Development of Lead-Free Materials for Radiation Shielding in Medical Settings: A Review

Radiation protection is an essential issue in diagnostic radiology to ensure the safety of patients, healthcare professionals, and the general public. Lead has traditionally been used as a shielding material due to its high atomic number, high density, and effectiveness in attenuating radiation. However, some concerns related to the long-term health effects of toxicity, environmental disease as well as heavy weight of lead have led to the search for alternative lead-free shielding materials. Leadfree multilayered polymer composites and non-lead nano-composite shields have been suggested as effective shielding materials to replace conventional lead-based and single metal shields. Using several elements with high density and atomic number, such as bismuth, barium, gadolinium, and tungsten, offer significant enhancements in the shielding ability of composites. This review focuses on the development and use of lead-free materials for radiation shielding in medical settings. It discusses the drawbacks of traditional lead shielding, such as toxicity, weight, and recycling challenges, and highlights the benefits of lead-free alternatives.

Multicentric characterization of organ-based tube current modulation in head computed tomography: A dosimetric and image quality study

PURPOSE

To evaluate the efficiency of organ-based tube current modulation (OBTCM) in head Computed Tomography (CT) for different radiology departments and manufacturers.

MATERIALS AND METHODS

Five CT scanners from four radiology departments were evaluated in this study. All scans were performed using a standard and a routine head protocol. A scintillating fiber optic detector was placed directly on the gantry to measure the tube exit kerma. Image quality was quantified on a 16-cm HEAD phantom by measuring the signal-to-noise ratio (SNR) and the standard deviation of the Hounsfield units (HU) of circular regions of interest placed in the phantom. The Noise Power Spectrum (NPS) was also studied. Measured values were compared on images with and without OBTCM.

RESULTS

The reduction rates in tube exit kerma, on the anterior part, vary between 11 % and 74 % depending on the CT scanner and the protocol used. The tube exit kerma on the posterior part remains unchanged in GE and Canon CT scanners. On the contrary, the tube exit kerma to the posterior part increases by up to 39 % in Siemens CT scanner. Image noise and SNR increase by up to 10 % in the five CT scanners. Nonetheless, the differences in noise and SNR are statistically significant (p-value < 0.05).The analysis of the NPS indicates that the noise texture remains unchanged.

CONCLUSION

OBTCM reduces the tube exit kerma to the anterior part of the gantry without reducing substantially image quality for head protocols.

Bismuth Shielding in Head Computed Tomography-Still Necessary?

Introduction: Cranial CT scans are associated with radiation exposure to the eye lens, which is a particularly radiosensitive organ. Children are more vulnerable to radiation than adults. Therefore, it is essential to use the available dose reduction techniques to minimize radiation exposure. According to the European Consensus on patient contact shielding by the IRCP from 2021, shielding is not recommended in most body areas anymore. This study aims to evaluate whether bismuth shielding as well as its combination with other dose-saving technologies could still be useful. Methods: Cranial CT scans of a pediatric anthropomorphic phantom were performed on two up-to-date MDCT scanners. Eye lens dose measurements were performed using thermoluminescent dosimeters. Furthermore, the impact of BS and of the additional placement of standoff foam between the patient and BS on image quality was also assessed. Results: Bismuth shielding showed a significant lens dose reduction in both CT scanners (GE: 41.50 ± 4.04%, p < 0.001; Siemens: 29.75 ± 6.55%, p = 0.00). When combined with AEC, the dose was lowered even more (GE: 60.75 ± 3.30%, p < 0.001; Siemens: 41.25 ± 8.02%, p = 0.00). The highest eye dose reduction was achieved using BS + AEC + OBTCM (GE: 71.25 ± 2.98%, p < 0.001; Siemens: 58.75 ± 5.85%, p < 0.001). BS caused increased image noise in the orbital region, which could be mitigated by foam placement. Eye shielding had no effect on the image noise in the cranium. Conclusions: The use of BS in cranial CT can lead to a significant dose reduction, which can be further enhanced by its combination with other modern dose reduction methods. BS causes increase in image noise in the orbital region but not in the cranium. The additional use of standoff foam reduces image noise in the orbital region.

Decreasing Lens Irradiation on Brain Imaging: A Multi-CT Scanner Quality Improvement Project

AIMS

Cataracts, a leading global cause of blindness, are associated with ionising radiation exposure. This audit aimed to enhance lens exclusion during non-contrast head computed tomography (CT) scans at Newham University Hospital (NUH) using two CT scanners.

METHODS

A retrospective audit of non-contrast head CT scans at NUH excluded scans for trauma and imaging of orbital structures. A one-week audit in April 2023 assessed lens exclusion, compared to the Royal College of Radiologists (RCR) standards. A total of 101 consecutive scans were analysed and 63 (62%) scans were included in the final study. Thirty-eight percent of the scans were excluded according to the exclusion criteria of head, neck and facial traumas, orbital infections and papilledema. Results were presented, followed by a three-month radiographer re-education period, emphasizing gantry tilt and patient positioning. A reaudit in August 2023 evaluated outcomes. For the reaudit, 183 consecutive scans were analysed, with 131 (72%) scans included in the final study and 52 (28%) scans excluded according to the same exclusion criteria as the first audit.

RESULTS

Lens exclusion in non-contrast head CT scans improved significantly from 0/63 (0%) compliance to 19/131 (14.50%) (p=0005) compliance with the standards. Variability in radiographer practices, 'near misses' and time constraints were identified as challenges. Staff turnover impacted compliance.

CONCLUSION

This audit has shed light on a critical aspect of patient care in the field of radiology. This research underscores the importance of rigorous and standardised protocols in radiological procedures, particularly when it comes to protecting the lens of the eye. By enhancing lens exclusion during non-contrast head CT scans, we have taken a significant step in mitigating the risk associated with ionising radiation exposure. Although substantial improvements were made, achieving the RCR audit standard remained elusive. Ongoing re-education, reaudits and a multidisciplinary approach are necessary to optimise radiographer adherence and reduce ionising radiation exposure to the lens during head CT scans. This quality improvement project proves that continued emphasis on gantry tilt and patient positioning in radiographer education and training can make a significant difference in patient safety. As we move forward, let us remember that even small improvements can make a big difference in safeguarding the health and well-being of patients.

Noise reduction performance of a deep learning-based reconstruction in brain computed tomography images acquired with organ-based tube current modulation

We aimed to evaluate the image quality of brain computed tomography (CT) images reconstructed using deep learning-based reconstruction (DLR) in organ-based tube current modulation (OB-TCM) acquisition. An anthropomorphic head phantom and a cylindrical low-contrast phantom were scanned at the standard dose level for adult brain CT in axial volume acquisition without OB-TCM. Moreover, image acquisition with OB-TCM was performed. The radiation dose on the eye lens was measured using a scintillation fibre-optic dosimeter placed on the anthropomorphic phantom's eye surface. The task transfer function (TTF), contrast-to-noise ratio (CNR), and low-contrast object specific CNR obtained from low-contrast phantom images reconstructed with filtered back projection (FBP), hybrid iterative reconstruction (HIR), and two types of DLR (DLRCTA and DLRLCD) were compared. In result, OB-TCM achieved a 32.5% dose reduction in the eye lens. Although HIR, DLRCTA, and DLRLCD showed lower TTF than FBP, the difference in TTF at the highest contributing spatial frequency corresponding to the contrast rod diameter was < 10%. Despite the OB-TCM acquisition, DLRCTA and DLRLCD achieved significantly lower noise and a higher CNR than FBP without OB-TCM (p < 0.05). However, low-contrast object specific CNR was equivalent among all reconstruction methods for the objective diameter of 5 mm and slightly improved in DLRLCD for the objective diameter of 7 mm. DLR with OB-TCM acquisition enabled dose reduction for the eye lens and high CNR image appearance, whereas the low contrast detectability evaluated by low-contrast object specific CNR did not always improve.

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.

RADIATION DOSE OF THE EYE LENS IN CT EXAMINATIONS OF THE BRAIN IN CLINICAL PRACTICE-THE EFFECT OF RADIOGRAPHER TRAINING TO OPTIMISE GANTRY TILT AND SCAN LENGTH

Lenses are always exposed to radiation in brain computed tomography (CT) scans. However, the lens dose can be reduced by excluding lens from scanning area by optimising gantry tilt and scan length. The object of this study is to retrospectively analyse if the optimisation by gantry tilt and scan length have been adequate in the CT scan of the brain, and to prospectively analyse the effect of radiographer training to the quality of the CT examinations. This study was conducted in two parts. In all, 329 brain CTs performed in the Tampere University Hospital from 2017 to 2019 were revised retrospectively. The prospective part included 51 brain CT studies conducted in October 2021. Dose to the eye of the lens was modelled using CT-Expo using zero-degree beam angle and scan lengths to expose the lens either to the primary or scattered radiation. Non-zero gantry tilt had been used in a large proportion of the CT examinations in the retrospective setting, 84.8%. However, the lenses were successfully excluded from the scan area in only 1.8% of the examinations. In the prospective part, the gantry tilt was used in 98% of the studies and the proportion of successful examinations rose from 1.8 to 11.8%. The lens dose decreased significantly when the eyes were excluded from the imaging area. The modelled lens dose in the large retrospective part was 25.9 mGy (17.8-49.2 mGy) when the eyes were included and 1.5 mGy (0.4-1.9 mGy) when the eyes were excluded. The lens dose was similar in the small prospective part. Despite the gantry tilt is widely used, unnecessary lens irradiation occurs extensively because of suboptimal gantry tilt and scan length. The training of radiographers reduces the radiation exposure to the lens by more optimal gantry tilt and scan length.

[Investigation of a Compensation Filter for Reduction of Dark Band Artifact in the Head and Neck CT]

PURPOSE

Dark band (DB) artifact in head and neck computed tomography (CT) is caused by beam hardening (BH), and decreased CT values in the X-ray target become a problem. Therefore, we investigated whether it is possible to reduce DB artifact in the head and neck with a compensation filter.

METHODS

We made 2 types of filters with alcohol and water. We set each of these filters in front of the chest phantom's clavicle and evaluated DB artifact. The evaluation method measured CT values in the DB artifact area and background (BG) area by changing each compensation filter thickness and the distance between the chest phantom's surface and each compensation filter. In addition, we measured average standard deviation (SD) in the BG area by the presence of each compensation filter.

RESULTS

CT values in the DB artifact area were approximate to those in the BG area by setting the thickness of each compensation filter to more than 30 mm. Furthermore, these CT values were decreased by separating the distance between the chest phantom's surface and each compensation filter. Average SD in the BG area showed no significant difference between no filter and each compensation filter.

CONCLUSION

It was possible to reduce DB artifact by a compensation filter for DB.

Application of ALARP cost-benefit analysis to hospital-based radiation protection

The UK Ionising Radiations Regulations 2017 require employers to restrict radiation doses to their employees and the public to be as low as reasonably practicable (ALARP). This article looks at the boundary between what might be considered to be reasonable and unreasonable in protecting staff and the general public in the field of hospital-based diagnostic radiology. Guidance on cost-benefit analysis in support of ALARP has been used to formulate relationships for the estimation of the cost at which a radiation protection intervention is no longer ALARP. These relationships allow for a direct link between a reduction in radiation exposure and the maximum reasonable ALARP cost of intervention. Application of the approach to hospital-based radiation protection situations show that the ALARP cost limits for protecting radiation workers against the residual risks in the hospital environment are relatively low. Conversely, the ALARP limit to investment in public dose reduction by means of reducing patient doses can be very high.

Organ-based tube current modulation and bismuth eye shielding in pediatric head computed tomography

BACKGROUND

Exposure of the eye lens to ionizing radiation results in cataract. Several dose optimization techniques to protect the lens are available for computed tomography (CT).

OBJECTIVE

The radiation dose to the eye lens, volume CT dose index (CTDI_vol) and image quality of various methods of dose optimization were evaluated for pediatric head CT: automated tube current modulation (ATCM), automated tube voltage selection (ATVS), organ-based tube current modulation (OBTCM) and bismuth shielding.

MATERIALS AND METHODS

An anthropomorphic phantom of a 5-year-old child was scanned with nine protocols: no dose optimization technique and then adding different dose optimization techniques alone and in combination. Dose to the eye, thyroid and breast were estimated using metal oxide semiconductor field effect transistor (MOSFET) dosimetry. CTDI_vol, influence of timing of shield placement, image noise and attenuation values in 13 regions of interest of the head and subjective image quality were compared.

RESULTS

The eye shield significantly reduced the eye lens dose when used alone, to a similar degree as when using all software-based techniques together. When used in combination with software-based techniques, the shield reduced the eye lens dose by up to 45% compared to the no dose optimization technique. Noise was significantly increased by the shield, most pronounced in the anterior portion of the eye.

CONCLUSION

The combination of ATCM, ATVS, OBTCM and a bismuth shield, with the shield placed after acquiring the localizer image, should be considered to reduce the radiation dose to the eye lens in pediatric head CT.

CONTRIBUTION OF ORGAN-BASED TUBE CURRENT MODULATION TO THE REDUCTION OF LENS EXPOSURE DOSE IN HEAD 4D CT IMAGING: A PHANTOM STUDY

The purpose of this study was to evaluate the effectiveness of organ effect modulation (OEM) in reducing the lens dose in 4D computed tomography (CT) of the head in volume-acquisition (NVA) mode. Six radiophotoluminescent dosemeters were placed on the head of a RANDO phantom. The doses absorbed by the organs and image noise change rate were determined. The lens doses without OEM (i.e. in the OEMoff case) were higher than those with the same target standard deviation and volume-computed tomography dose index (CTDIvol) as in the OEMoff case (p < 0.01). The image noise change rate was 11%. OEM reduced the lens dose during head 4D CT imaging in the NVA mode by 18%. Furthermore, the feasibility of lens dose reduction while ensuring sufficient image quality was confirmed under the condition in which OEM was employed with the same CTDIvol as in the OEMoff case.

The impact of vertical off-centering on image noise and breast dose in chest CT with organ-based tube current modulation: A phantom study

PURPOSE

To determine the effects of patient vertical off-centering when using organ-based tube current modulation (OBTCM) in chest computed tomography (CT) with focus on breast dose.

MATERIALS AND METHODS

An anthropomorphic adult female phantom with two different breast attachment sizes was scanned on GE Revolution EVO and Siemens Definition Edge CT systems using clinical chest CT protocols and anterior-to-posterior scouts. Scans with and without OBTCM were performed at different table heights (GE: centered, ±6 cm, and ± 3 cm; Siemens: centered, -6 cm, and ± 3 cm). The dose effects were studied with metal-oxidesemiconductor field-effect transistor dosimeters with complementary Monte Carlo simulations to determine full dose maps. Changes in image noise were studied using standard deviations of subtraction images from repeated acquisitions without dosimeters.

RESULTS

Patient off-centering affected both the behavior of the normal tube current modulation as well as the extent of the OBTCM. Generally, both OBTCM techniques provided a substantial decrease in the breast doses (up to 30% local decrease). Lateral breast regions may, however, in some cases receive higher doses when OBTCM is enabled. This effect becomes more prominent when the patient is centered too low in the CT gantry. Changes in noise roughly followed the expected inverse of the change in dose.

CONCLUSIONS

Patient off-centering was shown to affect the outcome of OBTCM in chest CT examination, and on some occasions, resulting in higher exposure. The use of modern dose optimization tools such as OBTCM emphasizes the importance of proper centering when preparing patients to CT scans.

Patient-specific radiation risk-based tube current modulation for diagnostic CT

PURPOSE

Modern CT scanners use automatic exposure control (AEC) techniques, such as tube current modulation (TCM), to reduce dose delivered to patients while maintaining image quality. In contrast to conventional approaches that minimize the tube current time product of the CT scan, referred to as mAsTCM in the following, we herein propose a new method referred to as riskTCM which aims at reducing the radiation risk to the patient by taking into account the specific radiation risk of every dose-sensitive organ.

METHODS

For current mAsTCM implementations, the mAs-product is used as a surrogate for the patient dose. Thus they do not take into account the varying dose sensitivity of different organs. Our riskTCM framework assumes that a coarse CT reconstruction, an organ segmentation and an estimation of the dose distribution can be provided in real time, e.g. by applying machine learning techniques. Using this information riskTCM determines a tube current curve that minimizes a patient risk measure, e.g. the effective dose, while keeping the image quality constant. We retrospectively applied riskTCM to 20 patients covering all relevant anatomical regions and tube voltages from 70 kV to 150 kV. The potential reduction of effective dose at same image noise is evaluated as a figure of merit and compared to mAsTCM and to a situation with a constant tube current referred to as noTCM.

RESULTS

Anatomical regions like the neck, thorax, abdomen and the pelvis benefit from the proposed riskTCM. On average, a reduction of effective dose of about 23 % for the thorax, 31 % for the abdomen, 24 % for the pelvis, and 27% for the neck have been evaluated compared to today's state-of-the-art mAsTCM. For the head, the resulting reduction of effective dose is lower, about 13 % on average compared to mAsTCM.

CONCLUSIONS

With a risk-minimizing tube current modulation, significant higher reduction of effective dose compared to mAs-minimizing tube current modulation is possible. This article is protected by copyright. All rights reserved.

Head CT dose reduction with organ-based tube current modulation

BACKGROUND

A helical head CT examination uses a pitch factor (PF) of < 1.0, resulting in a part of the slice being directly irradiated twice. This raises the possibility of double irradiation, which may increase the amount of radiation to the lens. Organ-based tube current modulation (OBTCM) is an effective method for reducing lens exposure because it reduces the dose to the anterior aspect of the patient. However, it is challenging to visualize the complex dose distribution when factoring in double irradiation.

PURPOSE

To visualize twice-irradiated areas in helical head CT in three dimensions and to clarify the exposure reduction effect of OBTCM.

MATERIAL AND METHODS

A leuco crystal violet (LCV) dosimeter was placed into an empty polyethylene terephthalate bottle 16.5 cm in diameter. Helical scans were performed without and with OBTCM using the following parameters: tube voltage 120 kV, tube current 600 mA, pitch factor 0.637, rotation time 0.5 s, 80 (detector rows) × 0.5 mm (detector collimation), and ten scans. Exposed areas were visualized using an optical computed tomography (OCT) system designed by our group. The dose reduction rate of OBTCM was defined as the ratio of the average values of the histogram with the dose value on the x-axis and the frequency on the y-axis without and with OBTCM at 90° to the anterior midline.

RESULTS

The LCV dosimeter visualized the spiral-shaped twice-irradiated areas. Double irradiation resulted in a dose of 2.19/1.90 Gy and 1.38/1.19 Gy (15.0% and 15.9% increase) without and with OBTCM, respectively. The dose reduction using OBTCM was 29.6% at 90° anterolateral.

CONCLUSION

The LCV dosimeter visualized the complex three-dimensional irradiated areas and enabled dose measurement in twice-irradiated areas. Increased exposure from double irradiation was attenuated by OBTCM. This article is protected by copyright. All rights reserved.

Systematic literature review on the benefit of patient protection shielding during medical X-ray imaging: Towards a discontinuation of the current practice

PURPOSE

Patient shielding during medical X-ray imaging has been increasingly criticized in the last years due to growing evidence that it often provides minimal benefit and may even compromise image quality. In Europe, and as also shown in a short assessment in Switzerland, the use of patient shielding is inhomogeneous. The aim of this study was to systematically review recent literature in order to assess benefits and appraise disadvantages related to the routine use of patient shielding.

METHODS

To evaluate benefits and disadvantages related to the application of patient shielding in radiological procedures, a systematic literature review was performed for CT, radiography, mammography and fluoroscopy-guided medical X-ray imaging. In addition, reports from medical physics societies and authorities of different countries were considered in the evaluation.

RESULTS

The literature review revealed 479 papers and reports on the topic, from which 87 qualified for closer analysis. The review considered in- and out-of-plane patient shielding as well as shielding for pregnant and pediatric patients. Dose savings and other dose and non-dose related effects of patient shielding were considered in the evaluation.

CONCLUSIONS

Although patient shielding has been used in radiological practice for many years, its use is no longer undisputed. The evaluation of the systematic literature review of recent studies and reports shows that dose savings are rather minimal while significant dose- and non-dose-related detrimental effects are present. Consequently, the routine usage of patient protection shielding in medical X-ray imaging can be safely discontinued for all modalities and patient groups.

Lens dose reduction with a bismuth shield in neuro cone-beam computed tomography: an investigation on optimum shield device placement conditions

This study aimed to determine the placement distance, number, and position of the bismuth shield for developing a lens protective device for cone-beam computed tomography (CBCT). To determine the dose reduction rate, the lens doses were measured using an anthropomorphic head phantom and a real-time dosimeter. The image quality assessment was determined by analyzing the change in the pixel value, caused by the bismuth shield, and the artifact index was calculated from the pixel value and image noise within various regions of interest in the head phantom. When the distance between the bismuth shield and the subject was increased, the image quality deteriorated less, but there was also a decrease in the lens dose reduction rate. Upon changing the number of bismuth shields from 1-ply to 2-ply, the dose reduction rate increased; however, there was a decrease in the image quality. Additionally, placing the bismuth shield outside of the subject improved the dose reduction rate without deteriorating the image quality. The optimum placement conditions of the bismuth shield were concluded as follows: positioned outside, placed 10 mm from the surface of the subject, and used a 1-ply bismuth shield. When these placement conditions were used, the lens dose reduction rate was 26.9 ± 0.36% (right-left average) for the "bismuth shield: separate". The protective device developed in this study will contribute to radiation dose reduction in CBCT scans.

MEASUREMENT OF RADIATION DOSE TO THE EYE LENS IN NON-ENHANCED CT SCANS OF THE BRAIN

Radiation can have undesirable effects on the eye, including a gradual loss of vision. Unnecessary radiation can reach the eye lens during non-enhanced computed tomography (CT) scans of the brain. The International Commission on Radiological Protection states the threshold for acute and chronic eye lens exposure is 500 mGy and the equivalent dose limit for the eye lens for public exposure is 15 mSv per year. Therefore, we measured the direct radiation dose to the eye lens during head CT scans using NanoDots in 216 adults. The mean absorbed dose to both eyes was 33.62 mGy (standard deviation ±12.442). The averages for the other variables were: tube current-time product: 260 mAs; dose-length product: 708 mGy cm and CT dose index: 35.5 mGy. Our findings encourage further study of radiation exposure and modifications in CT imaging protocols.

[Calculation of Lens Exposure Reduction Using Organ-effective Modulation in Pediatric Head CT]

PURPOSE

Using a pediatric head phantom constructed in our department, we examined a method to reduce exposure by using organ-effective modulation (OEM; Toshiba Medical Systems Corporation, Tochigi) to tilt the gantry during pediatric head computed tomography (CT) scanning.

METHOD

The radiation reduction and CT image standard deviation (SD) were measured at gantry angles at which the orbit was slightly irradiated, partially irradiated, and completely irradiated. The OEM incident surface dose reduction rate was measured using an automatic exposure control (AEC) phantom with a diameter of 6-18 cm.

RESULTS

The lens surface dose reduction rate using OEM was 21.2%. When the gantry was tilted and the orbit was completely out of the scanning range, the rate of reduction was 47.8%. OEM incident surface dose reduction rates were 27.4% for a phantom diameter of 18 cm, 22.0% for that of 16 cm, 17.8% for that of 14 cm, 17.2% for that of 12 cm, 8.4% for that of 10 cm, and 0% for that of 8 cm and 6 cm. OEM effectiveness decreased with decreasing phantom diameter. The use of OEM increased the rate of change of SD by 1.25´ when the gantry inclination was 0°, 1.27´ when the gantry inclination was 10°, and 1.27´ when the gantry inclination was 20°in the 12 o'clock position.

CONCLUSION

The degree of reduction in exposure dose to the lens in pediatric head CT imaging was 47.8% by completely removing the lens from the irradiation range using gantry tilt and 21.2% by using OEM. The effect of OEM changed in proportion to tube current. The exposure reduction effect of the OEM decreases with decreasing head size, indicating its reduced effectiveness in head CT scans of smaller infants.

Direct measurement of radiation exposure dose to individual organs during diagnostic computed tomography examination

Ionizing radiation from Computed tomography (CT) examinations and the associated health risks are growing concerns. The purpose of this study was to directly measure individual organ doses during routine clinical CT scanning protocols and to evaluate how these measurements vary with scanning conditions. Optically stimulated luminescence (OSL) dosimeters were surgically implanted into individual organs of fresh non-embalmed whole-body cadavers. Whole-body, head, chest, and abdomen CT scans were taken of 6 cadavers by simulating common clinical methods. The dosimeters were extracted and the radiation exposure doses for each organ were calculated. Average values were used for analysis. Measured individual organ doses for whole-body routine CT protocol were less than 20 mGy for all organs. The measured doses of surface/shallow organs were higher than those of deep organs under the same irradiation conditions. At the same tube voltage and tube current, all internal organ doses were significantly higher for whole-body scans compared with abdominal scans. This study could provide valuable information on individual organ doses and their trends under various scanning conditions. These data could be referenced and used when considering CT examination in daily clinical situations.

Radioprotection of eye lens using protective material in neuro cone-beam computed tomography: Estimation of dose reduction rate and image quality

PURPOSE

In cerebral angiography, for diagnosis and interventional neuroradiology, cone-beam computed tomography (CBCT) scan is frequently performed for evaluating brain parenchyma, cerebral hemorrhage, and cerebral infarction. However, the patient's eye lens is more frequently exposed to excessive doses in these scans than in the previous angiography and interventional neuroradiology (INR) procedures. Hence, radioprotection for the lenses is needed. This study selects the most suitable eye lens protection material for CBCT from among nine materials by evaluating the dose reduction rate and image quality.

METHODS

To determine the dose reduction rate, the lens doses were measured using an anthropomorphic head phantom and a real-time dosimeter. For image quality assessment, the artifact index was calculated based on the pixel value and image noise within various regions of interest in a water phantom.

RESULTS

The protective materials exhibited dose reduction; however, streak artifacts were observed near the materials. The dose reduction rate and the degree of the artifact varied significantly depending on the protective material. The dose reduction rates were 14.6%, 14.2%, and 26.0% when bismuth shield: normal (bismuth shield in the shape of an eye mask), bismuth shield: separate (two separate bismuth shields), and lead goggles were used, respectively. The "separate" bismuth shield was found to be effective in dose reduction without lowering the image quality.

CONCLUSION

We found that bismuth shields and lead goggles are suitable protective devices for the optimal reduction of lens doses.

REDUCING ABSORBED DOSE TO THYROID IN NECK CT EXAMINATIONS: THE EFFECTS OF SABA SHIELDING

Bi shielding has been used for the protection of radiosensitive organs during computed tomography (CT) for 20 years. In 2017, American Association of Physicists in Medicine recommended against Bi shielding due to its degrading effects on image quality. Saba shielding introduced recently protecting organs as Bi shielding without degrading image quality. In this study, the Saba shield was modified and primary radiation attenuation values of the shields and entrance skin dose (ESD) on the thyroid were measured with and without shielding. Furthermore, the quality of images obtained using Saba shielding was investigated quantitatively and qualitatively. Saba and Bi shielding reduced the ESD on the thyroid by about 50%. Saba shielding had about 5-7 HU less noise and about 51-65 HU less CT numbers shift in comparison with Bi shielding at a distance of 1 cm from the shields. Saba shielding had no degrading effects on image quality in the patient study.

Eye Shielding During Head CT Scans: Dose Reduction and Image Quality Evaluation

RATIONALE AND OBJECTIVES

In this study, we assessed the radiation dose to the lens and the impacts of various eye shields using either a fixed or modulated tube current.

MATERIALS AND METHODS

Patients undergoing head computed tomography (CT) examinations were recruited, and each was randomly assigned to one of five imaging groups, either without a CT eye shield or with one of two types of shielding and topogram-based tube current modulation (TCM). The radiation dose at the eye lens was estimated using Gafchromic films. All CT images were analyzed for quality in the orbit and brain areas. Two radiologists also qualitatively assessed image artifacts and their impacts on image quality using three-point Likert scales.

RESULTS

Both barium sulfate and bismuth-antimony shields significantly reduced radiation dose to the lens (by 28.60%-31.92% and 43.87%-47.00%, respectively) while significantly inducing image artifacts. The image quality of the intraocular structure, but not the intracranial structure, was significantly degraded by shielding. In addition, discriminating the periocular tissues was improved using a bismuth-antimony shield and topogram-based TCM. Compared to fixed tube current, topogram-based TCM provided better signal-to-noise and contrast-to-noise ratios in the intracranial structures when the bismuth-antimony and barium sulfate shields were applied, respectively.

CONCLUSION

Artifacts resulting from the application of eye shields during head CT examinations can be reduced by using topogram-based TCM instead of a fixed tube current. This could be an alternative approach for maintaining image quality in CT scans that do not encompass organ-based TCM.

Shielding characteristics of nanocomposites for protection against X- and gamma rays in medical applications: effect of particle size, photon energy and nano-particle concentration

In recent decades, nanomaterials have been extensively investigated for many applications. Composites doped with different metal nanoparticles have been suggested as effective shielding materials to replace conventional lead-based materials. The use of concretes as structural and radiation protective material has been influenced by the addition of nanomaterials. Several elements with high atomic number and density, such as lead, bismuth, and tungsten, have the potential to form nanoparticles that offer significant enhancements in the shielding ability of composites. Their performance for a range of particle concentrations, particle sizes, and photon energies have been investigated. This review is an attempt to gather the data published in the literature about the application of nanomaterials in radiation shielding, including the use of polymer composites and concretes for protection against X-rays and gamma radiation.

Hydrocephalus: Ventricular Volume Quantification Using Three-Dimensional Brain CT Data and Semiautomatic Three-Dimensional Threshold-Based Segmentation Approach

OBJECTIVE

To evaluate the usefulness of the ventricular volume percentage quantified using three-dimensional (3D) brain computed tomography (CT) data for interpreting serial changes in hydrocephalus.

MATERIALS AND METHODS

Intracranial and ventricular volumes were quantified using the semiautomatic 3D threshold-based segmentation approach for 113 brain CT examinations (age at brain CT examination ≤ 18 years) in 38 patients with hydrocephalus. Changes in ventricular volume percentage were calculated using 75 serial brain CT pairs (time interval 173.6 ± 234.9 days) and compared with the conventional assessment of changes in hydrocephalus (increased, unchanged, or decreased). A cut-off value for the diagnosis of no change in hydrocephalus was calculated using receiver operating characteristic curve analysis. The reproducibility of the volumetric measurements was assessed using the intraclass correlation coefficient on a subset of 20 brain CT examinations.

RESULTS

Mean intracranial volume, ventricular volume, and ventricular volume percentage were 1284.6 ± 297.1 cm³, 249.0 ± 150.8 cm³, and 19.9 ± 12.8%, respectively. The volumetric measurements were highly reproducible (intraclass correlation coefficient = 1.0). Serial changes (0.8 ± 0.6%) in ventricular volume percentage in the unchanged group (n = 28) were significantly smaller than those in the increased and decreased groups (6.8 ± 4.3% and 5.6 ± 4.2%, respectively; p = 0.001 and p < 0.001, respectively; n = 11 and n = 36, respectively). The ventricular volume percentage was an excellent parameter for evaluating the degree of hydrocephalus (area under the receiver operating characteristic curve = 0.975; 95% confidence interval, 0.948-1.000; p < 0.001). With a cut-off value of 2.4%, the diagnosis of unchanged hydrocephalus could be made with 83.0% sensitivity and 100.0% specificity.

CONCLUSION

The ventricular volume percentage quantified using 3D brain CT data is useful for interpreting serial changes in hydrocephalus.

Assessment of Eye Lens Dose Reduction When Using Lateral Lead Shields on the Patient's Head during Neurointerventional Fluoroscopic Procedures and Cone-beam Computed Tomography (CBCT) Scans

The purpose of this study was to evaluate the effect of placing small lead shields on the temple region of the skull to reduce radiation dose to the lens of the eye during interventional fluoroscopically-guided procedures and cone-beam computed tomography (CBCT) scans of the head. EGSnrc Monte-Carlo code was used to determine the eye lens dose reduction when using lateral lead shields for single x-ray projections, CBCT scans with different protocols, and interventional neuroradiology procedures with the Zubal computational head phantom. A clinical C-Arm system was used to take radiographic projections and CBCT scans of anthropomorphic head phantoms without and with lead patches, and the images were compared to assess the effect of the shields. For single lateral projections, a 0.1 (0.3)-mm-thick lead patch reduced the dose to the left-eye lens by 40% to 60% (55% to 80%) from 45° to 90° RAO and to the right-eye lens by around 30% (55%) from 70° to 90° RAO. For different CBCT protocols, the reduction of lens dose with a 0.3-mm-thick lead patch ranged from 20% to 53% at 110 kVp. For CBCT scans of the anthropomorphic phantom, the lead patch introduced streak artifacts that were mainly in the orbital regions but were insignificant in the brain region where most neurointerventional activity occurs. The dose to the patient's eye lens can be reduced considerably by placing small lead shields over the temple region of the head without substantially compromising image quality in neuro-imaging procedures.

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.

[Organ-based Tube-current Modulation Applied on Different MDCT Scanners: Reduction in the Radiation Dose to the Eye Lens at Head CT]

PURPOSE

Organ-based tube current modulation (OB-TCM) techniques, which are provided by three vendors, reduces the radiation dose to the lens of the eyes by decreasing the tube current, when the X-ray tube passes over the anterior surface of critical organs. However, the characteristics of dose modulation of these techniques are different. The purpose of this study was to understand the performance characteristics of OB-TCM technique of each computed tomography (CT) vendor at head CT.

METHODS

We used three CT scanners (SOMATOM Definition Flash; Siemens Healthcare, Revolution CT; GE Healthcare, and Aquilion ONE Genesis Edition; Canon Medical Systems). We measured the radiation dose to the lens surface as evaluation of radiation dose reduction and measured the image noise as index of image quality. We measured the radiation dose rate in the air for analysis of the characteristics of dose modulation in each OB-TCM.

RESULTS

When applying OB-TCM, the radiation doses for the lens surface were decreased by 28%, 22%, and 25% for Siemens, GE, and Canon CT scanners, respectively, and the image noise level was increased by 5.6%, 8.5%, and 15.1% for Siemens, GE, and Canon CT scanners, respectively. The characteristics of dose modulation in each OB-TCM were also confirmed by measured the radiation dose rate.

CONCLUSION

We confirmed that each OB-TCM has different influence on image quality and radiation doses for lens surface, due to the different characteristics of dose modulation for each CT vendor.

Radiation dose reduction to the eye lens in head CT using tungsten functional paper and organ-based tube current modulation

PURPOSE

We investigated whether a tungsten functional paper (TFP) shield and/or organ-based tube current modulation (TCM) can reduce the dose to the eye lens.

MATERIALS AND METHODS

All scans were performed using our routine head examination protocol (spiral acquisition, 120 kVp, noise Index 3.5) with an anthropomorphic head phantom. The dose reduction rate was measured by the following methods with a scintillation fiber optic dosimeter: (a) without any dose reduction techniques (Original scan), (b) TFP shield, (c) TCM, and (d) TFP shield plus TCM. Image noise and CT number were obtained and compared between the three groups. In addition, image noise in method (d) was measured with varying distances between the TFP shield and eye lens.

RESULTS

The reduction rates using TFP shield, TCM, and TFP shield plus TCM compared with those for the Original scan were 17.8 %, 13.6 %, and 27.7 %, respectively. Image noise (mean ± standard deviation) in the anterior region for the Original scan, TFP shield, TCM, and TFP shield plus TCM were 4.1 ± 0.2, 4.6 ± 0.2, 4.4 ± 0.3, and 5.0 ± 0.2, while the CT numbers were 19.3 ± 0.8, 23.8 ± 0.8, 19.6 ± 0.8, and 24.1 ± 0.8, respectively. Increasing the distance between the TFP and the eye significantly decreased the CT number when using TFP shield plus TCM (p < .05).

CONCLUSION

TFP shield plus TCM reduced the dose to the eye lens in head CT while maintaining image quality with an air gap between the TFP and skin surface.

Bismuth shield affecting CT image quality and radiation dose in adjacent and distant zones relative to shielding surface: A phantom study

BACKGROUND

To quantify image quality and radiation doses in regions adjacent to and distant from bismuth shields in computed tomography (CT).

METHODS

An American College of Radiology accreditation phantom with four solid rods embedded in a water-like background was scanned to verify CT number (CTN) accuracy when using bismuth shields. CTNs, image noise, and contrast-to-noise ratios (CNRs) were determined in the phantom at 80-140 kVp. Image quality was investigated on image portions in the zones adjacent (A zone) to and distant (D zone) from a bismuth shield. Surface radiation doses were measured using thermoluminescent dosimeters. Streak artefacts were graded on a 3-point-scale.

RESULTS

Changes in CTN caused by a bismuth shield resulted in changes in X-ray spectra. CTN changes were more apparent in the A zone than in the D zone, particularly for a low tube voltage. The degrees of CTN changes and image noise were proportional to the thickness of the bismuth shields. A 1-ply bismuth shield reduced surface radiation doses by 7.2%-15.5%. The overall CNRs were slightly degraded, and streak artefacts were acceptable.

CONCLUSIONS

Using a bismuth shield could result in significant CTN changes and perceivable artefacts, particularly for a superficial organ close to the shield, and is not recommended for quantification CT examinations or follow-up CT examinations.

COMPARISON OF ORGAN-BASED TUBE CURRENT MODULATION AND BISMUTH SHIELDING IN CHEST CT: EFFECT ON THE IMAGE QUALITY AND THE PATIENT DOSE

The aim of the study was to compare the absorbed doses and image quality of organ-based tube current modulation (OBTCM) and bismuth shielding of breasts and thyroid against regular tube current modulation in chest CT scan. An anthropomorphic phantom and MOSFET dosemeters were used to evaluate absorbed doses. Image quality was assessed from HU and noise. Relative to the reference scan, the average absorbed dose reduction with OBTCM was 5.2% and with bismuth shields 24.2%. Difference in HU values compared to the reference varied between -4.1 and 4.2 HU in OBTCM scan and between -22.2 and 118.6 HU with bismuth shields. Image noise levels varied between 10.0 to 26.3 HU in the reference scan, from 9.6 to 27.7 HU for the OBTCM scan and from 11.9 to 43.9 HU in the bismuth scan. The use of bismuth shields provided greatest dose reduction compared to the investigated OBTCM.

Targeted radiation energy modulation using Saba shielding reduces breast dose without degrading image quality during thoracic CT examinations

OBJECTIVE

Breasts dose during thoracic computed tomography examinations is a serious challenge and practical dose reduction strategies is needed. The bismuth shielding is an available method for dose reduction; however, its use is on debate due to degrading effects on image quality. The aim of this study is to explore and evaluate the efficiency of a new composition of the X-ray absorbing material to achieve a shield with a lower impact on image quality.

MATERIALS AND METHODS

Different shields were manufactured with combinations of various weight percentage of copper and bismuth. Dose reduction ratio and image quality were evaluated in phantom studies. A controlled trial with 20 female participants was conducted for image quality assessment. The shield with a lower impact on image quality, named Saba shielding, was used in the clinical trial.

RESULTS

Shielding by one (1 T) and three thickness (3 T) of the constructed shields reduced the mean entrance skin dose of breasts about 52% and 73%, respectively. The shield with a composition of 90% Cu and 10% Bi (Saba shielding) had the lowest while the shield with 100% bismuth had the highest degrading effect on image quality. The Saba shielding could provide 21% higher dose reduction than the Bi shielding at the equivalent image quality. The 1 T Saba shielding did not cause artifacts in the reconstructed images.

CONCLUSION

The Saba shielding is flexible, cheap and user-friendly for shielding breasts in thoracic CT examinations while do not have the degrading effect of the Bi shielding on image quality.

ESTIMATION OF PATIENT LENS DOSE ASSOCIATED WITH C-ARM CONE-BEAM COMPUTED TOMOGRAPHY USAGE DURING INTERVENTIONAL NEURORADIOLOGY

The purpose of this study was to investigate the dose distribution and lens doses associated with C-arm cone-beam computed tomography (CBCT), using a head phantom, and to estimate the contribution ratio of C-arm CBCT to each patient's lens dose during interventional neuroradiology ('lens dose ratio') in 109 clinical cases. In the phantom study, the peak skin doses and respective right and left lens doses of C-arm CBCT were as follows: 63.0 ± 1.9 mGy, 19.7 ± 1.4 mGy and 21.9 ± 0.8 mGy in whole brain C-arm CBCT and 39.2 ± 1.4 mGy, 4.7 ± 0.9 mGy and 3.6 ± 0.3 mGy in high-resolution C-arm CBCT. In the clinical study, the lens dose ratios were 25.4 ± 8.7% in the right lens and 19.1 ± 9.8% in the left lens. This study shows that, on average, ~25% of patients' total lens dose was contributed by C-arm CBCT.

Development of a novel artifact-free eye shield based on silicon rubber-lead composition in the CT examination of the head

The aim of this work was to develop a novel artifact-free eye shield and evaluate its effect on the dose received by the eye lens and the resulting image quality in the CT examination of the head. A new material for an eye shield was synthesised from silicon rubber (SR) and lead (Pb) using a simple method. The percentage of Pb was varied from 0 to 5% wt. An anthropomorphic head phantom was scanned with and without the SR-Pb eye shield, and compared with a tungsten paper (WP) eye shield. The distance from the eye shield and head was varied from 0 to 5 cm. The dose to the eye lens was measured using photo-luminescence detectors (PLDs). The presence of artifacts was determined by measuring CT numbers at different eye lens locations and by subtracting images with and without the eye shield. The dose reduction increases with increasing Pb content in the SR-Pb eye shield. A 5% wt SR-Pb eye shield reduced the eye lens dose by up to 50%, whereas the WP eye shield reduced the dose by up to 86%. The CT numbers in images with the SR-Pb eye shield in the regions of both eyes and the center of the head phantom is similar to those without the eye shield, indicating that there is no artifact in the resulting image. Using the WP eye shield, there is considerable artifact with the CT number increasing by up to 700% in the regions of both eyes and the center of the head. It is found that the distance between the SR-Pb eye shield and the head does not affect either the dose or the resulting images. A SR-Pb-based eye shield can be applied in clinical environments and should be placed directly above the eye surface for dose optimisation.

Use of bismuth shield for protection of superficial radiosensitive organs in patients undergoing computed tomography: a literature review and meta-analysis

The study aimed to assess the effect of bismuth (Bi) shielding on dose reduction and image quality in computed tomography (CT) through a literature review. A search was conducted in the following databases: Web of Science, PubMed, Google Scholar, and Scopus. Studies that reported estimated dose reduction with bismuth shielding during imaging of the eye, thyroid, and breast were included, and a meta-regression analysis was used to examine the influence of the CT scanner type on the dose reduction. The studies included a total of 237 patients and 34 pediatric and adult anthropomorphic phantoms for whom the radiation dose was reported. Bismuth shielding was recommended in 88.89% of the studies based on the maintenance of appropriate image quality under shielding. Noise associated with Bi shielding was 7.5%, 263%, and 23.5% for the eye, thyroid, and breast, respectively. The fixed-effects pooled estimate of dose reduction was 34% (95% CI: 13-55; p < 0.001) for the eye, 37% (95% CI 14-61; p < 0.001) for the thyroid, and 36% (95% CI 36-55; p < 0.001) for the breast. The image quality, usage of foams, CT scanner type, beam energies, and backscatter radiation were important factors that directly affected the efficacy of Bi shielding to reduce the radiation dose at the superficial radiosensitive organs.

Frequency and Diagnostic Implications of Image Artifacts by Eye-Lens Shielding in Head CT

OBJECTIVE

The eye lens is one of the most radiosensitive organs, and medical radiation is one of the main causes of cataracts. To protect the lens during head CT examinations, protectors have been developed; however, they can lead to image artifacts, which is a major disadvantage of their use. This study retrospectively evaluates the frequency and extent of artifacts caused by these protectors related to three anatomic regions (eye, brain, and bone) and their dependence on protector positioning.

MATERIALS AND METHODS

Datasets from 261 consecutive head CT examinations obtained during 3.5 months of routine clinical imaging were assessed. Diagnostic quality of the images was evaluated by objective measuring and subjective scoring on a 5-point Likert scale. Furthermore, the position of the lens protector in correlation to the eye lens and the intensity and frequency of artifacts were analyzed.

RESULTS

Only 4.6% of all analyzed examinations were completely free from artifacts; 95.4% showed artifacts at least in the orbital cavity. Although the brain was affected in 27.8% of cases, in only 5.8% of cases was there a risk of misinterpretation, such as suspected intracranial bleeding. In 24.9% of cases, the lens was not properly covered by the protector. A too cranial position of the protector was identified as the main risk factor for cerebral artifacts.

CONCLUSION

Eye shielding for brain CT examinations often leads to artifacts. However, in only a small percentage of cases do these artifacts affect tissue depiction in regions beyond the eye (i.e., brain or bones). Correct positioning is mandatory to minimize artifacts.

Topogram-based tube current modulation of head computed tomography for optimizing image quality while protecting the eye lens with shielding

BACKGROUND

Multiple rounds of head computed tomography (CT) scans increase the risk of radiation-induced lens opacification.

PURPOSE

To investigate the effects of CT eye shielding and topogram-based tube current modulation (TCM) on the radiation dose received by the lens and the image quality of nasal and periorbital imaging.

MATERIAL AND METHODS

An anthropomorphic phantom was CT-scanned using either automatic tube current modulation or a fixed tube current. The lens radiation dose was estimated using cropped Gafchromic films irradiated with or without a shield over the orbit. Image quality, assessed using regions of interest drawn on the bilateral extraorbital areas and the nasal bone with a water-based marker, was evaluated using both a signal-to-noise ratio (SNR) and contrast-noise ratio (CNR). Two CT specialists independently assessed image artifacts using a three-point Likert scale.

RESULTS

The estimated radiation dose received by the lens was significantly lower when barium sulfate or bismuth-antimony shields were used in conjunction with a fixed tube current (22.0% and 35.6% reduction, respectively). Topogram-based TCM mitigated the beam hardening-associated artifacts of bismuth-antimony and barium sulfate shields. This increased the SNR by 21.6% in the extraorbital region and the CNR by 7.2% between the nasal bones and extraorbital regions. The combination of topogram-based TCM and barium sulfate or bismuth-antimony shields reduced lens doses by 12.2% and 27.2%, respectively.

CONCLUSION

Image artifacts induced by the bismuth-antimony shield at a fixed tube current for lenticular radioprotection were significantly reduced by topogram-based TCM, which increased the SNR of the anthropomorphic nasal bones and periorbital tissues.

Feasibility of a low-dose orbital CT protocol with a knowledge-based iterative model reconstruction algorithm for evaluating Graves' orbitopathy

PURPOSE

To evaluate the clinical feasibility of low-dose orbital CT with a knowledge-based iterative model reconstruction (IMR) algorithm for evaluating Graves' orbitopathy.

METHODS

Low-dose orbital CT was performed with a CTDI_vol of 4.4 mGy. In 12 patients for whom prior or subsequent non-low-dose orbital CT data obtained within 12 months were available, background noise, SNR, and CNR were compared for images generated using filtered back projection (FBP), hybrid iterative reconstruction (iDose⁴), and IMR and non-low-dose CT images. Comparison of clinically relevant measurements for Graves' orbitopathy, such as rectus muscle thickness and retrobulbar fat area, was performed in a subset of 6 patients who underwent CT for causes other than Graves' orbitopathy, by using the Wilcoxon signed-rank test.

RESULTS

The lens dose estimated from skin dosimetry on a phantom was 4.13 mGy, which was on average 59.34% lower than that of the non-low-dose protocols. Image quality in terms of background noise, SNR, and CNR was the best for IMR, followed by non-low-dose CT, iDose⁴, and FBP, in descending order. A comparison of clinically relevant measurements revealed no significant difference in the retrobulbar fat area and the inferior and medial rectus muscle thicknesses between the low-dose and non-low-dose CT images.

CONCLUSIONS

Low-dose CT with IMR may be performed without significantly affecting the measurement of prognostic parameters for Graves' orbitopathy while lowering the lens dose and image noise.

Monte Carlo simulation of eye lens dose reduction from CT scan using organ based tube current modulation

PURPOSE

To investigate lens dose reduction with organ based tube current modulation (TCM) using the Monte Carlo method.

METHODS

To calculate lens dose with organ based TCM, 36 pairs of X-ray sources with bowtie filters were placed around the patient head using a projection angle interval of 10° for one rotation of Computed Tomography (CT). Each projection was simulated respectively. Both voxelized and stylized eye models and Chinese reference male phantoms were used in the simulation, and tube voltages 80, 100, 120 and 140 kVp were used.

RESULTS

Dose differences between two eye models were less than 20%, but large variations were observed among dose results from different projections of all tube voltages investigated. Dose results from 0° (AP) directions were 60 times greater than those from 180° (PA) directions, which enables organ based TCM reduce lens doses by more than 47%.

CONCLUSIONS

Organ based TCM may be used to reduce lens doses. Stylized eye models are more anatomically realistic compared with voxelized eye models and are more reliable for dose evaluation.

Lens Dose Reduction by Patient Posture Modification During Neck CT

OBJECTIVE

Radiation exposure of the lens during neck CT may increase a patient's risk of developing cataracts. Radiologists at the National Institutes of Health worked with technicians to modify the neck CT scanning procedure to include a reduction in the scanning range, a reduction in the tube potential (kilovoltage), and a change in neck positioning using a head tilt. We objectively quantified the organ dose changes after this procedure modification using a computer simulation.

MATERIALS AND METHODS

We retrospectively analyzed CT images of 40 patients (20 men and 20 women) scanned before and after the procedure change. Radiation dose to the lens delivered before and after the procedure change was calculated using an in-house CT dose calculator combined with computational human phantoms deformed to match head tilt angles. We also calculated the doses to other radiosensitive organs including the brain, pituitary gland, eye globes, and salivary glands before and after the procedure change.

RESULTS

Our dose calculations showed that modifying the neck position, shortening the scanning range, and reducing the tube potential reduced the dose to the lens by 89% (p < 0.0001). The median brain, pituitary gland, globes, and salivary gland doses also decreased by 59%, 52%, 66%, and 29%, respectively. We found that overranging significantly affects the lens dose.

CONCLUSION

Combining head tilt and scanning range reduction is an easy and effective method that significantly reduces radiation dose to the lens and other radiosensitive head and neck organs.

Cerebral Ventricular Dimensions After Decompressive Craniectomy: A Comparison Between Bedside Sonographic Duplex Technique and Cranial Computed Tomography

BACKGROUND

The objective of this study was to assess and compare ventricle diameters in patients after decompressive craniectomy by using cranial computed tomography (CCT) versus sonographic duplex technique (SDT).

METHODS

A total of 102 consecutive patients after decompressive craniectomy following brain infarct, bleeding and trauma were examined by CCT and SDT. SDT was performed within 24 h after repeated postinterventional control CCT and the correlation between both methods was assessed via measurement of dimensions of all four ventricles. In addition, midline shifts and overall cerebral anatomy was evaluated.

RESULTS

A high correlation was found between CCT and SDT in measuring the diameters of all four ventricles (right lateral r = 0.978, p < 0.001; left lateral r = 0.975, p < 0.001; third r = 0.987, p < 0.001 and fourth ventricle r = 0.954, p < 0.001). Deviations of midline structure was observed in SDT as well as in CCT (r = 0.992, p < 0.001).

CONCLUSION

SDT in patients after decompressive craniectomy may represent an additional bedside tool to assess the dimensions of the ventricular system, anatomical structures, e.g., subdural hygromas, hematomas, midline shifts, gyri and sulci. The measurement of the dimensions of all four ventricles by using SDT delivers accurate values and may be considered as an alternative to CCT or a trigger for CCT prior to further treatment.

Corneal Dose Reduction Using a Bismuth-Coated Latex Shield over the Eyes During Brain SPECT/CT

This study aimed to determine whether a bismuth-coated latex shield (B-shield) could protect the eyes during brain SPECT/CT. Methods: A shield containing the heavy metal bismuth (equivalent to a 0.15-mm-thick lead shield) was placed over a cylindric phantom and the eyes of a 3-dimensional brain phantom filled with ^99mTc solution. Subsequently, phantoms with and without the B-shield were compared using SPECT/CT. The CT parameters were 30-200 mA and 130 kV. The dose reduction achieved by the B-shield was measured using a pencil-shaped ionization chamber. The protective effects of the B-shield were determined by evaluating relative radioactivity concentration as well as artifacts (changes in CT number), linear attenuation coefficients, and coefficients of variation on SPECT images. Results: The radiation doses with and without the B-shield were 0.14-0.77 and 0.36-1.93 mGy, respectively, and the B-shield decreased the average radiation dose by about 60%. The B-shield also increased the mean CT number, but only at locations just beneath the surface of the phantom. Streaks of higher density near the underside of the B-shield indicated beam hardening. Linear attenuation coefficients and the coefficients of variation did not significantly differ between phantoms with and without the B-shield, and the relative ^99mTc radioactivity concentrations were not affected. Conclusion: The B-shield decreased the radiation dose without affecting estimated attenuation correction or radioactivity concentrations. Although surface artifacts increased with the B-shield, the quality of the SPECT images was acceptable. B-shields can help protect pediatric patients and patients with eye diseases who undergo SPECT imaging.