tailieunhanh - Evidence-Based Imaging - part 4

Vì vậy việc phát hiện sớm bệnh sốt xuất huyết phụ thuộc vào việc chuyển đổi oxyhemoglobin deoxyhemoglobin, được cho là xảy ra sau 12-24 giờ đầu tiên (20,23). Tuy nhiên, điều này giả định đầu đã được đặt câu hỏi với các báo cáo xuất huyết intraparenchymal phát hiện bởi MRI trong vòng 6 giờ, | 164 . Vo et al. iron exposed to surrounding water molecules in the form of deoxyhemoglobin creates signal loss making it easy to identify on susceptibility-weighted and T2-weighted T2W sequences 21 22 . Thus the earliest detection of hemorrhage depends on the conversion of oxyhemoglobin to deoxyhemoglobin which was believed to occur after the first 12 to 24 hours 20 23 . However this early assumption has been questioned with reports of intraparenchymal hemorrhage detected by MRI within 6 hours and as early as 23 minutes from symptom onset 24-26 . One of the studies prospectively demonstrated that MRI detected all nine patients with CT-confirmed intracerebral hemorrhage ICH suggesting the potential of MRI for the hyperacute evaluation of stroke limited evidence 24-26 . More recently a blinded study comparing MRI diffusion- T2- and T2 -weighted images to CT for the evaluation of ICH within 6 hours of onset demonstrated that ICH was diagnosed with 100 sensitivity and 100 accuracy by expert readers using MRI CT-detected ICH was used as the gold standard strong evidence 9 . Data regarding the detection of acute subarachnoid and intraventricular hemorrhage using MRI is limited. While it is possible that the conversion of blood to deoxyhemoglobin occurs much earlier than expected in hypoxic tissue this transition may not occur until much later in the oxygen-rich environment of the CSF 20 27 . Thus the susceptibility-weighted sequence may not be sensitive enough to detect subarachnoid blood in the hyperacute stage. This problem is further compounded by severe susceptibility artifacts at the skull base limiting detection in this area. The use of the fluid-attenuated inversion recovery FLAIR sequence has been advocated to overcome this problem. Increased protein content in bloody CSF appears hyperintense on FLAIR and can be readily detected. Three case-control series using FLAIR in patients with CT-documented subarachnoid or intraventricular hemorrhage demonstrated a .