RESUMO
Objective Using gradient-echo sampling of spin-echo (GESSE) sequence to study the change of oxygen extraction fraction (OEF) in patients with unilateral cerebral vessel stenosis and the relationship between OEF and cerebral blood flow (CBF). Methods Eight normal volunteers and 16 patients with unilateral cerebral vessel stenosis were enrolled in this study. Written informed consents were obtained from all subjects. Routine MRI, GESSE and arterial spin labeling (ASL) sequences were performed for all patients. Raw data from GESSE and VE-ASL sequences were transferred to PC to conduct postprocessing. To obtain quantitative OEF and CBF of the brain parenchyma, 6 ROIs were placed respectively in the anterior, middle and posterior part of both hemispheres. The relative CBF (rCBF) was defined as the ratio of CBF of ischemic hemisphere to that of contralateral hemisphere. T test was used for statistics. Results The mean value and normal range of OEF in the volunteers were 0. 318 ± 0. 023 and 0. 272-0. 364, respectively. In the 16 patients with unilateral cerebral vessel stenosis, 8 patients had ROIs with greater OEF in unilateral hemisphere than those in contralateral hemisphere. These cases presented multiple intracranial main arterial stenoses in digital subtraction angiography (DSA) or MR angiography (MRA) examination. The other 8 patients had normal OEF in all ROIs. And they only had single arterial stenosis in DSA or MRA. Set rCBF = 0. 50 as a dividing point, the mean OEF value was 0. 397 ±0. 010 in the patients with rCBF ＜ 0. 50. In the patients with rCBF ≥ 0. 5, the mean OEF value was 0. 325 ±0. 028. The difference between the two groups was statistically significant (t = - 8. 840, P = 0. 000).Conclusion Patients with chronic cerebral ischemia may present with various hemodynamic impairment.The more CBF decreases, the more OEF increases. Those with increased OEF tended to have more than one lesion in the major intracranial arteries.
RESUMO
Objective To evaluate the stability and repeatability of gradient-echo sampling of spinecho (GESSE) sequence in measuring the R2'value in volunteers, by comparison with traditional GRE sequence (T2* map and T2 map). Methods Eight normal healthy volunteers were enrolled in this study and written informed consents were obtained from all subjects. MR scanning including sequences of GESSE,T2 map and T2 * map were performed in these subjects at resting status. The same protocol was repeated one day later. Raw data from GESSE sequence were transferred to PC to conduct postprocessing with the software built in house. R2'map and OEF map were got consequently. To obtain quantitative R2'and OEF values in the brain parenchyma, six ROIs were equally placed in the anterior, middle and posterior part of bilateral hemispheres. Both mean and standard deviation of R2 'and OEF were recorded. All images from T2 * map and T2 map were transferred to the Workstation for postprocessing. The ROIs were put at the same areas as those for GESSE sequence. R2'is defined as R2' = R2 * -R2,R2* = 1/T2*. The R2'value of GESSE sequence were compared with that of GRE sequence. Results The mean R2 'values of GESSE at the first and second scan and those of the GRE were (4.21 ±0.92),(4.45 ±0. 94) Hz and (7.37 ±1.47), (6. 42 ±2. 33) Hz 0. 035 respectively. The R2'value and OEF value obtained from GESSE were not significantly different between the first and second scan ( t = - 0. 83, - 1.48, P ＞ 0. 05 ). The R2' value of first GRE imaging had significantly statistical difference from that of second GRE inaging ( t = 1.80, P ＜ 0. 05 ). The R2' value of GESSE sequence was less than that of GRE sequence, and there was significantly statistical difference between them(t = 1.71 ,P＜0. 05). Conclusion The GESSE sequence has good stability and repeatability with promising clinical practicability.