Current status of low dose multi-detector CT in the urinary tract

Over the past several years,advances in the technical domain of computed tomography(CT) have influenced the trend of imaging modalities used in the clinical evaluation of the urinary system.Renal collecting systems can be illustrated more precisely with the advent of multi-detector row CT through thinner slices,high speed acquisitions,and enhanced longitudinal spatial resolution resulting in improved reformatted coronal images.On the other hand,a significant increase in exposure to ionizing radiation,especially in the radiosensitive organs,such as the gonads,is a concern with the increased utilization of urinary tract CT.In this article,we discuss the strategies and techniques availablefor reducing radiation dose for a variety of urinary tractCT protocols with metabolic clinical examples.We also reviewed CT for hematuria evaluation and related scan parameter optimization such as,reducing the number of acquisition phases,CT angiography of renal donors and lowering tube potential,when possible.

有为腹的 CT 的非线性的适应过滤器的申请的放射剂量减小

AIM:To evaluate the effect of non-linear adaptive filters (NLAF) on abdominal computed tomography (CT) images acquired at different radiation dose levels.METHODS:Nineteen patients (mean age 61.6 ± 7.9 years,M:F=8:11) gave informed consent for an Institutional Review Board approved prospective study involving acquisition of 4 additional image series (200,150,100,50 mAs and 120 kVp) on a 64 slice multidetector row CT scanner over an identical 10 cm length in the abdomen.The CT images acquired at 150,100 and 50 mAs were processed with the NLAF.Two radiologists reviewed unprocessed and processed images for image quality in a blinded randomized manner.CT dose index volume,dose length product,patient weight,transverse diameters,objective noise and CT numbers wererecorded.Data were analyzed using Analysis of Variance and Wilcoxon signed rank test.RESULTS:Of the 31 lesions detected in abdominal CT images,28 lesions were less than 1 cm in size.Subjective image noise was graded as unacceptable in unprocessed images at 50 and 100 mAs,and in NLAF processed images at 50 mAs only.In NLAF processed images,objective image noise was decreased by 21% (14.4 ± 4/18.2 ± 4.9) at 150 mAs,28.3% (15.7 ± 5.6/21.9 ± 4) at 100 mAs and by 39.4% (18.8 ± 9/30.4 ± 9.2) at 50 mAs compared to unprocessed images acquired at respective radiation dose levels.At 100 mAs the visibility of smaller structures improved from suboptimal in unprocessed images to excellent in NLAF processed images,whereas diagnostic confidence was respectively improved from probably confident to fully confident.CONCLUSION:NLAF lowers image noise,improves the visibility of small structures and maintains lesion conspicuity at down to 100 mAs for abdominal CT.

Size-specific dose estimates: Localizer or transverse abdominal computed tomography images?

AIM: To investigate effect of body dimensions obtained from localizer radiograph and transverse abdominal computed tomography(CT) images on Size Specific Dose Estimate. METHODS: This study was approved by Institutional Review Board and was compliant with Health Insurance Portability and Accountability Act. Fifty patients with abdominal CT examinations(58 ± 13 years, Male: Female 28:22) were included in this study. Anteriorposterior(AP) and lateral(Lat) diameters were measured at 5 cm intervals from the CT exam localizer radiograph(simple X-ray image acquired for planning the CT exam before starting the scan) and transverse CT images. Average of measured AP and Lat diameters, as well as maximum, minimum and mid location AP and Lat were measured on both image sets. In addition, off centering of patients from the gantry iso-center was calculated from the localizers. Conversion factors from American Association of Physicists in Medicine(AAPM) report 204 were obtained for AP, Lat, AP + Lat, and effective diameter(√ AP * Lat) to determine size specificdose estimate(SSDE) from the CT dose index volume(CTDIvol) recorded from the dose reports. Data were analyzed using SPSS v19. RESULTS: Total number of 5376 measurements was done. In some patients entire body circumference was not covered on either projection radiograph or transverse CT images; hence accurate measurement of AP and Lat diameters was not possible in 11%(278/2488) of locations. Forty one patients were off-centered with mean of 1.9 ± 1.8 cm(range: 0.4-7 cm). Conversion factors for attained diameters were not listed on AAPM look-up tables in 3%(80/2488) of measurements. SSDE values were significantly different compared to CTDIvol, ranging from 32% lower to 74% greater than CTDIvol. CONCLUSION: There is underestimation and overestimation of dose comparing SSDE values to CTDIvol. Localizer radiographs are associated with overestimation of patient size and therefore underestimation of SSDE.

Assessment of sub-milli-sievert abdominal computed tomography with iterative reconstruction techniques of different vendors

AIM: To assess diagnostic image quality of reduced dose(RD) abdominal computed tomography(CT) with 9 iterative reconstruction techniques(IRTs) from 4 different vendors to the standard of care(SD) CT.METHODS: In an Institutional Review Board approved study, 66 patients(mean age 60 ± 13 years, 44 men, and 22 women) undergoing routine abdomen CT on multi-detector CT(MDCT) scanners from vendors A, B, and C(≥ 64 row CT scanners)(22 patients each) gave written informed consent for acquisition of an additional RD CT series. Sinogram data of RD CT was reconstructed with two vendor-specific and a vendor-neutral IRTs(A-1, A-2, A-3; B-1, B-2, B-3; and C-1, C-2, C-3) and SD CT series with filtered back projection. Subjective image evaluation was performed by two radiologists for each SD and RD CT series blinded and independently. All RD CT series(198) were assessed first followed by SD CT series(66). Objective image noise was measured for SD and RD CT series. Data were analyzed by Wilcoxon signed rank, kappa, and analysis of variance tests.RESULTS: There were 13/50, 18/57 and 9/40 missed lesions(size 2-7 mm) on RD CT for vendor A, B, and C, respectively. Missed lesions includes liver cysts, kidney cysts and stone, gall stone, fatty liver, and pancreatitis. There were also 5, 4, and 4 pseudo lesions(size 2-3 mm) on RD CT for vendor A, B, and C, respectively. Lesions conspicuity was sufficient for clinical diagnostic performance for 6/24(RD-A-1), 10/24(RD-A-2), and 7/24(RD-A-3) lesions for vendor A; 5/26(RD-B-1), 6/26(RD-B-2), and 7/26(RD-B-3) lesions for vendor B; and 4/20(RD-C-1) 6/20(RD-C-2), and 10/20(RD-C-3) lesions for vendor C(P = 0.9). Mean objective image noise in liver was significantly lower for RD A-1 compared to both RD A-2 and RD A-3 images(P < 0.001). Similarly, mean objective image noise lower for RD B-2(compared to RD B-1, RD B-3) and RD C-3(compared to RD C-1 and C-2)(P = 0.016).CONCLUSION: Regardless of IRTs and MDCT vendors, abdominal CT acquired at mean CT dose index volume 1.3 m Gy is not sufficient to retain clinical diagnostic performance.

Relationship between patient centering,mean computed tomography numbers and noise in abdominal computed tomography:Influence of anthropomorphic parameters

AIM:To determine the influence of anthropomorphic parameters on the relationship between patient centering,mean computed tomography(CT) numbers and quantitative image noise in abdominal CT.METHODS:Our Institutional Review Board approved study included 395 patients(age range 21-108,years;male:female = 195:200) who underwent contrast-enhanced abdominal CT on a 16-section multi-detector row scanner(GE LightSpeed 16).Patient centering in the gantry isocenter was measured from the lateral localizer radiograph(off center S = patient off centered superior to isocenter;off center I = patient off centered inferior to isocenter).Mean CT numbers(Hounsfield Units:HU) and noise(standard deviation of CT numbers:SD) were measured in the anterior(aHU,aSD) and posterior(pHU,pSD) abdominal wall subcutaneous fat and liver parenchyma(LivHU,LivSD) at the level of the porta hepatis.Patients' age,gender,weight,body mass index and maximal anteroposterior diameter were recorded.The data were analyzed using linear regression analysis.RESULTS:Most patients(81%;320/395) were not correctly centered in the gantry isocenter for abdominal CT scanning.Mean CT numbers in the abdominal wall increased significantly with an increase in the offcentering distance,regardless of the direction of the off-center(P < 0.05).There was a substantial increase in pSD(P = 0.01) and LivSD(P = 0.017) with off-centering.Change in mean CT numbers and image noise along the off-center distance was influenced by the patient size(P < 0.01).CONCLUSION:Inappropriate patient centering for CT scanning adversely affects the reliability of mean CT numbers and image noise.