CT Dose Reduction Research Articles

TH-E-217BCD-04: MA Modulation and Iterative Reconstruction: Evaluation Using a New CT Phantom

Purpose: The routine clinical CT use of tube current modulation (TCM) and iterative reconstruction algorithms, which can be used to reduce radiation dose, necessitates evaluating their effects on image quality. This study's purpose was to use a new phantom (Mercury Phantom) to evaluate the quality of images acquired with TCM and iterative reconstruction algorithms as implemented by two different CT manufacturers. Methods: The phantom consists of four cylindrical and three tapered regions. The phantom was designed to measure noise-power spectrum (NPS) and modulation transfer function (MTF) across a range of diameters'” 16, 23, 30, and 37 cm'”and at multiple, clinically relevant insert materials from air to iodinated tissue. Images were acquired on a Siemens Flash and GE 750HD using a range of TCM and proprietary reconstruction algorithms: ASIR, IRIS, and SAFIRE. Custom software measured the non-stationarity of NPS as a function of reconstruction and TCM. Contrast and MTF were measured for each insert for each reconstruction algorithm. Results: Measured HU of different materials varied minimally as a function of reconstruction algorithm and dose reduction technique. However, as a function of phantom size from the 16-cm to 37-cm diameter, the [air,Polystyrene,Acrylic,Teflon] HU of 120-kVp images changed by approximately [50,−20,−8,−130] for the 750HD and [35,0,6,−75] for the Flash. MTFs of the linear reconstruction algorithms were independent of size, TCM, and contrast, but for iterative algorithms, the MTFs depended on the object contrast and improved by as much as 25%. Peak NPS decreased from 37-cm to 16-cm (∼86%), decreased for iterative reconstruction relative to linear algorithms (∼21%), and decreased radially from the phantom's center (∼25%). mA modulation performance differed considerably between the two systems. Conclusion: The Mercury Phantom can be used to assess trade-offs in CT image quality and dose reduction techniques for a range of sizes incorporating TCM and iterative reconstruction. Joshua M. Wilson Funded, in part, by Research Agreement with GE Healthcare. Ehsan Samei Research grant: NIH R01 EB001838; Research grant: General Electric; Research grant: Siemens Medical; Research grant: Carestream Health; Share-holder: Zumatek Inc; Advisory Board: IBA

TH-E-217BCD-08: Simulating Reduced-Dose CT Imaging Using an Image-Based Virtual Sinogram Approach: Comparisons with Real Sinogram-Based Simulation

Purpose: Low dose CT simulation is promising technique which can be applied to dose optimization of the clinical CT images without repeating CT examinations for patients to obtain images at different dose levels. We present a virtual sinogram approach which enables low-dose CT simulation study using only conventional CT image data without requiring raw sinogram data. Also presented are comparison results of virtual sinogram-based and real sinogram-based simulated reduced-dose CT images. Methods: A virtual sinogram is generated by performing line integral of the CT number-based attenuation value, and a separate noise sinogram is generated using a noise model which incorporating X-ray photon flux depending on mAs, system electronic noise, and the virtual sinogram. A synthetic noise CT data is generated by applying FBP of the noise sinogram using an appropriate filter depending on reconstruction kernel of original CT. Finally, a simulated low-dose CT image is generated by adding the synthetic noise CT data to the original CT data. Two phantoms for use in QC study were scanned with different mAs levels, and virtual sinogram-based and real sinogram-based approaches were applied to generate simulated reduced dose images. For quantitative assessment, non-subtracted noise power spectrum (NPS) and standard deviation on selected ROIs were compared. Results: Visual comparison made it clear that the degree of streak noise pattern in image as well as the level of noise magnitude agrees very well. The %difference of standard deviations between real and simulated images ranged from 0 to 7.5%. Also NPS measurements validate the proper working of the proposed low-dose simulator. Conclusions: Proposed method could produce realistic reduced-dose CT images and its similarity was confirmed visually and quantitatively. Proposed method might be a useful tool for assessing low-dose CT application in various clinical settings even when raw sinogram data is not available. The research was supported by the Converging Research Center Program through the Ministry of Education, Science and Technology (Grant No. 2011K000718)

The Use of Adaptive Statistical Iterative Reconstruction in Pediatric Head CT: A Feasibility Study

Iterative reconstruction techniques facilitate CT dose reduction; though to our knowledge, no group has explored using iterative reconstruction with pediatric head CT. Our purpose was to perform a feasibility study to assess the use of ASIR in a small group of pediatric patients undergoing head CT. An Alderson-Rando head phantom was scanned at decreasing 10% mA intervals relative to our standard protocol, and each study was then reconstructed at 10% ASIR intervals. An intracranial region of interest was consistently placed to estimate noise. Our ventriculoperitoneal shunt CT protocol was subsequently modified, and patients were scanned at 20% ASIR with approximately 20% mA reductions. ASIR studies were anonymously compared with older non-ASIR studies from the same patients by 2 attending pediatric neuroradiologists for diagnostic utility, sharpness, noise, and artifacts. The phantom study demonstrated similar noise at 100% mA/0% ASIR (3.9) and 80% mA/20% ASIR (3.7). Twelve pediatric patients were scanned at reduced dose at 20% ASIR. The average CTDI(vol) and DLP values of the 20% ASIR studies were 22.4 mGy and 338.4 mGy-cm, and for the non-ASIR studies, they were 28.8 mGy and 444.5 mGy-cm, representing statistically significant decreases in the CTDI(vol) (22.1%, P = .00007) and DLP (23.9%, P = .0005) values. There were no significant differences between the ASIR studies and non-ASIR studies with respect to diagnostic acceptability, sharpness, noise, or artifacts. Our findings suggest that 20% ASIR can provide approximately 22% dose reduction in pediatric head CT without affecting image quality.

Evaluation of dose reduction and image quality in chest CT using adaptive statistical iterative reconstruction with the same group of patients

The objective of this study was to compare the image quality and radiation dose of chest CT images reconstructed with a blend of adaptive statistical iterative reconstruction (ASIR) and filtered back-projection (FBP) with images generated using conventional FBP. Patients with chest CT re-examinations were alternately assigned to two scanners with different reconstruction techniques. The study groups included noise index (NI) 11 with 30% ASIR (A30), NI 13 with 40% ASIR (A40), NI 15 with 50% ASIR (A50) and NI 17 with 60% ASIR (A60), sequentially changed every 2 months. The control images were obtained using FBP and NI 11. All acquisitions were performed with automatic dose modulation. Paired t-test and non-parameter test were applied to compare the difference. The radiation doses were significantly lower in the examinations that used ASIR (p<0.001). The mean dose reduction rate was 27.7%, 45.2%, 57.1% and 71.8% for Groups A30, A40, A50 and A60, respectively. The image quality of Groups A30-A50 was not inferior to that of the control examinations. The image noise of Group A60 was greater and subjective image quality was inferior to that of the control. ASIR enabled the use of a higher NI with automatic dose modulation. With 50% ASIR and a NI of 15, the effective radiation dose was reduced by 57%, without compromising image quality.

Organ-Based Dose Current Modulation and Thyroid Shields: Techniques of Radiation Dose Reduction for Neck CT

The purpose of this study was to assess the difference in absorbed organ dose and image quality for MDCT neck protocols using automatic tube current modulation alone compared with organ-based dose modulation and in-plane thyroid bismuth shielding. An anthropomorphic female phantom with metal oxide semiconductor field effect transistor (MOSFET) detectors was scanned on a 64-MDCT scanner. The protocols included a reference neck CT protocol using automatic tube current modulation and three modified protocols: organ-based dose modulation, automatic tube current modulation with thyroid shield, and organ-based dose modulation with thyroid shield. Image noise was evaluated quantitatively with the SD of the attenuation value, and subjectively by two neuroradiologists. Organ-based dose modulation, automatic tube current modulation with thyroid shield, and organ-based dose modulation with thyroid shield protocols reduced the thyroid dose by 28%, 33%, and 45%, respectively, compared with the use of automatic tube current modulation alone (p ≤ 0.005). Organ-based dose modulation also reduced the radiation dose to the ocular lens (33-47%) compared with the use of automatic tube current modulation (p ≤ 0.04). There was no significant difference in measured noise and subjective image quality between the protocols. Both organ-based dose modulation and thyroid shields significantly reduce the thyroid organ dose without degradation of subjective image quality compared with automatic tube current modulation. Organ-based dose modulation has the additional benefit of dose reduction to the ocular lens.

Model-based iterative reconstruction technique for radiation dose reduction in chest CT: comparison with the adaptive statistical iterative reconstruction technique

To prospectively evaluate dose reduction and image quality characteristics of chest CT reconstructed with model-based iterative reconstruction (MBIR) compared with adaptive statistical iterative reconstruction (ASIR). One hundred patients underwent reference-dose and low-dose unenhanced chest CT with 64-row multidetector CT. Images were reconstructed with 50 % ASIR-filtered back projection blending (ASIR50) for reference-dose CT, and with ASIR50 and MBIR for low-dose CT. Two radiologists assessed the images in a blinded manner for subjective image noise, artefacts and diagnostic acceptability. Objective image noise was measured in the lung parenchyma. Data were analysed using the sign test and pair-wise Student's t-test. Compared with reference-dose CT, there was a 79.0 % decrease in dose-length product with low-dose CT. Low-dose MBIR images had significantly lower objective image noise (16.93 ± 3.00) than low-dose ASIR (49.24 ± 9.11, P < 0.01) and reference-dose ASIR images (24.93 ± 4.65, P < 0.01). Low-dose MBIR images were all diagnostically acceptable. Unique features of low-dose MBIR images included motion artefacts and pixellated blotchy appearances, which did not adversely affect diagnostic acceptability. Diagnostically acceptable chest CT images acquired with nearly 80 % less radiation can be obtained using MBIR. MBIR shows greater potential than ASIR for providing diagnostically acceptable low-dose CT images without severely compromising image quality. • Model-based iterative reconstruction (MBIR) creates high-quality low-dose CT images. • MBIR significantly improves image noise and artefacts over adaptive statistical iterative techniques. • MBIR shows greater potential than ASIR for diagnostically acceptable low-dose CT. • The prolonged processing time of MBIR may currently limit its routine use in clinical practice.

Radiation Dose Reduction in Temporal Bone CT with Iterative Reconstruction Technique

Iterative reconstruction of CT images is characterized by reduced image noise and may allow reduction in radiation exposure. We investigated the influence of an IRT technique on image quality and radiation dose savings when applied to temporal bone CT. Based on the typical image quality level of adult subjects using routine radiation dose and FBP, an exsomatized cadaveric head with CNR characteristics closest to the level of clinical subjects was identified. Cadaver acquisitions were performed at multiple levels of tube current exposure. Reconstructions were performed using FBP and IRT (iDose), with multiple iDose levels applied for each acquisition. Transverse and coronal reformations of all reconstructions were evaluated subjectively and objectively. Phantom tests were performed to validate the protocol optimizations with iDose, specifically the spatial resolution relative to routine dose acquisitions. Finally, the results of protocol optimization with iDose were clinically validated in 50 patients. At the same radiation dose, the image CNR of iDose reconstructions was higher than that of FBP and progressively increased with higher iDose levels. The combination of 100 mAs/section and iDoseL5 was the lowest dose that met the requirements for diagnostic acceptability, with CNR slightly higher than our routine institution protocol of 200 mAs/section with FBP reconstruction. Spatial resolution characteristics were similar between FBP and iDose at all different strengths. The findings were consistent among the cadaver, phantom, and clinical acquisitions. The iDose IRT can help reduce radiation dose of temporal bone CT by 50% relative to routine institution protocols with FBP, while maintaining diagnostic image quality.

Optimizing CT Dose and Image Quality for Radiotherapy Patients

With the successes of CT dose reduction programs such as Image Gently [1] and Image WiselyTM 2], many organizations have signed n to these programs, and CT proocols across the country have been djusted to match CT dose to the mage quality necessary for a given iagnostic examination. Most of he protocols call for lower doses ompared with the technique in use reviously to scan patients, again n the basis of obtaining sufficient mage quality to allow a diagnosis o be made. With the increased meia attention to CT protocol errors nd misadministrations using highose CT techniques and the inreased frequency of physicians’ orering CT studies to obtain diagnoses, here has been a plethora of articles sugesting CT dose reduction strategies in he recent literature [3-6]. Although CT dose reduction strtegies have been used across the ountry in response to these efforts, hey may not apply to all patients ho require CT scans for their medcal conditions. In particular, patients resenting for CT scans for radioherapy planning may not benefit rom the extremely reduced dose trategies. These patients will have igh-energy x-radiation (an order of agnitude greater than what is reeived with imaging) through the rea being scanned for planning puroses (about 10-80 Gy), and the CT ose (about 1-100 mGy) presents nly a small fraction of the dose the atients will receive to control their disease. In fact, the new techniques in radiation oncology will use further low-energy imaging techniques to align patients during their radiotherapy procedures (“image-guided radiation therapy”). Hence, as mentioned, the CT planning doses will not be of great concern to these patients and their attending radiation oncologists. From the viewpoint of obtaining sufficient image quality for the myriad radiotherapy planning procedures in use today, radiology and radiation oncology department staff members should consult with the attending radiation oncologist to adjust CT scan protocols to obtain sufficient CT image rendition for the planning procedure at hand. This may require an actual increase in CT scan technique from that used for reduced-dose diagnostic techniques. This is especially important when using CT imaging for planning whose image sets will be fused with those from other imaging modalities, such as MRI or PET/CT, to allow the radiation oncologist to accurately contour the tumor targets that will be the subject of the radiotherapy procedure. Image fusion requires matching anatomic regions in both the CT image set and the MRI data, for example, to attack intracranial tumors that are more visible on the MRI data sets. If the CT data set for this fusion is suboptimal (“noisy”) because a reduced-dose CT technique was used, the image fusion may not be rendered accurately,

Iterative reconstruction methods in two different MDCT scanners: Physical metrics and 4-alternative forced-choice detectability experiments – A phantom approach

This paper characterizes and evaluates the potential of three commercial CT iterative reconstruction methods (ASIR™, VEO™ and iDose4 (™)) for dose reduction and image quality improvement. We measured CT number accuracy, standard deviation (SD), noise power spectrum (NPS) and modulation transfer function (MTF) metrics on Catphan phantom images while five human observers performed four-alternative forced-choice (4AFC) experiments to assess the detectability of low- and high-contrast objects embedded in two pediatric phantoms. Results show that 40% and 100% ASIR as well as iDose4 levels 3 and 6 do not affect CT number and strongly decrease image noise with relative SD constant in a large range of dose. However, while ASIR produces a shift of the NPS curve apex, less change is observed with iDose4 with respect to FBP methods. With second-generation iterative reconstruction VEO, physical metrics are even further improved: SD decreased to 70.4% at 0.5 mGy and spatial resolution improved to 37% (MTF50%). 4AFC experiments show that few improvements in detection task performance are obtained with ASIR and iDose4, whereas VEO makes excellent detections possible even at an ultra-low-dose (0.3 mGy), leading to a potential dose reduction of a factor 3 to 7 (67%–86%). In spite of its longer reconstruction time and the fact that clinical studies are still required to complete these results, VEO clearly confirms the tremendous potential of iterative reconstructions for dose reduction in CT and appears to be an important tool for patient follow-up, especially for pediatric patients where cumulative lifetime dose still remains high.

Adaptive Statistical Iterative Reconstruction Technique for Radiation Dose Reduction in Chest CT: A Pilot Study

Adaptive Statistical Iterative Reconstruction Technique for Radiation Dose Reduction in Chest CT: A Pilot Study

Radiation Dose Reduction of Chest CT with Iterative Reconstruction in Image Space - Part II: Assessment of Radiologists' Preferences Using Dual Source CT

ObjectiveTo evaluate the impact of radiation dose and reconstruction algorithms on radiologists' preferences, and whether an iterative reconstruction in image space (IRIS) can be used for dose reduction in chest CT.Materials and MethodsStandard dose chest CT (SDCT) in 50 patients and low dose chest CT (LDCT) in another 50 patients were performed, using a dual-source CT, with 120 kVp and same reference mAs (50 mAs for SDCT and 25 mAs for LDCT) employed to both tubes by modifying the dual-energy scan mode. Full-dose data were obtained by combining the data from both tubes and half-dose data were separated from one tube. These were reconstructed by using a filtered back projection (FBP) and IRIS: full-dose FBP (F-FBP); full-dose IRIS (F-IRIS); half-dose FBP (H-FBP) and half-dose IRIS (H-IRIS). Ten H-IRIS/F-IRIS, 10 H-FBP/H-IRIS, 40 F-FBP/F-IRIS and 40 F-FBP/H-IRIS pairs of each SDCT and LDCT were randomized. The preference for clinical usage was determined by two radiologists with a 5-point-scale system for the followings: noise, contrast, and sharpness of mediastinum and lung.ResultsRadiologists preferred IRIS over FBP images in the same radiation dose for the evaluation of the lungs in both SDCT (p = 0.035) and LDCT (p < 0.001). When comparing between H-IRIS and F-IRIS, decreased radiation resulted in decreased preference. Observers preferred H-IRIS over F-FBP for the lungs in both SDCT and LDCT, even with reduced radiation dose by half in IRIS image (p < 0.05).ConclusionRadiologists' preference may be influenced by both radiation dose and reconstruction algorithm. According to our preliminary results, dose reduction at 50% with IRIS may be feasible for lung parenchymal evaluation.

Cranial CT with Adaptive Statistical Iterative Reconstruction: Improved Image Quality with Concomitant Radiation Dose Reduction

To safeguard patient health, there is great interest in CT radiation-dose reduction. The purpose of this study was to evaluate the impact of an iterative-reconstruction algorithm, ASIR, on image-quality measures in reduced-dose head CT scans for adult patients. Using a 64-section scanner, we analyzed 100 reduced-dose adult head CT scans at 6 predefined levels of ASIR blended with FBP reconstruction. These scans were compared with 50 CT scans previously obtained at a higher routine dose without ASIR reconstruction. SNR and CNR were computed from Hounsfield unit measurements of normal GM and WM of brain parenchyma. A blinded qualitative analysis was performed in 10 lower-dose CT datasets compared with higher-dose ones without ASIR. Phantom data analysis was also performed. Lower-dose scans without ASIR had significantly lower mean GM and WM SNR (P = .003) and similar GM-WM CNR values compared with higher routine-dose scans. However, at ASIR levels of 20%-40%, there was no statistically significant difference in SNR, and at ASIR levels of ≥60%, the SNR values of the reduced-dose scans were significantly higher (P < .01). CNR values were also significantly higher at ASIR levels of ≥40% (P < .01). Blinded qualitative review demonstrated significant improvements in perceived image noise, artifacts, and GM-WM differentiation at ASIR levels ≥60% (P < .01). These results demonstrate that the use of ASIR in adult head CT scans reduces image noise and increases low-contrast resolution, while allowing lower radiation doses without affecting spatial resolution.

Ultra-low dose CT attenuation correction for PET/CT

A challenge for positron emission tomography/computed tomography (PET/CT) quantitation is patient respiratory motion, which can cause an underestimation of lesion activity uptake and an overestimation of lesion volume. Several respiratory motion correction methods benefit from longer duration CT scans that are phase matched with PET scans. However, even with the currently available, lowest dose CT techniques, extended duration cine CT scans impart a substantially high radiation dose. This study evaluates methods designed to reduce CT radiation dose in PET/CT scanning. We investigated selected combinations of dose reduced acquisition and noise suppression methods that take advantage of the reduced requirement of CT for PET attenuation correction (AC). These include reducing CT tube current, optimizing CT tube voltage, adding filtration, CT sinogram smoothing and clipping. We explored the impact of these methods on PET quantitation via simulations on different digital phantoms. CT tube current can be reduced much lower for AC than that in low dose CT protocols. Spectra that are higher energy and narrower are generally more dose efficient with respect to PET image quality. Sinogram smoothing could be used to compensate for the increased noise and artifacts at radiation dose reduced CT images, which allows for a further reduction of CT dose with no penalty for PET image quantitation. When CT is not used for diagnostic and anatomical localization purposes, we showed that ultra-low dose CT for PET/CT is feasible. The significant dose reduction strategies proposed here could enable respiratory motion compensation methods that require extended duration CT scans and reduce radiation exposure in general for all PET/CT imaging.

Utility of Iodine Overlay Technique and Virtual Unenhanced Images for the Characterization of Renal Masses by Dual-Energy CT

The objective of our study was to assess the utility of dual-energy CT for characterizing renal masses using iodine overlay techniques and virtual unenhanced images and to measure the potential radiation dose reduction for two-phase kidney CT compared with a standard three-phase protocol. Sixty patients with suspected renal masses underwent dual-energy CT including true unenhanced, dual-energy corticomedullary, and dual-energy late nephrographic phase imaging. Iodine overlay and virtual unenhanced images were derived from the corticomedullary and late nephrographic phases, respectively. The CT numbers of renal masses were calculated using the iodine overlay images superimposed on the virtual unenhanced images. The overall imaging quality of the true unenhanced images and of the virtual unenhanced images was also evaluated. The effective radiation doses for dual-energy CT and for true unenhanced imaging were calculated. For overlay or enhancement values on iodine overlay images, 36 simple cysts and 10 hemorrhagic cysts had an attenuation value of less than 20 HU, whereas 21 renal cell carcinomas showed an attenuation value of 20 HU or greater. Eleven angiomyolipomas contained macroscopic fat tissue. All renal masses were accurately classified on the basis of dual-energy CT. The imaging quality of the virtual unenhanced images from the corticomedullary and late nephrographic phases was inferior to the image quality of the true unenhanced images (p < 0.01). The mean effective doses for the three-phase protocol and for true unenhanced images were 12.6 and 2.4 mSv, respectively. Our results show that dual-energy CT using iodine overlay techniques and virtual unenhanced images may be useful for characterizing renal masses.

Bismuth Shields for CT Dose Reduction: Do They Help or Hurt?

Bismuth shielding has been used to reduce the dose from CT to superficial radiosensitive organs, such as the breast, lens of the eye, and thyroid [1]. Bismuth-impregnated latex shields are placed over the organ of interest to attenuate the x-ray beam entering the patient. Although studies have confirmed a reduction in superficial dose [2-5], the disadvantages of using bismuth shielding have not been widely recognized. We summarize here the primary arguments for and against its use in CT.

Organ and effective dose reduction in adult chest CT using abdominal lead shielding

The purpose of this study was to evaluate and compare organ and effective dose savings that could be achieved using conventional lead aprons and a new, custom-designed shield as out-of-plane shielding devices during chest CT scans. Thermoluminescent dosimeters were used to measure doses throughout the abdomen and pelvis during CT scans of the chest of a RANDO phantom. Dose measurements were made with no shielding, with lead aprons and with the new shield around the abdomen and pelvis in order to quantify the achievable organ and effective dose reductions. Average dose savings in the 10 phantom sections ranged from 5% to 78% with the highest point dose saving of 93% being found in the mid-pelvis. When shielding was used, the maximum measured organ dose reduction was a 72% dose saving to the testes. Significant dose savings were found throughout the abdomen and pelvis, which contributed to an effective dose saving of 4% that was achieved over and above the dose savings obtained through conventional optimisation strategies. This could yield significant population dose savings and reductions in collective radiation risk. In this study significant organ and effective dose reductions have been achieved through the use of abdominal shielding during chest CT examinations and it is therefore recommended that out-of-plane patient shielding devices should be used for all chest CT scans and potentially for every CT scan, irrespective of body part.

Radiation Risks: CT Dose-Reduction Technologies: A Review

Radiation Risks: CT Dose-Reduction Technologies: A Review

Real-time estimation of dose reduction for pediatric CT using bismuth shielding

The purpose of this study is to estimate the dose reduction of bismuth shielding for pediatric CT using a real-time CT dose probe. Routine CT examinations of head, chest and abdomen were performed on a 10-year pediatric anthropomorphic phantom, with and without bismuth shield. A solid-state dosimeter was used to obtain real-time dose measurements and to estimate the dose reduction. The maximum dose reduction of eyes using bismuth shield for in-plane CT scanning can achieve 56% during spiral head scanning interval. The average dose reduction is around 25% for in-plane CT scanning, and reaches 62% combining the technique of automatic tube current modulation. The solid-state probe can provide fast and convenient measurements for dose estimation of superficial organs. It is suggested to use Bismuth shielding in routine CT examinations to protect the radiosensitive tissues.

CT dose reduction in practice

Greater than 10% of diagnostic imaging studies performed in developed countries are CT examinations. In the United States, as many as 60 million CT studies are performed each year, up to 7 million of which are performed in pediatric patients. In the spirit of the ALARA principle, both adult and pediatric radiologists should strive to decrease pediatric radiation exposure whenever possible. This can be achieved by utilizing imaging studies that do not require the use of ionizing radiation, thus decreasing the number of CT studies performed. If a CT study is indicated, the delivered dose should be optimized to use the lowest possible dose level while still answering the clinical question.

Is there a case for dose reduction in orthopaedic CT

Is there a case for dose reduction in orthopaedic CT