| Background:With the advent of modern256slice multidetector computed tomography(MDCT) scanners, the scan acquisition time has greatly reduced and the image qualityhas further improved owing to its high sapital as well as temporal resolution. Howeverwith the development of new Hybrid Iterative Reconstruction (HIR) algorithm up to80%dose reduction,68%sapital resolution improvement can be achieved.Craniocervical computed tomography angiography (CTA) has become an importanttool for the assessment of the extracranial and intracranial vessels.Purpose:The purpose of this study is to prospectively compare the image quality andradiation dose in two different256-slice MDCT using different parameters i.e.120kV,250mAs and100kV,225mAs technique for craniocervical CT angiography.Materials and Methods:This prospective study was approved by institutional review board (IRB) andinformed consent was obtained from all the patients. Thirty patients were randomlyassigned into two groups (Group A and B), each comprising15patients. All patientsunderwent craniocervical CTA examination. Group A (10men,5women; mean age57.13±11.27; age range41–73years) received120kV X-ray tube potential and250mAs tube current with image analysis performed on Extended Brilliance Workspace[EBW] version4.5.2.40007. Group B (9men,6women; mean age58.80±12.55; agerange41–76years) received100kV X-ray tube potential and225mAs tube currentwith image analysis performed on Intelli Space Portal [ISP] version5.0.1.10050. Thentwo blinded radiologist analyzed image quality of craniocervical CTA independently.They performed subjective image and objective image quality. The subjective imagequality was measured in four parameters, image graininess, vessel sharpness, streakartifact, and overall image quality, assessed according to4-point scoring scale. Theobjective image quality was measured in terms of signal to noise ratio (SNR), andcontrast to noise ratio (CNR). The radiation dose was also measured in both groups.The effective radiation dose (ED) was calculated using CT dose volume Index (CTDIvol.), dose-length product (DLP) and conversion coefficient for chest(conversion factor k=0.014mSv mGy-1cm-1).Result:The quantitative image quality of iterative reconstruction algorithm wassignificant compared to FBP. The mean image noise of100kV protocol was0.51times lesser than120kV protocol (5.96±1.24vs11.59±1.41respectively; P-value<0.001). The mean attenuation value with100kV is1.45times lesser than in120kVprotocol (230.52±26.83vs333.96±35.68respectively; P-value <0.0001).The objective image quality of the reduced protocol of100kv with225mAs wassignificantly better than the120kV with250mAs (mean SNR39.97±7.33vs29.08±3.04respectively; P <0.001and mean CNR,29.11±4.65vs23.98±1.96respectively; P <0.0001).The subjective image quality between two protocols (120kV protocol and100kV protocol) by2radiologist. In subjective image quality assessment parametersimage graininess and artifact was statistically significant in radiologist I while onlyimage graininess in radiologist II. The mean image scores in both the groups byradiologist1and radiologist2was (3.65±0.48vs3.33±0.63respectively, p=0.002)and (3.73±0.45vs3.40±0.69respectively, p=0.002). The inter-observerreproducibility was slight0.2for all four parameters.The radiation dose was found to be reduced by55%in group B (100kV,225mAs) compared to group A (120kV,250mAs); ED (6.24±0.45vs.11.35±0.83;P<0.0001) in craniocervical CTA.Conclusion:Hybrid Iterative Reconstruction (HIR) Algorithm significantly improve theimage quality in craniocervical CT, as well as helps to lower the radiation dose whilemaintaining the image quality. |
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