Influence of Iterative Reconstruction Algorithm on Image Quality of Ultra Low-Dose CT Protocol of the Lumber Spine

Israa Jamal Mostafa Odeh
اسراء جمال مصطفى عودة
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Al-quds University
Quantitative computed tomography (QCT) or QCT Densitometry is a new examination in computed tomography (CT) used to diagnose bone mineral density. QCT scan is a low-dose protocol with an effective dose value of 1 millisievert (mSv)The dose reduction technique leads to a significant reduction in effective dose at the expense of image quality as it uses the traditional filtered back projection (FBP) method. This study aims to evaluate the impact of the iterative reconstruction (IR) algorithm on image quality and measure the effective dose from low-dose QCT protocol of the lumbar spine CT. This study consisted of 33 patients ( all patients files in the selected period) from both genders aged who were clinically suspected of lower back pain and Osteoporosis during the period from 7th July 2021 to the date of ethical approval. Different types of algorithms, FBP, Sinogram Affirmed Iterative Reconstruction (SAFIRE), and iterative beam hardening correction (iBHC) were applied. The image quality criteria including CT number, noise, and signal were analyzed by three regions of interest (ROIs). The three RIOs represent the following anatomy (intervertebral disc, right psoas muscle, and dural sac) respectively, from region 1 – region 3. In addition, for qualitative analysis, the images reconstructed by SAFIRE level 5 (s5) were compared with the grading system by European standards for CT for the evaluation of disc herniation and lumber spine. The noticed results for the signal-to-noise ratio (SNR) and contrast-to-nose ratio (CNR), showed optimization for images when reconstructed by SAFIRE level 5, with mean SNR of 2.9 which is significantly higher than other reconstruction algorithms (p<0.05). Also, the mean CNR was 2.9 which is significantly higher than other reconstruction techniques (p<0.05). The mean effective dose for the whole population was 1.9 mSv. The SAFIRE algorithm was able to reduce the noise levels at all RIO. The quality of the images according to the grading system by European standards for CT for the evaluation of disc herniation and lumber spine.was similar among the radiologists with good agreement. There is no relationship between body mass index (BMI) and SNR, CNR, and effective dose. In conclusion the use of QCT and using SAFIRE level 5 resulted in higher SNR, CNR, and fewer noise values compared to classic FBP and other levels of SAFIRE. Also, QCT using SAFIRE level 5 revealed equivalent image quality compared to standard protocols of the lumbar spine CT.