Organ-based tube current modulation versus spectral shaping via tin prefiltration: What does bismuth breast shielding add in low-dose lung CT?

PURPOSE: Since organ-based tube current modulation (OBTCM) and tin prefiltration are limited on their own in lowering the dose of lung CT examinations, this experimental study was designed to investigate whether combinations with anterior patient shielding can increase the dose reduction potential. MATERIAL AND METHODS: Three pairs of scan protocols without/with breast shield (P1/P2: standard 120kVp, P3/P4: OBTCM at 100 kVp, P5/P6: Sn 100 kVp) were employed for radiation exposure and image quality comparisons on an anthropomorphic Alderson-Rando phantom. Equivalent doses were measured in eleven sites via thermoluminescent dosimetry and the effective dose was obtained by summation of the weighted organ doses. Dose-weighted contrast-to-noise ratios (CNRD) were calculated and four radiologists independently assessed the quality of images generated with each protocol. RESULTS: While no significant difference was determined between standard and OBTCM protocols regardless of breast shield (p ≥ 0.068), equivalent doses with spectral shaping were substantially lower (p ≤ 0.003). The highest effective dose was ascertained for standard scans (P1/P2: 7.3/6.8 mSv) with a dose reduction of 8.0 % via breast shielding. The use of a bismuth shield was more beneficial in OBTCM (P3/P4: 6.6/5.3 mSv) and spectral shaping (P5/P6: 0.7/0.6 mSv), reducing the effective dose by 19.8 % and 13.9 %, respectively. Subjective assessment favoured standard protocol P1 over tin prefiltration low-dose scans (p ≤ 0.032), however, no scan protocol entailed diagnostically insufficient image quality. CONCLUSIONS: Whereas breast shielding is particularly beneficial in combination with OBTCM, spectral shaping via tin prefiltration facilitates the most pronounced dose reduction in lung CT imaging with acceptable image quality.

Thermoluminescence Dosimetry in Abdominal CT for Urinary Stone Detection: Effective Radiation Dose Reduction With Tin Prefiltration at 100 kVp.

OBJECTIVES: Spectral shaping via tin prefiltration has gained recognition for dose saving in high-contrast imaging tasks. The aim of this phantom dosimetry study was to investigate whether the use of tin filters can also reduce the effective radiation dose in 100 kVp abdominal computed tomography (CT) compared with standard low-dose scans for suspected urolithiasis. METHODS: Using a third-generation dual-source CT scanner, 4 scan protocols each were used on a standard (P1-P4) and a modified obese Alderson-Rando phantom (P5-P8), in which 11 urinary stones of different compositions were placed. Hereby 1 scan protocol represented standard low-dose settings (P1/P5: 110 kVp/120 kVp), whereas 3 experimental protocols used low-kilovoltage spectral shaping (P2/P3/P4 and P6/P7/P8: 100 kVp with tin prefiltration). Radiation dose was recorded by thermoluminescent dosimeters at 24 measurement sites. For objective assessment of image quality, dose-weighted contrast-to-noise ratios were calculated and compared between scan protocols. Additional subjective image quality analysis was performed by 2 radiologists using equidistant 5-point scales for estimation image noise, artifacts, kidney stone detectability, and delineation of bone and soft tissue. RESULTS: Both conventional low-dose protocols without tin prefiltration were associated with the highest individual equivalent doses and the highest effective radiation dose in the experimental setup (P1: 0.29-6.43 mGy, 1.45-1.83 mSv; P5: 0.50-9.35 mGy, 2.33-2.79 mSv). With no false-positive diagnoses, both readers correctly detected each of the 11 urinary calculi irrespective of scan protocol and phantom configuration. Protocols using spectral shaping via tin prefiltration allowed for effective radiation dose reduction of up to 38% on the standard phantom and 18% on the modified obese phantom, while maintaining overall diagnostic image quality. Effective dose was approximately 10% lower in a male versus female anatomy and could be reduced by another 10% if gonadal protection was used ( P < 0.001). CONCLUSIONS: Spectral shaping via tin prefiltration at 100 kVp is a suitable means to reduce the effective radiation dose in abdominal CT imaging of patients with suspected urolithiasis. The dose reduction potential is slightly less pronounced in a modified phantom emulating an obese body composition compared with a standard phantom.

Tin-filtered 100 kV Ultra-low-dose Abdominal CT for Calculi Detection in the Urinary Tract: A Comparative Study of 510 Cases.

OBJECTIVES: For detection of urinary calculi, unenhanced low-dose computed tomography is the method of choice, outperforming radiography and ultrasound. This retrospective monocentric study aims to compare a clinically established, dedicated low-dose imaging protocol for detection of urinary calculi with an ultra-low-dose protocol employing tin prefiltration at a standardized tube voltage of 100 kVp. METHODS: Two study arms included a total of 510 cases. The "low-dose group" was comprised of 290 individuals (96 women; age 49 ± 16 years; BMI 27.23 ± 5.60 kg/m2). The "ultra-low-dose group" with Sn100 kVp consisted of 220 patients (84 women; age 47 ± 17 years; BMI 26.82 ± 5.62 kg/m2). No significant difference was ascertained for comparison of age (p = 0.132) and BMI (p = 0.207) between cohorts. For quantitative assessment of image quality, image noise was assessed. RESULTS: No significant difference regarding frequency of calculi detection was found between groups (p = 0.596). Compared to the low-dose protocol (3.08 mSv; IQR 2.22-4.02 mSv), effective dose was reduced by 62.35% with the ultra-low-dose protocol employing spectral shaping (1.16 mSv; IQR 0.89-1.54 mSv). Image noise was calculated at 18.90 (IQR 17.39-21.20) for the low-dose protocol and at 18.69 (IQR 17.30-21.62) for the ultra-low-dose spectral shaping protocol. No significant difference was ascertained for comparison between groups (p = 0.793). CONCLUSION: For urinary calculi detection, ultra-low-dose scans utilizing spectral shaping by means of tin prefiltration at 100 kVp allow for considerable dose reduction of up to 62% over conventional low-dose CT without compromising image quality.

Low-Dose CT Imaging of the Pelvis in Follow-up Examinations-Significant Dose Reduction and Impact of Tin Filtration: Evaluation by Phantom Studies and First Systematic Retrospective Patient Analyses.

OBJECTIVES: Low-dose (LD) computed tomography (CT) is still rarely used in musculoskeletal (MSK) radiology. This study evaluates the potentials of LD CT for follow-up pelvic imaging with special focus on tin filtration (Sn) technology for normal and obese patients with and without metal implants. MATERIALS AND METHODS: In a phantom study, 5 different LD and normal-dose (ND) CT protocols with and without tin filtration were tested using a normal and an obese phantom. Iterative reconstruction (IR) and filtered back projection (FBP) were used for CT image reconstruction. In a subsequent retrospective patient study, ND CT images of 45 patients were compared with follow-up tin-filtered LD CT images with a 90% dose reduction. Sixty-four percent of patients contained metal implants at the follow-up examination. Computed tomography images were objectively (image noise, contrast-to-noise ratio [CNR], dose-normalized contrast-to-noise ratio [CNRD]) and subjectively, using a 6-point Likert score, evaluated. In addition, the figure of merit was calculated. For group comparisons, paired t tests, Wilcoxon signed rank test, analysis of variance, or Kruskal-Wallis tests were used, where applicable. RESULTS: The LD Sn protocol with 67% dose reduction resulted in equal values in qualitative (Likert score) and quantitative image analysis (image noise) compared with the ND protocol in the phantom study. For follow-up examinations, dose could be reduced up to 90% by using Sn LD CT scans without impairment in the clinical study. However, metal implants resulted in a mild impairment of Sn LD as well as ND CT images. Cancellous bone ( P < 0.001) was assessed worse and cortical bone ( P = 0.063) equally in Sn LD CT images compared with ND CT images. Figure of merit values were significant ( P ≤ 0.02) lower and hence better in Sn LD as in ND protocols. Obese patients benefited in particular from tin filtration in LD MSK imaging in terms of image noise and CNR ( P ≤ 0.05). CONCLUSIONS: Low-dose CT scans with tin filtration allow maximum dose reduction while maintaining high image quality for certain clinical purposes, for example, follow-up examinations, especially metal implant position, material loosening, and consolidation controls. Overweight patients benefit particularly from tin filter technology. Although metal implants decrease image quality in ND as well as in Sn LD CT images, this is not a relevant limitation for assessability.

Metal Artifact Reduction With Tin Prefiltration in Computed Tomography: A Cadaver Study for Comparison With Other Novel Techniques.

OBJECTIVES: With the aging population and thus rising numbers of orthopedic implants (OIs), metal artifacts (MAs) increasingly pose a problem for computed tomography (CT) examinations. In the study presented here, different MA reduction techniques (iterative metal artifact reduction software [iMAR], tin prefilter technique, and dual-energy CT [DECT]) were compared. MATERIALS AND METHODS: Four human cadaver pelvises with OIs were scanned on a third-generation DECT scanner using tin prefilter (Sn), dual-energy (DE), and conventional protocols. Virtual monoenergetic CT images were generated from DE data sets. Postprocessing of CT images was performed using iMAR. Qualitative (bony structures, MA, image noise) image analysis using a 6-point Likert scale and quantitative image analysis (contrast-to-noise ratio, standard deviation of background noise) were performed by 2 observers. Statistical testing was performed using Friedman test with Nemenyi test as a post hoc test. RESULTS: The iMAR Sn 150 kV protocol provided the best overall assessability of bony structures and the lowest subjective image noise. The iMAR DE protocol and virtual monochromatic image (VMI) ± iMAR achieved the most effective metal artifact reduction (MAR) (P < 0.05 compared with conventional protocols). Bony structures were rated worse in VMI ± iMAR (P < 0.05) than in tin prefilter protocols ± iMAR. The DE protocol ± iMAR had the lowest contrast-to-noise ratio (P < 0.05 compared with iMAR standard) and the highest image noise (P < 0.05 compared with iMAR VMI). The iMAR reduced MA very efficiently. CONCLUSIONS: When considering MAR and image quality, the iMAR Sn 150 kV protocol performed best overall in CT images with OI. The iMAR generated new artifacts that impaired image quality. The DECT/VMI reduced MA best, but experienced from a lack of resolution of bony fine structures.

Low-Dose CT in Pelvic Imaging: Comparing Dose and Image Quality in Relation to Clinical Value in a Phantom Study.

OBJECTIVE. The aim of this phantom study was to determine whether low-dose CT of the pelvis can be performed using a dose similar to that used in a standard radio-graphic examination and to ascertain whether CT, with its better delineation of complex structures, has greater clinical value than radiography and therefore will result in improved patient care. Special consideration was given to CT performed using the tin filtration technique. MATERIALS AND METHODS. For dose comparison, an anthropomorphic phantom with 20 thermoluminescent dosimeters, two different CT scanners, and three conventional radiography devices were used. Seven CT protocols (including tin filtration) and four different radiographic examinations were performed. Dose calculations, objective and subjective evaluations of image quality, and figure-of-merit calculations were compared among the techniques. Furthermore, the images obtained were evaluated in a clinical context. Intraclass correlation was determined for the subjective results. RESULTS. The dose values of the tested low-dose CT protocols, in particular those using the tin filtration technique, corresponded to or were only slightly higher than the dose values of conventional pelvic radiographic images obtained in three views. Low-dose CT examinations were rated sufficient for consolidation control and had an informative value that was significantly higher than that of conventional radiography. Tin filtering showed the best results for low-dose CT in terms of combining dose and clinically relevant image quality. CONCLUSION. In this phantom study, low-dose CT was superior to radiography for visualizing and evaluating the dorsal pelvic ring, with only marginally higher radiation exposure occurring when the latest-generation CT systems were used. Tin filtration can improve image quality, create further dose reductions, or provide both benefits.

Dose Reduction in Dental CT: A Phantom Study With Special Focus on Tin Filter Technique.

OBJECTIVE. The purpose of this study was to determine in a phantom the dose exposure of different dental 3D sectional imaging methods (CT and cone-beam CT [CBCT]) and different CT protocols. The aim was to establish optimal protocols with the lowest possible dose and diagnostically high image quality with special consideration given to tin prefiltration. MATERIALS AND METHODS. Dose was determined with thermoluminescence detectors at 20 different measuring points on an anthropomorphic phantom. Eight different CT protocols with and without tin filtering were compared with iterative reconstruction methods and a standard CBCT protocol. Objective and subjective image evaluations and a figure-of-merit analysis of the image data were performed by radiologists and maxillofacial surgeons. RESULTS. The determined dose-length products of the nine examinations were 5.0-111.9 mGy · cm with a calculated effective whole body dose of 20.7-505.9 µSv. Cone-beam CT was in the upper midfield with an effective dose of 229.3 µSv. On the basis of dose, objective image quality, and clinical evaluation results, tin filter protocols performed best. Protocols with higher doses were significantly less useful in the figure of merit comparison but because of their detailed bony representation are particularly necessary to answer certain questions about trauma and tumors. CONCLUSION. The use of tin filtering can reduce dose in dental CT examinations, compared with standard low-dose examinations, while maintaining good image quality. The dose performance is significantly inferior even to that of a cone-beam CT examination. High-dose protocols are necessary only for certain questions.