Quantification of blood velocity and flow rates in the uterine vessels using echo planar imaging at 0.5 Tesla.

PURPOSE: To measure uterine artery and vein blood velocity and flow rate profiles using MRI during normal pregnancy. MATERIALS AND METHODS: A two-shot velocity magnitude-encoded echo planar imaging (EPI) sequence is used at a magnetic field 0.5T. Data analysis procedures, necessary to overcome problems associated with low signal to noise ratio (SNR), and a spatial resolution comparable to the vessel size were used. RESULTS: The measured blood flow values averaged over nine volunteers for the mean velocity are 5.33 and 3.97 cm/s and for the unilateral flow rate are 203 and 274 mL/min (for the arteries and veins respectively). Values for the flow rate are consistent with ultrasound Doppler studies. Arterial velocity measurements are more pulsatile than venous ones and validation calculations performed on average velocity values would suggest that the nature of blood flow in the uterine vessels is laminar. CONCLUSION: This study presents the first report of noninvasive quantitative measurements of uterine artery and vein blood velocity and flow rate profiles using MRI during normal pregnancy. Consistent and reproducible measurements have been obtained by subject specific sequence optimization and data analysis procedures.

Correction of spatial distortion in EPI due to inhomogeneous static magnetic fields using the reversed gradient method.

PURPOSE: To derive and implement a method for correcting spatial distortion caused by in vivo inhomogeneous static magnetic fields in echo-planar imaging (EPI). MATERIALS AND METHODS: The reversed gradient method, which was initially devised to correct distortion in images generated by spin-warp MRI, was adapted to correct distortion in EP images. This method provides point-by-point correction of distortion throughout the image. EP images, acquired with a 3 T MRI system, of a phantom and a volunteer's head were used to test the correction method. RESULTS: Good correction was observed in all cases. Spatial distortion in the uncorrected images ranged up to 4 pixels (12 mm) and was corrected successfully. CONCLUSION: The correction was improved by the application of a nonlinear interpolation scheme. The correction requires that two EP images be acquired at each slice position. This increases the acquisition time, but an improved signal-to-noise ratio (SNR) is seen in the corrected image. The local SNR gain decreases with increasing distortion. In many EPI acquisition schemes, multiple images are averaged at each slice position to increase the SNR; in such cases the reversed gradient correction method can be applied with no increase in acquisition duration.

Malformaçöes vasculares do canal vertebral: estudo comparativo com ressonância magnética e angiografia em 17 casos / MRI appearances of intraspinal vascular malformations: review of 17 cases in comparative study with angiography

As malformaçöes vasculares do canal vertebral säo lesöes relativamente infreqüentes e a avaliaçäo dessas lesöes por ressonância magnética tem sido advogada como o melhor método diagnóstico de "screening" atualmente disponível. No presente trabalho, os autores apresentam 17 casos de malformaçöes vasculares do canal vertebral analisados retrospectivamente e classificados em dois grupos: grupo I, que inclui 12 casos de informaçöes vasculares angiograficamente diagnosticadas, e grupo II, com cinco casos de lesöes angiograficamente ocultas (angiomas cavernosos). Em todos os casos foram realizados exames de ressonância magnética e angiografia espinhal. Nas lesöes do grupo I os autores däo ênfase às características anatômicas das lesöes encontradas, tais como a presença de um ninho vascular nas malformaçöes arteriovenosas, localizaçäo do ponto de fístulas arteriovenosas e análise das alteraçöes medulares. No grupo II, a elevada sensibilidade da ressonância do diagnóstico dessas lesöes foi confirmada por meio de cirurgia em três dos cinco casos.