Radiation Dose Reduction In Computed Tomography Research Articles

CT radiation dose reduction with tin filter for localisation/characterisation level image quality in PET-CT: a phantom study

BackgroundThe tin filter has allowed radiation dose reduction in some standalone diagnostic computed tomography (CT) applications. Yet, ‘low-dose’ CT scans are commonly used in positron emission tomography (PET)-CT for lesion localisation/characterisation (L/C), with higher noise tolerated. Thus, dose reductions permissible with the tin filter at this image quality level may differ. The aim was to determine the level of CT dose reduction permitted with the tin filter in PET-CT, for comparable image quality to the clinical reference standard (CRS) L/C CT images acquired with standard filtration.Materials and methodsA whole-body CT phantom was scanned with standard filtration in CRS protocols, using 120 kV with 20mAs-ref for bone L/C (used in 18F-Sodium Fluoride (NaF) PET-CT) and 40mAs-ref for soft tissue L/C (used in 18F-Fluorodeoxyglucose (FDG) PET-CT), followed by tin filter scans at 100 kV (Sn100kV) and 140 kV (Sn140kV) with a range of mAs settings. For each scan, effective dose (ED) in an equivalent-sized patient was calculated, and image quality determined in 5 different tissues through quantitative (contrast-to-noise ratio) and qualitative (visual) analyses. The relative dose reductions which could be achieved with the tin filter for comparable image quality to CRS images were calculated.ResultsQuantitative analysis demonstrated dose savings of 50–76% in bone, 27–51% in lung and 8–61% in soft tissue with use of the tin filter at Sn100kV. Qualitative analysis demonstrated dose reductions using Sn100kV in general agreement with the dose reductions indicated by quantitative analysis. Overall, CT dose reductions of around 85% were indicated for NaF bone PET-CT, allowing whole-body CT at just 0.2mSv ED, and a 30–40% CT dose reduction for FDG PET-CT using Sn100kV (1.7-2.0mSv), providing comparable image quality to current CRS images with standard filtration. Sn140kV demonstrated limited value in CT dose reduction.ConclusionsLarge CT dose reductions can be made using the tin filter at Sn100kV, when imaging bone, lung and soft tissue at L/C level CT image quality in PET-CT. As well as reducing the risk of inducing a cancer in later life, such dose reductions may also impact PET-CT practice, such as justifying cross-sectional over planar imaging or justifying PET-CT in younger patients.

Radiation dose reduction and image quality in pediatric paranasal sinus CT: with automatic tube current modulation and iterative reconstruction technique.

Our objective is to evaluate radiation dose and image quality in pediatric paranasal sinus computed tomography (CT) with automatic tube current modulation (ATCM) and sinogram-affirmed iterative reconstruction algorithm (SAFIRE). CT scans from 80 patients were divided into two groups: Group A [80 kVp, pitch 1.5, 40 mAs, the filtered back projection (FBP) algorithm] and Group B (70 kVp, pitch 3, ATCM with reference at 40 mAs, SAFIRE strengths 1-5). We have evaluated image quality and radiation dose. Group B demonstrated significantly lower volume computed tomography dose index, dose-length product, and effective dose than Group A (0.13±0.03 vs. 1.57±0.01mGy, 2.27±0.82 vs. 19.88±2.01mGy·cm, and 0.0081±0.0017 vs. 0.079±0.013mSv, respectively; P<.001). Increasing SAFIRE strengths correlated with noise reduction and SNR enhancement. Group B's noise and SNRsoft at SAFIRE strength 5 were comparable with Group A. Images reconstructed with SAFIRE strength 5 in Group B exhibit comparable image quality with FBP in Group A.

Evaluation of radiation dose reduction in head CT using the half-dose method

PurposeThe present study introduced the half-dose method (HDM), which halves the radiation dose for conventional head computed tomography (CT), for postoperative hydrocephalus and follow-up for craniosynostosis at a children’s hospital. This study aimed to evaluate the contribution of selective head CT scanning optimization towards the overall reduction of radiation exposure.Materials and methodsWe retrospectively assessed 1227 and 1352 head CT examinations acquired before and after the introduction of the HDM, respectively, in children aged 0–15 years. The radiation exposure was evaluated using the CT dose index volume (CTDI-vol), dose-length product (DLP), rate of HDM introduction, and effect of reducing in-hospital radiation dose before and after the introduction of the HDM. For an objective evaluation of the image quality, head CT scans acquired with HDM and full-dose method (FDM) were randomly selected, and the image noise standard deviation (SD) was measured for each scan. In addition, some HDM images were randomly selected and independently reviewed by two radiologists.ResultsThe HDM was introduced in 27.9% of all head CTs. The mean CTDI-vol of all head CTs was 21.5 ± 6.9 mGy after the introduction, a 14.9% reduction. The mean DLP was 418.4 ± 152.9 mGy.cm after the introduction, a 17.2% reduction. Compared to the FDM images, the noise SD of the HDM ones worsened by almost 0.9; however, none of the images were difficult or impossible to evaluate.ConclusionThe HDM yielded diagnostically acceptable images. In addition, a change in protocol for only two diseases successfully reduced the patients’ overall radiation exposure by approximately 15%. Introducing and optimizing the HDM for frequently performed target diseases will be useful in reducing the exposure dose for the hospital’s patient population.

Application of Deep Learning-Based Denoising Technique for Radiation Dose Reduction in Dynamic Abdominal CT: Comparison with Standard-Dose CT Using Hybrid Iterative Reconstruction Method.

The purpose is to evaluate whether deep learning-based denoising (DLD) algorithm provides sufficient image quality for abdominal computed tomography (CT) with a 30% reduction in radiation dose, compared to standard-dose CT reconstructed with conventional hybrid iterative reconstruction (IR). The subjects consisted of 50 patients who underwent abdominal CT with standard dose and reconstructed with hybrid IR (ASiR-V50%) and another 50 patients who underwent abdominal CT with approximately 30% less dose and reconstructed with ASiR-V50% and DLD at low-, medium- and high-strength (DLD-L, DLD-M and DLD-H, respectively). The standard deviation of attenuation in liver parenchyma was measured as image noise. Contrast-to-noise ratio (CNR) for portal vein on portal venous phase was calculated. Lesion conspicuity in 23 abdominal solid mass on the reduced-dose CT was rated on a 5-point scale: 0 (best) to -4 (markedly inferior). Compared with hybrid IR of standard-dose CT, DLD-H of reduced-dose CT provided significantly lower image noise (portal phase: 9.0 (interquartile range, 8.7-9.4) HU vs 12.0 (11.4-12.7) HU, P < 0.0001) and significantly higher CNR (median, 5.8 (4.4-7.4) vs 4.3 (3.3-5.3), P = 0.0019). As for DLD-M of reduced-dose CT, no significant difference was found in image noise and CNR compared to hybrid IR of standard-dose CT (P > 0.99). Lesion conspicuity scores for DLD-H and DLD-M were significantly better than hybrid IR (P < 0.05). Dynamic contrast-enhanced abdominal CT acquired with approximately 30% lower radiation dose and generated with the DLD algorithm exhibit lower image noise and higher CNR compared to standard-dose CT with hybrid IR.

The use of deep learning methods in low-dose computed tomography image reconstruction: a systematic review

Conventional reconstruction techniques, such as filtered back projection (FBP) and iterative reconstruction (IR), which have been utilised widely in the image reconstruction process of computed tomography (CT) are not suitable in the case of low-dose CT applications, because of the unsatisfying quality of the reconstructed image and inefficient reconstruction time. Therefore, as the demand for CT radiation dose reduction continues to increase, the use of artificial intelligence (AI) in image reconstruction has become a trend that attracts more and more attention. This systematic review examined various deep learning methods to determine their characteristics, availability, intended use and expected outputs concerning low-dose CT image reconstruction. Utilising the methodology of Kitchenham and Charter, we performed a systematic search of the literature from 2016 to 2021 in Springer, Science Direct, arXiv, PubMed, ACM, IEEE, and Scopus. This review showed that algorithms using deep learning technology are superior to traditional IR methods in noise suppression, artifact reduction and structure preservation, in terms of improving the image quality of low-dose reconstructed images. In conclusion, we provided an overview of the use of deep learning approaches in low-dose CT image reconstruction together with their benefits, limitations, and opportunities for improvement.

Radiation dose reduction in extremity multi-detector CT: A comparison of image quality with a standard dose protocol

PurposeTo analyze the quantitative and qualitative image quality of computed tomography (CT) of the extremities (shoulder, wrist, pelvis, and ankle joints) with low-dose radiation and standard-dose radiation. Materials and methodsIn this study, we included 400 individuals who underwent CT of the extremities, comprising 50 cases of each joint (shoulder, wrist, pelvis, and ankle) at low and standard dose regimens. Low-dose CTs were performed using identical voltage and parameters with the exception of decreased (half of standard dose) tube current. Low-dose and standard-dose images were compared in terms of radiation dose, objective image quality according to the standard deviation (SD) of the Hounsfield unit value of the medulla, cortex, muscle, subcutaneous fat, and air, and subjective image quality according to noise, sharpness, diagnostic acceptability, and artifacts. ResultsIn the shoulder and pelvis, the mean value of the SD for all tissue on low dose CT images was significantly higher than that of standard dose CT, except for the SD of cortex in the shoulder joint and marrow in the pelvis. In the wrist, the mean value of the SD for all tissue was not significantly different between low dose and standard CT (p > 0.05). In the ankle, the mean value of the SD of the medulla and cortex was not different (p > 0.05), but the remaining measurements were significantly higher in low dose CT. Subjective image quality in the shoulder and pelvis were significantly reduced in low dose CT. In the wrist, all categories of subjective image quality except artifacts were similar. In the ankle, all categories of subjective image quality except for artifacts were degraded in low dose CT. ConclusionsObjective image noise is more increased in low dose CT images of the shoulder and pelvis. Although diagnostic performance was acceptable, mean subjective image quality also decreased. In the wrist, objective image noise and subjective image quality were not degraded in low dose CT. In the ankle, some measurements of objective and subjective image quality were similar between low dose and standard dose CT.

Dose Reduction Methods in Chest Computed Tomography

Introduction: Computed tomography is one of the most powerful tools for investigating thorax disease, because it shows progression of lung disease much clearer than chest radiography. Technical advances in CT scanners have led to some abilities for CT scanners such as coverage of larger volume, lower noise and ability for acquiring image in one respiratory phase. However, this will be accompanied by more radiation exposure to patient and research shows that CT gives higher exposure dose to patient in comparison with conventional radiography.1 Materials and Methods: In each computed tomography (CT), patient dose is dependent on the scan parameters. Scan parameters are included kV, mA, scan field of view (SFOV), rotation time, focal spot size, slice width and pitch. Also, shielding of sensitive organs such as breast which is not interest organ during chest CT scanning is one of the dose reduction methods. Furthermore, Type of scanner, methods and protocols of scanning, for example in multi-slice scanners there is some more cases like collimation, which effect on patient dose, and therefore all of these options should be adjusted, accurately. It is considerable that scan parameters such as reconstructed matrix and reconstruction algorithms have considered in this paper; however, these parameters do not impact directly on patient dose but they have some affects through changing the characteristics of the image indirectly. In this study twenty methods for radiation dose reduction in thorax CT were explained. Conclusion: According to the principle of ALARA, the aim of applying optimization techniques is to reduce the amount of receiving dose while maintaining image quality.

Advanced Modeled Iterative Reconstruction (ADMIRE) Facilitates Radiation Dose Reduction in Abdominal CT

This study aimed to determine the potential degree of radiation dose reduction achievable using Advanced Modeled Iterative Reconstruction (ADMIRE) in abdominal computed tomography (CT) while maintaining image quality. Moreover, this study compared differences in image noise reduction of this iterative algorithm with radiation dose reduction. Eleven consecutive patients scheduled for abdominal CT were scanned according to our institute's standard protocol (100 kV, 289 reference mAs). Using a proprietary reconstruction software, CT images of these patients were reconstructed as either full-dose weighted filtered back projections or with simulated radiation dose reductions down to 10% of the full-dose level and ADMIRE at either strength 3 or strength 5. Images were marked with arrows pointing on anatomic structures of the abdomen, differing in their contrast to the surrounding tissue. Structures were grouped into high-, medium-, and low-contrast subgroups. In addition, the intrinsic noise of these structures was measured. That followed, image pairs were presented to observers, with five readers assessing image quality using two-alternative-forced-choice comparisons. In total, 3000 comparisons were performed that way. Both ADMIRE 3 and 5 decreased noise of the anatomic structures significantly compared to the filtered back projection, with an additional significant difference between ADMIRE 3 and 5. Radiation dose reduction potential for ADMIRE ranged from 29.0% to 53.5%, with no significant differences between ADMIRE 3 and 5 within the contrast subgroups.The potential levels of radiation dose reduction for ADMIRE 3 differed significantly between high-, medium-, and low-contrast structures, whereas for ADMIRE 5, there was only a significant difference between the high- and the medium-contrast subgroups. Although ADMIRE 5 permits significantly higher noise reduction potential than ADMIRE 3, it does not facilitate higher levels of radiation dose reduction. ADMIRE nonetheless holds remarkable potential for radiation dose reduction, which features a certain dependency on the contrast of the structure of interest. Applying ADMIRE with a strength of 3 in abdominal CT may permit radiation dose reduction of about 30%.

Adaptive statistical iterative reconstruction use for radiation dose reduction in pediatric lower-extremity CT: impact on diagnostic image quality.

For the past several years, increased levels of imaging radiation and cumulative radiation to children has been a significant concern. Although several measures have been taken to reduce radiation dose during computed tomography (CT) scan, the newer dose reduction software adaptive statistical iterative reconstruction (ASIR) has been an effective technique in reducing radiation dose. To our knowledge, no studies are published that assess the effect of ASIR on extremity CT scans in children. To compare radiation dose, image noise, and subjective image quality in pediatric lower extremity CT scans acquired with and without ASIR. The study group consisted of 53 patients imaged on a CT scanner equipped with ASIR software. The control group consisted of 37 patients whose CT images were acquired without ASIR. Image noise, Computed Tomography Dose Index (CTDI) and dose length product (DLP) were measured. Two pediatric radiologists rated the studies in subjective categories: image sharpness, noise, diagnostic acceptability, and artifacts. The CTDI (p value = 0.0184) and DLP (p value <0.0002) were significantly decreased with the use of ASIR compared with non-ASIR studies. However, the subjective ratings for sharpness (p < 0.0001) and diagnostic acceptability of the ASIR images (p < 0.0128) were decreased compared with standard, non-ASIR CT studies. Adaptive statistical iterative reconstruction reduces radiation dose for lower extremity CTs in children, but at the expense of diagnostic imaging quality. Further studies are warranted to determine the specific utility of ASIR for pediatric musculoskeletal CT imaging.

Effect of topogram-tube angle combination on CT radiation dose reduction

This study assessed the ability of various types of topograms, when used with an automatic tube current modulation (ATCM) technique, to reduce radiation dose from computed tomography (CT) scans. Three types of topograms were used with the ATCM technique: (i) anteroposterior (AP) topograms alone, (ii) AP topograms followed by lateral topograms, and (iii) lateral topograms followed by AP topograms. Various regions (chest, abdomen and whole-body) of a humanoid phantom were scanned at several tube voltages (80, 100 and 120 kVp) with the selected topograms. Although the CT dose depended on the order of topograms, the CT dose with respect to patient positioning depended on the number of topograms performed. The magnitude of the difference in CT dose between number and order of topograms was greater for the scans of the abdomen than the chest. These results suggest that, for the Siemens SOMATOM Definition AS CT scanner, choosing the right combination of CT scan conditions with the ATCM technique can minimize radiation dose to a patient.

Image quality, diagnostic accuracy, and potential for radiation dose reduction in thoracoabdominal CT, using Sinogram Affirmed Iterative Reconstruction (SAFIRE) technique in a longitudinal study.

ObjectiveTo step-wise evaluate image quality of sinogram-affirmed iterative reconstruction (SAFIRE) in reduced-dose (RD) thoracoabdominal computed tomography (CT) compared to full-dose (FD) and RD filtered back projection (FBP) in a longitudinal study.Materials and methods122 patients were included in this prospective study. 49 patients (14 men: mean age ± SD, 56±0.4 years; 35 women: 58±1.3 years) completed FD, RD1 (80%-dose) and RD2 (60%-dose) thoracoabdominal CT. Each CT dataset was reconstructed with FBP and SAFIRE. For quantitative image analysis image noise was measured in defined tissue regions. Qualitative image evaluation was performed according to the European Guidelines on Quality criteria for CT. Additionally artifacts, lesion conspicuity, and edge sharpness were assessed.ResultsCompared to FD-FBP noise in soft tissue increased by 12% in RD1-FBP and 27% in RD2-FBP reconstructions, whereas SAFIRE lead to a decrease of 28% (RD1) and 17% (RD2), respectively (all p <0.001). Visually sharp reproduction, lesion conspicuity, edge sharpness of pathologic findings, and overall image quality did not differ statistically significant between FD-FBP and RD-SAFIRE datasets. Image quality decreased in RD1- and RD2-FBP compared to FD-FBP, reaching statistically significance in RD2 datasets (p <0.001). In RD1- and RD2-FBP (p <0.001) streak artifacts were noted.ConclusionUsing SAFIRE the reference mAs in thoracoabdominal CT can be reduced by at least 30% in clinical routine without loss of image quality or diagnostic information.

CT Radiation Dose Reduction in Robot-assisted Pediatric Spinal Surgery.

Retrospective consecutive cohort series. The aim of this study was to develop a low-dose computed tomography (CT) protocol for use in robot-assisted pediatric spinal surgery. CT scans are utilized preoperatively for preoperative planning, by navigation software during robot-assisted surgery, and postoperatively to assess surgical implant placement. Traditionally high radiation doses produced by CT scanning are a concern in the highly radiosensitive pediatric population. We developed a low-dose protocol using phantom scans. A cohort of patients undergoing CT scanning using the low-dose protocol was collected. Further, a matching cohort of patients who underwent standard scanning was collected. Image quality was assessed by observer ratings. Radiation doses and image quality metrics were compared for the standard and low-dose protocol patients. Effective dose significantly decreased 84% to 91% depending on patient size and whether the scan was preoperative or postoperative. All scans were compatible with the navigation software. No clinically significant differences in image quality were observed between low-dose and standard patient cohorts. Task-based CT protocol optimization can produce acceptable image quality with dose comparable to standard two-view radiography. 2.

Substantial CT radiation dose reduction does not affect the preference for CT over direct digital radiography to diagnose isolated zygomatic fractures – A study in human cadavers

IntroductionZygomatic fractures can be diagnosed with either computed tomography (CT) or direct digital radiography (DR). The aim of the present study was to assess the effect of CT dose reduction on the preference for facial CT versus DR for accurate diagnosis of isolated zygomatic fractures. Materials and methodsEight zygomatic fractures were inflicted on four human cadavers with a free fall impactor technique. The cadavers were scanned using eight CT protocols, which were identical except for a systematic decrease in radiation dose per protocol, and one DR protocol. Single axial CT images were displayed alongside a DR image of the same fracture creating a total of 64 dual images for comparison. A total of 54 observers, including radiologists, radiographers and oral and maxillofacial surgeons, made a forced choice for either CT or DR. ResultsForty out of 54 observers (74%) preferred CT over DR (all with P < 0.05). Preference for CT was maintained even when radiation dose reduced from 147.4 μSv to 46.4 μSv (DR dose was 6.9 μSv). Only a single out of all raters preferred DR (P = 0.0003). The remaining 13 observers had no significant preference. ConclusionThis study demonstrates that preference for axial CT over DR is not affected by substantial (∼70%) CT dose reduction for the assessment of zygomatico-orbital fractures.

Spine Computed Tomography Radiation Dose Reduction: Protocol Refinement Based on Measurement Variation at Simulated Lower Radiation Acquisitions.

Retrospective dose-simulation comparison. To determine if sufficient detail for preoperative analysis of bony anatomy can be acquired at substantially lower doses than those typically used. Computed tomography (CT) is a preoperative planning tool for spinal surgery. The pediatric population is at risk to express the harmful effects of ionizing radiation. Preoperative CT scans are presently performed at standard pediatric radiation doses not tailored for surgical planning. We used the validated GE Noise Injection software to retrospectively modify existing spine and chest CT scans from 10 patients to create CT images that simulated a standard dose (100%), 50% dose, and 25% dose scans. 4 orthopedic surgeons and a pediatric radiologist, blinded to dose, measured minimum medial-lateral pedicle width and maximum anterior-posterior bony length along the axis of presumed pedicle screw placement. A total of 90 axial images were generated to create our sample set. Measurements were evaluated for accuracy, precision, and consistency. For any given rater, there was no clinically relevant difference between measurements at the different dose levels and no apparent degradation in precision at the different dose levels. Consistent variation was observed between raters, the likely result of individual differences in measurement approach. Spinal CT scans done for preoperative planning can be performed at 25% of current radiation doses without a loss in surgical planning measurement accuracy or precision. These 25% dose-reduced scans would have average Computed Tomography Dose Index volume dose levels of roughly 1.0 to 2.5 mGy (depending on patient size) and size-specific dose estimates of roughly 2.5 mGy representing a substantial dose savings compared to current practice for many sites. Standardization of consistent landmarks may be useful to further improve inter-rater concordance.

Imaging of congenital heart disease in adults.

Imaging is fundamental to the lifelong care of adult congenital heart disease (ACHD) patients. Echocardiography remains the first line imaging for inpatient, outpatient, or perioperative care. Cross-sectional imaging with cardiovascular magnetic resonance (CMR) or computed tomography (CT) provides complementary and invaluable information on cardiac and vascular anatomy and other intra-thoracic structures. Furthermore, CMR provides quantification of cardiac function and vascular flow. Cardiac catheterization is mostly reserved for assessment of pulmonary vascular resistance, ventricular end-diastolic pressure, and percutaneous interventions. There have been further advances in non-invasive imaging for ACHD including the application of advanced echocardiographic techniques, faster automated CMR imaging, and radiation dose reduction in CT. As a result ACHD, a heterogeneous population, benefit from appropriate application of multiple imaging modalities matched with tertiary ACHD expertise.

Strategies for Computed Tomography Radiation Dose Reduction in Pediatric Neuroimaging.

Radiation exposure from diagnostic imaging is a significant concern, particularly in the care of pediatric patients. Computed tomography (CT) scanning is a significant source of radiation. To demonstrate that diagnostic quality CT images can be obtained while minimizing the effective radiation dose to the patient. In this retrospective cross-sectional study, noncontrast head CT scan data were reviewed, and indications for scans and estimated radiation dose delivered were recorded. The estimated effective radiation dose (EERD) for each CT protocol was reviewed. We identified 251 head CT scans in a single month. Of these, 96 scans were using a low-dose shunt protocol with a mean EERD of 0.82 mSv. The remaining 155 scans were performed using the standard protocol, and the mean EERD was 1.65 mSv. Overall, the EERD was minimized while maintaining diagnostic scan quality. Although replacing a CT with magnetic resonance imaging is ideal to completely avoid ionizing radiation, this is not always practical or preferred. Therefore, it is important to have CT protocols in place that minimize radiation dose without sacrificing diagnostic quality. The protocols in place at our institution could be replicated at other academic and community hospitals and imaging centers.

Effect of radiation dose reduction on image quality in adult head CT with noise-suppressing reconstruction system with a 256 slice MDCT.

The purpose of our study was to investigate the effect of iterative reconstruction (IR) as a dose reduction system on the image quality (IQ) of the adult head computed tomography (CT) at various low‐dose levels, and to identify ways of setting the amount of dose reduction. We performed two noncontrast low‐dose (LD) adult head CT protocols modified by lowering the tube current with IR which were decided in the light of a group of phantom studies. Two groups of patients, each 100 underwent noncontrast head CT with LD‐I and LD‐II, respectively. These groups were compared with 100 consecutive standard dose (STD) adult head CT protocol in terms of quantitative and qualitative IQ. The signal‐to‐noise ratio (SNR) of the white matter (WM) and gray matter (GM) and contrast‐to‐noise ratio (CNR) values in the LD groups were higher than the STD group. The differences were statistically significant. When the STD and the LD groups were compared qualitatively, no significant differences were found in overall quality. By selecting the appropriate level of IR 34%, radiation dose reduction in adult head CT can be achieved without compromising IQ.PACS number: 87.57.‐s

Strategies of computed tomography radiation dose reduction: justification and optimization

Medical imaging is an indispensible diagnostic tool in modern medicine enabling fast and accurate diagnosis. Recent technological advances in medical equipment and increased utilization of the imaging modality have resulted in a significant increase in the exposure to ionizing radiation. After the rapid adoption of multi-detector computed tomography, computed tomography (CT) is now the single largest source of diagnostic radiation exposure to patients. The risks and benefits from radiation must be carefully considered in all examinations using ionizing radiation, and the principles of justification and optimization should be considered in the proper use of CT examination. Justification means that the examination must be medically indicated and useful. Optimization means that the imaging should be performed using doses that are ALARA (as low as reasonably achievable), consistent with the diagnostic task. This includes understanding and changing CT protocols to perform the same diagnostic task with the minimal amount of radiation exposure while maintaining diagnostic accuracy. Protocols and guidelines are important tools for radiation dose reduction. Understanding the parameters and dose information for CT examination is essential for optimization. If the exam is justified, then the parameters must be optimized to the imaging indication, scan area, body size, age, and weight of the patients. The physician should always assess the radiation risk-benefit ratio for each patient before ordering an examination that uses radiation. Continuing education is essential for the implementation of the principles of patient radiation dose reduction. Physicians and radiologists must be aware of the radiation risks associated with CT exams.

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

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

The impact of CT radiation dose reduction and iterative reconstruction algorithms from four different vendors on coronary calcium scoring.

To analyse the effects of radiation dose reduction and iterative reconstruction (IR) algorithms on coronary calcium scoring (CCS). Fifteen ex vivo human hearts were examined in an anthropomorphic chest phantom using computed tomography (CT) systems from four vendors and examined at four dose levels using unenhanced prospectively ECG-triggered protocols. Tube voltage was 120 kV and tube current differed between protocols. CT data were reconstructed with filtered back projection (FBP) and reduced dose CT data with IR. CCS was quantified with Agatston scores, calcification mass and calcification volume. Differences were analysed with the Friedman test. Fourteen hearts showed coronary calcifications. Dose reduction with FBP did not significantly change Agatston scores, calcification volumes and calcification masses (P > 0.05). Maximum differences in Agatston scores were 76, 26, 51 and 161 units, in calcification volume 97, 27, 42 and 162 mm(3), and in calcification mass 23, 23, 20 and 48 mg, respectively. IR resulted in a trend towards lower Agatston scores and calcification volumes with significant differences for one vendor (P < 0.05). Median relative differences between reference FBP and reduced dose IR for Agatston scores remained within 2.0-4.6%, 1.0-5.3%, 1.2-7.7% and 2.6-4.5%, for calcification volumes within 2.4-3.9%, 1.0-5.6%, 1.1-6.4% and 3.7-4.7%, for calcification masses within 1.9-4.1%, 0.9-7.8%, 2.9-4.7% and 2.5-3.9%, respectively. IR resulted in increased, decreased or similar calcification masses. CCS derived from standard FBP acquisitions was not affected by radiation dose reductions up to 80%. IR resulted in a trend towards lower Agatston scores and calcification volumes. In this ex vivo study, radiation dose could be reduced by 80% for coronary calcium scoring. Iterative reconstruction resulted in a trend towards lower Agatston scores and calcification volumes. Caution should be taken for coronary calcium scoring with iterative reconstruction.