Dose Modulation Technique Research Articles

Denoising Multiphase Functional Cardiac CT Angiography Using Deep Learning and Synthetic Data.

Coronary CT angiography is increasingly used for cardiac diagnosis. Dose modulation techniques can reduce radiation dose, but resulting functional images are noisy and challenging for functional analysis. This retrospective study describes and evaluates a deep learning method for denoising functional cardiac imaging, taking advantage of multiphase information in a three-dimensional convolutional neural network. Coronary CT angiograms (n = 566) were used to derive synthetic data for training. Deep learning-based image denoising was compared with unprocessed images and a standard noise reduction algorithm (block-matching and three-dimensional filtering [BM3D]). Noise and signal-to-noise ratio measurements, as well as expert evaluation of image quality, were performed. To validate the use of the denoised images for cardiac quantification, threshold-based segmentation was performed, and results were compared with manual measurements on unprocessed images. Deep learning-based denoised images showed significantly improved noise compared with standard denoising-based images (SD of left ventricular blood pool, 20.3 HU ± 42.5 [SD] vs 33.4 HU ± 39.8 for deep learning-based image denoising vs BM3D; P < .0001). Expert evaluations of image quality were significantly higher in deep learning-based denoised images compared with standard denoising. Semiautomatic left ventricular size measurements on deep learning-based denoised images showed excellent correlation with expert quantification on unprocessed images (intraclass correlation coefficient, 0.97). Deep learning-based denoising using a three-dimensional approach resulted in excellent denoising performance and facilitated valid automatic processing of cardiac functional imaging. Keywords: Cardiac CT Angiography, Deep Learning, Image Denoising Supplemental material is available for this article. © RSNA, 2024.

Feasibility of a Novel Sparse Orthogonal Collimator-Based Preclinical Total Marrow Irradiation for Enhanced Dosimetric Conformality.

Total marrow irradiation (TMI) has significantly improved radiation conditioning for hematopoietic cell transplantation in hematologic diseases by reducing conditioning-induced toxicities and improving survival outcomes in relapsed/refractory patients. Recently, preclinical three-dimensional image–guided TMI has been developed to enhance mechanistic understanding of the role of TMI and to support the development of experimental therapeutics. However, a dosimetric comparison between preclinical and clinical TMI reveals that the preclinical TMI treatment lacks the ability to reduce the dose to some of the vital organs that are very close to the skeletal system and thus limits the ability to evaluate radiobiological relevance. To overcome this limit, we introduce a novel Sparse Orthogonal Collimator (SOC)–based TMI and evaluate its ability to enhance dosimetric conformality. The SOC-TMI–based dose modulation technique significantly improves TMI treatment planning by reducing radiation exposures to critical organs that are close to the skeletal system that leads to reducing the gap between clinical and preclinical TMI.

CONSTRUCTION AND APPLICATION OF BREP PHANTOM FOR CHINESE WOMEN OF CHILDBEARING AGE IN RADIATION PROTECTION.

The purpose of this study is to construct boundary representation (BREP) phantom for Chinese women of childbearing age, to estimate the external radiation dose and to analyze radiation protection scheme. The BREP phantom for Chinese women of childbearing age was constructed by image segmentation, 3D reconstruction, non-uniform rational B-spline surface construction and voxelization. The photon-irradiated organ absorbed dose-conversion coefficients (DCCK) of the three female specific organs and the photon effective dose-conversion coefficient (ECCK) were calculated by Monte-Carlo method. The results showed that age, body fat-tissue thickness, direction and area of irradiation, organ location and volume all affected the dose of women specific organs when receiving medical exposure. In the case of ensuring the quality of the diagnosis, radiation protection for female specific organs can be achieved by organ dose modulation techniques and reducing exposure area or volume.

Japanese Survey of Radiation Dose Associated With Coronary Computed Tomography Angiography - 2013 Data From a Multicenter Registry in Daily Practice.

Although coronary computed tomography angiography (CTA) is frequently used for identifying coronary artery disease, no studies have investigated the radiation dose in detail in Japan. The aim of this study was to estimate the radiation dose of coronary CTA in Japanese clinical practice and to identify the independent predictors associated with radiation dose. A multicenter, retrospective, observational study (54 institutions) was conducted for estimating the radiation dose of coronary CTA in 2,469 patients between January and December 2013. Independent predictors associated with radiation dose were investigated on linear regression analysis. Median dose-length product (DLP) was 809.0 mGy·cm (IQR, 350.0-1,368.8 mGy·cm), corresponding to an estimated radiation dose of 11 mSv. The DLP per site significantly differed between institutions (median DLP per site, 92-2,131 mGy·cm; P<0.05). Independent predictors associated with radiation dose on multivariable linear regression were body weight, heart rate, non-stable sinus rhythm, scan length, tube voltage setting, electrocardiogram (ECG)-gated scanning protocol, and the image reconstruction technique (P<0.05 each). The coronary CTA radiation dose was relatively high in 2013, and it varied significantly between institutions. Effective strategies for radiation dose reduction were low tube voltage ≤100 kVp, retrospective ECG-gated scanning with dose modulation technique, prospective ECG-gated scanning, and the iterative reconstruction technique.

The influence of ODM technique on the radiation dose received by patients during head CT scan

Introduction. Computed tomography (CT) is inexpensive radiological examination of high diagnostic effectiveness. However, common use of CT tests has led to increased exposure to ionizing radiation in the population. Aim. To assess the effect of organ dose modulation (ODM) technique on the radiation dose received by patients during head CT scan. Material and methods. A retrospective analysis of 120 tests in two groups of patients who had CT scans without and with ODM. Every group consisted of 60 people (30 women and 30 men in each). The ability to perform tests in two algorithms (without and with ODM) resulted from the fact that after installing the apparatus, tests were carried out using standard technique, and only then the ODM function was launched. Results. We found that during examinations with ODM, patients received a reduced dose of ionizing radiation. The mean DLP value with ODM is 9.4% lower than the mean DLP value without ODM by comparing the tests with and without contrasting agent. The mean DLP value obtained in men using ODM was 11.9% lower than the mean dose without ODM, and in women this difference was 6.6%. Conclusion. The mean DLP value received by men with ODM was by 11.9% lower than the mean dose without ODM, and in women this difference was 6.6%. Patients receive a lower dose both in tests with and without a contrasting agent compared to the tests where ODM was not used. A statistical significance of the obtained results was found.

Reduction of patient radiation dose with a new organ based dose modulation technique for thoraco-abdominopelvic computed tomography (CT) (Liver dose right index).

To evaluate the radiation dose reduction, image quality and diagnostic confidence with thoraco-abdominopelvic computed tomography (TACT) using a new organ based dose modulation system (liver dose right index [Liver DRI]), compared to TACT using a standard automatic exposure control adjusting mA according to attenuation. A total of 37 patients who had two TACT examinations on 2 different CT scanners, one using standard automatic exposure control (combination of a DoseRight automatic current selection and Z modulation) and one using Liver DRI were included. There were 19 men and 18 women with a mean age of 67.6±11.7 (SD) years (range: 36-85 years) For each patient, volume CT dose index (CTDIvol), size-specific dose estimates (SSDE) and signal-to-noise ratio (SNR) were evaluated at each anatomic level (lung, breast, liver and pelvis area) for each protocol. Two radiologists assessed independently image quality, artifacts and diagnostic confidence. The radiation dose decreased significantly using Liver DRI compared to standard automatic exposure control on the total scan length, lung, breast and pelvis area, with a significant CTDIvol reduction of 27% (P=0.0001), 23% (P=0.0002), 24% (P=0.0002) and 31% (P=0.0001), respectively; and a significant SSDE reduction of 23% (P=0.0001), 28% (P=0.0001), 23% (P=0.0002) and 29% (P=0.0001), respectively. No significant SNR reductions were observed in all measured tissues at the level of the aortic arch, celiac trunk and iliac bifurcation, except in the muscle (P=0.0013) and fat tissue (P=0.0052) at the level of the ureteral meatus. No significant differences were noted between both protocols in overall image quality, artifacts and diagnostic confidence with an excellent inter observer agreement between radiologists (Kappa values of 0.83, 0.85 and 0.88, respectively). Liver DRI organ based dose modulation technique allows significant dose reduction compared to standard automatic exposure control while preserving diagnostic image quality in all thoraco-abdominopelvic areas.

Efficacy of Lens Protection Systems: Dependency on Different Cranial CT Scans in The Acute Stroke Setting.

To evaluate the dose-reduction potential with different lens protectors for patients undergoing cranial computed tomography (CT) scans. Eye lens dose was assessed in vitro (α-Al2O3:C thermoluminescence dosemeters) using an Alderson-Rando phantom® in cranial CT protocols at different CT scanners (SOMATOM-Definition-AS+®(CT1) and SOMATOM-Definition-Flash® (CT2)) using two different lens-protection systems (Somatex® (SOM) and Medical Imaging Systems® (MIS)). Summarised percentage of the transmitted photons: (1) CT1 (a) unenhanced CT (nCT) with gantry angulation: SOM = 103%, MIS = 111%; (2) CT2 (a) nCT without gantry angulation: SOM = 81%, MIS = 91%; (b) CT angiography (CTA) with automatic dose-modulation technique: SOM = 39%, MIS = 74%; (c) CTA without dose-modulation technique: SOM = 22%, MIS = 48%; (d) CT perfusion: SOM = 44%, MIS = 69%. SOM showed a higher dose-reduction potential than MIS maintaining equal image quality. Lens-protection systems are most effective in CTA protocols without dose-reduction techniques. Lens-protection systems lower the average eye lens dose during CT scans up to 1/3 (MIS) and 2/3 (SOM), respectively, if the eye lens is exposed to the direct beam of radiation. Considering both the CT protocol and the material of lens protectors, they seem to be mandatory for reducing the radiation exposure of the eye lens.

SPECT/CT radiation dosimetry

Single-photon emission computed tomography combined with X-ray computed tomography (SPECT/CT) improves diagnostic accuracy by allowing better localization and definition of scintigraphic findings. However, the combined acquisition of functional and anatomical images can substantially increase radiation exposure to patients, particularly when using a hybrid system with diagnostic CT capabilities. At the same time, the introduction of new SPECT and CT reconstruction techniques (based on the use of iterative algorithms), and of CT automatic dose modulation techniques, has opened the way for possible reductions in patient dose and/or improvements of image quality. It is, therefore, essential to carefully balance the diagnostic needs and the radiation protection requirements, optimizing the choice of radiopharmaceutical and administered activity, and the image acquisition and processing modalities both in SPECT and in CT. This is particularly important in the case of pediatric examinations. In short, to maximize benefit to patients, SPECT/CT studies have to be optimized, adopting dose-reduction measures both from CT and SPECT practices. In SPECT, shorter lived gamma emitters should be preferred and the amount of activity administered must be carefully adjusted to the patient’s size. In CT, scanning parameters (scanning length, tube current, tube voltage, filtration, collimation, slice thickness, pitch, automatic dose modulation method, reconstruction technique, and image processing) must be chosen carefully, remembering that normally the scanned images are used only for the purposes of attenuation correction and/or a more precise localization of scintigraphic findings, which require lower quality and consequently entail a lower dose to the patient. On the other hand, good quality diagnostic CT images, obtained at higher dose levels, are necessary if a diagnostic CT examination must still be planned for the patient. The purpose of this review on SPECT/CT radiation dosimetry is to provide updated information on the total effective dose and total equivalent doses to critical organs due to both radiopharmaceutical administration and CT scan modality for both adults and pediatric patients. The use of new solid-state detectors (cadmium zinc telluride) for SPECT cameras will also be considered. Finally, the means of easily determining SPECT/CT dose to patients will be provided.

A novel application of CT angiography to detect extracoronary vascular abnormalities in patients with spontaneous coronary artery dissection

BackgroundSpontaneous coronary artery dissection (SCAD) is associated with extracoronary vascular abnormalities, which depending on type and location may warrant treatment or provide additional diagnostic or prognostic information about this uncommon entity. Fibromuscular dysplasia (FMD), aneurysms, and dissections have been detected in multiple vascular territories by magnetic resonance angiography, CT angiography (CTA), and catheter angiography. The optimal modality to detect extracoronary vascular abnormalities is unknown. We highlight the technique and feasibility of a novel CTA protocol to detect extracoronary vascular abnormalities in these patients, incorporating patient safety and convenience. MethodsThe complete CTA protocol consisting of a single CTA of the neck, chest, abdomen, and pelvis was performed on 39 SCAD outpatients. All examinations were performed with 200 mL of low-osmolar contrast agent and used radiation dose modulation techniques. Average volume CT dose index was 9 mGy for the chest, abdomen, and pelvis portions and 21 mGy for the neck portion. Studies were independently reviewed by 2 senior vascular radiologists. ResultsTwo patients had nondiagnostic CTA neck evaluation because of technical acquisition errors. Extracoronary vascular abnormalities were detected in 27 of 39 patients (69%). Catheter angiography detected brachial artery FMD in 1 patient, a vascular bed not included in the SCAD CTA protocol. Extracoronary vascular abnormalities were common, including FMD, aneurysms, dissection, and aortic tortuosity, and were seen in the iliac (36%), carotid and/or vertebral (31%), splanchnic (10%), and renal (26%) arteries and in the thoracic and/or abdominal aorta (10%). ConclusionsThe frequency of extracoronary vascular abnormalities and extent of territories identified the CTA protocol in our cohort are high. A tailored CTA may be the optimal imaging technique for detecting extracoronary vascular abnormalities in patients with suspected underlying vasculopathy. Although the clinical significance of extracoronary vascular abnormalities remains unclear, detection of these abnormalities has identified patients in whom cerebral imaging and serial monitoring have been recommended.

To Shield or Not to Shield: Application of Bismuth Breast Shields

The purposes of this essay are to describe the effects of bismuth breast shielding on radiation exposure of the breast and posterior chest wall and to present arguments for and against the use of breast shields. Breast tissue may receive substantial radiation doses during CT examinations. Bismuth shields effectively reduce breast exposure at the expense of increased noise and artifacts. Because bismuth shields reduce radiation transmission in all directions, posterior-to-anterior irradiation results in wasted exposure of posterior tissues. Similar breast radiation reductions can be achieved without shielding by globally reducing tube current. In general, more advanced methods of reducing exposure, including dose modulation and iterative reconstruction techniques, are superior if available.

Adenosine-stress dynamic myocardial perfusion imaging using 128-slice dual-source CT: optimization of the CT protocol to reduce the radiation dose

The aim of this study was to compare the radiation dose and image quality of different adenosine-stress dynamic myocardial perfusion CT protocols using a 128-slice dual-source computed tomography (DSCT) scanner. We included 330 consecutive patients with suspected coronary artery disease. Protocols employed the following dynamic scan parameters: protocol I, a 30-s scan with a fixed tube current (FTC, n = 172); protocol II, a 30-s scan using an automatic tube current modulation (ATCM) technique (n = 108); protocol III, a 14-s scan using an ATCM (n = 50). To determine the scan interval for protocol III, we analyzed time-attenuation curves of 26 patients with myocardial perfusion who had been scanned using protocol I or II. The maximum attenuation difference between normal and abnormal myocardium occurred at 18.0 s to 30.3 s after initiation of contrast injection. Myocardial perfusion images of FTC and ATCM were of diagnostic image quality based on visual analysis. The mean radiation dose associated with protocols I, II, and III was 12.1 ± 1.6 mSv, 7.7 ± 2.5 mSv, and 3.8 ± 1.3 mSv, respectively (p < 0.01). Use of a dose-modulation technique and a 14-s scan duration for adenosine-stress CT enables significant dose reduction while maintaining diagnostic image quality.

Emergency unenhanced multi-slice computed tomography in suspected urinary calculi—with dose reduction method (care dose 4D)

Objectives: To assess urinary calculi and the secondary signs of obstruction, in patients referred from the accident and emergency department, by unenhanced computed tomography examination and to review the radiation dose the patients received with the use of automatic dose modulation technique, care dose 4D. Material and methods Medical records of unenhanced multi-slice computed tomography (MSCT) examinations for 114 patients referred to the emergency department for analysis of suspected urinary calculi were reviewed retrospectively. Their treatment involved automatic tube current modulation, a dose reduction method (care dose 4D), in Hamad General Hospital. The cases were analyzed for the presence of stones, size, site, density and the secondary signs of obstruction, namely hydronephrosis, hydroureter, perinephric fat stranding, peri-ureteric fat stranding and renal enlargement. A search for alternate diagnosis was made if no stone was found. The final diagnosis was noted from the discharge summary in m...

64-slice single source CT와 128-slice dual source CT를 이용한 관상동맥 조영 검사 시 환자선량 비교

본 연구는 64-절편 단선원 CT(SSCT)와 128-절편 이중선원(DSCT)을 이용한 관상동맥조영 CT 검사 시 방사선량에 대해 알아보고, 이 선량으로 인한 암 발생의 잠재적 위험(LAR)을 평가해 보았다. SSCT의 후향적동조화(RGH)스캔의 유효선량은 13.86 mSv 이었고, DSCT의 RGH 스캔의 유효선량은 11.87 mSv 이었다. DSCT의 전향적동조화 (PGT) 스캔 중 선량변조를 적용치 않은 모드의 유효선량은 5.61 mSv, 선량변조를 적용하였을 때는 3.04 mSv 이었다. 1회 스캔하는 FLASH 모드는 0.98 mSv 이었다. SSCT의 RGH 스캔의 LAR은 1,176명 중 1명, DSCT의 RGH에서는 1,960명 중 1명이었다. DSCT의 PGT는 3,030명 중 1명, 선량변조를 하면 5,882명 중 1명에서 발암 위험이 있었다. 따라서 SSCT와 DSCT를 이용한 관상동맥조영 CT 검사는 암발생 귀속위험과 관련성이 있음을 인지하여야 하고, 환자선량을 줄이기 위해 RGH보다 PGT, FLASH 등의 프로토콜을 적용하는 것이 필요하다. The purpose of this study was to estimate radiation doses from 64-slice single source Computed Tomography(SSCT) coronary angiography(CA) and 128-slice dual source Computed Tomography(DSCT). With SSCT CA, the effective dose averaged approximately 13.86 mSv when two dose modulation was not. The mean effective dose for DSCT CA with retrospectively gated helical(RGH) technique was 11.87 mSv, when prospective ECG gating transverse(PGT) without dose modulation technique was 5.61 mSv. The one with dose modulation in PGT technique and flash mode were 3.04 mSv and flash mode was 0.98 mSv respectively. The lifetime attributable risk(LAR) of cancer incidence from SSCT RGH mode averaged approximately 1 for 1,176, and DSCT averaged 1 for 1,960(RGH mode), 1 for 3,030(PGT without modulation), 1 for 5,882(PGT with modulation). Because of CTCA is associated with non-negligible risk of cancer. Doses can be reduced by application PGT, FLASH than RGH using DSCT.

WE‐B‐214‐01: CT Dose Reduction Strategies

The number of CT examinations performed in the United States has been growing at an annual rate of approximately 10% leading to more than 70 million procedures in 2008. The apparent increase in the number of CT procedures,new protocols and the associated radiation dose and risks has drawn considerable attention. It appears that the so‐called ‘slice wars’ with regard to the number of slices provided per CT gantry rotation may be reaching a plateau and increasing concerns about radiation dose due to CT examinations are fueling the efforts to reduce radiation dose and leading to the beginning of the so‐called ‘dose wars’.A number of radiation dose reduction strategies are been considered and many new are been developed. At the same time, efforts to optimize CT protocols, dose modulation techniques and further improvement in image quality and image quantificationsare gaining ground.There is an increasing demand for the medical physicists to assist clinicians in developing, reviewing and recommending changes to the clinical protocols. Therefore, it is critical for the medical physicists to become familiar with the various dose reduction strategies that are currently available and thenew technologies that are been developed. In this lecture, variousCT dose reduction strategies will be discussed.Educational Objectives:1. To become familiar with radiation dose reduction strategies in CT.2. To understand various image quality improvements in CT.

SU‐E‐I‐92: Application of Dose Modulation for the Clinic

Purpose: To investigate the application of different CT dose modulation techniques on image quality for general and critical ill patients in the hospital setting. Methods: Automatic current selection (or dose modulation) has been a major dose reduction technique which becomes standard feature available from all major CT scanner vendors. However, each vendor approaches the issue differently, and the effect of this technique for patients with different clinical indications varies dramatically. Abdominal studies present the most challenging situation because the level of contrast detectability required for diagnostic quality of CT images of this region. Tube currents for each image slice have been manually recorded and plotted against the scout images for both angular and longitudinal modulation cases. Results: For most chest/abdomen/pelvis studies, the tube current experiences a minimum below the diaphragm, as the computer system adjust the tube current in real time lacks the anatomy. This poses a risk for oncology patients that are under routine follow up for small metastasis in the liver and/or other upper GI organs. It will be more beneficial not using these techniques for these patients. Outpatient management has been changed to provide better image quality and lower radiation dose for the patients. Conclusions: Specific continued education for operators and quality control is very important for the optimum application of new techniques developed for clinical uses.

Observations of an ACR CT Accreditation Program Reviewer

As a reviewer for the ACR CT accreditation program for about 4 years, I have had the opportunity to observe a broad spectrum of work from across the country that I would otherwise have not been privy to in my private radiology practice. Unfortunately, communication with the submitting group is only available through the ACR evaluation. Because there is no mechanism to discuss my overall mpressions with the radiology ommunity at large, I have taken his opportunity to discuss my bservations of submitted mateial with the goal of improving mage quality, decreasing radiaion exposure, and passing ACR ccreditation. Most of the submissions to the CR CT accreditation program hat I review take advantage of the ewer features available on curent-generation scanners (under arious names depending on the anufacturer), such as dose modlation, contrast bolus detection, nd acquisition of multiple thinection images with multiplanar eformatting. Regrettably, basic eatures of the scanners are undeused. A recurrent example is the imited use of different recontruction algorithms. Most curent and recent generation scaners offer different reconstruction lgorithms (or filters) to maxiize soft tissue or bony detail or ptimize for lung imaging. Scaners can reconstruct the same imge data set with multiple algoithms, often automatically. Yet, ead CT scans are filmed with soft tissue and bone windows from the same soft tissue reconstruction. Chest CT scans are filmed at soft tissue and lung windows from the same soft tissue reconstruction without the benefit of a separate lung reconstruction. Field of view is initially set at the time of scanning but can be adjusted after image acquisition to optimally display anatomy, yet sinus CT scans are submitted with large fields of view, minimizing the anatomy of interest. Temporal bone CT scans can be reconstructed bilaterally with a field of view as small as 9 to 10 cm (using a bone algorithm) to maximize the display of small anatomic structures. Submitted cases often do not take advantage of this capability. As mentioned above, many of the body CT cases use some type of dose modulation technique to minimize radiation exposure to the patient. Other simpler methods to reduce radiation exposure are overlooked, such as protocols with multiple series. Many scans submitted have 3 or even 4 acquisitions, such as routine abdomen CT protocols consisting of noncontrast, arterial, venous, and delayed acquisitions. Eliminating one or more acquisitions would decrease radiation dose by 25% to 75%. One or two acquisitions, depending on the indication, are usually sufficient. Many scans acquire images beyond the area of interest, such as axial sinus CT obtaining images above the frontal sinuses or head CT scans with images acquired below the

Patient radiation doses in cardiac computed tomography: comparison of published results with prospective and retrospective acquisition

Prospective ECG triggering has the potential of reducing radiation exposure while maintaining diagnostic accuracy of cardiac computed tomography (CT). The aim of this study is to review patient radiation doses associated with coronary artery calcium scoring (CACS) and CT coronary angiography (CTCA) and to compare results between prospective and retrospective acquisition schemes. Patient radiation doses from CACS and CTCA were extracted from 67 relevant studies. Mean effective dose for CACS and CTCA with prospective ECG triggering is significantly lower than retrospective acquisition, 0.9±0.4 vs. 3.1±1.4 mSv, p < 0.001, and 3.4±1.4 vs. 11.1±5.4 mSv, p < 0.001, respectively. In both cardiac CT examinations, application of dose modulation techniques result in significantly lower doses in retrospective schemes, however, even with dose modulation, retrospective acquisition is associated with significantly higher doses than prospective acquisition. The number of slices acquired per rotation and the number of X-ray sources of the CT scanner (single or dual source) do not have a significant effect on patient dose.

Optimization of patient dose and image quality with z-axis dose modulation for computed tomography (CT) head in acute head trauma and stroke

The purpose of this study is to retrospectively analyze the effect of z-axis modulation for CT head protocols on patient dose and image quality in patients with acute head trauma and stroke. The study was approved by the Institutional Review Board. We retrospectively evaluated the effect of dose modulation on unenhanced CT head examinations in patients with acute head trauma and stroke. Two series of 100 consecutive studies were reviewed: 100 studies performed without dose modulation, 100 studies performed with z-axis dose modulation. Multidetector 16-section CT was performed sequentially and axial 5-mm-thick slices were obtained from base of skull to vertex. With z-axis dose modulation, the same tube current range was maintained, but a computer algorithm altered the tube current applied to each CT section. For each examination, the weighted volume CT dose index (CTDI (vol)) and dose-length product (DLP) were recorded and noise was measured. Each study was also reviewed for image quality by two independent, blinded readers. The variables (CTDI (vol) and DLP, image quality, and noise) in the two groups were compared by using student t test and Wilcoxon rank-sum test. For unenhanced CT head examinations, the CTDI (vol) and DLP, respectively, were reduced by 35.8% and 35.2%, respectively, by using z-axis dose modulation. Image quality and noise were unaffected by the use of this dose modulation technique (P < 0.004). Utilization of z-axis modulation technique for CT head examination in patients with acute head trauma and stroke offers significant radiation dose reduction while image quality is optimally maintained.

Implementation of E-Beam Proximity Effect Correction using linear programming techniques for the fabrication of asymmetric bow-tie antennas

Asymmetric nano-bow-tie antennas offer the possibility of direct light-to-electrical energy conversion. These nano-antennas are easily integrated with Metal-Insulator-Metal (MIM) tunnel junctions in between the antenna segments for the purpose of coupled signal rectification. The architecture of the tunnel junction together with the antenna size precision require nano-scale patterning accuracy. Electron Beam Lithography (EBL) is used for patterning purposes. In this paper Proximity Effect (PE), a very common resolution problem in EBL, is reduced by a dose modulation technique employing linear programming (LP) algorithms. Production of tightly controlled antenna segment dimensions is achieved in conjunction with a small area tip and a small tunnel junction gap. It is expected that precise control of the gap geometry will enhance detection speed, enabling the utilization of the device for the visible range energy harvest purposes.

Radiation doses during chest examinations using dose modulation techniques in multislice CT scanner

Objective:To evaluate the radiation dose and image quality using a manual protocol and dose modulation techniques in a 6-slice CT scanner.Materials and Methods:Two hundred and twenty-one patients who underwent contrast-enhanced CT of the chest were included in the study. For the manual protocol settings, constant tube potential (kV) and tube current–time product (mAs) of 140 kV and 120 mAs, respectively, were used. The angular and z-axis dose modulation techniques utilized a constant tube potential of 140 kV; mAs values were automatically selected by the machine. Effective doses were calculated using dose–length product (DLP) values and the image quality was assessed using the signal-to-noise (SNR) ratio values.Results:Mean effective doses using manual protocol for patients of weights 40–60 kg, 61–80 kg, and 81 kg and above were 8.58 mSv, 8.54 mSv, and 9.07 mSv, respectively. Mean effective doses using z-axis dose modulation for patients of weights 40–60 kg, 61–80 kg, and 81 kg and above were 4.95 mSv, 6.87 mSv, and 10.24 mSv, respectively. The SNR at the region of the liver for patients of body weight of 40–60 kg was 5.1 H, 6.2 H, and 8.8 H for manual, angular, and z-axis dose modulation, respectively.Conclusion:Dose reduction of up to 15% was achieved using angular dose modulation and of up to 42% using z-axis dose modulation, with acceptable diagnostic image quality compared to the manual protocol.