Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_3850_Библиотеки_им_академика_М_И_Перельмана

Department of Thoracic and Cardiovascular Surgery Mie University Hospital 2-174 Edobashi, Tsu Mie 514-8507 Japan

motion artifact suppression, improved z-axis resolution, higher axial spatial resolution, decreased total dose of iodinated contrast medium and real-time interactive 3D display facilities on workstations.

Traditionally, MRI, using T1-weighted spin-echo (black blood) imaging and cine-MRI is well suited for evalua­tion of the gross anatomy of the thoracic aorta, as well as for evaluation of pericardial, pleural and mediastinal effusions [9]. Flow-based methods of imaging (using time-of-flight or phase-contrast properties) yield bright blood images using gradient-echo techniques [10]. The limitation of the latter techniques, however, is that they rely on the physical properties of flowing blood (velo­city, direction, etc.), making the technique susceptible for artifacts, which may result in overestimation of ste­noses or even a false diagnosis of occlusion of a vessel. Furthermore the spatial resolution and signal-to-noise ratio provided by these 2D techniques do not allow evaluation of small vessel lesions or small side branches [11].

The most-suited technique currently used in the evaluation of thoracic aortic anatomy and disease is dy­namic subtraction MRA, using gadolinium (0.2 mmol/ kg, flow rate of antecubital injection 2 ml/s) as the in­travenous contrast agent [10, 12±16]. Gadolinium short­ens the T1 of blood, and therefore allows shorter imag­ing times. Thus, fewer flow-related and motion-related artifacts occur, and therefore the technique can demon­strate subtle aortic lesions, such as penetrating ulcers, and small intercostal arteries. After a plain MRI, intra­venous contrast agent is administered. Using bolus tim­ing (either by using a test bolus or real-time fluoro­scopic triggering) the arrival of the contrast agent can be timed, and the contrast-enhanced sequence is per­formed [10, 17]. This is followed by subtraction of the two series. The limitation of this test-bolus technique is the potential for diminished artery-to-vein contrast, as­sociated additional cost of test-bolus contrast and the potential difficulty to observe the test bolus in distal vessels or in cases with slow flow [17]. To further re­duce respiratory motion artifacts and artifacts related to cardiac motion and pulsatile flow, electrocardio­graphic triggering techniques can be used [9, 18]. The images thus obtained can either be viewed on a slice­to-slice basis, or can be reconstructed on a computer workstation into a MIP image. The appearance of MIP reconstructions resembles that of conventional angio­graphy, and MIP reconstructions are therefore useful in planning of surgical procedures [13]. Using 3D recon­struction techniques it is also possible to obtain an in­ternal view of the vessel and its walls (virtual intra-arte­rial endoscopy) [13]. It is of importance to evaluate