Assessment of dose & optimisation of image quality in the XVI cone beam CT system

Background: Colour and power Doppler have become integral parts of many clinical ultrasound investigations and, due to this, refinements are made to the current technology to ensure accurate results for clinical perception of image quality.Method: The aim of this study was to modify and evaluate existing Doppler Ultrasound devices for the assessment of Colour Doppler spatial resolution. In this study a convention flow phantom design was modified to have a set of line pairs of varying     

Novel X-ray image noise reduction technology reduces patient radiation dose while maintaining image quality in coronary angiography

Aims

The consequences of high radiation dose for patient and staff demand constant improvements in X-ray dose reduction technology. This study assessed non-inferiority of image quality and quantified patient dose reduction in interventional cardiology for an anatomy-specific optimised cine acquisition chain combined with advanced real-time image noise reduction algorithms referred to as ‘study cine’, compared with conventional angiography.

Methods

Fifty patients underwent two coronary angiographic acquisitions: one with advanced image processing and optimised exposure system settings to enable dose reduction (study cine) and one with standard image processing and exposure settings (reference cine). The image sets of 39 patients (18 females, 21 males) were rated by six experienced independent reviewers, blinded to the patient and image characteristics. The image pairs were randomly presented. Overall 85 % of the study cine images were rated as better or equal quality compared with the reference cine (95 % CI 0.81–0.90). The median dose area product per frame decreased from 55 to 26 mGy.cm²/frame (53 % reduction, p < 0.001).

Conclusion

This study demonstrates that the novel X-ray imaging technology provides non-inferior image quality compared with conventional angiographic systems for interventional cardiology with a 53 % patient dose reduction.     

Performance of longitudinal and volumetric tube current modulation in a 64-slice CT with different choices of acquisition and reconstruction parameters

Aim of the study was to evaluate the performance of a tube current modulation (TCM) system (^SUREExposure 3D).On a 64 detector-row CT scanner (Aquilion 64, Toshiba), performance of fixed tube current, longitudinal TCM, and volumetric TCM acquisitions were assessed. A homogeneous cone-shaped phantom and an anthropomorphic phantom were used. Tube current and noise profiles were quantitatively analysed by box and whisker plots when phantom size, acquisition, and reconstruction parameters were varied.At similar median noise, fixed tube current scanning showed a noise range of 16.8–38.3 HU, while longitudinal TCM showed a range of 19.4–31.4 HU and volumetric TCM showed an even lower range of 20.7–28.7 HU. When acquisitions resulting in similar image quality (noise) were compared, the use of volumetric compared to longitudinal TCM resulted in a variable radiation dose reduction up to 6.6%.In conclusion, ^SUREExposure 3D resulted in more uniform image quality at a lower dose. Volumetric TCM shows improved results over longitudinal TCM.     

Prospective image planning in radiation therapy for optimization of image quality and reduction of patient dose

IntroductionCT simulation data in image-guided radiation therapy (IGRT) provides patient-specific subject contrast. This information can be exploited to establish, a priori, a suitable imaging goal and to select patient-specific imaging acquisition parameters that optimize the similarity between reference and daily set-up images and reduce imaging dose. This study aims to describe and clinically validate a computerized algorithm designed to provide such optimization.Material and methodsAn image planning system (IPS) was developed to assist in planar kV imaging technique selection for radiation therapy. The system's patient-specific image quality and dose reduction capabilities were validated herein. Anthropomorphic phantom and clinical data were acquired. Mutual information (MI) was used to compare simulated and measured images in both phantom and clinical tests. Variations in contrast resolution resulting from imaging panel underexposure, saturation and a contrast plateau were investigated. For evaluation of patient-specific imaging dose reduction, the IPS was used to modify acquisition settings for six patients.ResultsPhantom data confirmed the IPS's predictive capability regarding image contrast. Measured and simulated images showed similar progressions from under-exposure, image quality peak, and loss of contrast due to detector saturation. Clinical data demonstrated that contrast resolution and imaging dose could be prospectively improved without loss of image contrast. The algorithm reduced imaging dose by an average of 47%, and a maximum of 80%.ConclusionsLoss of image contrast resulting from under-exposure or over-exposure, as well as a contrast plateau can be predicted by use of a prospective image planning algorithm. Image acquisition parameters can be predicted that reduce patient dose without loss of useful contrast.     

Comparison between integrated backscatter intravascular ultrasound and 64-slice multi-detector row computed tomography for tissue characterization and volumetric assessment of coronary plaques

ABSTRACT: BACKGROUND: The purpose of this study was to determine the cut-off values of Hounsfield units (HU) for the discrimination of plaque components and to evaluate the feasibility of measurement of the volume of plaque components using multi-detector row computed tomography (MDCT). Methods: Coronary lesions (125 lesions in 125 patients) were visualized by both integrated backscatter intravascular ultrasound (IB-IVUS) and 64-slice MDCT at the same site. The IB values were used as a gold standard to determine the cut off values of HU for the discrimination of plaque components. Results: Plaques were classified as lipid pool (n =50), fibrosis (n =65) or calcification (n =35) by IB-IVUS. The HU of lipid pool, fibrosis and calcification were 18 +/- 18 HU (-19 to 58 HU), 95 +/- 24 HU (46 to 154 HU) and 378 +/- 99 HU (188 to 605 HU), respectively. Using receiver operating characteristic curve analysis, a threshold of 50 HU was the optimal cutoff values to discriminate lipid pool from fibrosis. Lipid volume measured by MDCT was correlated with that measured by IB-IVUS (r =0.66, p <0.001), whereas fibrous volume was not (r =0.21, p =0.059). Conclusion: Lipid volume measured by MDCT was moderately correlated with that measured by IB-IVUS. MDCT may be useful for volumetric assessment of the lipid volume of coronary plaques, whereas the assessment of fibrosis volume was unstable.     

Impact of miscentering on patient dose and image noise in x-ray CT imaging: Phantom and clinical studies

The operation of the bowtie filter in x-ray CT is correct if the object being scanned is properly centered in the scanner’s field-of-view. Otherwise, the dose delivered to the patient and image noise will deviate from optimal setting. We investigate the effect of miscentering on image noise and surface dose on three commercial CT scanners. Six cylindrical phantoms with different size and material were scanned on each scanner. The phantoms were positioned at 0, 2, 4 and 6 cm below the isocenter of the scanner’s field-of-view. Regression models of surface dose and noise were produced as a function of miscentering magnitude and phantom’s size. 480 patients were assessed using the calculated regression models to estimate the influence of patient miscentering on image noise and patient surface dose in seven imaging centers. For the 64-slice CT scanner, the maximum increase of surface dose using the CTDI-32 phantom was 13.5%, 33.3% and 51.1% for miscenterings of 2, 4 and 6 cm, respectively. The analysis of patients’ scout scans showed miscentering of 2.2 cm in average below the isocenter. An average increase of 23% and 7% was observed for patient dose and image noise, respectively. The maximum variation in patient miscentering derived from the comparison of imaging centers using the same scanner was 1.6 cm. Patient miscentering may substantially increase surface dose and image noise. Therefore, technologists are strongly encouraged to pay greater attention to patient centering.     

64层螺旋CT增强扫描对结直肠癌术前T分期的临床应用价值

目的:探讨64层螺旋CT增强扫描检查对结直肠癌术前T分期的临床应用价值。方法:对2012年3月~10月在我院行64层螺旋CT增强扫描,术后病理证实为结直肠癌的173例患者的CT成像结果进行回顾性分析。将CT分期的结果与术后病理分期结果进行一致性比较分析,并对肿瘤长度、CT值、病理分型等进行相关分析及比较。结果:CT术前T分期:T1-2期、T3期、T4期的灵敏度分别为60.90%(14/23)、89.92%(116/129)、95.24%(20/21),特异度为95.33%(143/150)、77.27%(34/44)、96.05%(146/152),准确率为66.67%(14/21)、92.01%(116/126)、76.92%(20/26),诊断一致性检验结果 Kappa=0.685,P=0.000,P0.05,有统计意义。不同病理分期中肿瘤长度及不同病理分型中肿瘤CT值方差分析结果,P0.05,有统计意义。不同病理分期中CT值方差分析结果,P0.05,没有统计意义。病理分期与病理分型的X2检验结果,P0.05,有统计意义。对T1-2过分期和T3低分期两组病例进一步分析,发现增强扫描后强化程度、管壁僵硬和浆膜不光整有助于鉴别T1-2过分期和T3期低分期,能够提高T1-2期和T3期的准确性。结论:64层螺旋CT增强扫描多种征象的相互结合有助于提高结直肠癌术前分期的准确性,对临床诊治有重要价值。     

Two examples of indication specific radiation dose calculations in dental CBCT and Multidetector CT scanners

PurposeTo calculate organ doses and estimate the effective dose for justification purposes in patients undergoing orthognathic treatment planning purposes and temporal bone imaging in dental cone beam CT (CBCT) and Multidetector CT (MDCT) scanners.MethodsThe radiation dose to the ICRP reference male voxel phantom was calculated for dedicated orthognathic treatment planning acquisitions via Monte Carlo simulations in two dental CBCT scanners, Promax 3D Max (Planmeca, FI) and NewTom VGi evo (QR s.r.l, IT) and in Somatom Definition Flash (Siemens, DE) MDCT scanner. For temporal bone imaging, radiation doses were calculated via MC simulations for a CBCT protocol in NewTom 5G (QR s.r.l, IT) and with the use of a software tool (CT-expo) for Somatom Force (Siemens, DE). All procedures had been optimized at the acceptance tests of the devices.ResultsFor orthognathic protocols, dental CBCT scanners deliver lower doses compared to MDCT scanners. The estimated effective dose (ED) was 0.32 mSv for a normal resolution operation mode in Promax 3D Max, 0.27 mSv in VGi-evo and 1.18 mSv in the Somatom Definition Flash. For temporal bone protocols, the Somatom Force resulted in an estimated ED of 0.28 mSv while for NewTom 5G the ED was 0.31 and 0.22 mSv for monolateral and bilateral imaging respectively.ConclusionsTwo clinical exams which are carried out with both a CBCT or a MDCT scanner were compared in terms of radiation dose. Dental CBCT scanners deliver lower doses for orthognathic patients whereas for temporal bone procedures the doses were similar.     

Noise reduction and image quality improvement of low dose and ultra low dose brain perfusion CT by HYPR-LR processing

Purpose

To evaluate image quality and signal characteristics of brain perfusion CT (BPCT) obtained by low-dose (LD) and ultra-low-dose (ULD) protocols with and without post-processing by highly constrained back-projection (HYPR)–local reconstruction (LR) technique.

Methods and Materials

Simultaneous BPCTs were acquired in 8 patients on a dual-source-CT by applying LD (80 kV,200 mAs,14×1.2 mm) on tube A and ULD (80 kV,30 mAs,14×1.2 mm) on tube B. Image data from both tubes was reconstructed with identical parameters and post-processed using the HYPR-LR. Correlation coefficients between mean and maximum (MAX) attenuation values within corresponding ROIs, area under attenuation curve (AUC), and signal to noise ratio (SNR) of brain parenchyma were assessed. Subjective image quality was assessed on a 5-point scale by two blinded observers (1:excellent, 5:non-diagnostic).

Results

Radiation dose of ULD was more than six times lower compared to LD. SNR was improved by HYPR: ULD vs. ULD+HYPR: 1.9±0.3 vs. 8.4±1.7, LD vs. LD+HYPR: 5.0±0.7 vs. 13.4±2.4 (both p<0.0001). There was a good correlation between the original datasets and the HYPR-LR post-processed datasets: r = 0.848 for ULD and ULD+HYPR and r = 0.933 for LD and LD+HYPR (p<0.0001 for both). The mean values of the HYPR-LR post-processed ULD dataset correlated better with the standard LD dataset (r = 0.672) than unprocessed ULD (r = 0.542), but both correlations were significant (p<0.0001). There was no significant difference in AUC or MAX. Image quality was rated excellent (1.3) in LD+HYPR and non-diagnostic (5.0) in ULD. LD and ULD+HYPR images had moderate image quality (3.3 and 2.7).

Conclusion

SNR and image quality of ULD-BPCT can be improved to a level similar to LD-BPCT when using HYPR-LR without distorting attenuation measurements. This can be used to substantially reduce radiation dose. Alternatively, LD images can be improved by HYPR-LR to higher diagnostic quality.     

Pin-photodiode array for the measurement of fan-beam energy and air kerma distributions of X-ray CT scanners

PurposePatient dose estimation in X-ray computed tomography (CT) is generally performed by Monte Carlo simulation of photon interactions within anthropomorphic or cylindrical phantoms. An accurate Monte Carlo simulation requires an understanding of the effects of the bow-tie filter equipped in a CT scanner, i.e. the change of X-ray energy and air kerma along the fan-beam arc of the CT scanner. To measure the effective energy and air kerma distributions, we devised a pin-photodiode array utilizing eight channels of X-ray sensors arranged at regular intervals along the fan-beam arc of the CT scanner.MethodsEach X-ray sensor consisted of two plate type of pin silicon photodiodes in tandem – front and rear photodiodes – and of a lead collimator, which only allowed X-rays to impinge vertically to the silicon surface of the photodiodes. The effective energy of the X-rays was calculated from the ratio of the output voltages of the photodiodes and the dose was calculated from the output voltage of the front photodiode using the energy and dose calibration curves respectively.ResultsThe pin-photodiode array allowed the calculation of X-ray effective energies and relative doses, at eight points simultaneously along the fan-beam arc of a CT scanner during a single rotation of the scanner.ConclusionsThe fan-beam energy and air kerma distributions of CT scanners can be effectively measured using this pin-photodiode array.     

Effect of diagnostic cone-beam computed tomography protocols on image quality,patient dose,and lesion detection

ObjectiveTo evaluate the effect of cone-beam computed tomography (CBCT) image acquisition protocols on image quality, lesion detection, delineation, and patient dose.Methods100-patients and a CTDI phantom combined with an electron density phantom were examined using four different CBCT-image acquisition protocols during image-guided transarterial chemoembolization (TACE). Protocol-1 (time: 6 s, tube rotation: 360°), protocol-2 (5 s, 300°), protocol-3 (4 s, 240°) and protocol-4 (3 s, 180°) were used. The protocols were first investigated using a phantom. The protocols that were found to be clinically appropriate in terms of image quality and radiation dose were then assessed on patients. A higher radiation dose and/or a poor image quality were inappropriate for the patient imaging. Patient dose (patient-entrance dose and dose-area product), image quality (Hounsfield Unit, noise, signal-to-noise ratio and contrast-to-noise ratio), and lesion delineation (tumor-liver contrast) were assessed and compared using appropriate statistical tests. Lesion detectability, sensitivity, and predictive values were estimated for CBCT-image data using pre-treatment patient magnetic resonance imaging.ResultsThe estimated patient dose showed no statistical significance (p > 0.05) between protocols-2 and -3; the assessed image quality between these protocols manifested insignificant difference (p > 0.05). Two other phantom protocols were not considered for patient imaging due to significantly higher dose (protocols-1) and poor image quality (protocol-4). Lesion delineation and detection were insignificant (p > 0.05) between protocols-2 and -3. Lesion sensitivities generated were 81–89% (protocol-2) and 81–85% (protocol-3) for different lesion types.ConclusionData acquisition using protocols-2 and -3 provided good image quality, lesion detection and delineation with acceptable patient dose during CBCT-imaging mainly due to similar frame numbers acquired.     

64排螺旋CT下肢血管成像技术与DSA评估动脉狭窄的效果对比研究

目的探讨64排螺旋CTA评估下肢动脉狭窄闭塞性疾病的效果。方法对43例下肢动脉闭塞性疾病患者行64排螺旋CTA扫描,18例一周后行双下肢DSA检查,将每侧下肢血管分成8段,动脉狭窄程度分为：正常、轻度狭窄、中度狭窄、重度狭窄、闭塞5个级别。并以DSA为标准来评估。结果对18例患者双侧下肢共288段血管进行研究,CTA与DSA对血管狭窄程度显示一致的有275段,被CTA高估有ll段血管,低估有2段血管。结论64排螺旋CTA是下肢动脉狭窄硬化性疾病可靠的评估方法。     

64排螺旋CT三维透明化VR重建在内耳畸形诊断中的应用

目的:研究三维透明化VR重建在内耳畸形中的表现,为先天性内耳疾病提供准确的影像诊断和临床治疗信息.方法:回顾32耳内耳畸形的64排HRCT容积数据,行三维透明化重建处理,按内耳畸形分类总结三维透明化重建方法及影像表现.结果:32耳的三维透明化VR重建图像结合透明化MPR重组图像均能很好揭示内耳畸形病变部位及程度,其中VR图像可以直观、立体地显示畸形的空间形态结构,透明化MPR重组图像可很好显示病变细节.本组先天内耳发育畸形有以下几种:耳蜗未发育(2耳);共同腔畸形(4耳);不完全分隔Ⅰ型(2耳,两例患者对侧耳均为共同腔畸形);不完全分隔Ⅱ型(即Mondini型)(16耳,多合并前庭、半规管及前庭导水管畸形);单纯前庭-半规管畸形2耳;单纯前庭导水管扩大(6耳).结论:三维透明化个性重建能准确评价内耳先天性疾病的类型和程度,为临床治疗提供重要的参考依据.     

Effect of varying dose-per-pulse and average dose rate in X-ray beam irradiation on cultured cell survival

Characterizing the biological effects of flattening filter-free (FFF) X-ray beams from linear accelerators is of importance, due to their increasing clinical availability. The purpose of this work is to determine whether in vitro cell survival is affected by the higher dose-per-pulse present in FFF beams in comparison with flattened X-ray beams. A Varian TrueBeam^® linear accelerator was used to irradiate the T98G, V79-4 and U87-MG cell lines with a single fraction of 5 Gy or 10 Gy doses of X-rays. Beams with energies of 6 MegaVolt (MV), 6 MV FFF and 10 MV FFF were used, with doses-per-pulse as measured at the monitor chamber of 0.28, 0.78 and 1.31 mGy/pulse for 6 MV, 6 MV FFF and 10 MV FFF, respectively. The dose delivered to each Petri dish was verified by means of ionization chamber measurements. No statistically significant effects on survival fraction were observed for any of the cell lines considered, either as a function of dose-per-pulse, average dose rate or total dose delivered. Biological effects of higher instantaneous rates should not be excluded on the basis of in vitro experimental results such as the ones presented in this work. The next step toward an assessment of the biological impact of FFF beams will require in vivo studies.     

Effective dose and image quality for intraoperative imaging with a cone-beam CT and a mobile multi-slice CT in spinal surgery: A phantom study

PurposeTo compare the effective dose (ED) and image quality (IQ) of O-arm cone-beam CT (Medtronic, Minneapolis, MN, USA) and Airo multi-slice CT (Brainlab AG, Munich, Germany) for intraoperative-CT (i-CT) in spinal surgery.MethodsThe manufacturer-defined protocols available in the O-arm and Airo systems for three-dimensional lumbar spine imaging were compared.Organ dose was measured both with thermo-luminescent dosimeters and GafChromic films in the Alderson Radiation Therapy anthropomorphic phantom.A subjective analysis was performed by neurosurgeons to compare the clinical IQ of the anthropomorphic phantom images acquired with the different i-CT systems and imaging protocols.Image uniformity, noise, contrast-to-noise-ratio (CNR), and spatial resolution were additionally assessed with the Catphan 504 phantom.ResultsO-arm i-CT caused 56% larger ED than Airo due to the high definition (HD) imaging protocol.The noise was larger for O-arm images leading to a lower CNR than that measured for Airo. Moreover, scattering and beam hardening effects were observed in the O-arm images. Better spatial resolution was measured for the O-arm system (9 lp/cm) than for Airo (4 lp/cm).For all the investigated protocols, O-arm was found to be better for identifying anatomical features important for accurate pedicle screw positioning.ConclusionsAccording to phantom measurements, the HD protocol of O-arm offered better clinical IQ than Airo but larger ED. The larger noise of O-arm images did not compromise the clinical IQ while the superior spatial resolution of this system allowed a better visibility of anatomical features important for pedicle screw positioning in the lumbar region.     

A study to determine the impact of IMPT optimization techniques on prostate synthetic CT image sets dose comparison against CT image sets

BackgroundThe objective of this study is to determine the impact of intensity modulated proton therapty (IMPT) optimization techniques on the proton dose comparison of commercially available magnetic resonance for calculating attenuation (MRCA T) images, a synthetic computed tomography CT (sCT) based on magnetic resonance imaging (MRI) scan against the CT images and find out the optimization technique which creates plans with the least dose differences against the regular CT image sets.Material and methodsRegular CT data sets and sCT image sets were obtained for 10 prostate patients for the study. Six plans were created using six distinct IMPT optimization techniques including multi-field optimization (MFO), single field uniform dose (SFUD) optimization, and robust optimization (RO) in CT image sets. These plans were copied to MRCA T, sCT datasets and doses were computed. Doses from CT and MRCA T data sets were compared for each patient using 2D dose distribution display, dose volume histograms (DVH), homogeneity index (HI), conformation number (CN) and 3D gamma analysis. A two tailed t-test was conducted on HI and CN with 5% significance level with a null hypothesis for CT and sCT image sets.ResultsAnalysis of ten CT and sCT image sets with different IMPT optimization techniques shows that a few of the techniques show significant differences between plans for a few evaluation parameters. Isodose lines, DVH, HI, CN and t-test analysis shows that robust optimizations with 2% range error incorporated results in plans, when re-computed in sCT image sets results in the least dose differences against CT plans compared to other optimization techniques. The second best optimization technique with the least dose differences was robust optimization with 5% range error.ConclusionThis study affirmatively demonstrates the impact of IMPT optimization techniques on synthetic CT image sets dose comparison against CT images and determines the robust optimization with 2% range error as the optimization technique which gives the least dose difference when compared to CT plans.     

The influence of respiratory motion on dose distribution in accelerated partial breast irradiation using volumetric modulated arc therapy

PurposeAccelerated partial breast irradiation (APBI) is alternative treatment option for patients with early stage breast cancer. The interplay effect on volumetric modulated arc therapy APBI (VMAT-APBI) has not been clarified. This study aimed to evaluate the feasibility of VMAT-APBI for patients with small breasts and investigate the amplitude of respiratory motion during VMAT-APBI delivery that significantly affects dose distribution.MethodsThe VMAT-APBI plans were generated with 28.5 Gy in five fractions. We performed patient-specific quality assurance using Delta⁴ phantom under static conditions. We also measured point dose and dose distribution using the ionization chamber and radiochromic film under static and moving conditions of 2, 3 and 5 mm. We compared the measured and calculated point doses and dose distributions by dose difference and gamma passing rates.ResultsA total of 20 plans were generated; the dose distributions were consistent with those of previous reports. For all measurements under static conditions, the measured and calculated point doses and dose distributions showed good agreement. The dose differences for chamber measurement were within 3%, regardless of moving conditions. The mean gamma passing rates with 3%/2 mm criteria in the film measurement under static conditions and with 2 mm, 3 mm, and 5 mm of amplitude were 95.0 ± 2.0%, 93.3 ± 3.3%, 92.1 ± 6.2% and 84.8 ± 7.8%, respectively. The difference between 5 mm amplitude and other conditions was statistically significant.ConclusionsRespiratory management should be considered for the risk of unintended dose distribution if the respiratory amplitude is >5 mm.     

Patient dose monitoring systems: A new way of managing patient dose and quality in the radiology department

PurposeDue to the upcoming European Directive (2013/59/EURATOM) and the increased focus on patient safety in international guidelines and regulations, Patient Dose Monitoring Systems, also called Dose Management Systems (DMS), are introduced in medical imaging departments. This article focusses on the requirements for a DMS, its benefits and the necessary implementation steps.MethodThe implementation of a DMS can be perceived as a lengthy, yet worthy, procedure: users have to select the appropriate system for their applications, prepare data collection, validate, perform configuration, and start using the results in quality improvement projects.ResultsA state of the art DMS improves the quality of service, ensures patient safety and optimizes the efficiency of the department. The gain is multifaceted: the initial goal is compliance monitoring against diagnostic reference levels. At a higher level, the user gets an overview of the performance of the devices or centers that are under his supervision. Error identification, generation of alerts and workflow analysis are additional benefits. It can also enable a more patient-centric approach with personalized dosimetry. Skin dose, size-specific dose estimates and organ doses can be calculated and evaluated per patient.ConclusionA DMS is a powerful tool and essential for improved quality and patient care in a radiology department. It can be configured to the needs of medical physicists, radiologists, technologists, even for the management of the hospital. Collaboration between all health professionals and stakeholders, input-output validation and communication of findings are key points in the process of a DMS implementation.