CONVENTIONAL MRA AND CONTRAST-ENHANCED MR A OF EXTRACRANIAL VESSEL SEGMENTS

The introduction of fast gradient systems allows a reliable visualizat ion of the extracranial carotid vessels by the magnetic resonance angi ography (MRA) which meanwhile is implemented into clinical routine. By the mainly applied time-of-flight (TOF) technique, vessels can be ima ged without contrast agent (CA). Due to the application of ultra-fast gradient-echo-sequences, the first-pass evaluation of an intravenous b olus-injection of Gadolinium in the carotids from the aortic arch up t o the skull base can be performed in less than 30 s. In this study, ad vantages and disadvantages of both techniques are discussed. For a qua litatively optimal contrast enhanced MRA (CE-MRA) timing parameters li ke injection delay, flow rate and the adjustment of sequence parameter s have to be considered in relation to the fast Venous return from the sinus to the jugular veins. First, the optimal time point of the data acquisition have been determined at a model and with a computer simul ation in reference to the presence of CA in the arteries. As a result, 90 % of the contrast contribution is defined by 16 % of the symmetric ally acquired central k-space lines. A measuring protocol for clinical use was obtained by a gradual variation of spacial resolution, measur ing time and CA-injection parameters and was proved in normal voluntee rs and patients. An exact determination of the bolus-arrival-time by m eans of a test-bolus injection was acquired. The best qualitative resu lts were achieved by a double-dose injection at 2 ml/s injection rate. The temporal reserves of ultra-fast sequences should be invested in t he improvement of the spatial resolution. To date, further investigati ons related to the problem of optimal CA-application may improve the p otentials of CE-MRA procedures.