Automated Computed Tomography Dose-Saving Algorithm to Protect Radiosensitive Tissues: Estimation of Radiation Exposure and Image Quality Considerations

Comparison of selected photon shield and organ-based tube current modulation for radiation dose reduction in head computed tomography: A phantom study

OBJECTIVE

The aim of this study is to investigate the radiation dose and image quality of head CT using SPS and OBTCM techniques.

METHODS

Three anthropomorphic head phantoms (1-yr-old, 5-yr-old, and adult) were used. Images were acquired using four modes (Default protocol, OBTCM, SPS, and SPS+OBTCM). Absorbed dose to the lens, anterior brain (brain_A), and posterior brain (brain_P) was measured and compared. Image noise and CNR were assessed in the selected regions of interest (ROIs).

RESULTS

Compared with that in the Default protocol, the absorbed dose to the lens reduced by up to 28.33%,71.38%, and 71.12% in OBTCM, SPS, and SPS+OBTCM, respectively. The noise level in OBTCM slightly (≤1.45HU) increased than that in Default protocol, and the SPS or SPS+OBTCM mode resulted in a quantitatively small increase (≤2.58HU) in three phantoms. There was no significant difference in CNR of different phantoms under varies scanning modes (p >  0.05).

CONCLUSIONS

During head CT examinations, the SPS mode can reduce the radiation dose while maintaining image quality. SPS+OBTCM couldn't further effectively reduce the absorbed dose to the lens for 1-yr and 5-yr-old phantoms. Thus, SPS mode in pediatric and SPS+OBTCM mode in adult are better than other modes, and should be used in clinical practice.

Trade-off between breast dose and image quality using composite bismuth shields in computed tomography: A phantom study

INTRODUCTION

Many researchers have suggested that bismuth composite shields (BCS) reduce breast dose remarkably; however, the level of this reduction and its impact on image quality has not been assessed. This study aimed to evaluate the efficiency of nano- and micro- BCS in reducing the dose and image quality during chest computed tomography (CT) scans.

MATERIALS AND METHODS

Bismuth shields composed of 15 weighting percentage (wt%) and 20 wt% bismuth oxide (Bi₂O₃) nano- and micro-particles mixed in silicon rubber polymer were constructed in 1 and 1.5 mm thicknesses. The physical properties of nanoparticles were assessed using a scanning electron microscope (SEM), X-ray diffraction (XRD), and energy-dispersive X-ray (EDX). Breast radiation doses were measured experimentally during chest CT using PMMA standard dosimetry phantom (body phantom, 76-419-4150, Fluke Biomedical) in the presence of the shields. The image quality was assessed by calculating signal and noise values in different regions.

RESULTS

The SEM images showed that the average size of Bi₂O₃ nano- and micro-particles was about 70 nm and 150 μm, respectively. The breast doses were reduced by increasing the shield thickness/bismuth weight percentage. The maximum dose reduction was related to the 20% weight of Bi₂O₃ nano-particles and a thickness of 1.5 mm. The minimum dose reduction was related to the 15% weight of Bi₂O₃ micro-particles with a thickness of 1 mm. The mean noise was higher in nano-particle bismuth shields than in micro-particles.

CONCLUSION

Composite shields containing bismuth nano- and micro-particles can reduce the breast dose during chest CT examinations while negatively impacting diagnostic image quality. Several critical factors, such as bismuth concentration, particle size, and shield thickness, directly affect the efficiency.

Optimized Camera-Based Patient Positioning in CT: Impact on Radiation Exposure

OBJECTIVE

The aim of this study was to evaluate whether a 3-dimensional (3D) camera can outperform highly trained technicians in precision of patient positioning and whether this transforms into a reduction in patient exposure.

MATERIALS AND METHODS

In a single-center study, 3118 patients underwent computer tomography (CT) scans of the chest and/or abdomen on a latest generation single-source CT scanner supported with an automated patient positioning system by 3D camera. One thousand five hundred fifty-seven patients were positioned laser-guided by a highly trained radiographer (camera off) and 1561 patients with 3D camera (camera on) guidance. Radiation parameters such as effective dose, organ doses, CT dose index, and dose length product were analyzed and compared. Isocenter accuracy and table height were evaluated between the 2 groups.

RESULTS

Isocenter positioning was significantly improved with the 3D camera ( P < 0.001) as compared with visual laser-guided positioning. Absolute table height differed significantly ( P < 0.001), being higher with camera positioning (165.6 ± 16.2 mm) as compared with laser-guided positioning (170.0 ± 20.4 mm). Radiation exposure decreased using the 3D camera as indicated by dose length product (321.1 ± 266.6 mGy·cm; camera off: 342.0 ± 280.7 mGy·cm; P = 0.033), effective dose (3.3 ± 2.7 mSv; camera off: 3.5 ± 2.9; P = 0.053), and CT dose index (6.4 ± 4.3 mGy; camera off: 6.8 ± 4.6 mGy; P = 0.011). Exposure of radiation-sensitive organs such as colon ( P = 0.015) and red bone marrow ( P = 0.049) were also lower using the camera.

CONCLUSIONS

The introduction of a 3D camera improves patient positioning in the isocenter of the scanner, which results in a lower and also better balanced dose reduction for the patients.

Image quality and clinical usefulness of automatic tube current modulation technology in female chest computed tomography screening

The study was aimed to evaluate the image quality and radiation dose during female chest computed tomography (CT) screening using organ-based tube current modulation technology X-ray combined applications to reduce exposure (XCARE).Five hundred sixty female individuals undergoing chest CT scan were prospectively enrolled and divided into 4 groups based on body mass index (BMI). Then they were randomly and equally divided into control and experimental subgroup and respectively accepted conventional low-dose and XCARE technology spiral CT scan with same parameters. Signal-to-noise ratio and contrast-to-noise ratio were calculated. The quality of the images was evaluated by 2 radiologists using a 5-point scale.Among experimental subgroups of the 4 BMI groups, Signal-to-noise ratios, CT dose index of volume, dose-length product, effective dose, and contrast-to-noise ratio all displayed significant differences, as well as in control subgroups (P < .001). Both the experimental and control subgroups showed an increasing trend in radiation dose with the increasing of BMI. Parameters of image quality and radiation dose displayed no significant differences between control and experimental subgroups in the 4 groups. In multiple linear regression analysis, age and scanning protocol were not associated with radiation dose (P > .05), while BMI was significantly associated with increased CT dose index of volume (P < .05). The display of the lesions for the patients in the control and experimental subgroups of the 4 groups with different BMIs exhibited no statistically significant difference.The same image quality and radiation dose can be obtained using XCARE technology compared to conventional chest CT scans, which can be used regularly in female patients.Advances in knowledge: Using automatic tube current modulation technology to reduce exposure in breast. In this study, we sought a radiation protection method for sensitive tissue in chest CT screening.

Evaluation of an organ-based tube current modulation tool in pediatric CT examinations

Objectives

To investigate the effect of an organ-based tube current modulation (OTCM) technique on organ absorbed dose and assess image quality in pediatric CT examinations.

Methods

Four physical anthropomorphic phantoms that represent the average individual as neonate, 1-year-old, 5-year-old, and 10-year-old were used. Standard head and thorax acquisitions were performed with automatic tube current modulation (ATCM) and ATCM+OTCM. Dose calculations were performed by means of Monte Carlo simulations. Radiation dose was measured for superficial and centrally located radiosensitive organs. The angular range of the OTCM exposure window was determined for different tube rotation times (t) by means of a solid-state detector. Image noise was measured as the standard deviation of the Hounsfield unit value in regions of interest drawn at selected anatomical sites.

Results

ATCM+OTCM resulted in a reduction of radiation dose to all radiosensitive organs. In head, eye lens dose was reduced by up to 13% in ATCM+OTCM compared with ATCM. In thorax, the corresponding reduction for breast dose was up to 10%. The angular range of the OTCM exposure window decreased with t. For t = 0.4 s, the angular range was limited to 74° in head and 135° for thorax. Image noise was significantly increased in ATCM+OTCM acquisitions across most examined phantoms (p < 0.05).

Conclusions

OTCM reduces radiation dose to exposed radiosensitive organs with the eye lens and breast buds exhibiting the highest dose reduction. The OTCM exposure window is narrowed at short t. An increase in noise is inevitable in images located within the OTCM-activated imaged volume.

Key Points

• In pediatric CT, organ-based tube current modulation reduces radiation dose to all major primarily exposed radiosensitive organs.

• Image noise increases within the organ-based tube current modulation enabled imaged volume.

• The angular range of the organ-based tube current modulation low exposure window is reduced with tube rotation time.

Organ-based tube current modulation in chest CT. A comparison of three vendors

INTRODUCTION

Organ-based tube current modulation (OBTCM) is designed for anterior dose reduction in Computed Tomography (CT). The purpose was to assess dose reduction capability in chest CT using three organ dose modulation systems at different kVp settings. Furthermore, noise, diagnostic image quality and tumour detection was assessed.

METHODS

A Lungman phantom was scanned with and without OBTCM at 80-135/140 kVp using three CT scanners; Canon Aquillion Prime, GE Revolution CT and Siemens Somatom Flash. Thermo-luminescent dosimeters were attached to the phantom surface and all scans were repeated five times. Image noise was measured in three ROIs at the level of the carina. Three observers visually scored the images using a fivestep scale. A Wilcoxon Signed-Rank test was used for statistical analysis of differences.

RESULTS

Using the GE revolution CT scanner, dose reductions between 1.10 mSv (12%) and 1.56 mSv (24%) (p < 0.01) were found in the anterior segment and no differences posteriorly and laterally. Total dose reductions between 0.64 (8%) and 0.91 mSv (13%) were found across kVp levels (p < 0.00001). Maximum noise increase with OBTCM was 0.8 HU. With the Canon system, anterior dose reductions of 6-10% and total dose reduction of 0.74-0.76 mSv across kVp levels (p < 0.001) were found with a maximum noise increase of 1.1 HU. For the Siemens system, dose increased by 22-51% anteriorly; except at 100 kVp where no dose difference was found. Noise decreased by 1 to 1.5 HU.

CONCLUSION

Organ based tube current modulation is capable of anterior and total dose reduction with minimal loss of image quality in vendors that do not increase posterior dose.

IMPLICATIONS FOR PRACTICE

This research highlights the importance of being familiar with dose reduction technologies.

Precise and Automatic Patient Positioning in Computed Tomography: Avatar Modeling of the Patient Surface Using a 3-Dimensional Camera

OBJECTIVES

The aim of this study was to evaluate the accuracy of a 3-dimensional (3D) camera algorithm for automatic and individualized patient positioning based on body surface detection and to compare the results of the 3D camera with manual positioning performed by technologists in routinely obtained chest and abdomen computed tomography (CT) examinations.

MATERIALS AND METHODS

This study included data of 120 patients undergoing clinically indicated chest (n = 68) and abdomen (n = 52) CT. Fifty-two of the patients were scanned with CT using a table height manually selected by technologists; 68 patients were automatically positioned with the 3D camera, which is based on patient-specific body surface and contour detection. The ground truth table height (TGT) was defined as the table height that aligns the axial center of the patient's body region in the CT scanner isocenter. Off-centering was defined as the difference between the ground truth table height (TGT) and the actual table position used in all CT examinations. The t test was performed to determine significant differences in the vertical offset between automatic and manual positioning. The χ test was used to check whether there was a relationship between patient size and the magnitude of off-centering.

RESULTS

We found a significant improvement in patient centering (offset 5 ± 3 mm) when using the automatic positioning algorithm with the 3D camera compared with manual positioning (offset 19 ± 10 mm) performed by technologists (P < 0.005). Automatic patient positioning based on the 3D camera reduced the average offset in vertical table position from 19 mm to 7 mm for chest and from 18 mm to 4 mm for abdomen CT. The absolute maximal offset was 39 mm and 43 mm for chest and abdomen CT, respectively, when patients were positioned manually, whereas with automatic positioning using the 3D camera the offset never exceeded 15 mm. In chest CT performed with manual patient positioning, we found a significant correlation between vertical offset greater than 20 mm and patient size (body mass index, >26 kg/m, P < 0.001). In contrast, no such relationship was found for abdomen CT (P = 0.38).

CONCLUSIONS

Automatic individualized patient positioning using a 3D camera allows for accurate patient centering as compared with manual positioning, which improves radiation dose utilization.

Estimating the Patient-specific Dose to the Thyroid and Breasts and Overall Risk in Chest CT When Using Organ-based Tube Current Modulation

Purpose To assess the potential dose reduction to the thyroid and breasts in chest computed tomography (CT) with organ-based tube current modulation (OBTCM). Materials and Methods In this retrospective study (from January 2015 to December 2016), the location of the breasts with respect to the reduced tube current zone was determined. With Monte Carlo simulations, patient-specific dose distributions of chest CT scans were calculated for 50 female patients (mean age, 53.7 years ± 17.5; range, 20-80 years). The potential dose reduction with OBTCM was assessed. In addition, simulations of clinical OBTCM scans were made for 17 of the 50 female patients (mean age, 43.8 years ± 17.1; range, 20-69 years). Posterior organs in the field of view were analyzed and lifetime attributable risk (LAR) of cancer incidence and mortality was estimated. Image quality between standard CT and OBTCM scans was compared. Results No women had all breast tissue within the reduced tube current zone. Dose reductions of 18% in the thyroid and 9% in the breasts were observed, whereas the doses in lung, liver, and kidney were 17%, 11%, and 26% higher. Overall, the LAR for cancer incidence was not significantly different between conventional and OBTCM scanning (P = .06). Image quality improved with OBTCM (P < .002). Conclusion The potential benefit of OBTCM to the female breast in chest CT is overestimated because of a limited reduced tube current zone; despite a 9% dose reduction to the female breast, posterior organs will absorb up to 26% more radiation, resulting in no reduction in radiation-induced malignancies. ^© RSNA, 2018.

Low-dose CT perfusion with projection view sharing

PURPOSE

CT Perfusion (CTP) is a widely used clinical imaging modality. However, CTP typically involves the use of substantial radiation dose (CTDI_vol ≥~200 mGy). The purpose of this study is to present a low-dose CTP technique using a projection view-sharing reconstruction algorithm originally developed for dynamic MRI - "K-space Weighted Image Contrast" (KWIC).

METHODS

The KWIC reconstruction is based on an angle-bisection scheme. In KWIC, a Fourier transform was performed along each projection to form a "k-space"-like CT data space, based on the central-slice theorem. As a projection view-sharing technique, KWIC preserves the spatiotemporal resolution of undersampled CTP data by progressively increasing the number of projection views shared for more distant regions of "k-space". KWIC reconstruction was evaluated on a digital FORBILD head phantom with numerically simulated time-varying objects. The numerically simulated scans were undersampled using the angle-bisection scheme to achieve 50%, 25%, and 12.5% of the original dose (288, 144, and 72 projections, respectively). The area-under-the-curve (AUC), time-to-peak (TTP), and full width half maximum (FWHM) were measured in KWIC recons and compared to fully sampled filtered back projection (FBP) reconstructions. KWIC reconstruction and dose reduction was also implemented for three clinical CTP cases (45 s, 1156 projections per turn, 1 s/turn, CTDI_vol 217 mGy). Quantitative perfusion metrics were computed and compared between KWIC reconstructed CTP data and those of standard FBP reconstruction.

RESULTS

The AUC, TTP, and FWHM in the numerical simzulations were unaffected by the undersampling/dose reduction (down to 12.5% dose) with KWIC reconstruction compared to the fully sampled FBP reconstruction. The normalized root-mean-square-error (NRMSE) of the AUC in the FORBILD head phantom is 0.04, 0.05, and 0.07 for 50%, 25%, and 12.5% KWIC, respectively, as compared to FBP reconstruction. The cerebral blood flow (CBF) and cerebral blood volume had no significant difference between FBP and 50%, 25%, and 12.5% KWIC reconstructions (P > 0.05).

CONCLUSIONS

This study demonstrates that KWIC preserves perfusion metrics for CTP with substantially reduced dose. Clinical implementation will require further investigation into methods of rapid switching of a CT x-ray source.

Introduction of a Dedicated Emergency Department MR Imaging Scanner at the Barrow Neurological Institute

Use of advanced imaging in the emergency department has been increasing in the United States during the past 2 decades. This trend has been most notable in CT, which has increased concern over the effects of increasing levels of medical ionizing radiation. MR imaging offers a safe, nonionizing alternative to CT and is diagnostically superior in many neurologic conditions encountered in the emergency department. Herein, we describe the process of developing and installing a dedicated MR imaging scanner in the Neuroscience Emergency Department at the Barrow Neurological Institute and its effects on neuroradiology and the emergency department in general.

Do we need 3D tube current modulation information for accurate organ dosimetry in chest CT? Protocols dose comparisons

OBJECTIVES

To compare the lung and breast dose associated with three chest protocols: standard, organ-based tube current modulation (OBTCM) and fast-speed scanning; and to estimate the error associated with organ dose when modelling the longitudinal (z-) TCM versus the 3D-TCM in Monte Carlo simulations (MC) for these three protocols.

METHOD

Five adult and three paediatric cadavers with different BMI were scanned. The CTDI_vol of the OBTCM and the fast-speed protocols were matched to the patient-specific CTDI_vol of the standard protocol. Lung and breast doses were estimated using MC with both z- and 3D-TCM simulated and compared between protocols.

RESULTS

The fast-speed scanning protocol delivered the highest doses. A slight reduction for breast dose (up to 5.1%) was observed for two of the three female cadavers with the OBTCM in comparison to the standard. For both adult and paediatric, the implementation of the z-TCM data only for organ dose estimation resulted in 10.0% accuracy for the standard and fast-speed protocols, while relative dose differences were up to 15.3% for the OBTCM protocol.

CONCLUSION

At identical CTDI_vol values, the standard protocol delivered the lowest overall doses. Only for the OBTCM protocol is the 3D-TCM needed if an accurate (<10.0%) organ dosimetry is desired.

KEY POINTS

• The z-TCM information is sufficient for accurate dosimetry for standard protocols. • The z-TCM information is sufficient for accurate dosimetry for fast-speed scanning protocols. • For organ-based TCM schemes, the 3D-TCM information is necessary for accurate dosimetry. • At identical CTDI _vol , the fast-speed scanning protocol delivered the highest doses. • Lung dose was higher in XCare than standard protocol at identical CTDI _vol .

Technical Note: Phantom study to evaluate the dose and image quality effects of a computed tomography organ-based tube current modulation technique

PURPOSE

This technical note quantifies the dose and image quality performance of a clinically available organ-dose-based tube current modulation (ODM) technique, using experimental and simulation phantom studies. The investigated ODM implementation reduces the tube current for the anterior source positions, without increasing current for posterior positions, although such an approach was also evaluated for comparison.

METHODS

Axial CT scans at 120 kV were performed on head and chest phantoms on an ODM-equipped scanner (Optima CT660, GE Healthcare, Chalfont St. Giles, England). Dosimeters quantified dose to breast, lung, heart, spine, eye lens, and brain regions for ODM and 3D-modulation (SmartmA) settings. Monte Carlo simulations, validated with experimental data, were performed on 28 voxelized head phantoms and 10 chest phantoms to quantify organ dose and noise standard deviation. The dose and noise effects of increasing the posterior tube current were also investigated.

RESULTS

ODM reduced the dose for all experimental dosimeters with respect to SmartmA, with average dose reductions across dosimeters of 31% (breast), 21% (lung), 24% (heart), 6% (spine), 19% (eye lens), and 11% (brain), with similar results for the simulation validation study. In the phantom library study, the average dose reduction across all phantoms was 34% (breast), 20% (lung), 8% (spine), 20% (eye lens), and 8% (brain). ODM increased the noise standard deviation in reconstructed images by 6%-20%, with generally greater noise increases in anterior regions. Increasing the posterior tube current provided similar dose reduction as ODM for breast and eye lens, increased dose to the spine, with noise effects ranging from 2% noise reduction to 16% noise increase. At noise equal to SmartmA, ODM increased the estimated effective dose by 4% and 8% for chest and head scans, respectively. Increasing the posterior tube current further increased the effective dose by 15% (chest) and 18% (head) relative to SmartmA.

CONCLUSIONS

ODM reduced dose in all experimental and simulation studies over a range of phantoms, while increasing noise. The results suggest a net dose/noise benefit for breast and eye lens for all studied phantoms, negligible lung dose effects for two phantoms, increased lung dose and/or noise for eight phantoms, and increased dose and/or noise for brain and spine for all studied phantoms compared to the reference protocol.

Ultra-low-dose chest CT with iterative reconstruction does not alter anatomical image quality

PURPOSE

To evaluate the effect of dose reduction with iterative reconstruction (IR) on image quality of chest CT scan.

MATERIALS AND METHODS

Eighteen human cadavers had chest CT with one reference CT protocol (RP-CT; 120kVp/200mAs) and two protocols with dose reduction: low-dose-CT (LD-CT; 120kVp/40mAs) and ultra-low-dose CT (ULD-CT; 120kVp/10mAs). Data were reconstructed with filter-back-projection (FBP) for RP-CT and with FBP and IR (sinogram affirmed iterative reconstruction [SAFIRE^®]) algorithm for LD-CT and ULD-CT. Volume CT dose index (CTDIvol) were recorded. The signal-to-noise (SNR), contrast-to-noise (CNR) ratios of LD-CT and ULD-CT and quantitative parameters were compared to RP-CT. Two radiologists reviewed the CT examinations assessed independently the quality of anatomical structures and expressed a confidence level using a 2-point scale (50% and 95%).

RESULTS

CTDIvol was 2.69 mGy for LD-CT (-80%; P<0.01) and 0.67 mGy for ULD-CT (-95%; P<0.01) as compared to 13.42 mGy for RP-CT. SNR and CNR were significantly decreased (P<0.01) for LD-CT and ULD-CT, but IR improved these values satisfactorily. No significant differences were observed for quantitative measurements. Radiologists rated excellent/good the RP-CT and LD-CT images, whereas good/fair the ULD-CT images. Confidence level for subjective anatomical analysis was 95% for all protocols.

CONCLUSIONS

Dose reduction with a dose lower than 1 mGy, used in conjunction with IR allows performing chest CT examinations that provide a high quality of anatomical structures.

Comparison of Image Quality and Radiation Dose between High-Pitch Mode and Low-Pitch Mode Spiral Chest CT in Small Uncooperative Children: The Effect of Respiratory Rate

OBJECTIVES

To compare image quality and radiation dose between high-pitch mode (HPM) and low-pitch mode (LPM) CT in young children.

MATERIALS AND METHODS

Forty-seven children (mean age 35.6 months; range, 0-126 months) underwent 49 CT examinations in HPM or LPM and were divided into high or low respiratory rate (RR) groups. A qualitative image quality was compared between the two modes. The volume CT dose index (CTDIvol) and dose-length product (DLP) were evaluated from the dose reports, and effective doses were assessed using a paediatric phantom.

RESULTS

Image quality was generally better for HPM than LPM (diagnostic acceptance score, 4.00 vs. 3.46, P = 0.004); the difference was more prominent in the high RR group (4.00 vs. 3.22, P = 0.001). However, there was no significant difference in the low RR group. The mean DLP value was higher in HPM than LPM (29.48 mGy · cm vs. 23.46 mGy · cm, P = 0.022), while CTDIvol was not significantly different. The total effective radiation dose was 26 % higher in HPM than LPM (1.82 mSv vs. 1.44 mSv).

CONCLUSIONS

LPM can be considered for paediatric lung evaluation in young children with low RRs to reduce radiation dose while maintaining favourable image quality.

KEY POINTS

• Radiation exposure is higher on high-pitch "Flash spiral mode" than on low-pitch "X-CARE mode". • "Flash spiral mode" generally showed better image quality than "X-CARE mode". • Difference in image quality was more prominent in the high RR group. • There was no difference in image quality in the low RR group. • "X-CARE mode" should be considered in a limited population with low RRs.

Evaluation of the impact of organ-specific dose reduction on image quality in pediatric chest computed tomography

BACKGROUND

Organ-specific dose reduction significantly reduces the radiation exposure of radiosensitive organs.

OBJECTIVE

The purpose of this study was to assess the impact of a novel organ-specific dose reduction algorithm on image quality of pediatric chest CT.

MATERIALS AND METHODS

We included 28 children (mean age 10.9 ± 4.8 years, range 3-18 years) who had contrast-enhanced chest CT on a 128-row scanner. CT was performed at 100 kV using automated tube current modulation and a novel organ-specific dose-reduction algorithm (XCare™; Siemens, Forchheim, Germany). Seven children had a previous chest CT performed on a 64-row scanner at 100 kV without organ-specific dose reduction. Subjective image quality was assessed using a five-point scale (1-not diagnostic; 5-excellent). Contrast-to-noise ratio (CNR) and signal-to-noise ratio (SNR) were assessed in the descending aorta.

RESULTS

Overall mean subjective image quality was 4.1 ± 0.6. In the subgroup of the seven children examined both with and without organ-specific dose reduction, subjective image quality was comparable (score 4.4 ± 0.5 with organ-specific dose reduction vs. 4.4 ± 0.7 without it; P > 0.05). There was no significant difference in mean signal-to-noise ratio and contrast-to-noise ratio with organ-specific dose reduction (38.3 ± 10.1 and 28.5 ± 8.7, respectively) and without the reduction (35.5 ± 8.5 and 26.5 ± 7.8, respectively) (P > 0.05). Volume computed tomography dose index (CTDIvol) and size-specific dose estimates did not differ significantly between acquisitions with the organ-specific dose reduction (1.7 ± 0.8 mGy) and without the reduction (1.7 ± 0.8 mGy) (P > 0.05).

CONCLUSION

Organ-specific dose reduction does not have an impact on image quality of pediatric chest CT and can therefore be used in clinical practice to reduce radiation dose of radiosensitive organs such as breast and thyroid gland.

Dose reduction of the female breast in chest CT

OBJECTIVE

Organ-based tube current modulation has been shown to significantly reduce the radiation dose to the female breast in phantom studies. We sought to assess the proportions of female breast and glandular tissues that are within the range of organ-based tube current modulation in different age groups and whether these proportions could be optimized by clothing. The secondary objective of our study was to determine whether metal parts of brassieres cause artifacts that impair the diagnostic value.

SUBJECTS AND METHODS

Five hundred seventy-eight female patients undergoing chest CT were included in this study. Two hundred nine patients were prospectively examined wearing a brassiere (group A), and the control patients (group B; n = 369) were scanned according to our previous standard without wearing a brassiere during CT. The two groups were subdivided according to cup size (A-E). For CT data acquisition, an angle-dependent tube current modulation, which reduces the tube current for anterior tube position to minimize direct exposure to anteriorly located organs, was used. The proportion of breast tissue and glandular tissue located within and outside the region of tube current reduction was assessed.

RESULTS

The results showed that 60.4% of total breast tissue and 67.1% of glandular tissue was inside the region of tube current reduction in group B; the proportions were significantly improved, to an average of 91.3% and 96%, respectively, in group A. Diagnostically relevant artifacts were introduced in none of the patients. Patients' age correlated with this effect, with higher rates of improvement in the older patient group. Angle-dependent tube current modulation was most effective in patients with cup size A while wearing a brassiere. In this group, 97.5% of breast tissue and 98.1% of glandular tissue was inside the region of tube current reduction. Women with a cup size of E had the largest effect of wearing a brassiere, increasing the rate of breast tissue that was affected by angle-dependent tube current modulation from 30.0% to 83.3% and that of glandular tissue from 31.8% to 90.0%.

CONCLUSION

We show that wearing a brassiere increases the percentage of breast tissue within the region of reduced tube current and, therefore, improves the performance of angle-dependent tube current modulation technique.

[State of the art and future trends in technology for computed tomography dose reduction]

The introduction of helical and multislice acquisitions in CT scanners together with decreased image reconstruction times has had a tremendous impact on radiological practice. Technological developments in the last 10 to 12 years have enabled very high quality images to be obtained in a very short time. Improved image quality has led to an increase in the number of indications for CT. In parallel to this development, radiation exposure in patients has increased considerably. Concern about the potential health risks posed by CT imaging, reflected in diverse initiatives and actions by official organs and scientific societies, has prompted the search for ways to reduce radiation exposure in patients without compromising diagnostic efficacy. To this end, good practice guidelines have been established, special applications have been developed for scanners, and research has been undertaken to optimize the clinical use of CT. Noteworthy technical developments incorporated in scanners include the different modes of X-ray tube current modulation, automatic selection of voltage settings, selective organ protection, adaptive collimation, and iterative reconstruction. The appropriate use of these tools to reduce radiation doses requires thorough knowledge of how they work.

Effect of x-ray tube parameters and iodine concentration on image quality and radiation dose in cerebral pediatric and adult CT angiography: a phantom study

OBJECTIVES

The aim of the present phantom study was to investigate the effect of x-ray tube parameters and iodine concentration on image quality and radiation dose in cerebral computed tomographic (CT) angiographic examinations of pediatric and adult individuals.

MATERIALS AND METHODS

Four physical anthropomorphic phantoms that represent the average individual as neonate, 1-year-old, 5-year-old, and 10-year-old children and the RANDO phantom that simulates the average adult individual were used. Cylindrical vessels were bored along the brain-equivalent plugs of each physical phantom. To simulate the brain vasculature, vessels of 0.6, 1, 2, and 3 mm in diameter were created. These vessels were filled with contrast medium (CM) solutions at different iodine concentrations, that is, 5.6, 4.2, 2.7, and 1.4 mg I/mL. The phantom heads were scanned at 120, 100, and 80 kV. The applied quality reference tube current-time product values ranged from a minimum of 45 to a maximum of 680. The CT acquisitions were performed on a 16-slice CT scanner using the automatic exposure control system. Image quality was evaluated on the basis of image noise and contrast-to-noise ratio (CNR) between the contrast-enhanced iodinated vessels and the unenhanced regions of interest. Dose reduction was calculated as the percentage difference of the CT dose index value at the quality reference tube current-time product and the CT dose index at the mean modulated tube current-time product.

RESULTS

Image noise that was measured using the preset tube current-time product settings varied significantly among the different phantoms (P < 0.0001). Hounsfield unit number of iodinated vessels was linearly related to CM concentration (r² = 0.907) and vessel diameter (r² = 0.918). The Hounsfield unit number of iodinated vessels followed a decreasing trend from the neonate phantom to the adult phantom at all kilovoltage settings. For the same image noise level, a CNR improvement of up to 69% and a dose reduction of up to 61% may be achieved when CT acquisition is performed at 80 kV compared with 120 kV. For the same CNR, a reduction by 25% of the administered CM concentration may be achieved when CT acquisition is performed at 80 kV compared with 120 kV.

CONCLUSIONS

In cerebral CT angiographic studies, appropriate adjustment of the preset tube current-time product settings is required to achieve the same image noise level among participants of different age. Cerebral CT angiography at 80 kV significantly improves CNR and significantly reduces radiation dose. Moreover, at 80 kV, a considerable reduction of the administered amount of the CM may be reached, thus reducing potential risks for contrast-induced nephropathy.

Reduced radiation exposure of the female breast during low-dose chest CT using organ-based tube current modulation and a bismuth shield: comparison of image quality and radiation dose

OBJECTIVE

The objective of our study was to evaluate the effect of organ-based tube current modulation and bismuth shielding on image quality and breast radiation dose in women undergoing low-dose chest CT.

SUBJECTS AND METHODS

From March 2011 through July 2011, 80 women prospectively underwent low-dose chest CT to screen for lung cancer. The patients were randomly assigned to a control group (n = 20), organ-based tube current modulation group (n = 20), breast shield group (n = 20), or breast shield plus organ-based tube current modulation group (n = 20). Axial slice images of the aortic arch, carina, and inferior pulmonary vein were used to analyze image quality. Three radiologists scored the image quality in terms of artifact and noise and then characterized the overall image quality as optimal (does not affect the diagnostic accuracy) or suboptimal (affects the diagnostic accuracy). Noise levels were measured in the anterior and posterior lung in each image. A phantom dose study was conducted to measure radiation dose.

RESULTS

Images with artifacts or noise were more frequently obtained in the breast shield groups; however, the overall image quality was not significantly different among the four groups. Measured noise levels in the anterior lung were significantly higher in the breast shield groups than the control group; however, no statistical significance was found among the four groups with regard to noise level in the posterior lung. In the phantom dose study, a 16-37.5% dose reduction in the breast was achieved using the breast shield, organ-based tube current modulation protocol, or both.

CONCLUSION

The radiation dose in the female breast may be reduced using a breast shield or organ-based tube current modulation during low-dose chest CT with acceptable image quality. The use of organ-based tube current modulation reduced the radiation dose in the breast without inducing image quality deterioration.

Impact of organ-specific dose reduction on the image quality of head and neck CT angiography

OBJECTIVES

Organ-specific dose reduction (OSDR) algorithms can reduce radiation on radiosensitive organs up to 59 %. This study evaluates the influence of a new OSDR algorithm on image quality of head and neck computed tomographic angiography (CTA) in clinical routine.

METHODS

Sixty-two consecutive patients (68 ± 13 years) were randomised into two groups and imaged using 128-row multidetector CT. Group A (n = 31) underwent conventional CTA and group B (n = 31) CTA with a novel OSDR algorithm. Subjective and objective image quality were statistically compared. Subjective image quality was rated on a five-point scale. Signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) were calculated with region-of-interest measurements.

RESULTS

The SNR of the common carotid artery and middle cerebral artery was 53.6 ± 22.7 and 43.3 ± 15.3 (group A) versus 54.1 ± 20.5 and 46.2 ± 14.6 (group B). The CNR was 40.0 ± 19.3 and 29.7 ± 12.0 (group A) compared with 40.7 ± 16.8 and 32.9 ± 10.9 (group B), respectively. Subjective image quality was excellent in both groups (mean score 4.4 ± 0.7 versus 4.4 ± 0.6). Differences between the two groups were not significant.

CONCLUSIONS

The novel OSDR algorithm does not compromise image quality of head and neck CTA. Its application can be recommended for CTA in clinical routine to protect the thyroid gland and ocular lenses from unnecessary high radiation.

KEY POINTS

• Organ-specific dose reduction (OSDR) can significantly reduce radiation exposure during CT • OSDR does not compromise image quality of head and neck CTA • OSDR can significantly lower the risk of radiation damage to sensitive organs • OSDR can easily be applied in routine clinical practice.

Radiation dose reduction in abdominal computed tomography during the late hepatic arterial phase using a model-based iterative reconstruction algorithm: how low can we go?

OBJECTIVE

The aim of this study was to compare the image quality of abdominal computed tomography scans in an anthropomorphic phantom acquired at different radiation dose levels where each raw data set is reconstructed with both a standard convolution filtered back projection (FBP) and a full model-based iterative reconstruction (MBIR) algorithm.

MATERIALS AND METHODS

An anthropomorphic phantom in 3 sizes was used with a custom-built liver insert simulating late hepatic arterial enhancement and containing hypervascular liver lesions of various sizes. Imaging was performed on a 64-section multidetector-row computed tomography scanner (Discovery CT750 HD; GE Healthcare, Waukesha, WI) at 3 different tube voltages for each patient size and 5 incrementally decreasing tube current-time products for each tube voltage. Quantitative analysis consisted of contrast-to-noise ratio calculations and image noise assessment. Qualitative image analysis was performed by 3 independent radiologists rating subjective image quality and lesion conspicuity.

RESULTS

Contrast-to-noise ratio was significantly higher and mean image noise was significantly lower on MBIR images than on FBP images in all patient sizes, at all tube voltage settings, and all radiation dose levels (P < 0.05). Overall image quality and lesion conspicuity were rated higher for MBIR images compared with FBP images at all radiation dose levels. Image quality and lesion conspicuity on 25% to 50% dose MBIR images were rated equal to full-dose FBP images.

CONCLUSION

This phantom study suggests that depending on patient size, clinically acceptable image quality of the liver in the late hepatic arterial phase can be achieved with MBIR at approximately 50% lower radiation dose compared with FBP.

Screening computed tomography colonography with 256-slice scanning: should patient radiation burden and associated cancer risk constitute a major concern?

OBJECTIVES

The aim of this study was to determine the radiation burden and the lifetime attributable risk (LAR) of radiation-induced cancer in patients undergoing screening 256-slice computed tomography colonography (CTC) and compare CTC-related radiogenic risks to corresponding nominal lifetime intrinsic risk of cancer.

MATERIALS AND METHODS

A Monte Carlo simulation software dedicated for computed tomography (CT) dosimetry was used to determine absorbed doses to primarily exposed radiosensitive organs of 31 women and 29 men subjected to screening CTC on a 256-slice CT scanner. Effective dose was estimated from (a) organ dose data and (b) dose-length product. Organ-specific and total LARs of cancer were estimated using published risk factors. Cumulative LARs from repeated CTC studies on individuals participating in a colorectal cancer screening program were compared with corresponding lifetime intrinsic risks.

RESULTS

The mean organ dose-derived effective dose was estimated to be 2.92 and 2.61 mSv for female and male individuals, respectively. The dose-length product method was found to overestimate effective dose from CTC by 26% and 13% in female and male individuals, respectively. Compared with previously published results for 64-slice CT scanners, 256-slice CTC was found to be associated with up to 45% less radiation burden. The cumulative LAR of radiation-induced cancer from repeated quinquennial screening CTC studies between the ages of 50 and 80 years was estimated to increase the lifetime intrinsic risk of cancer by less than 0.2%.

CONCLUSION

The level of patient radiation burden and theoretical radiogenic cancer risks associated with screening CTC performed using modern low-dose protocols and techniques may not justify disapproval of CTC as a mass screening tool.