| SECTION1 IMPACT OF SYNCHRONOUS AND ASYNCHRONOUS SCANNING ON IMAGE QUALITY OF VOLUME CT DIGITAL SUBTRACTION ANGIOGRAPHYObjective: To investigate the effects on image quality of volume computed tomographic digital subtraction angiography (VCTDSA) with synchronous and asynchronous scanning.Methods: Vascular model which was closely attached to bony structures was scanned by 64-slice spiral CT.â‘ Helical scanning was performed without contrast medium injection for 20 times and the tube exposure time was 2.1 s, scanning intervals differently were 1.9 s, 3.9 s, 5.9 s, 7.9 s, 9.9 s, 11.9 s, 13.9 s, 15.9 s, 17.9 s, 19.9 s, 2.9 s, 4.9 s, 6.9 s, 8.9 s, 10.9 s, 3.0 s, 4.0 s, 5.0 s, 6.0 s, 7.0 s.â‘¡After contrast medium injection, the vascular model was scanned for 10 times using the same parameters as above, but the scanning intervals differently were 9.9 s, 11.9 s, 13.9 s, 15.9 s, 17.9 s, 10.9 s, 12.9 s, 11.0 s, 12.0 s, 13.0 s. The resulting images were reformatted as 3D volume rendering (3D VR) and maximum intensity projection (MIP) images. The quality of subtraction images was then analyzed. CT values of the overall view were measured on subtracted images and the differences of tube exposure angle were recorded.Results: Subtracted images quality of VCTDSA was rated gradeâ… with synchronous scanning for 15 times before and after contrast medium injection, while with asynchronous scanning for 15 times, 2 times were gradeâ… , 12 times were gradeâ…¡and 1 time was gradeâ…¢. In 20 times, the average CT value of subtracted images with asynchronous scans was higher than which with synchronous scans without contrast injection. The differences of tube exposure angle with synchronous scans were obviously less than which with asynchronous scans.Conclusion: The position of tube can be well matched with synchronous scanning, so the image quality of VCTDSA is improved significantly. SECTION2 ESTABLISHMENT OF SYNCHRONOUS MMBE AND COMPARATIVE STUDY BETWEEN SYNCHRONOUS MMBE AND VCTDSAObjective: To evaluate the feasibility of subtraction CT angiography of the cerebral vessels with synchronous matched mask bone elimination(MMBE)technique and compare the image quality of MMBE with that of volume computed tomographic digital subtraction angiography (VCTDSA).Methods:Vascular model was scanned by 64-slice spiral CT. (1) Synchronous and asynchronous scans were independently performed for 10 times without contrast medium injection. (2)Then with contrast medium injection, the same scans mentioned above were repeatedly performed each for 5 times. The image quality of MMBE was analyzed, which were reformatted and displayed with 3D volume rendering (VR) and maximum intensity projection (MIP). The CT value of the overall view was measured on subtracted images (without contrast medium). Two sets of bone masks were extracted for subtraction and the image quality was evaluated (without contrast medium). Also the image quality of VCTDSA was compared with those of synchronous MMBE.Results: With synchronous and asynchronous scan,the image quality of MMBE was both rated gradeâ…¡in 13 cases, gradeâ…¢in 2 cases. There was no significant difference in the average CT value of subtracted images between the two methods.(P>0.05). With synchronous scan the image quality of subtracted bone mask was rated gradeâ… in 10 cases. While with asynchronous scan,1 case was gradeâ… , 8 cases were gradeâ…¡and 1 case was gradeâ…¢. The image quality of synchronous MMBE was rated gradeâ…¡in 13 cases, gradeâ…¢in 2 cases. For VCTDSA, the image quality was rated gradeâ… in 15 cases. Conclusion:Synchronous MMBE is a feasible imaging method for evaluation of cerebral vessels. The subtracted image quality is significantly improved with this technique. However, the image quality of VCTDSA is still superior to that of synchronous MMBE. PART2 THE COMPARATIVE STUDY ON THE CLINICAL APPLICATION OF VCTDSA AND SYNCHRONOUS MMBE SECTION1 OPTIMIZATION FOR THRESHOLD OF SYNCHRONOUS MMBE Objective: To investigate the optimal threshold of bone mask which used for synchronous MMBE.Methods:VCTDSA data that matches research inclusion criteria of 30 patients in our hospital were analyzed.Five points of threshold were set which increased by turns.There were differently 107HU,126HU,145HU,160HU and 183HU. F ive sets of bone masks were extracted according to the five points of threshold. Then five sets of subtracted data were obtained with MMBE. The resulting images were reformatted as 3D volume rendering (3D VR) and maximum intensity projection (MIP) images.Then the image quality of MMBE was analyzed according to two sets of observed objects, which were differently cerebral artery and cerebral vein systems, and the grade of images were recorded.Results:When the cerebral artery was observed , the image quality of MMBE was rated gradeâ… in 16 cases, gradeâ…¡in 14 cases and gradeâ…¢in 2 cases , as the threshold of bone masks was 145HU. As the threshold was 107HU, the image quality of MMBE was rated gradeâ…¡in 7 cases , gradeâ…¢in 23 cases, and no case in gradeâ… . The subtracted image quality was optimal when the threshold was 145HU.As the central threshold of 145HU, the image quality got degraded with the threshold increased and decreased progressively. When the cerebral vein was observed , the image quality of MMBE was rated gradeâ… in 24 cases, gradeâ…¡in 6 cases and no case in gradeâ…¢, as the threshold was 160HU. As the threshold was 107HU, the image quality of MMBE was rated gradeâ…¡in 4 cases , gradeâ…¢in 26 cases, and no case in gradeâ… . And the subtracted image quality was optimal when the threshold was 160HU.Also as the central threshold of 160HU, the image quality got degraded with the threshold increased and decreased progressively.Conclusion:When the cerebral artery is observed,the threshold of 145HU is optimal.While the cerebral vein is observed,the threshold of 160HU is optimal. So the image quality of MMBE is improved with different threshold setting when different objects are observed. It is helpful to display vascular lesion.SECTION2 COMPARISON OF VCTDSA AND SYNCHRONOUS MMBE IN THE DIAGNOSIS OF INTRACRANIAL ANEURYSMSObjective:To investigate the diagnostic performance of volume computed tomography digital subtraction angiography(VCTDSA) and synchronous matched mask bone elimination(MMBE)in the detection of intracranial aneurysms.Methods: VCTDSA datas of 57 patients that suspected of having intracranial aneurysms in clinic in our hospital were analyzed.47 patients of the total were confirmed by 3 Dementional digital subtraction angiography (3-D DSA) and/or by surgery. With VCTDSA , The subtracted image quality,time of reconstruction,location and size of aneurysms, sensitivity , specificity , Positive Predictive Value (PPV) and Negative Predictive Value (NPV) in aneurysms detection were compared with synchronous MMBE.Results:53 aneurysms were detected in 41 patients who confirmed by 3-D DSA and/or by surgery. On a per-patient basis, the sensitivity, specificity, and positive and negative predictive values for VCTDSA were all 100%,which higher than that of synchronous MMBE.On a per-aneurysm basis, the sensitivity, specificity, and positive and negative predictive values for VCTDSA respectively were 96%, 100%, and 100% and 75%, which all higher than that of synchronous MMBE. On a per-location basis, the sensitivity, specificity, and positive and negative predictive values for VCTDSA were 94%, 100%, and 100% and 90% in detection of internal carotid artery aneurysm, which also all higher than that of synchronous MMBE. As for the other three locations of anterior cerebral artery, middle cerebral artery and posterior circulation, there was no significant difference between the two methods in detection aneurysms. Aneurysms smaller than 3 mm could be detected both by VCTDSA and synchronous MMBE .The sensitivity(87%) of VCTDSA was obviously higher than that(67%) of synchronous MMBE in detection of aneurysms smaller than 3 mm.The image quality of VCTDSA was superior to that of synchronous MMBE. And the postprocessing time of VCTDSA was shorter than that of synchronous MMBE.Conclusion: VCTDSA is a convenient and fast technique, and the resulting images are actual and reliable.VCTDSA is superior to synchronous MMBE in detection and diagnosis of intracranial aneurysm.
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