Iterative reconstruction technique for reducing body radiation dose at CT: feasibility study. AJR Am J Roentgenol. 2009;193:764-771. [PMID: 19696291 DOI: 10.2214/ajr.09.2397]

Radiation exposure of ovarian cancer patients: contribution of CT examinations performed on different MDCT (16 and 64 slices) scanners and image quality evaluation: an observational study

The objective of this study is to compare radiation doses given to ovarian cancer patients by different computed tomographies (CTs) and to evaluate association between doses and subjective and objective image quality.CT examinations included were performed either on a 16-slice CT, equipped with automatic z-axis tube current modulation, or on a 64-slice CT, equipped with z-axis, xy-axis modulation, and adaptive statistical iterative algorithm (ASIR). Evaluation of dose included the following dose descriptors: volumetric CT dose index (CTDIvol), dose length product (DLP), and effective dose (E). Objective image noise was evaluated in abdominal aorta and liver. Subjective image quality was evaluated by assessment of image noise, spatial resolution and diagnostic acceptability.Mean and median CTDIvol, DLP, and E; correlation between CTDIvol and DLP and patients' weight; comparison of objective noise for the 2 scanners; association between dose descriptors and subjective image quality.The 64-slice CT delivered to patients 24.5% lower dose (P < 0.0001) than 16-slice CT. There was a significant correlation between all dose descriptors (CTDIvol, DLP, E) and weight (P < 0.0001). Objective noise was comparable for the 2 CT scanners. There was a significant correlation between dose descriptors and image noise for the 64-slice CT, and between dose descriptors and spatial resolution for the 16-slice CT.Current dose reduction systems may reduce radiation dose without significantly affecting image quality and diagnostic acceptability of CT exams.

Degradation of CT Low-Contrast Spatial Resolution Due to the Use of Iterative Reconstruction and Reduced Dose Levels

PURPOSE

To determine the dose reduction that could be achieved without degrading low-contrast spatial resolution (LCR) performance for two commercial iterative reconstruction (IR) techniques, each evaluated at two strengths with many repeated scans.

MATERIALS AND METHODS

Two scanner models were used to image the American College of Radiology (ACR) CT accreditation phantom LCR section at volume CT dose indexes of 8, 12, and 16 mGy. Images were reconstructed by using filtered back projection (FBP) and two manufacturers' IR techniques, each at two strengths (moderate and strong). Data acquisition and reconstruction were repeated 100 times for each, yielding 1800 images. Three diagnostic medical physicists reviewed the LCR images in a blinded fashion and graded the visibility of four 6-mm rods with a six-point scale. Noninferiority and inferiority-superiority analyses were used to interpret the differences in LCR relative to FBP images acquired at 16 mGy.

RESULTS

LCR decreased with decreasing dose for all reconstructions. Relative to FBP and full dose, 25%-50% dose reductions resulted in inferior LCR for vendors 1 and 2 for FBP and 25% dose reductions resulted in inferior and equivalent performance for vendor 1 and equivalent and superior performance for vendor 2 at moderate and strong IR settings, respectively. When dose was reduced by 50%, both IR techniques resulted in inferior LCR at both strength settings.

CONCLUSION

For radiation dose reductions of 25% or more, the ability to resolve the four 6-mm rods in the ACR CT accreditation phantom can be lost.

United iterative reconstruction for spectral computed tomography

Spectral computed tomography (CT) has attracted considerable attention because of its energy-resolving capability in identifying and discriminating materials. The use of a narrow energy bin can improve energy resolution. However, a narrow energy bin has high noise ratio, which degrades the imaging quality of spectral CT. To address this problem, this study exploits the structure correlations of images in the energy domain and proposed two types of united iterative reconstruction (UIR) algorithms. One type uses the well-reconstructed broad-spectrum image, with all available photons, as a constraint, whereas the other type uses a pseudo narrow-energy image, which is estimated with the use of our proposed structure-coupling (SC) method, as a constraint. The SC method utilizes local structures to connect images that are reconstructed with broad-spectrum and narrow-energy CT datasets. Given a broad-spectrum image, the SC method can accurately estimate its corresponding narrow-energy image. Results show that UIR algorithms significantly outperform conventional iterative reconstruction algorithms for narrow-energy image reconstruction in spectral CT. Among the UIR algorithms, SC-UIR yields the best results.

Radiation dose and image quality in pediatric chest CT: effects of iterative reconstruction in normal weight and overweight children

BACKGROUND

New CT reconstruction techniques may help reduce the burden of ionizing radiation.

OBJECTIVE

To quantify radiation dose reduction when performing pediatric chest CT using a low-dose protocol and 50% adaptive statistical iterative reconstruction (ASIR) compared with age/gender-matched chest CT using a conventional dose protocol and reconstructed with filtered back projection (control group) and to determine its effect on image quality in normal weight and overweight children.

MATERIALS AND METHODS

We retrospectively reviewed 40 pediatric chest CT (M:F = 21:19; range: 0.1-17 years) in both groups. Radiation dose was compared between the two groups using paired Student's t-test. Image quality including noise, sharpness, artifacts and diagnostic acceptability was subjectively assessed by three pediatric radiologists using a four-point scale (superior, average, suboptimal, unacceptable).

RESULTS

Eight children in the ASIR group and seven in the control group were overweight. All radiation dose parameters were significantly lower in the ASIR group (P < 0.01) with a greater than 57% dose reduction in overweight children. Image noise was higher in the ASIR group in both normal weight and overweight children. Only one scan in the ASIR group (1/40, 2.5%) was rated as diagnostically suboptimal and there was no unacceptable study.

CONCLUSION

In both normal weight and overweight children, the ASIR technique is associated with a greater than 57% mean dose reduction, without significantly impacting diagnostic image quality in pediatric chest CT examinations. However, CT scans in overweight children may have a greater noise level, even when using the ASIR technique.

MDCT arthrography of the hip: value of the adaptive statistical iterative reconstruction technique and potential for radiation dose reduction

OBJECTIVE

The purpose of this article is to assess the effect of the adaptive statistical iterative reconstruction (ASIR) technique on image quality in hip MDCT arthrography and to evaluate its potential for reducing radiation dose.

SUBJECTS AND METHODS

Thirty-seven patients examined with hip MDCT arthrography were prospectively randomized into three different protocols: one with a regular dose (volume CT dose index [CTDIvol], 38.4 mGy) and two with a reduced dose (CTDIvol, 24.6 or 15.4 mGy). Images were reconstructed using filtered back projection (FBP) and four increasing percentages of ASIR (30%, 50%, 70%, and 90%). Image noise and contrast-to-noise ratio (CNR) were measured. Two musculoskeletal radiologists independently evaluated several anatomic structures and image quality parameters using a 4-point scale. They also jointly assessed acetabular labrum tears and articular cartilage lesions.

RESULTS

With decreasing radiation dose level, image noise statistically significantly increased (p=0.0009) and CNR statistically significantly decreased (p=0.001). We also found a statistically significant reduction in noise (p=0.0001) and increase in CNR (p≤0.003) with increasing percentage of ASIR; in addition, we noted statistically significant increases in image quality scores for the labrum and cartilage, subchondral bone, overall diagnostic quality (up to 50% ASIR), and subjective noise (p≤0.04), and statistically significant reductions for the trabecular bone and muscles (p≤0.03). Regardless of the radiation dose level, there were no statistically significant differences in the detection and characterization of labral tears (n=24; p=1) and cartilage lesions (n=40; p≥0.89) depending on the ASIR percentage.

CONCLUSION

The use of up to 50% ASIR in hip MDCT arthrography helps to reduce radiation dose by approximately 35-60%, while maintaining diagnostic image quality comparable to that of a regular-dose protocol using FBP.

HRCT in cystic fibrosis in patients with CFTR I1234V mutation: Assessment of scoring systems with low dose technique using multidetector system and correlation with pulmonary function tests

Background and Aims:

Pulmonary changes in patients with cystic fibrosis (CF) with CFTR I1234V mutation have not been extensively documented. Impact of geographic influence on phenotypical expression is largely unknown. This descriptive clinical study presents the high-resolution computed tomography (HRCT) pulmonary findings and computed tomography (CT) scoring with respect to pulmonary function tests (PFT) in a small subset of CF group.

Materials and Methods:

We examined 29 patients between 2 and 31 years of age with CFTR I1234V mutation. HRCT and PFT were performed within 2 weeks of each other. Imaging abnormalities on HRCT were documented and analyzed by utilizing the scoring system described by Bhalla et al., Brody et al., Helbich et al.,and Santamaria et al. Efficacy of the scoring system with respect to PFT was compared.

Statistical Analysis:

Inter-observer reliability of the scoring systems was tested using intraclass correlation (ICC) between the two observers. Spearman correlation coefficients were calculated between the scoring systems and between the scoring systems and PFT results.

Results:

In our study, right upper and middle lobes were the most frequently involved sites of involvement. Bronchiectasis and peribronchial thickening were the most frequent imaging findings. Scores with all four scoring systems were reproducible, with good ICC coefficient of 0.69. There was good agreement between senior radiologists in all scoring systems.

Conclusion:

We noted pulmonary imaging abnormalities in a large majority (96%) of our CF patients. There was no significant difference in the CT scores observed from various systems. The CT evaluation system by Broody is detailed and time consuming, and is ideal for research and academic setup. On the other hand, the systems by Bhalla and Santamaria are easy to use, quick, and equally informative. We found the scoring system by Santamaria preferable over that of Bhalla by virtue of additional points of evaluation and ease of use, and therefore better suited for busy clinical practice.

CT of the pancreas: comparison of image quality and pancreatic duct depiction among model-based iterative, adaptive statistical iterative, and filtered back projection reconstruction techniques

The purpose of this study is to compare CT images of the pancreas reconstructed with model-based iterative reconstruction (MBIR), adaptive statistical iterative reconstruction (ASiR), and filtered back projection (FBP) techniques for image quality and pancreatic duct (PD) depiction. Data from 40 patients with contrast-enhanced abdominal CT [CTDIvol: 10.3 ± 3.0 (mGy)] during the late arterial phase were reconstructed with FBP, 40% ASiR-FBP blending, and MBIR. Two radiologists assessed the depiction of the main PD, image noise, and overall image quality using 5-point scale independently. Objective CT value and noise were measured in the pancreatic parenchyma, and the contrast-to-noise ratio (CNR) of the PD was calculated. The Friedman test and post-hoc multiple comparisons with Bonferroni test following one-way ANOVA were used for qualitative and quantitative assessment, respectively. For the subjective assessment, scores for MBIR were significantly higher than those for FBP and 40% ASiR (all P < 0.001). No significant differences in CT values of the pancreatic parenchyma were noted among FBP, 40% ASiR, and MBIR images (P > 0.05). Objective image noise was significantly lower and CNR of the PD was higher with MBIR than with FBP and 40% ASiR (all P < 0.05). Our results suggest that pancreatic CT images reconstructed with MBIR have lower image noise, better image quality, and higher conspicuity and CNR of the PD compared with FBP and ASiR.

Diagnostic Performance and Dose Comparison of Filtered Back Projection and Adaptive Iterative Dose Reduction Three-dimensional CT Enterography in Children and Young Adults

PURPOSE

To investigate diagnostic performance and radiation dose with the use of computed tomographic (CT) enterography in children and young adults and to compare reconstruction with filtered back projection (FBP) to that with adaptive iterative dose reduction (AIDR) with three-dimensional (3D) processing.

MATERIALS AND METHODS

This retrospective investigation was HIPAA compliant and approved by the institutional review board. Informed consent was waived. CT enterographic examinations performed between October 2008 and June 2009 with FBP and between August 2012 and April 2014 with AIDR 3D in patients who had received histologic evaluation within 45 days of imaging were included. Two reviewers retrospectively and independently evaluated the studies for findings of active inflammation, and diagnostic performance and interreader reliability were assessed. The reference standard was histologic findings. Objective and subjective image quality also was assessed. The size-specific dose estimate was compared between the two groups. Two-sample t tests or analysis of variance tests were performed to assess for differences in diagnostic accuracy, image quality, and radiation dose between the FBP and AIDR 3D examinations.

RESULTS

Fifty patients were included in the FBP group (mean age, 14.1 years; range, 8-21 years) and 68 patients were in the AIDR 3D group (mean age, 13.2 years; range, 2-29 years). Sensitivity and specificity for detection of active inflammation were 96% (26 of 27) and 96% (22 of 23), respectively, for the FBP group and 90% (45 of 50) and 89% (16 of 18), respectively, for the AIDR 3D group. Dichotomous interreader reliability (κ) for the entire group was 0.86. The mean size-specific dose estimate for all weights was significantly lower for the AIDR 3D group (6.1 mGy ± 2.1) than that for the FBP group (16.7 mGy ± 5.2; P < .0001). No significant difference was found in objective image noise for soft-tissue structures (P = .2-.8).

CONCLUSION

CT enterography is highly accurate for detection of active inflammation in pediatric patients and has excellent interreader reliability. Reduced-dose CT enterography with AIDR 3D allowed substantial dose reduction compared with that used with FBP CT enterographic examinations, while maintaining a high diagnostic performance.

High-pitch, low-voltage and low-iodine-concentration CT angiography of aorta: assessment of image quality and radiation dose with iterative reconstruction

Objective

To assess the image quality of aorta obtained by dual-source computed tomography angiography (DSCTA), performed with high pitch, low tube voltage, and low iodine concentration contrast medium (CM) with images reconstructed using iterative reconstruction (IR).

Methods

One hundred patients randomly allocated to receive one of two types of CM underwent DSCTA with the electrocardiogram-triggered Flash protocol. In the low-iodine group, 50 patients received CM containing 270 mg I/mL and were scanned at low tube voltage (100 kVp). In the high-iodine CM group, 50 patients received CM containing 370 mg I/mL and were scanned at the tube voltage (120 kVp). The filtered back projection (FBP) algorithm was used for reconstruction in both groups. In addition, the IR algorithm was used in the low-iodine group. Image quality of the aorta was analyzed subjectively by a 3-point grading scale and objectively by measuring the CT attenuation in terms of the signal- and contrast-to-noise ratios (SNR and CNR, respectively). Radiation and CM doses were compared.

Results

The CT attenuation, subjective image quality assessment, SNR, and CNR of various aortic regions of interest did not differ significantly between two groups. In the low-iodine group, images reconstructed by FBP and IR demonstrated significant differences in image noise, SNR, and CNR (p<0.05). The low-iodine group resulted in 34.3% less radiation (4.4 ± 0.5 mSv) than the high-iodine group (6.7 ± 0.6 mSv), and 27.3% less iodine weight (20.36 ± 2.65 g) than the high-iodine group (28 ± 1.98 g). Observers exhibited excellent agreement on the aortic image quality scores (κ = 0.904).

Conclusions

CT images of aorta could be obtained within 2 s by using a DSCT Flash protocol with low tube voltage, IR, and low-iodine-concentration CM. Appropriate contrast enhancement was achieved while maintaining good image quality and decreasing the radiation and iodine doses.

A quantitative comparison of noise reduction across five commercial (hybrid and model-based) iterative reconstruction techniques: an anthropomorphic phantom study

OBJECTIVE. The objective of our study was to compare the performance of three hybrid iterative reconstruction techniques (IRTs) (ASiR, iDose4, SAFIRE) and their respective strengths for image noise reduction on low-dose CT examinations using filtered back projection (FBP) as the standard reference. Also, we compared the performance of these three hybrid IRTs with two model-based IRTs (Veo and IMR) for image noise reduction on low-dose examinations. MATERIALS AND METHODS. An anthropomorphic abdomen phantom was scanned at 100 and 120 kVp and different tube current-exposure time products (25-100 mAs) on three CT systems (for ASiR and Veo, Discovery CT750 HD; for iDose4 and IMR, Brilliance iCT; and for SAFIRE, Somatom Definition Flash). Images were reconstructed using FBP and using IRTs at various strengths. Nine noise measurements (mean ROI size, 423 mm(2)) on extracolonic fat for the different strengths of IRTs were recorded and compared with FBP using ANOVA. Radiation dose, which was measured as the volume CT dose index and dose-length product, was also compared. RESULTS. There were no significant differences in radiation dose and image noise among the scanners when FBP was used (p > 0.05). Gradual image noise reduction was observed with each increasing increment of hybrid IRT strength, with a maximum noise suppression of approximately 50% (48.2-53.9%). Similar noise reduction was achieved on the scanners by applying specific hybrid IRT strengths. Maximum noise reduction was higher on model-based IRTs (68.3-81.1%) than hybrid IRTs (48.2-53.9%) (p < 0.05). CONCLUSION. When constant scanning parameters are used, radiation dose and image noise on FBP are similar for CT scanners made by different manufacturers. Significant image noise reduction is achieved on low-dose CT examinations rendered with IRTs. The image noise on various scanners can be matched by applying specific hybrid IRT strengths. Model-based IRTs attain substantially higher noise reduction than hybrid IRTs irrespective of the radiation dose.

Impact of model-based iterative reconstruction on image quality of contrast-enhanced neck CT

BACKGROUND AND PURPOSE

Improved image quality is clinically desired for contrast-enhanced CT of the neck. We compared 30% adaptive statistical iterative reconstruction and model-based iterative reconstruction algorithms for the assessment of image quality of contrast-enhanced CT of the neck.

MATERIALS AND METHODS

Neck contrast-enhanced CT data from 64 consecutive patients were reconstructed retrospectively by using 30% adaptive statistical iterative reconstruction and model-based iterative reconstruction. Objective image quality was assessed by comparing SNR, contrast-to-noise ratio, and background noise at levels 1 (mandible) and 2 (superior mediastinum). Two independent blinded readers subjectively graded the image quality on a scale of 1-5, (grade 5 = excellent image quality without artifacts and grade 1 = nondiagnostic image quality with significant artifacts). The percentage of agreement and disagreement between the 2 readers was assessed.

RESULTS

Compared with 30% adaptive statistical iterative reconstruction, model-based iterative reconstruction significantly improved the SNR and contrast-to-noise ratio at levels 1 and 2. Model-based iterative reconstruction also decreased background noise at level 1 (P = .016), though there was no difference at level 2 (P = .61). Model-based iterative reconstruction was scored higher than 30% adaptive statistical iterative reconstruction by both reviewers at the nasopharynx (P < .001) and oropharynx (P < .001) and for overall image quality (P < .001) and was scored lower at the vocal cords (P < .001) and sternoclavicular junction (P < .001), due to artifacts related to thyroid shielding that were specific for model-based iterative reconstruction.

CONCLUSIONS

Model-based iterative reconstruction offers improved subjective and objective image quality as evidenced by a higher SNR and contrast-to-noise ratio and lower background noise within the same dataset for contrast-enhanced neck CT. Model-based iterative reconstruction has the potential to reduce the radiation dose while maintaining the image quality, with a minor downside being prominent artifacts related to thyroid shield use on model-based iterative reconstruction.

Half-dose abdominal CT with sinogram-affirmed iterative reconstruction technique in children - comparison with full-dose CT with filtered back projection

BACKGROUND

Iterative reconstruction can be helpful to reduce radiation dose while maintaining image quality. However, this technique has not been fully evaluated in children during abdominal CT.

OBJECTIVE

To compare objective and subjective image quality between half-dose images reconstructed with iterative reconstruction at iteration strength levels 1 to 5 (half-S1 to half-S5 studies) and full-dose images reconstructed with filtered back projection (full studies) in pediatric abdominal CT.

MATERIALS AND METHODS

Twenty-one children (M:F = 13:8; mean age 8.2 ± 5.7 years) underwent dual-source abdominal CT (mean effective dose 4.8 ± 2.1 mSv). The objective image quality was evaluated as noise. Subjective image quality analysis was performed comparing each half study to the full study for noise, sharpness, artifact and diagnostic acceptability.

RESULTS

Both objective and subjective image noise decreased with increasing iteration strength. Half-S4 and -S5 studies showed objective image noise similar to or lower than that of full studies. The half-S2 and -S3 studies produced the greatest sharpness and the half-S5 studies were the worst from a blocky appearance. Full and half studies did not differ in artifacts. Half-S3 studies showed the best diagnostic acceptability.

CONCLUSION

Half-S4 and -S5 studies objectively and half-S3 studies subjectively showed comparable image quality to full studies in pediatric abdominal CT.

Radiation dose and image quality of 70 kVp cerebral CT angiography with optimized sinogram-affirmed iterative reconstruction: comparison with 120 kVp cerebral CT angiography

OBJECTIVES

To evaluate radiation dose, image quality, and optimal level of sinogram-affirmed iterative reconstruction (SAFIRE) of cerebral CT angiography (CTA) at 70 kVp.

METHODS

One hundred patients were prospectively classified into two groups: Group A (n = 50), 70 kVp cerebral CTA with 5 levels of SAFIRE reconstruction (S1-S5); and Group B (n = 50), 120 kVp with filtered back projection (FBP) reconstruction. CT attenuation values, noise, signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) of the internal carotid artery (ICA) and middle cerebral artery (MCA) were measured. Subjective image quality was evaluated. Effective dose (ED) was estimated.

RESULTS

CT attenuation and noise of the ICA and MCA in Group A were higher than those of Group B (all P < 0.001) while the SNRICA, SNRMCA, CNRICA, and CNRMCA of Group A at S4-5 were comparable to (P > 0.05) or higher than in Group B (P < 0.05). There was no difference in overall image quality between Group A S3-5 and Group B (P > 0.05). ED was 0.2 ± 0.0 mSv for Group A with 85 % ED reduction in comparison to Group B (1.3 ± 0.2 mSv).

CONCLUSION

Cerebral CTA at 70 kVp is feasible, allowing for substantial radiation dose reduction. SAFIRE S4 level is recommended for obtaining optimal image quality.

KEY POINTS

• 70 kVp cerebral CTA is feasible and provides diagnostic image quality. • 70 kVp cerebral CTA resulted in 85% effective dose reduction. • S4 level of SAFIRE is recommended for 70 kVp cerebral CTA.

Computed tomography enterography and magnetic resonance enterography in the diagnosis of Crohn's disease

Imaging of the small bowel is complicated by its length and its overlapping loops. Recently, however, the development of crosssectional imaging techniques, such as computed tomography enterography (CTE) and magnetic resonance enterography (MRE) has shifted fundamental paradigms in the diagnosis and management of patients with suspected or known Crohn's disease (CD). CTE and MRE are noninvasive imaging tests that involve the use of intraluminal oral and intravenous contrast agents to evaluate the small bowel. Here, we review recent advances in each cross-sectional imaging modality, their advantages and disadvantages, and their diagnostic performances in the evaluation of small bowel lesions in CD.

[Imaging in smoldering (asymptomatic) multiple myeloma. Past, present and future]

CLINICAL ISSUE

Emerging clinical trial data support treatment of high-risk smoldering multiple myeloma (SMM) upon diagnosis, and not only at the time of progression to symptomatic complications (multiple myeloma). Early detection of bone and/or bone marrow involvement by sensitive imaging modalities may help define SMM patients at a high risk of progression.

STANDARD RADIOLOGICAL METHODS

Current (2011) consensus guidelines recognize skeletal survey as a cornerstone modality for assessment of bone involvement at initial diagnosis and during follow-up of SMM. Skeletal survey has severe limitations related to underdetection of bone lesions and also provides no information on bone marrow abnormalities.

METHODICAL INNOVATIONS

Modern imaging strategies such as fluorodeoxyglucose positron-emission tomography/CT (FDG PET/CT) and MRI, in conjunction with functional innovations, provide improved estimates of global abnormalities in the bone marrow and bone compartments. These methods have the potential to objectively quantify early transformation from SMM to multiple myeloma.

PERFORMANCE

Although frequently used for staging and risk prognostication in multiple myeloma, modern imaging techniques have only been evaluated to a limited extent in SMM. Scant data in SMM indicate the prognostic value of two or more MRI-detected focal bone marrow abnormalities, which, if present, predict rapid progression to multiple myeloma. Data evaluating the role of FDG PET/CT in detecting early bone marrow abnormalities as an aid to predicting risk or directing treatment in SMM is currently lacking.

ACHIEVEMENTS

The superior specificity and sensitivity of modern imaging techniques compared to skeletal survey suggest that these should have a place in standard practice management of patients at a high risk of SMM progression. The model imaging of the future should be an all-in-one strategy offering high diagnostic performance for bone marrow abnormalities and low-volume bone lesions, as well as allowing monitoring by minimizing radiation exposure and the need for contrast agents.

PRACTICAL RECOMMENDATIONS

Newer imaging techniques need to be validated in prospective clinical trials assessing the SMM to multiple myeloma transition, with the aim of enabling appropriate management decisions. Efforts are also needed to improve the costs and availability of whole-body MRI and/or FDG PET/CT, in order to facilitate their widespread adoption as first-line detection modalities. Future clinical trials of therapeutic agents using earlier detection strategies will have to be carefully designed and take into consideration the risk of lead-time and length-time biases, which might falsely demonstrate longer overall survival. The English full text version of this article is available at SpringerLink (under "Supplemental").

Emerging techniques for dose optimization in abdominal CT

Recent advances in computed tomographic (CT) scanning technique such as automated tube current modulation (ATCM), optimized x-ray tube voltage, and better use of iterative image reconstruction have allowed maintenance of good CT image quality with reduced radiation dose. ATCM varies the tube current during scanning to account for differences in patient attenuation, ensuring a more homogeneous image quality, although selection of the appropriate image quality parameter is essential for achieving optimal dose reduction. Reducing the x-ray tube voltage is best suited for evaluating iodinated structures, since the effective energy of the x-ray beam will be closer to the k-edge of iodine, resulting in a higher attenuation for the iodine. The optimal kilovoltage for a CT study should be chosen on the basis of imaging task and patient habitus. The aim of iterative image reconstruction is to identify factors that contribute to noise on CT images with use of statistical models of noise (statistical iterative reconstruction) and selective removal of noise to improve image quality. The degree of noise suppression achieved with statistical iterative reconstruction can be customized to minimize the effect of altered image quality on CT images. Unlike with statistical iterative reconstruction, model-based iterative reconstruction algorithms model both the statistical noise and the physical acquisition process, allowing CT to be performed with further reduction in radiation dose without an increase in image noise or loss of spatial resolution. Understanding these recently developed scanning techniques is essential for optimization of imaging protocols designed to achieve the desired image quality with a reduced dose.

Comparison of iterative model-based reconstruction versus conventional filtered back projection and hybrid iterative reconstruction techniques: lesion conspicuity and influence of body size in anthropomorphic liver phantoms

PURPOSE

This study aimed to determine whether an iterative model-based reconstruction (IMR) can improve lesion conspicuity and depiction on computed tomography (CT) compared with filtered back projection (FBP) and hybrid iterative reconstruction (iDose) using anthropomorphic phantoms.

MATERIALS AND METHODS

One small and one large anthropomorphic body phantoms, each containing 8 simulated focal liver lesions (FLLs), were scanned using a 256-channel CT scanner at 120 kVp with variable tube current-time products (10-200 mAs). Scans were divided into 3 groups based on radiation dose (RD) as follows: (a) full dose (FD), (b) low dose (FD50), and (c) ultralow dose (FD25 for the large phantom, FD15 for the small phantom). All images were reconstructed using FBP, iDose, and IMR. Image noise and lesion-to-liver contrast were assessed quantitatively and qualitatively. Thereafter, 6 radiologists independently evaluated conspicuity of FLLs, and then, compared the number of invisible FLLs on 3 image sets of each RD group.

RESULTS

Image noise was significantly lower with IMR than with FBP and iDose at the same RD. Iterative model-based reconstruction improved conspicuity of low-contrast FLLs in all RD groups compared to the others (P < 0.001). Furthermore, compared to FBP and iDose, the number of visible FLLs significantly increased on IMR images in the FD15 group of the small phantom 52.8% [38/72], 68.1% [49/72], and 84.8% [61/72], respectively; P < 0.001) and in the FD 25, FD50 groups of the large phantom (FD50: 56.9% [41/72], 76.4% [55/72], and 84.7% [61/72], respectively; P < 0.05).

CONCLUSIONS

Iterative model-based reconstruction reduced image noise and improved low-contrast FLL conspicuity, compared to FBP and iDose. Therefore, depiction of low-contrast FLLs on FBP could be improved using IMR.

Model-based vs hybrid iterative reconstruction technique in ultralow-dose submillisievert CT colonography

OBJECTIVE

To compare image quality of different reconstruction techniques in submillisievert ultralow-dose CT colonography (CTC) and to correlate colonic findings with subsequent optical colonoscopy.

METHODS

58 patients underwent ultralow-dose CTC. The images were reconstructed with filtered back projection (FBP), hybrid iterative reconstruction (HIR) or model-based iterative reconstruction (MBIR) techniques. In each segment, endoluminal noise (expressed as standard deviation of endoluminal density) was measured and image quality was rated on a five-point Likert scale by two independent readers. Colonic lesions were evaluated in consensus and correlated with subsequent optical colonoscopy where possible.

RESULTS

The estimated radiation dose was 0.41 ± 0.05 mSv for the supine and 0.42 ± 0.04 mSv for the prone acquisitions. In the endoluminal view, the image quality was rated better in HIR, whereas better scores were obtained in MBIR in the cross-sectional view, where the endoluminal noise was the lowest (p < 0.0001). Five (26%) polyps were not identified using both computer-aided detection and endoluminal inspection in FBP images vs only one (5%) in MBIR and none in HIR images.

CONCLUSION

This study showed that in submillisievert ultralow-dose CTC, the image quality for the endoluminal view is better when HIR is used, whereas MBIR yields superior images for the cross-sectional view. The inferior quality of images reconstructed with FBP may result in decreased detection of colonic lesions.

ADVANCES IN KNOWLEDGE

Radiation dose from CTC can be safely reduced <1 mSv for both positions when iterative reconstruction is used. MBIR provides better image quality in the cross-sectional view and HIR in the endoluminal view.

Spatial resolution in CBCT machines for dental/maxillofacial applications-what do we know today?

Spatial resolution is one of the most important parameters objectively defining image quality, particularly in dental imaging, where fine details often have to be depicted. Here, we review the current status on assessment parameters for spatial resolution and on published data regarding spatial resolution in CBCT images. The current concepts of visual [line-pair (lp) measurements] and automated [modulation transfer function (MTF)] assessment of spatial resolution in CBCT images are summarized and reviewed. Published measurement data on spatial resolution in CBCT are evaluated and analysed. Effective (i.e. actual) spatial resolution available in CBCT images is being influenced by the two-dimensional detector, the three-dimensional reconstruction process, patient movement during the scan and various other parameters. In the literature, the values range between 0.6 and 2.8 lp mm(-1) (visual assessment; median, 1.7 lp mm(-1)) vs MTF (range, 0.5-2.3 cycles per mm; median, 2.1 lp mm(-1)). Spatial resolution of CBCT images is approximately one order of magnitude lower than that of intraoral radiographs. Considering movement, scatter effects and other influences in real-world scans of living patients, a realistic spatial resolution of just above 1 lp mm(-1) could be expected.

Effects of adaptive statistical iterative reconstruction on radiation dose reduction and diagnostic accuracy of pediatric abdominal CT

BACKGROUND

Since children are more radio-sensitive than adults, there is a need to minimize radiation exposure during CT exams.

OBJECTIVE

To evaluate the effects of adaptive statistical iterative reconstruction (ASIR) on radiation dose reduction, image quality and diagnostic accuracy in pediatric abdominal CT.

MATERIALS AND METHODS

We retrospectively reviewed the abdominal CT examinations of 41 children (24 boys and 17 girls; mean age: 10 years) with a low-dose radiation protocol and reconstructed with ASIR (the ASIR group). We also reviewed routine-dose abdominal CT examinations of 41 age- and sex-matched controls reconstructed with filtered-back projection (control group). Image quality was assessed objectively as noise measured in the liver, spleen and aorta, as well as subjectively by three pediatric radiologists for diagnostic acceptability using a four-point scale. Radiation dose and objective image qualities of each group were compared with the paired t-test. Diagnostic accuracy was evaluated by reviewing follow-up imaging studies and medical records in 2012 and 2013.

RESULTS

There was 46.3% dose reduction of size-specific dose estimates in ASIR group (from 13.4 to 7.2 mGy) compared with the control group. Objective noise was higher in the liver, spleen and aorta of the ASIR group (P < 0.001). However, the subjective image quality was average or superior in 84-100% of studies. Only one image was subjectively rated as unacceptable by one reviewer. There was only one case with interpretational error in the control group and none in the ASIR group.

CONCLUSION

Use of the ASIR technique resulted in greater than a 45% reduction in radiation dose without impairing subjective image quality or diagnostic accuracy in pediatric abdominal CT, despite increased objective image noise.

Imaging techniques in IBD and their role in follow-up and surveillance

The assessment of extent and severity of IBD is crucial for directing treatment decisions. Clinical symptoms alone are neither sensitive nor specific for the assessment of lesion severity in IBD. Cross-sectional imaging techniques, as well as small-bowel capsule endoscopy (SBCE) and device-assisted enteroscopy, have a high accuracy for assessing the extent of mucosal lesions, and are reliable alternatives to ileocolonoscopy. New endoscopic techniques and devices are emerging for improved follow-up and surveillance. In this Review, we discuss different imaging techniques that are used to assess IBD activity and to survey patients with IBD, and highlight the latest developments in each area. Moreover, technical improvements and new tools that aim to measure intestinal fibrosis, postoperative recurrence, activity indices and endoscopic features are analysed. All of these imaging techniques are aimed at changing the paradigm from symptom-driven to lesion-driven treatment of IBD.

Contrast agent and radiation dose reduction in abdominal CT by a combination of low tube voltage and advanced image reconstruction algorithms

OBJECTIVES

To assess image quality in abdominal CT at low tube voltage combined with two types of iterative reconstruction (IR) at four reduced contrast agent dose levels.

METHODS

Minipigs were scanned with standard 320 mg I/mL contrast concentration at 120 kVp, and with reduced formulations of 120, 170, 220 and 270 mg I/mL at 80 kVp with IR. Image quality was assessed by CT value, dose normalized contrast and signal to noise ratio (CNRD and SNRD) in the arterial and venous phases. Qualitative analysis was included by expert reading.

RESULTS

Protocols with 170 mg I/mL or higher showed equal or superior CT values: aorta (278-468 HU versus 314 HU); portal vein (205-273 HU versus 208 HU); liver parenchyma (122-146 HU versus 115 HU). In the aorta, all 170 mg I/mL protocols or higher yielded equal or superior CNRD (15.0-28.0 versus 13.7). In liver parenchyma, all study protocols resulted in higher SNRDs. Radiation dose could be reduced from standard CTDIvol = 7.8 mGy (6.2 mSv) to 7.6 mGy (5.2 mSv) with 170 mg I/mL.

CONCLUSION

Combining 80 kVp with IR allows at least a 47 % contrast agent dose reduction and 16 % radiation dose reduction for images of comparable quality.

KEY POINTS

• There is a balance between image quality, contrast dose and radiation dose. • Iterative reconstruction has a major, positive impact on this balance. • Both contrast dose and radiation dose can be reduced in abdominal CT. • The trade-off can be quantitatively described by a 3D model. • Contrast and radiation dose can be tailored according to specific safety concerns.

Submillisievert chest CT with filtered back projection and iterative reconstruction techniques

OBJECTIVE

The purpose of this study was to compare submillisievert chest CT images reconstructed with filtered back projection (FBP), SafeCT, adaptive statistical iterative reconstruction (ASIR), and model-based iterative reconstruction (MBIR) with standard of care FBP images.

SUBJECTS AND METHODS

Fifty patients (33 men and 17 women; mean age [± SD], 62 ± 10 years) undergoing routine chest CT gave written informed consent for acquisition of an additional submillisievert chest CT series with reduced tube current but identical scanning length as standard of care chest CT. Sinogram data of the submillisievert series were reconstructed with FBP, SafeCT, ASIR, and MBIR and compared with FBP images at standard-dose chest CT (n = 8 × 50 = 400 series). Two thoracic radiologists performed independent comparison for visualization of lesion margin, visibility of small structures, and diagnostic acceptability. Objective noise measurements and noise spectral density were obtained.

RESULTS

Of 287 detected lesions, 162 were less than 1-cm noncalcified nodules. Lesion margins were well seen on all submillisievert reconstruction images except MBIR, on which they were poorly visualized. Likewise, only submillisievert MBIR images were suboptimal for visibility of normal structures, such as pulmonary vessels in the outer 2 cm of the lung, interlobular fissures, and subsegmental bronchial walls. MBIR had the lowest image noise compared with other techniques.

CONCLUSION

FBP, SafeCT, ASIR, and MBIR can enable optimal lesion evaluation on chest CT acquired at a volume CT dose index of 2 mGy. However, all submillisievert reconstruction techniques were suboptimal for visualization of mediastinal structures. Submillisievert MBIR images were suboptimal for visibility of normal lung structures despite showing lower image noise.

Quantitative computed tomography of pulmonary emphysema and ventricular function in chronic obstructive pulmonary disease patients with pulmonary hypertension

Objective

This study strived to evaluate the relationship between degree of pulmonary emphysema and cardiac ventricular function in chronic obstructive pulmonary disease (COPD) patients with pulmonary hypertension (PH) using electrocardiographic-gated multidetector computed tomography (CT).

Materials and Methods

Lung transplantation candidates with the diagnosis of COPD and PH were chosen for the study population, and a total of 15 patients were included. The extent of emphysema is defined as the percentage of voxels below -910 Hounsfield units in the lung windows in whole lung CT without intravenous contrast. Heart function parameters were measured by electrocardiographic-gated CT angiography. Linear regression analysis was conducted to examine the associations between percent emphysema and heart function indicators.

Results

Significant correlations were found between percent emphysema and right ventricular (RV) measurements, including RV end-diastolic volume (R² = 0.340, p = 0.023), RV stroke volume (R² = 0.406, p = 0.011), and RV cardiac output (R² = 0.382, p = 0.014); the correlations between percent emphysema and left ventricular function indicators were not observed.

Conclusion

The study revealed that percent emphysema is correlated with RV dysfunction among COPD patients with PH. Based on our findings, percent emphysema can be considered for use as an indicator to predict the severity of right ventricular dysfunction among COPD patients.

Image comparative assessment using iterative reconstructions: clinical comparison of low-dose abdominal/pelvic computed tomography between adaptive statistical, model-based iterative reconstructions and traditional filtered back projection in 65 patients

OBJECTIVES

The objective of this study was to compare image quality (objective and subjective parameters) and confidence in lesion detection between 3 image reconstruction algorithms in computed tomographic (CT) examinations of the abdomen/pelvis.

MATERIALS AND METHODS

This prospective institutional review board-approved study included 65 patients (mean [SD] age, 71.3 ± 9 years; mean [SD] body mass index, 24.4 [4.8] kg) who underwent routine CT examinations of the abdomen/pelvis followed immediately by 2 low-dose scans. Raw data sets were reconstructed by using filtered back projection (FBP), adaptive statistical iterative reconstruction (ASIR), and a model-based iterative reconstruction (MBIR). Measurements of objective noise and CT numbers were compared using repeated-measures analysis of variance. Six subjective image quality parameters were scored. Diagnostic confidence and accuracy in detection of various elementary lesions were performed.

RESULTS

Objectively, mean image noise for MBIR was significantly superior at all dose levels (P < 0.001). Subjectively, standard-dose ASIR and low-dose MBIR scans were better than standard-dose FBP scan in all parameters assessed (P < 0.05). Low-dose MBIR scans were comparable with standard-dose ASIR scans in all parameters except at noise index of 70 (approximately 85% dose reduction), where, in this case, the detection of liver lesions less than 5 mm were rated inferior (P < 0.05) with diagnostic accuracy reducing to 77.4%.

CONCLUSIONS

Low-dose MBIR scan shows superior objective noise reduction compared with standard-dose FBP and ASIR. Subjectively, low-dose MBIR scans at 76% dose reduction were also superior compared with standard-dose FBP and ASIR. However, at dose reductions of 85%, small liver lesions may be missed.

Imaging quality and diagnostic reliability of low-dose computed tomography lumbar spine for evaluating patients with spinal disorders

BACKGROUND CONTEXT

Computed tomography (CT) scans of the lumbar spine (CTLS) have demonstrated a higher level of accuracy than plain films and have been used to assess patients with spinal disorder when magnetic resonance imaging is not available. Nevertheless, radiation exposure remains a serious safety concern. Iterative reconstruction (IR) decreases the CT radiation dose for diagnostic imaging. However, the feasibility of using IR in CTLS is unclear.

PURPOSE

To evaluate the imaging quality and diagnostic reliability of CTLS with IR.

STUDY DESIGN

A prospective study.

PATIENT SAMPLE

All patients from outpatient departments who suffered from spinal disorders and were referred for CTLS.

OUTCOME MEASURES

In acquired CT images, the signal-to-noise ratio (SNR) of the dural sac (DS), intervertebral disc (IVD), psoas muscle (PM), and L5 vertebral body, the contrast-to-noise ratio between the DS and IVD (D-D CNR), and the subjective imaging qualities were compared across groups. Interobserver agreement was evaluated with kappa values.

METHODS

Patients receiving low radiation CTLS were divided into three groups. A 150 mAs tube current with 120 kVp tube voltage was used with Group A and a 230 mAs tube current with 100 kVp tube voltage with Group B. Intended end radiation exposure was 50% less than that of the control group. Tube modulation was active for all groups. The images of the two low-radiation groups were reconstructed by IR; those of the control group by filtered back-projection (FBP).

RESULTS

The SNRs of the DS, IVD, PM, BM, and D-D CNR of Group A were not inferior to those of the control group. All SNRs and D-D CNRs for Group B were inferior to those of the control group. Except for that of the facet joint, all subjective imaging ratings for anatomic regions were equivalent between Groups A and B. Interobserver agreement was highest for the control group (0.72-0.88), followed by Group A (0.69-0.83) and B (0.55-0.83).

CONCLUSIONS

Fifty percent tube current reduction combined with IR provides equivalent diagnostic accuracy and improved patient safety when compared with conventional CTLS. Our results support its use as a screening tool. With the tube modulation technique, further adjustments in weighting IR and FBP algorithms based on body mass index become unnecessary.

Quarter regular dose non-enhanced CT for urinary stone: added value of adaptive statistical iterative reconstruction

BACKGROUND

As urinary stone diseases are common in young adults and have a high recurrence rate, repetitive computed tomography (CT) scans would increase the radiation hazard. Therefore, CT radiation dose reduction is needed in the diagnosis of urinary stones.

PURPOSE

To prospectively evaluate the added value of adaptive statistical iterative reconstruction (ASIR) applied to half-dose (HDCT) and quarter regular dose non-enhanced CT (QDCT) for the detection of urinary stones.

MATERIAL AND METHODS

One hundred and twelve consecutive patients who presented with acute flank pain and had clinically suspected urinary stones were initially eligible. All patients underwent non-enhanced CT that consisted of HDCT (120 kVp, 100 mAs) and QDCT (120 kVp, 40 mAs). The images were reconstructed separately with a 50% ASIR blending ratio. Two radiologists independently performed a 2-week interval reading to detect urinary stones on a per stone basis (size ≥1 mm) from the QDCT images to the ASIR applied images. Two weeks later, the HDCT images were analyzed in the same manner. The CT image noise was measured for each image set. The sensitivity for urinary stone detection for each set was compared using the McNemar test.

RESULTS

A total of 114 urinary stones were found in 48 patients (37 men, 11 women; mean age, 46 years; range, 19-71 years). After applying ASIR to the QDCT images, the sensitivity increased from 70% to 80% for reader 1 and from 69% to 82% for reader 2 (P = 0.001, respectively). However, in the HDCT images, the sensitivity was unchanged for both readers (reader 1, 87%; reader 2, 89%). The measured noise significantly decreased from 40.2 to 27.7 after applying ASIR to the QDCT images and from 25.1 to 17.6 after applying ASIR to the HDCT images (P = 0.001 for both).

CONCLUSION

Although ASIR showed no added diagnostic value for HDCT images, it improved the sensitivity for the detection of urinary stones based on QDCT images.

Iterative reconstruction: how it works, how to apply it

Computed tomography acquires X-ray projection data from multiple angles though an object to generate a tomographic rendition of its attenuation characteristics. Filtered back projection is a fast, closed analytical solution to the reconstruction process, whereby all projections are equally weighted, but is prone to deliver inadequate image quality when the dose levels are reduced. Iterative reconstruction is an algorithmic method that uses statistical and geometric models to variably weight the image data in a process that can be solved iteratively to independently reduce noise and preserve resolution and image quality. Applications of this technology in a clinical setting can result in lower dose on the order of 20-40% compared to a standard filtered back projection reconstruction for most exams. A carefully planned implementation strategy and methodological approach is necessary to achieve the goals of lower dose with uncompromised image quality.

Pilot study of low-dose nonenhanced computed tomography with iterative reconstruction for diagnosis of urinary stones

Purpose

To evaluate the efficacy of low-dose computed tomography (LDCT) for detecting urinary stones with the use of an iterative reconstruction technique for reducing radiation dose and image noise.

Materials and Methods

A total of 101 stones from 69 patients who underwent both conventional nonenhanced computed tomography (CCT) and LDCT were analyzed. Interpretations were made of the two scans according to stone characteristics (size, volume, location, Hounsfield unit [HU], and skin-to-stone distance [SSD]) and radiation dose by dose-length product (DLP), effective dose (ED), and image noise. Diagnostic performance for detecting urinary stones was assessed by statistical evaluation.

Results

No statistical differences were found in stone characteristics between the two scans. The average DLP and ED were 384.60±132.15 mGy and 5.77±1.98 mSv in CCT and 90.08±31.80 mGy and 1.34±0.48 mSv in LDCT, respectively. The dose reduction rate of LDCT was nearly 77% for both DLP and ED (p<0.01). The mean objective noise (standard deviation) from three different areas was 23.0±2.5 in CCT and 29.2±3.1 in LDCT with a significant difference (p<0.05); the slight increase was 21.2%. For stones located throughout the kidney and ureter, the sensitivity and specificity of LDCT remained 96.0% and 100%, with positive and negative predictive values of 100% and 96.2%, respectively.

Conclusions

LDCT showed significant radiation reduction while maintaining high image quality. It is an attractive option in the diagnosis of urinary stones.

Hybrid iterative reconstruction technique for liver CT scans for image noise reduction and image quality improvement: evaluation of the optimal iterative reconstruction strengths

PURPOSE

This study sought to investigate the effect of the hybrid iterative reconstruction (IR) algorithm (iDose, Philips Healthcare) on the improvement of image quality of computed tomography (CT) scans of the liver and determine the appropriate level of IR strength for clinical use.

MATERIALS AND METHODS

A total of 75 patients (41 men and 34 women; mean age, 59.5 years) with a primary abdominal malignancy who underwent two-phase liver CT scans for the work-up of their liver metastases, were included in this study. The CT images during the portal phase were reconstructed using either filtered back projection (FBP) or the hybrid IR algorithm with six different levels of IR strengths. The signal-to-noise ratio of the liver (SNR(liver)) and the contrast-to-noise ratio of the portal vein to muscle (CNR(pv to m)) were measured. For qualitative analysis, image noise, visibility of small intrahepatic vascular structures, beam-hardening artefact, lesion conspicuity, and overall image quality were graded by two radiologists.

RESULTS

Quantitative analysis demonstrated that image noise was significantly reduced along with the increasing level of iDose and that the values of SNR(liver) and CNR(pv to m) were significantly better with iDose than those of FBP images. Qualitative assessment also showed significantly better results with iDose compared with FBP (p < 0.05) and the parameters for subjective image quality were highest with iDose level 4.

CONCLUSIONS

The hybrid IR technique is able to reduce image noise and to provide better image quality than FBP, and an intermediate strength of iDose (level 4) provided the highest quality images.

What is the preferred strength setting of the sinogram-affirmed iterative reconstruction algorithm in abdominal CT imaging?

Our primary objective in this study was to determine the preferred strength setting for the sinogram-affirmed iterative reconstruction algorithm (SAFIRE) in abdominal computed tomography (CT) imaging. Sixteen consecutive clinical CT scans of the abdomen were reconstructed by use of traditional filtered back projection (FBP) and 5 SAFIRE strengths: S1-S5. Six readers of differing experience were asked to rank the images on preference for overall diagnostic quality. The contrast-to-noise ratio was not significantly different between SAFIRE S1 and FBP, but increased with increasing SAFIRE strength. For pooled data, S2 and S3 were preferred equally but both were preferred over all other reconstructions. S5 was the least preferred, with FBP the next least preferred. This represents a marked disparity between the image quality based on quantitative parameters and qualitative preference. Care should be taken to factor in qualitative in addition to quantitative aspects of image quality when one is optimizing iterative reconstruction images.

Radiation exposure in gastroenterology: improving patient and staff protection

Medical imaging involving the use of ionizing radiation has brought enormous benefits to society and patients. In the past several decades, exposure to medical radiation has increased markedly, driven primarily by the use of computed tomography. Ionizing radiation has been linked to carcinogenesis. Whether low-dose medical radiation exposure will result in the development of malignancy is uncertain. This paper reviews the current evidence for such risk, and aims to inform the gastroenterologist of dosages of radiation associated with commonly ordered procedures and diagnostic tests in clinical practice. The use of medical radiation must always be justified and must enable patients to be exposed at the lowest reasonable dose. Recommendations provided herein for minimizing radiation exposure are based on currently available evidence and Working Party expert consensus.

Effect of the CT table strap on radiation exposure and image quality during cervical spine CT

BACKGROUND AND PURPOSE

The CT table strap may impair shoulder lowering during cervical spine CT. The purpose of this investigation was to evaluate the effect of the CT table strap on radiation exposure and image quality during CT of the cervical spine.

MATERIALS AND METHODS

Patients undergoing cervical spine CT were prospectively randomized to having the CT table strap placed around the torso and arms (control group) or around the torso only (intervention group). Radiation exposure, shoulder position, and image quality were evaluated. Potential confounders, including neck diameter and scan length, were also assessed.

RESULTS

Fifty-eight patients were enrolled and randomized, and 51 subjects were included in the final study population. There was a 21% decrease in radiation exposure in the intervention group compared with the control group (mean dose-length product, 540 ± 152 versus 686 ± 200 mGy × cm, P = .005). Subjects in the intervention group achieved shoulder lowering of an average of >1 vertebral body lower than the control group (mean shoulder level, 7.7 ± 1.3 versus 6.5 ± 1.3, P = .001). Subjective image quality, determined by the lowest level of spinal cord visibility, was also better in the intervention group (mean cord visibility level, 6.9 ± 1.3 versus 5.9 ± 1.3, P = .006). No differences in neck diameter (P = .28) or scan length (P = .55) were observed between groups.

CONCLUSIONS

The CT table strap inhibits shoulder lowering during CT of the cervical spine. Placement of the patient's arms outside the CT table strap results in decreased radiation exposure and increased image quality compared with patients whose arms are placed inside the strap.

Reducing radiation dose without compromising image quality in preoperative perforator flap imaging with CTA using ASIR technology

Computed tomographic angiography (CTA) has become a mainstay in preoperative perforator flap planning in the modern era of reconstructive surgery. However, the increased use of CTA does raise the concern of radiation exposure to patients. Several techniques have been developed to decrease radiation dosage without compromising image quality, with varying results. The most recent advance is in the improvement of image reconstruction using an adaptive statistical iterative reconstruction (ASIR) algorithm. We sought to evaluate the image quality of ASIR in preoperative deep inferior epigastric perforator (DIEP) flap surgery, through a direct comparison with conventional filtered back projection (FBP) images. A prospective review of 60 consecutive ASIR and 60 consecutive FBP CTA images using similar protocol (except for radiation dosage) was undertaken, analyzed by 2 independent reviewers. In both groups, we were able to accurately identify axial arteries and their perforators. Subjective analysis of image quality demonstrated no statistically significant difference between techniques. ASIR can thus be used for preoperative imaging with similar image quality to FBP, but with a 60% reduction in radiation delivery to patients.

Radiation dose reduction in CT-guided spine biopsies does not reduce diagnostic yield

BACKGROUND AND PURPOSE

CT-guided biopsy is the most commonly used method to obtain tissue for diagnosis in suspected cases of malignancy involving the spine. The purpose of this study was to demonstrate that a low-dose CT-guided spine biopsy protocol is as effective in tissue sampling as a regular-dose protocol, without adversely affecting procedural time or complication rates.

MATERIALS AND METHODS

We retrospectively reviewed all patients who underwent CT-guided spine procedures at our institution between May 2010 and October 2013. Biopsy duration, total number of scans, total volume CT dose index, total dose-length product, and diagnostic tissue yield of low-dose and regular-dose groups were compared.

RESULTS

Sixty-four patients were included, of whom 31 underwent low-dose and 33 regular-dose spine biopsies. There was a statistically significant difference in total volume CT dose index and total dose-length product between the low-dose and regular-dose groups (P < .0001). There was no significant difference in the total number of scans obtained (P = .3385), duration of procedure (P = .149), or diagnostic tissue yield (P = .6017).

CONCLUSIONS

Use of a low-dose CT-guided spine biopsy protocol is a practical alternative to regular-dose approaches, maintaining overall quality and efficiency at reduced ionizing radiation dose.

Perspectives on radiation dose in abdominal imaging

Reported instances of patients' overexposure to imaging-related radiation have spurred the radiology and medical physics communities to identify and develop methods for decreasing the amount of radiation used to achieve diagnostic-quality images. These initiatives include examining and optimizing conventional CT scanning parameters, introducing innovative scan protocols, and incorporating novel dose reduction technologies. The greatest challenge to effective dose reduction in the abdomen and pelvis remains patient size. Here, we review the state of the art in abdominopelvic CT in both adult and pediatric patients and describe some of our own efforts in dose reduction for these types of examinations.