (sitting) postures. A Cine phase-contrast MRI technique was used to image the pulsatile blood flow to the brain, the venous outflow through the internal jugular, epidural, and vertebral veins, and the bi-directional CSF flow between the cranium and the spinal canal. Previously published analyses were applied to calculate and compare total cerebral blood flow (TCBF), intracranial compliance and pressure in both postures. A lower (12%) mean TCBF was measured in the upright position compared to supine position. A considerable smaller amount of CSF flow between the cranium and the spinal canal (58%), a much larger intracranial compliance (a 2.8-fold increase), and a corresponding decrease in the MRI-derived ICP were also measured in the sitting position. These changes suggest that the increased cerebrovascular and intracranial compliances in the upright posture are primarily due to reduced amounts of blood and CSF residing in their respective intracranial compartments in the upright position. This work demonstrates the ability to quantify neurophysiologic parameters associated with regulation of cerebral hemodynamics and hydrodynamics from dynamic MR imaging of blood and CSF flows.
Asunto(s)
Velocidad del Flujo Sanguíneo/fisiología , Encéfalo/irrigación sanguínea , Encéfalo/fisiología , Circulación Cerebrovascular/fisiología , Presión Intracraneal/fisiología , Imagen por Resonancia Magnética , Postura/fisiología , Adaptación Fisiológica/fisiología , Adulto , Elasticidad , Femenino , Humanos , Interpretación de Imagen Asistida por Computador/métodos , MasculinoRESUMEN
The optical flow method is used for visualizing and quantifying the dynamics of tissue changes observed by MRI during thermal ablations. An approach was implemented for parallel two-dimensional optical flow calculations including the replacement of spurious velocities. Velocity magnitude results were found to be accurate in low-noise cases in tests using series of synthetic images. Optical flow results are presented from thermal ablation experiments utilizing a homogeneous polyacrylamide gel phantom and heterogeneous rabbit liver tissue in vivo, exhibiting heating and cooling with the accompanying quantitative characterization of the dilation and contraction of the thermally affected region. Results demonstrate that optical flow is capable of noninvasive real-time monitoring and control of interstitial laser therapy (ILT).
Asunto(s)
Coagulación con Láser , Hígado/anatomía & histología , Imagen por Resonancia Magnética , Monitoreo Intraoperatorio/métodos , Óptica y Fotónica , Resinas Acrílicas , Animales , Geles , Procesamiento de Imagen Asistido por Computador , Hígado/cirugía , Modelos Teóricos , Fantasmas de Imagen , Conejos , Reproducibilidad de los Resultados , Sensibilidad y EspecificidadRESUMEN
Our purpose was to develop temperature-sensitive MR sequences and image-processing techniques to assess their potential of monitoring interstitial laser therapy (ILT) in brain tumors (n = 3) and liver tumors (n = 7). ILT lasted 2 to 26 minutes, whereas images from T1-weighted fast-spin-echo (FSE) or spoiled gradient-recalled (SPGR) sequences were acquired within 5 to 13 seconds. Pixel subtraction and visualization of T1-weighted images or optical flow computation was done within less than 110 msec. Alternating phase-mapping of real and imaginary components of SPGR sequences was performed within 220 msec. Pixel subtraction of T1-weighted images identified thermal changes in liver and brain tumors but could not evaluate the temperature values as chemical shift-based imaging, which was, however, more affected by susceptibility effects and motion. Optical flow computation displayed the predicted course of thermal changes and revealed that the rate of heat deposition can be anisotropic, which may be related to heterogeneous tumor structure and/or vascularization.
Asunto(s)
Neoplasias Encefálicas/cirugía , Procesamiento de Imagen Asistido por Computador/métodos , Terapia por Láser , Neoplasias Hepáticas/cirugía , Imagen por Resonancia Magnética/métodos , Neoplasias Encefálicas/patología , Ensayos Clínicos como Asunto , Humanos , Cuidados Intraoperatorios , Terapia por Láser/métodos , Neoplasias Hepáticas/patología , Espectroscopía de Resonancia MagnéticaRESUMEN
Steadfast progress has been made from biopsy to surgery with interventional MRI (iMRI). Such image-guided interventions require specialized instrumentation due to the unusual elements of the MR environment. Suppliers/manufacturers of MR-compatible instrumentation were few in 1994, but now there are more than 50. We present fundamental issues of MR compatibility and a list of known suppliers/manufacturers.
Asunto(s)
Imagen por Resonancia Magnética , Equipo Quirúrgico , Instrumentos Quirúrgicos , Humanos , Cuidados Intraoperatorios/instrumentación , Imagen por Resonancia Magnética/instrumentaciónRESUMEN
Laser-induced interstitial thermal therapy (LITT) is a preferred method of minimally invasive therapy. MRI is a noninvasive method by which to monitor the thermal effects of LITT. To properly control such effects, changes in MRI parameters during and after LITT should be correlated with changes in the tissue. T1-weighted fast spin echo (FSE) MRI (1 image/10 seconds) at 1.5 T monitored LITT in vivo in rabbit liver (n = 6) using an interstitial bare delivery fiber (600-microm diameter; 3.0 W; 1,064 nm; 150 seconds). During laser irradiation, MRI signal intensity decreased around the fiber tip; after irradiation, this hypointensity proved reversible and permanent lesions were evident. The lesions had hyperintense margins that were brighter than surrounding normal tissue (P < .001); the tissue in these bright regions was mapped to tissue necrosis characterized by the presence of thermally damaged ghost red blood cells amid generally normal hepatocytes. T1-FSE identified the spatial extent of the LITT lesions.
Asunto(s)
Rayos Láser/efectos adversos , Hígado/lesiones , Hígado/patología , Imagen por Resonancia Magnética , Animales , Hipertermia Inducida , Terapia por Láser , ConejosRESUMEN
BACKGROUND AND OBJECTIVE: Magnetic resonance imaging's (MRI) potential to monitor interstitial laser photocoagulation (ILP) has been previously demonstrated and is further tested here with improved spatial and temporal resolution. STUDY DESIGN/MATERIALS AND METHODS: In vivo experiments employed fiber-delivered 1,064 nm light (3.0 W, 150 sec) in six rabbit livers monitored under T1-weighted FSE MRI as 1 image/10 sec and a 3 mm thick 8 cm FOV. Image signal intensities (SI) were compared with temperatures (T) at 7, 10, and 15 mm from the fiber. RESULTS: Data showed 33 degrees C < T < 60 degrees C. SI did not vary inverselinearly with T; changes in the tissue altered the MRI signal interfering with the SI changes due to temperature. CONCLUSION: MRI cannot map SI-derived temperatures over the entire treatment site. The role of MRI's temperature sensitivity must be coordinated with organ- and dose-specific tissue changes.
Asunto(s)
Coagulación con Láser , Hígado/patología , Hígado/cirugía , Animales , Calor , Imagen por Resonancia Magnética/métodos , ConejosRESUMEN
For thermal interventional therapy, near real-time monitoring of temperature changes in the treated area is desirable. In this study, various fast T1-weighted magnetic resonance (MR) imaging protocols were compared to determine the sensitivity and resolution of signal intensity for temperatures within the range of 36 degrees C-66 degrees C in gel phantoms and in vitro porcine liver specimens. The results showed that a T1-weighted fast spin-echo sequence with a TR of 100 msec had better temperature sensitivity and resolution than other sequences with comparable temporal resolutions. The longer imaging times required for fast spin-echo sequences with a TR of 300 msec did not improve temperature sensitivity. The methods introduced to evaluate temperature sensitivity and resolution should prove useful in selecting appropriate MR protocols for monitoring thermal treatment modalities such as interstitial laser therapy, focused ultrasound therapy, or radio-frequency heating.
Asunto(s)
Temperatura Corporal , Hipertermia Inducida , Imagen por Resonancia Magnética/métodos , Monitoreo Fisiológico/métodos , Animales , Técnicas In Vitro , Hígado/anatomía & histología , Modelos Estructurales , PorcinosRESUMEN
We have used MR monitoring to guide and evaluate the effects of the Nd:YAG interstitial laser on a well-characterized rat brain tumor model (C6). MRI was used to determine the tumor size, verify the location of the interstitial probe, and evaluate the size and location of the laser-induced lesion during and after treatment. During laser irradiation, an irreversible loss of signal intensity at the fiber tip and a reversible decrease in signal intensity around it were observed with MRI. None of the treatment protocols affected mean rat survival significantly. Although MRI-guided interstitial laser therapy appears to be safe and easy, it does not provide a curative treatment for spatially disseminated gliomas where a "target volume" cannot be adequately defined. Better results can be expected, especially in well-defined tumors, with improvements of both the imaging techniques and the laser treatment protocol.
Asunto(s)
Neoplasias Encefálicas/radioterapia , Glioma/cirugía , Terapia por Láser , Imagen por Resonancia Magnética , Animales , Neoplasias Encefálicas/diagnóstico , Neoplasias Encefálicas/patología , Glioma/diagnóstico , Glioma/patología , Imagen por Resonancia Magnética/métodos , Masculino , Ratas , Ratas Endogámicas F344RESUMEN
We applied diffusion-sensitive echo planar (Instascan) imaging to study thermal changes caused by a Nd:YAG laser. Images of phantom materials and normal rabbit brain tissue in vivo, acquired in 150 ms, every 2s, clearly showed the dynamics of temperature-related signal intensity changes in the regions irradiated by the laser.