| Objective To determine the usefulness of the ratios of the maximum relative cerebral blood volume (rCBV) and the values of relative permeability derived by perfusion MR imaging in the preoperative assessment of histological grade of astrocytoma.Materials and Methods The datum of perfusion MR imaging and pathology of 34 patients with astrocytomas over a 9 months period between June 2002 and March 2003 were analysed. Twenty-three of the patients were male and 11 were female. They ranged in age from 6 to 78 years old, mean 41.6 years old.All cases were divided into three group whose grading according to the world health organization grading system revised in 1993.Grade 2 and grade one were designated as low-grade astrocytomas , grade 3 and grade 4 were designated as anaplastic and glioblastomas respectively. The final diagnoses were 12 low-grade astrocytomas, 9 anapllasticastrocytomas, 13 glioblastomas. MR examination performed on a 1.5T signa superconducting system (GE company ,America) following imaging sequences :axial spin-echo Trweighted, axial fast spin-echo T2-weighted, sagittal spin-echo T1-weighted, perfusion-weighted and three directional postcontrast spin-echo T1-weighted. Perfusion weighted imaging was performed by using a gradient-echo echo-planar T2-weighted imaging. The first 4 acquistions were performed before contrast agent injection to establish a precontrast baseline .At the 4 acquisition, GD-DTPA(0. 2mmol/l, Bei Lu company ,China)was injected at a rate of 3~ 4ml/sec via a 18-20 gauge intravenous catheter which was inserted in theforearm vein. The multisection images were acquired to overlap the whole volume of the tumors. The total scaning time was 78sec and the number of the image was 480. All echo-planar images were postprocessed by the Functool software .The signal over time curve according the signal reduction of each pixel was described and rCBV map was generated by the change of the T2* relaxation rate. The maximal rCBV ratio was calculated by following equation: maximum rCBV of tumor/contralateral maximum rCBV of white matter. The signal intensity decreased percentage-time curves of the most hot area of the color rCBV map was obtained which were used to calculated signal reduced ratios acording the follow equation SRRend =SIpre - SIend/SIend × 100% and produce the MTT map to obtain MTT, The equation rP =SRRend × 100/MTT was used to calculated the relative permeability value of the tumor vessel. SPSS for 10. 0 statistical software package was used to assess the difference of maximum rCBV ratios and rP between three groups and the relationship between maximum rCBV ratio and histologic grade of the tumors. The level of significant defined as p<0. 05.Results The maximum rCBV ratios were 1.44-4.48 (3.23 ± 0.92) in low grade astrocytomas, 4.76-5.80(5.18±0.34) in anaplastic astrocytomas, 5.23-7.07(5.05±0.66)in glioblastoma. The difference in rCBV ratios between low grade astrocytomas and anaplastic astrocytomas was significant (P<0.01), The difference in rCBV ratios between low grade astrocytomas and glioblastoma was significant, (P<0. 05). The maximum rP of three groups were 0.46-1.88 (1. 34 ± 0.46), 1.62-2.71(2.17± 0. 28), 2. 23-2. 78 (2. 59±0. 60) respectively. The differences in rP between low-grade astrocytomas, anaplastic astrocytomas and glioblastoma were significant (P<0.01).There was a significantly positive correlation between rP and rCBV. (r=0. 853).Conclusion Perfusion MR imaging is useful and reliable techniquein the preoperative assessment of astrocytomas of histological grade . moreover, it has many advantages such as high temporal and spatial resolution, noninvasive, repeatable et al. |
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