Takao Kodama MD, PhD, Presenter: Nothing to Disclose

Takanori Yano MD, PhD, Abstract Co-Author: Nothing to Disclose

Shozo Tamura MD, PhD, Abstract Co-Author: Nothing to Disclose

Tokunori Kimura PhD, Abstract Co-Author: Nothing to Disclose

We developed a new sequence of cranial MR angiography (MRA), hybrid MRA (HMRA), combining the contrast of time-of-flight and black-blood MRA by using the dual-echo data acquisition. The purpose of this study was to evaluate the utility of this technique from the initial clinical experiences.

36 patients underwent MR examination including a 3D TOF MRA and HRMA (total of 39 examination). Pulse sequence of the HMRA was designed with a 3D dual-echo gradient-echo sequence, and TR of 31.2 ms and TE of 6.4 / 23.8 ms were selected in this study. The gradient moment nulling (GMN) and dephasing gradient was applied to obtain the first and second echo respectively. Original images of the HMRA were made by subtracting the 2nd-echo images from the 1st-echo images. The information of the 2nd echo could be handled as “positive” signal. Following two type of subtraction could be used, 1) simple-weighted subtraction (SWS): simple subtraction with a variable weighted coefficient, 2) filter-weighted subtraction (FSW): subtraction based on the frequency characteristics. 3D TOF MRA was performed with single or two slabs acquisition, and preparation pulses such as a magnetization transfer contrast or fat saturation was used.

Visualization of the peripheral vessels was better on the HMRA compared with the single-slab TOF MRA using MTC pulse in 17/19 examination．Vessels not visualized on the TOF MRA were observed on the HMRA in a patient with MCA occlusion and two patients with moyamoya disease. In 17 examinations of patients who had undergone EC-IC bypass operation, HMRA seemed to be of equal value with 2 slab TOF MRA using fat saturation and MTC pulses in spite of its shorter acquisition time. One of the problems of this technique was the subtraction error due to the magnetic susceptibility and chemical shift. This problem could be partially overcome by using FWS technique. Another problem was artificial signal loss of the proximal major arteries and stenotic portions.

Although there is some problems to be resolved, HMRA can be a feasible tool for evaluating intracranial arteries, especially in patients with steno-occlusive vascular diseases.

Hybrid MRA, which combine the contrast of TOF and black-bloodMRA by using the dual-echo data acquisition, can be a feasible tool for evaluating intracranial arteries.

Kodama, T, Yano, T, Tamura, S, Kimura, T, Hybrid MRA: A Novel Technique of Cranial MRA for Improving Visualization of Peripheral Vasculatures.  Radiological Society of North America 2008 Scientific Assembly and Annual Meeting, February 18 - February 20, 2008 ,Chicago IL. http://archive.rsna.org/2008/6016668.html