Estimating the CTDIvol with helical acquisitions: Results from a national generalizability study.

Radiation exposure of the public as a result of medical imaging has significantly increased during the last decades. To have a tool to register and control patient dose exposure, we implemented dose monitoring software at our institution and first connected our computed tomography (CT) scanners. CT dose data from July 2014 to February 2015 was retrospectively analyzed using dose monitoring software. We evaluated a number of scans above predefined dose thresholds ("alerts"), assessed reasons for alerts and compared data of two CT scanners, one located close to the emergency room ("emergency CT scanner") and one mainly used on an outpatient basis ("clinical routine CT scanner"). To check for statistically significant differences between scanners, chi-square-tests were performed. A total of 8883 scans were acquired (clinical routine CT scanner, n = 3415; emergency CT scanner, n = 5468) during which 316 alerts were encountered (alert quota, 4 %). The overall alert quota ranged from 2 - 5 % with significantly higher values for the clinical routine CT scanner. Reasons for alerts were high BMI (51 %), patient off-centering (24 %), scan repetition (11 %), orthopedic hardware (9 %), or other (5 %). Scan repetition was necessary significantly more often with the emergency CT scanner (p = 0.019), while high BMI, off-centering and orthopedic hardware were more frequently seen with the clinical routine CT scanner (for all, p < 0.05). There was a good correlation between high body weight and dose above threshold (r = 0.585). Implementation of dose monitoring software in the clinical routine was successfully accomplished and provides important information regarding patient radiation protection. ∙ Implementation of dose monitoring software in the clinical routine can be successfully accomplished. · Dose notifications are due to human error or patient-specific factors. · Dose monitoring software provides important information regarding radiation protection of patients.

Automated assessment of noise level in clinical computed tomography (CT) images is a crucial technique for evaluating and ensuring the quality of these images. There are various factors that can impact CT image noise, such as statistical noise, electronic noise, structure noise, texture noise, artifact noise, etc. In this study, a method was developed to measure the global noise index (GNI) in clinical CT scans due to the fluctuation of x-ray quanta. Initially, a noise map is generated by sliding a 10 × 10 pixel for calculating Hounsfield unit (HU) standard deviation and the noise map is further combined with the gradient magnitude map. By employing Boolean operation, pixels with high gradients are excluded from the noise histogram generated with the noise map. By comparing the shape of the noise histogram from this method with Christianson’s tissue-type global noise measurement algorithm, it was observed that the noise histogram computed in anthropomorphic phantoms had a similar shape with a close GNI value. In patient CT images, excluding the HU deviation due the structure change demonstrated to have consistent GNI values across the entire CT scan range with high heterogeneous tissue compared to the GNI values using Christianson’s tissue-type method. The proposed GNI was evaluated in phantom scans and was found to be capable of comparing scan protocols between different scanners. The variation of GNI when using different reconstruction kernels in clinical CT images demonstrated a similar relationship between noise level and kernel sharpness as observed in uniform phantom: sharper kernel resulted in noisier images. This indicated that GNI was a suitable index for estimating the noise level in clinical CT images with either a smooth or grainy appearance. The study’s results suggested that the algorithm can be effectively utilized to screen the noise level for a better CT image quality control.

Intramyocardial microvessels demonstrate functional changes in cardiomyopathies. However, clinical computed tomography (CT) does not have adequate spatial resolution to assess the microvessels. Our hypothesis is that these functional changes manifest as altered heterogeneity of the spatial distribution of arteriolar perfusion territories. Our goal was to determine whether the spatial analysis of perfusion CT could clinically detect changes in the function and structure of the intramyocardial microcirculation in a non-ischemic dilated cardiomyopathy (DCM). Two groups were studied: (1) a Control group (12 male plus 12 female) with no risk factors nor evidence of coronary artery disease, and (2) a DCM group (12 male plus 12 female) with left ventricular ejection fraction ≤40% and no evidence of coronary artery disease. Using the CT scan, the LV free wall thickness and its radius of curvature were measured. The DCM group was sub divided into those with LV free wall thickness <11.5 mm and those with thickness ≥11.5 mm. In the myocardial opacification phase of the CT scan sequence, myocardial perfusion (F) and intramyocardial blood volume (Bv) for multiple intramyocardial regions were computed. No significant differences between the groups were demonstrable in overall myocardial F or Bv. However, the myocardial regional data showed significantly increased spatial heterogeneity in the DCM group when compared to the Control group. The findings demonstrate that altered function of the subresolution intramyocardial microcirculation can be quantified with myocardial perfusion CT and that significant changes in these parameters occur in the DCM subjects with LV wall thickness greater than 11.5 mm.

Reply

Fabrication of 3D printed patient-derived anthropomorphic breast phantoms for mammography and digital breast tomosynthesis: Imaging assessment with clinical X-ray spectra

Deep Learning Method for Rapid Simultaneous Multistructure Temporal Bone Segmentation.

Recent events showed that dose administration has become a major concern regarding clinical computed tomography (CT) examinations. A simple solution to lower this dose is the use of more appropriate CT image reconstruction methods. Iterative reconstruction has not yet fully reached clinical applications, mostly due to computer speed and memory limitations. A method is proposed to compute a 3D system matrix using a polar-like voxel representation, allowing the modeling of highly resolved fields of view with a minimal random-access memory usage. As opposed to conventional ray-tracing, which is usually done over Cartesian coordinates, the proposed method uses cylindrical or spherical coordinates. The azimuthal symmetries present in those systems allow to compute only the detector responses of the first projection and use them as-is for all other projections. During reconstruction, only the azimuthal index has to be recomputed, and this is done using a simple addition. The ray-tracing and reconstruction algorithms were implemented and images of analytical phantoms were successfully reconstructed. Fully 3D images of phantoms and small animals acquired with a Gamma Medica Triumph X-O™ CT scanner are also presented to demonstrate the accuracy and robustness of the proposed approach. Under a reasonable set of assumptions, the memory size of the system matrix can be reduced by a factor corresponding to the number of projections. Using this strategy, iterative reconstruction from high resolution clinical and preclinical systems can be performed on general-purpose personal computers.

A novel pendulum-based impulse method to measure CT temporal resolution.

X-ray Computed Tomography (CT), e.g. clinical CT scanners, basically provides Linear Attenuation Coefficients (LACs) of objects under study by the means of algorithmic reconstruction of acquired views of attenuated X-ray passing through the samples in different angles around the imaged sample. Micro Computed Tomography (micro-CT) basically works the same as clinical CT. It provides volumetric information representing the inner structure of objects with a resolution in the micron range. LOTUS-inVivo is a micro-CT scanner dedicated to imaging of small animals and ex-vivo biological samples. In the present study the spatial resolution and Low Contrast Detectability (LCD) of LOTUS-inVivo scanner were evaluated using standard phantoms. We aimed to prove the capability of LOTUS-inVivo for small animal and ex-vivo biological samples imaging using the measured image quality parameters, i.e. spatial resolution and low contrast detectability. By the means of analysis of bar and LCD phantom images, the limiting resolution of LOTUS-inVivo micro-CT scanner was measured about 2.7 µm and has been shown that it’s capable of resolving sizes greater than 12.5 µm. Also, we concluded that LOTUS-inVivo is capable of discriminating tissues with 3% differences in contrast relative to the background, for 1 mm bar size. Thus, the provided technical characteristics in this study have made LOTUS-inVivo as a suitable tool for small animal imaging.

Background: This study aimed to test the possibility of using Magnetic Resonance (MR) images to create anthropomorphic breast phantoms for X-ray imaging and to compare the performance of fused deposition modeling (FDM) and 2D inkjet printing with radiopaque inks. Materials and Methods: Two physical phantoms were produced using either an inkjet printer on paper or an FDM technique, both based on clinical MR data. The paper phantom was printed with 1.2 g of KI dissolved in 20 ml of water. For the FDM phantom, the extrusion rate was adjusted according to clinical Hounsfield unit (HU) values. These phantoms underwent imaging using a clinical computed tomography (CT) device at two energy spectra, and their CT images were assessed in terms of HUs, histogram distributions, spectral and subjective analyses, as well as cost. The objective CT analysis of the phantoms revealed that HU values and β-values, indicating the anatomical complexity of the breast parenchyma, were in line with those expected, with an advantage for the FDM-based phantom. In both cases, the β-values were close to those for clinical breast images acquired with highresolution CT scanners. Subjective evaluation, however, indicated a need for refining the realism of the phantoms, particularly in terms of preserving the fine details. Conclusion: Breast MR Images offer the possibility of constructing breast phantoms. However, the method fails to replicate fine details in phantom CT images. Addressing this challenge requires improvement in segmentation processes and manufacturing accuracy.

Prediction Value of the Canadian CT Head Rule and the New Orleans Criteria for Positive Head CT Scan and Acute Neurosurgical Procedures in Minor Head Trauma: A Multicenter External Validation Study

Photon counting x-ray detectors (PCXDs) are an emerging technology in x-ray computed tomography (CT) as they have the potential to overcome some of the most significant limitations of current CT with energy integrating detectors. Among these are: insufficient tissue contrast, relatively high radiation dose, tissue non-specificity, and the non-quantitative nature. In contrast, CT with PCXDs has shown promise in producing higher contrast, tissue specific, quantitative images at lower dose. Novel applications for PCXDs include k-edge and functional imaging and material decomposition. A limiting factor, however, is the high photon flux that occurs in clinical applications resulting in signal pulse pile up in the detector. Faster detectors and new strategies for data corrections and image reconstruction algorithms are needed to overcome these limitations. A research tabletop x-ray CT scanner was developed with the following aims: 1) to characterize and calibrate the PCXD; 2) to acquire CT projection data under conditions similar to those of clinical CT; and 3) to reconstruct images using correction schemes specific for PCXDs. The scanner employs a commercial clinical x-ray tube, a PCXD with two energy thresholds, and allows scanning of objects of up to 40 cm in diameter. This paper presents measurements of detector quantities crucial for data corrections and calibration, such as energy response, deadtime, and count rates. Reconstructed CT images are presented and qualitative results from material decomposition are shown.

This study aims to evaluate the measurement accuracy of computed tomography (CT) systems, focusing on the necessity of using calibration phantoms for enhanced precision. Both clinical CT and micro-CT systems were evaluated using a specially designed two-ball phantom, which provides a reliable reference for spatial resolution and geometric accuracy. The study involved scanning the phantom with two micro-CT devices (the oversize micro-CT SkyScan 1173 and the high-resolution micro-CT SkyScan 1272) and a clinical CT device, a third-generation dual-source CT scanner (SOMATOM Force), measuring the distance between the centres of two ruby balls. The results showed significant differences in measurement accuracy between the devices. The high-resolution micro-CT provided the most consistent measurements with minimal variance, indicating its superiority in applications requiring high precision. In contrast, the oversize micro-CT exhibited larger errors, particularly at smaller voxel sizes, suggesting that internal calibration affected its accuracy. The dual source CT system had the smallest mean error but a larger standard deviation, indicating less consistency compared to micro-CT systems. Calibration with the two-ball phantom improved measurement accuracy across all devices. This improvement underscores the importance of using calibration phantoms to ensure accurate measurements, especially in fields that require high precision, such as clinical diagnostics and materials science. We concluded that routine calibration with phantoms is essential to achieve high measurement accuracy in CT imaging, thereby increasing the reliability of CT-based analyses in various disciplines.

Purpose: To investigate the effect of the helical pitch, patient size, and beam width on point dose measurements of superficial organs in MSCT. Methods: Three sizes of cylindrical PMMA phantoms were utilized; 32cm (body), 16cm (adult head), and 10cm (pediatric head). For each phantom, helical scans were performed with different pitch factors (0.7, 1.0, and 1.3) and collimations (12mm and 24mm). In each scan, a strip of gafchromic film, measuring 12×1.5cm2, was taped onto the top of the phantom along its z‐axis. Film strips were scanned, red channel was extracted and pixel values were converted into optical densities from which doses (mGy) were obtained using a calibration curve. Results: The periodic pattern of peaks and valleys in dose profiles along the z‐axis of phantom surface was more obvious with the body phantom; the highest variation (% difference between peak and valley) was 56%. Adult and pediatric head phantoms showed significantly less variation; highest = 30% and 24%, respectively. These values were found with pitch 1.3 and collimation 24mm. When collimation was changed from 12mm to 24mm, the amount of variation was nearly doubled (at pitch 0.7 and 1.3). With pitch 1, dose variation was different; in the pediatric phantom the variation was similar in either collimation (7%). In adult and pediatric head phantoms it increased from 6% to 9% and from 17% to 39%, respectively. Conclusions: If point dose measurements were to be taken on patient surface or for superficial organs such as breast or thyroid using small dosimeters in anthropomorphic phantoms, the combined effect of helical pitch, patient size, and collimation on dose assessment accuracy should be taken into consideration. Variation of about 60% may result with large patients, high pitch, and wide collimation. Variations will be largely reduced with smaller patients, pitch close to 1 and narrow collimation.

This study aimed to assess the feasibility and short-term results for percutaneous radiofrequency ablation in the treatment of primary and secondary lung tumors. Between May 2003 and July 2004, 15 patients (mean age, 64.9 years; range, 51-80 years) with 18 pulmonary lesions (9 primitive non-small cell lung cancers and 9 metastases) underwent the ablation procedure. All the patients had absolute contraindications to the surgery. The procedure was performed under computed tomography (CT) guidance with anesthesiologic assistance using a coaxial Le Veen needle electrode. The results were evaluated by postprocedural CT scan, and then by clinical and laboratory examination and CT scan 1, 3, 6, 9, and 12 months after the treatment. A complete ablation was obtained for 16 of 18 lesions (88.9%), and a partial ablation was achieved for the remaining 2 lesions (central tumors). In terms of complications, there were five cases of pneumothorax (2 resolved spontaneously and 3 were drained through a coaxial needle), four middle pleural reactions, and one hemothorax that required draining surgically. Follow-up evaluation was performed for 16 of 18 lesions. Stability was observed in one of two central tumors that received partial ablation. The remaining 15 tumors that received a complete ablation were followed up for a mean of 5 months (range, 1-12 months). All 15 lesions appeared to be hypodense at the CT examination. Dimension reduction with progressive fibrotic scar formation was observed in seven of seven lesions during a follow-up period of 6 months or more. A recurrence at the site of the treatment for two of three lesions was observed during a 12-month follow-up period. One of these received a second radiofrequency ablation. Five patients experienced systemic disease progression. In four of these five patients, this progression was not associated with recurrence at the site of the treatment. Radiofrequency ablation seems to be possible for "nonsurgical" patients with primary and secondary lung tumors. Good results in terms of local tumor control were observed during short-term follow-up evaluation.