Helical Acquisition Research Articles

Audit of radiation dose delivered in time-resolved four-dimensional computed tomography in a radiotherapy department.

To review the dose delivered to patients in time-resolved computed tomography (4D CT) used for radiotherapy treatment planning. 4D CT is used at Peter MacCallum Cancer Centre since July 2007 for radiotherapy treatment planning using a Philips Brilliance Wide Bore CT scanner (16 slice, helical 4D CT acquisition). All scans are performed at 140 kVp and reconstructed in 10 datasets for different phases of the breathing cycle. Dose records were analysed retrospectively for 387 patients who underwent 4D CT procedures between 2007 and 2013. A total of 444 4D CT scans were acquired with the majority of them (342) being for lung cancer radiotherapy. Volume CT dose index (CTDIvol) as recorded over this period was fairly constant at approximately 20 mGy for adults. The CTDI for 4D CT for lung cancers of 19.6 ± 9.3 mGy (n = 168, mean ± 1SD) was found to be 63% higher than CTDIs for conventional CT scans for lung patients that were acquired in the same period (CTDIvol 12 ± 4 mGy, sample of n = 25). CTDI and dose length product (DLP) increased with increasing field of view; however, no significant difference between DLPs for different indications (breast, kidney, liver and lung) could be found. Breathing parameters such as breathing rate or pattern did not affect dose. 4D CT scans can be acquired for radiotherapy treatment planning with a dose less than twice the one required for conventional CT scanning.

Impact of the reconstruction plan on image quality for CT images

Impact of the reconstruction plan on image quality for CT images

MO‐PIS‐Exhibit Hall‐01: Imaging: CT Dose Optimization Technologies I

MO‐PIS‐Exhibit Hall‐01: Imaging: CT Dose Optimization Technologies I

TH-C-18A-07: A Software Tool for Automated Analysis of CT Quality Assurance Phantoms

Purpose: Automated software can save time, reduce cost and minimize human error in the analysis of quality-assurance phantom images. The goal of this work was to develop a software tool to facilitate an efficient, enterprise-wide, CT quality-assurance program and to perform the daily water QC tests recommended by the ACR. Methods: The QC software was developed in Matlab and includes tools for automating analysis of the daily water phantom and all four modules of the ACR CT phantom. The daily water phantom analysis follows guidelines from the ACR's 2012 CT quality control manual, which requires ROI analysis in the center and leading/trailing image of an image stack of both axial and helical acquisitions. A DICOM receiver on a dedicated workstation was configured to run the software automatically after receiving phantom images from a scanner. Results are added to a Matlab structure that serves as a database for tracking data trends, and a standardized report is automatically generated. Performance of the automated ACR phantom analysis was compared to that of trained observers for two tasks requiring subjective user decisions (slice thickness and high-contrast spatial resolution tasks). Images with multiple slice thicknesses and reconstruction kernels were evaluated by two observers and their results compared to the automated analyses. Results: As part of an ongoing pilot study, preliminary tests of the software have been performed on two scanners. Results are available within seconds of scanning the QC phantom. In the human observer study, the software-estimated slice thickness was within +/− 0.5 mm and the highest frequency bar pattern was within +/− 1 line pairs/cm. Conclusion: The developed software provides a robust tool for efficiently managing quality assurance of a large number of scanners. The workflow features an efficient web-based design that automatically analyzes QC images sent from the scanner and generates user-customizable reports.

A Novel Fast Helical 4D-CT Acquisition Technique to Generate Low-Noise Sorting Artifact–Free Images at User-Selected Breathing Phases

To develop a novel 4-dimensional computed tomography (4D-CT) technique that exploits standard fast helical acquisition, a simultaneous breathing surrogate measurement, deformable image registration, and a breathing motion model to remove sorting artifacts. Ten patients were imaged under free-breathing conditions 25 successive times in alternating directions with a 64-slice CT scanner using a low-dose fast helical protocol. An abdominal bellows was used as a breathing surrogate. Deformable registration was used to register the first image (defined as the reference image) to the subsequent 24 segmented images. Voxel-specific motion model parameters were determined using a breathing motion model. The tissue locations predicted by the motion model in the 25 images were compared against the deformably registered tissue locations, allowing a model prediction error to be evaluated. A low-noise image was created by averaging the 25 images deformed to the first image geometry, reducing statistical image noise by a factor of 5. The motion model was used to deform the low-noise reference image to any user-selected breathing phase. A voxel-specific correction was applied to correct the Hounsfield units for lung parenchyma density as a function of lung air filling. Images produced using the model at user-selected breathing phases did not suffer from sorting artifacts common to conventional 4D-CT protocols. The mean prediction error across all patients between the breathing motion model predictions and the measured lung tissue positions was determined to be 1.19 ± 0.37 mm. The proposed technique can be used as a clinical 4D-CT technique. It is robust in the presence of irregular breathing and allows the entire imaging dose to contribute to the resulting image quality, providing sorting artifact-free images at a patient dose similar to or less than current 4D-CT techniques.

Practical Strategies to Reduce Pediatric CT Radiation Dose

The objective of this article is to provide a brief review of CT scanning radiation sensitivity in children and explain CT scan parameters that affect radiation dose. We discuss key factors influencing radiation dose and study quality and how these factors can be used to optimize scan protocols with the goal of reducing pediatric CT radiation dose without compromising diagnostic quality. Finally, we provide some practical tips for reducing radiation doses to children.

Helical differential X-ray phase-contrast computed tomography

We report on the first experimental results of helical differential phase-contrast computed tomography (helical DPC-CT) with a laboratory X-ray tube source and a Talbot–Lau grating interferometer. The results experimentally verify the feasibility of helical data acquisition and reconstruction in phase-contrast imaging, in analogy to its use in clinical CT systems. This allows fast and continuous volumetric scans for long objects with lengths exceeding the dimension of the detector. Since helical CT revolutionized the field of medical CT several years ago, we anticipate that this method will bring the same significant impact on the future medical and industrial applications of X-ray DPC-CT.

Emergency department CT screening of patients with nontraumatic neurological symptoms referred to the posterior fossa: comparison of thin versus thick slice images

Evaluation of the posterior fossa (PF) on 5-mm-thick helical CT images (current default) has improved diagnostic accuracy compared to 5-mm sequential CT images; however, 5-mm-thick images may not be ideal for PF pathology due to volume averaging of rapid changes in anatomy in the Z-direction. Therefore, we sought to determine if routine review of 1.25-mm-thin helical CT images has superior accuracy in screening for nontraumatic PF pathology. MRI proof of diagnosis was obtained within 6 h of helical CT acquisition for 90 consecutive ED patients with, and 88 without, posterior fossa lesions. Helical CT images were post-processed at 1.25 and 5-mm-axial slice thickness. Two neuroradiologists blinded to the clinical/MRI findings reviewed both image sets. Interobserver agreement and accuracy were rated using Kappa statistics and ROC analysis, respectively. Of the 90/178 (51 %) who were MR positive, 60/90 (66 %) had stroke and 30/90 (33 %) had other etiologies. There was excellent interobserver agreement (κ > 0.97) for both thick and thin slice assessments. The accuracy, sensitivity, and specificity for 1.25-mm images were 65, 44, and 84 %, respectively, and for 5-mm images were 67, 45, and 85 %, respectively. The diagnostic accuracy was not significantly different (p > 0.5). In this cohort of patients with nontraumatic neurological symptoms referred to the posterior fossa, 1.25-mm-thin slice CT reformatted images do not have superior accuracy compared to 5-mm-thick images. This information has implications on optimizing resource utilizations and efficiency in a busy emergency room. Review of 1.25-mm-thin images may help diagnostic accuracy only when review of 5-mm-thick images as current default is inconclusive.

Recent micro-CT scanner developments at UGCT

This paper describes two X-ray micro-CT scanners which were recently developed to extend the experimental possibilities of microtomography research at the Centre for X-ray Tomography (www.ugct.ugent.be) of the Ghent University (Belgium). The first scanner, called Nanowood, is a wide-range CT scanner with two X-ray sources (160kVmax) and two detectors, resolving features down to 0.4μm in small samples, but allowing samples up to 35cm to be scanned. This is a sample size range of 3 orders of magnitude, making this scanner well suited for imaging multi-scale materials such as wood, stone, etc. Besides the traditional cone-beam acquisition, Nanowood supports helical acquisition, and it can generate images with significant phase-contrast contributions. The second scanner, known as the Environmental micro-CT scanner (EMCT), is a gantry based micro-CT scanner with variable magnification for scanning objects which are not easy to rotate in a standard micro-CT scanner, for example because they are physically connected to external experimental hardware such as sensor wiring, tubing or others. This scanner resolves 5μm features, covers a field-of-view of about 12cm wide with an 80cm vertical travel range. Both scanners will be extensively described and characterized, and their potential will be demonstrated with some key application results.

Optimizing image quality for pediatric torso computed tomography: the use of advanced iterative reconstruction and wide-detector scanning techniques.

To compare radiation exposure and image quality in children undergoing torso helical acquisition computed tomography (CT) using filtered back projection (FBP) or adaptive iterative dose reduction (AIDR) 3D reconstruction algorithms. A secondary purpose is to compare radiation exposure and image quality in children undergoing torso CT acquired with helical or wide-detector techniques reconstructed with AIDR 3D. The study was approved by the institutional review board. Phase 1 included 200 helical torso CT studies: 100 using FBP and 100 using AIDR 3D. The size-specific dose estimate (SSDE) was calculated for each study. Region of interest (ROI) noise measurements were recorded in the thorax, abdomen, and pelvis for each study. Unpaired t tests compared SSDE and image noise for each group. Phase 2 included 100 wide-detector CT torso studies using AIDR 3D. Size-specific dose estimate and ROI noise measurements were calculated. Unpaired t tests compared helical and wide-detector SSDE and ROI. Additional t tests looked for age- and weight-specific differences in the helical and wide-detector groups. Phase 1: AIDR 3D showed significant reduction in SSDE (P = 0.0001) and significant improvement in image quality. Phase 2: no significant difference in SSDE was observed. Children younger than 6 years had a significant reduction in SSDE with wide-detector technique (P = 0.0445) with no loss in image quality. Adaptive iterative dose reduction 3D produces significant reduction in radiation dose without degradation to image quality compared with FBP. Significant dose reduction without loss of image quality can also be obtained in younger, smaller children using wide-detector technique.

Image Quality and Feasibility of an Ultralow-dose High-pitch Helical Triple–rule-out Computed Tomography Angiography Acquired in the Caudocranial Direction

The aim of this study was to assess the feasibility and image quality of a low-dose triple-rule-out (TRO) computed tomography (CT) angiogram on a second-generation dual-source CT scanner using a high-pitch helical acquisition. Ten men (mean age 56.3 y, average body mass index 24.2) underwent TRO CT angiography using a high-pitch helical acquisition. Patients were imaged from the lung bases to the thoracic inlet in a caudocranial direction. A biphasic injection was administered at 6 mL/s. Study parameters including kVp, mAs, CT dose index volume, dose-length product, and effective dose were calculated. Image quality was independently assessed by 2 cardiothoracic radiologists using the following scale: 1-nondiagnostic; 2-moderately limited diagnostic ability; 3-mild limitation but diagnostic; 4-ideal. For each patient up to 23 structures were evaluated: 17 coronary segments, 3 pulmonary artery levels, 2 aortic sections, and the lung parenchyma. The unpaired t test and the Fisher exact test were used for comparison between patients scored at 80 and 100 kV. The average CT dose index volume, dose-length product, and effective dose for the TRO scans was 2.65, 81.9, and 1.39 mSv, respectively. Readers 1 and 2 scored 171/203 (83%) and 173/203 (84%) of the evaluated regions as ideal and 26/203 (12.8%) and 24/203 (11.8%) as being mildly limited, respectively. Each reader graded 6/203 (3.9%) as being moderately limited. No areas were nondiagnostic. Patients scanned at 80 kV had a significantly higher number of limited segments for readers 1 (P=0.0012) and 2 (P=0.0027). Low-dose, high-image quality TRO scans can be effectively performed using a high-pitch helical acquisition.

Comprehensive low-dose imaging of carotid and coronary arteries with a single-injection dual-source CT angiography protocol

To assess the feasibility of a fast single-bolus combined carotid and coronary computed tomography angiography (CTA) protocol in asymptomatic patients. Thirty-three consecutive patients (18 women and 15 men) with a median age of 61 ± 14 years old (range 37-87 years) with known or suspected atherosclerotic disease were enrolled in this prospective study. A single breath-hold, single biphasic injection protocol (50 ml at 3 ml/s, 50 ml at 5 ml/s, 50 ml saline flush at 5 ml/s) was used for combined CTA imaging of the supra-aortic (SAA) and coronary arteries (CA) on a 64-slice dual-source CT (DSCT) machine. Helical CTA acquisition of the SAA was followed by prospective electrocardiography (ECG)-triggered coronary CTA. Subjective (four-point scale) image quality and objective signal-to-noise (SNR) and contrast-to-noise (CNR) measurements were performed. Vascular disease was graded on a four-point scale (grade 1: absent; grade 2: mild, grade 3: moderate; grade 4: severe). The radiation dose was recorded for each patient. The average enhancement and subjective quality score of SAA and CA segments were 396 HU/358 HU and 1.2 ± 0.3/1.72 ± 0.4, respectively. The SNR was 27.1 ± 1.7 in the SAA and 21.6 ± 1.6 in the CA (p < 0.0001). The CNR was 18.1 ± 1.2 and 15.9 ± 1.8, respectively (p = 0.4). Four percent of SAA and 14% of CA segments (mostly due to peri-venous streak artefacts and small calibre, respectively) produced non-diagnostic images. SAA findings were as follows: 26/33 (79%) patients showed no disease and 6/33 (18%) had grade 2 and 1/33 (3%) had grade 3 disease. CA findings were as follows: 25/33 (76%) showed no disease and 6/33 (18%) patients had grade 2 and 2/33 (6%) had grade 3 disease. Five patients had disease in both districts. The average radiation dose for the combined CTA angiogram was 4.3 ± 0.6 mSv. A fast, low-dose combined DSCT angiography protocol appears technically feasible for imaging carotid and coronary atherosclerotic disease.

Estado actual y tendencia en el desarrollo tecnológico para la reducción de dosis en los equipos de tomografía computarizada

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

Comparison of Radiation Dose Estimates and Scan Performance in Pediatric High-Resolution Thoracic CT for Volumetric 320-Detector Row, Helical 64-Detector Row, and Noncontiguous Axial Scan Acquisitions

Efforts to decrease radiation exposure during pediatric high-resolution thoracic computed tomography (HRCT), while maintaining diagnostic image quality, are imperative. The objective of this investigation was to compare organ doses and scan performance for pediatric HRCT using volume, helical, and noncontiguous axial acquisitions. Thoracic organ doses were measured using 20 metal oxide semiconductor field-effect transistor dosimeters. Mean and median organ doses and scan durations were determined and compared for three acquisition modes in a 5-year-old anthropomorphic phantom using similar clinical pediatric scan parameters. Image noise was measured and compared in identical regions within the thorax. There was a significantly lower dose in lung (1.8 vs 2.7 mGy, P < .02) and thymus (2.3 vs 2.7 mGy, P < .02) between volume and noncontiguous axial modes and in lung (1.8 vs 2.3 mGy, P < .02), breast (1.8 vs 2.6 mGy, P < .02), and thymus (2.3 vs 2.4 mGy, P < .02) between volume and helical modes. There was a significantly lower median image noise for volume compared to helical and axial modes in lung (55.6 vs 79.3 and 70.7) and soft tissue (76.0 vs 111.3 and 89.9). Scan times for volume, helical, and noncontiguous axial acquisitions were 0.35, 3.9, and 24.5 seconds, respectively. Volumetric HRCT provides an opportunity for thoracic organ dose and image noise reduction, at significantly faster scanning speeds, which may benefit pediatric patients undergoing surveillance studies for diffuse lung disease.

Volumetric low-tube-voltage CT imaging for evaluating hypervascular hepatocellular carcinoma; effects on radiation exposure, image quality, and diagnostic performance

To assess the value of hepatic arterial-phase (HAP) imaging with a low tube voltage (80 kVp), using non-helical, volumetric acquisition with a 320-detector-rows area-detector CT (ADCT) scanner for evaluating hypervascular hepatocellular carcinoma (HCC) compared with routine 120-kVp HAP imaging. This study enrolled 128 patients with 148 HCCs. Seventy-six patients with 79 HCCs underwent HAP imaging with 80 kVp obtained using a 320-detector-rows ADCT scanner. The remaining 52 patients with 69 HCCs underwent routine HAP imaging with 120 kVp obtained by 64-slice helical acquisition. Image noise and tumor to liver contrast-to-noise ratio (CNR) of the two sets of images were compared. Three radiologists evaluated both sets of images using receiver operating characteristic analyses. Although there was a two-fold increase in the mean image noise with 80 kVp over that with 120 kVp (p < 0.001), no significant differences were observed in CNR among the two sets. The mean area under the curve (Az value) and the sensitivity for detecting HCC with 80 kVp (0.980, 78/79, respectively) were higher than that of 120 kVp (0.892, 55/69, respectively). HAP imaging with 80 kVp obtained by an ADCT scanner significantly improves the diagnostic performance for evaluating hypervascular HCC.

TU‐G‐141‐01: BEST IN PHYSICS (JOINT IMAGING‐THERAPY)‐A Novel 4D CT Acquisition and Analysis Technique to Generate Low Noise Artifact‐Free Images at User Selected Breathing Phases

Purpose: To develop a novel 4DCT technique that exploits standard fast helical acquisition, a simultaneous breathing surrogate measurement, deformable image registration, and a breathing motion model to remove motion‐induced artifacts. Methods: Five patients were imaged under free breathing conditions 25 successive times in alternating directions with a 64‐slice CT scanner using a low dose fast helical protocol. A pneumatic bellows around the abdomen was used to as a breathing surrogate. The lungs were segmented from each image. Deformable registration was used to register the first to the subsequent 24 segmented images. Voxel‐based motion model parameters were determined using a published breathing motion model. A low‐noise image was created by averaging the 25 images deformed to the first image geometry, reducing statistical noise by a factor of 5. The motion model was used to deform the low noise image to any user‐selected breathing phase. Accurate HU values were assigned to each voxel in the reconstructed images. Results: Images produced using the model at user‐selected breathing phases did not suffer from motion artifacts. The mean discrepancy between the breathing motion model results and the measured positions corresponding to each scan was determined to be 0.7mm (standard deviation of 0.4mm). In each patient, regions near to the myocardium exhibited mean discrepancies greater than 1 mm, which were likely due to uncompensated cardiac motion. Conclusion: The proposed technique can be employed as a clinical 4DCT technique providing motion artifact free images at user‐selected breathing phases. It is robust in the presence of irregular breathing, and allows the entire imaging dose to contribute to the resulting image quality, providing motion artifact free images at a patient dose similar to or less than current 4DCT techniques. We are currently modifying the protocol to work on 16‐slice CT scanners.This work supported in part by NIH R01CA096679

A novel CT acquisition and analysis technique for breathing motion modeling

To report on a novel technique for providing artifact-free quantitative four-dimensional computed tomography (4DCT) image datasets for breathing motion modeling. Commercial clinical 4DCT methods have difficulty managing irregular breathing. The resulting images contain motion-induced artifacts that can distort structures and inaccurately characterize breathing motion. We have developed a novel scanning and analysis method for motion-correlated CT that utilizes standard repeated fast helical acquisitions, a simultaneous breathing surrogate measurement, deformable image registration, and a published breathing motion model. The motion model differs from the CT-measured motion by an average of 0.65 mm, indicating the precision of the motion model. The integral of the divergence of one of the motion model parameters is predicted to be a constant 1.11 and is found in this case to be 1.09, indicating the accuracy of the motion model. The proposed technique shows promise for providing motion-artifact free images at user-selected breathing phases, accurate Hounsfield units, and noise characteristics similar to non-4D CT techniques, at a patient dose similar to or less than current 4DCT techniques.

Comparison of radiation dose estimates, image noise, and scan duration in pediatric body imaging for volumetric and helical modes on 320-detector CT and helical mode on 64-detector CT

Advanced multidetector CT systems facilitate volumetric image acquisition, which offers theoretic dose savings over helical acquisition with shorter scan times. Compare effective dose (ED), scan duration and image noise using 320- and 64-detector CT scanners in various acquisition modes for clinical chest, abdomen and pelvis protocols. ED and scan durations were determined for 64-detector helical, 160-detector helical and volume modes under chest, abdomen and pelvis protocols on 320-detector CT with adaptive collimation and 64-detector helical mode on 64-detector CT without adaptive collimation in a phantom representing a 5-year-old child. Noise was measured as standard deviation of Hounsfield units. Compared to 64-detector helical CT, all acquisition modes on 320-detector CT resulted in lower ED and scan durations. Dose savings were greater for chest (27-46%) than abdomen/pelvis (18-28%) and chest/abdomen/pelvis imaging (8-14%). Noise was similar across scanning modes, although some protocols on 320-detector CT produced slightly higher noise. Dose savings can be achieved for chest, abdomen/pelvis and chest/abdomen/pelvis examinations on 320-detector CT compared to helical acquisition on 64-detector CT, with shorter scan durations. Although noise differences between some modes reached statistical significance, this is of doubtful diagnostic significance and will be studied further in a clinical setting.

Evolution of Coronary Computed Tomography Radiation Dose Reduction at a Tertiary Referral Center

PurposeWe aimed to assess the temporal change in radiation doses from coronary computed tomography angiography (CCTA) during a 6-year period. High CCTA radiation doses have been reduced by multiple technologies that, if used appropriately, can decrease exposures significantly. MethodsA total of 1277 examinations performed from 2005 to 2010 were included. Univariate and multivariable regression analysis of patient- and scan-related variables was performed with estimated radiation dose as the main outcome measure. ResultsMedian doses decreased by 74.8% (P<.001), from 13.1 millisieverts (mSv) (interquartile range 9.3-14.7) in period 1 to 3.3 mSv (1.8-6.7) in period 4. Factors associated with greatest dose reductions (P<.001) were all most frequently applied in period 4: axial-sequential acquisition (univariate: −8.0 mSv [−9.7 to −7.9]), high-pitch helical acquisition (univariate: −8.8 mSv [−9.3 to −7.9]), reduced tube voltage (100 vs 120 kV) (univariate: −6.4 mSv [−7.4 to −5.4]), and use of automatic exposure control (univariate: −5.3 mSv [−6.2 to −4.4]). ConclusionsCCTA radiation doses were reduced 74.8% through increasing use of dose-saving measures and evolving scanner technology.

Recent advances in medical imaging: anatomical and clinical applications

The aim of this paper was to present an overview of the most important recent advances in medical imaging and their potential clinical and anatomical applications. Dramatic changes have been particularly observed in the field of computed tomography (CT) and magnetic resonance imaging (MRI). Computed tomography (CT) has been completely overturned by the successive development of helical acquisition, multidetector and large area-detector acquisition. Visualising brain function has become a new challenge for MRI, which is called functional MRI, currently based principally on blood oxygenation level-dependent sequences, which could be completed or replaced by other techniques such as diffusion MRI (DWI). Based on molecular diffusion due to the thermal energy of free water, DWI offers a spectrum of anatomical and clinical applications, ranging from brain ischemia to visualisation of large fibrous structures of the human body such as the anatomical bundles of white matter with diffusion tensor imaging and tractography. In the field of X-ray projection imaging, a new low-dose device called EOS has been developed through new highly sensitive detectors of X-rays, allowing for acquiring frontal and lateral images simultaneously. Other improvements have been briefly mentioned. Technical principles have been considered in order to understand what is most useful in clinical practice as well as in the field of anatomical applications. Nuclear medicine has not been included.