Measured CT Numbers Research Articles

Improved Discriminability of Severe Lung Injury and Atelectasis in Thoracic Trauma at Low keV Virtual Monoenergetic Images from Photon-Counting Detector CT

Objectives: To evaluate the value of virtual monoenergetic images (VMI) from photon-counting detector CT (PCD-CT) for discriminability of severe lung injury and atelectasis in polytraumatized patients. Materials & Methods: Contrast-enhanced PCD-CT examinations of 20 polytraumatized patients with severe thoracic trauma were included in this retrospective study. Spectral PCD-CT data were reconstructed using a noise-optimized virtual monoenergetic imaging (VMI) algorithm with calculated VMIs ranging from 40 to 120 keV at 10 keV increments. Injury-to-atelectasis contrast-to-noise ratio (CNR) was calculated and compared at each energy level based on CT number measurements in severely injured as well as atelectatic lung areas. Three radiologists assessed subjective discriminability, noise perception, and overall image quality. Results: CT values for atelectasis decreased as photon energy increased from 40 keV to 120 keV (mean Hounsfield units (HU): 69 at 40 keV; 342 at 120 keV), whereas CT values for severe lung injury remained near-constant from 40 keV to 120 keV (mean HU: 42 at 40 keV; 44 at 120 keV) with significant differences at each keV level (p < 0.001). The optimal injury-to-atelectasis CNR was observed at 40 keV in comparison with the remaining energy levels (p < 0.001) except for 50 keV (p > 0.05). In line with this, VMIs at 40 keV were rated best regarding subjective discriminability. VMIs at 60–70 keV, however, provided the highest subjective observer parameters regarding subjective image noise as well as image quality. Conclusions: Discriminability between severely injured and atelectatic lung areas after thoracic trauma can be substantially improved by virtual monoenergetic imaging from PCD-CT with superior contrast and visual discriminability at 40–50 keV.

Carotid artery assessment in dual-source photon-counting CT: impact of low-energy virtual monoenergetic imaging on image quality, vascular contrast and diagnostic assessability.

Preliminary dual-energy CT studies have shown that low-energy virtual monoenergetic (VMI) + reconstructions can provide superior image quality compared to standard 120kV CTA series. The purpose of this study is to evaluate the impact of low-energy VMI reconstructions on quantitative and qualitative image quality, vascular contrast, and diagnostic assessability of the carotid artery in patients undergoing photon-counting CTA examinations. A total of 122 patients (67 male) who had undergone dual-source photon-counting CTA scans of the carotid artery were retrospectively analyzed in this study. Standard 120kV CT images and low-keV VMI series from 40 to 100keV with an interval of 15keV were reconstructed. Quantitative analyses included the evaluation of vascular CT numbers, signal-to-noise ratio (SNR), and contrast-to-noise ratio (CNR). CT number measurements were performed in the common, external, and internal carotid arteries. Qualitative analyses were performed by three board-certified radiologists independently using five-point scales to evaluate image quality, vascular contrast, and diagnostic assessability of the carotid artery. Mean attenuation, CNR and SNR values were highest in 40keV VMI reconstructions (HU, 1362.32 ± 457.81; CNR, 33.19 ± 12.86; SNR, 34.37 ± 12.89) followed by 55-keV VMI reconstructions (HU, 736.94 ± 150.09; CNR, 24.49 ± 7.11; SNR, 26.25 ± 7.34); all three mean values at these keV levels were significantly higher compared with the remaining VMI series and standard 120kV CT series (HU, 154.43 ± 23.69; CNR, 16.34 ± 5.47; SNR, 24.44 ± 7.14) (p < 0.0001). The qualitative analysis showed the highest rating scores for 55keV VMI reconstructions followed by 40keV and 70keV VMI series with a significant difference compared to standard 120kV CT images series regarding image quality, vascular contrast, and diagnostic assessability of the carotid artery (all comparisons, p < 0.01). Low-keV VMI reconstructions at a level of 40-55keV significantly improve image quality, vascular contrast, and the diagnostic assessability of the carotid artery compared with standard CT series in photon-counting CTA.

Improved Pulmonary Artery Evaluation Using High-Pitch Photon-Counting CT Compared to High-Pitch Conventional or Routine-Pitch Conventional Dual-Energy CT.

Pulmonary CT angiography (CTA) to detect pulmonary emboli can be performed using conventional dual-source CT with single-energy acquisition at high-pitch (high-pitch conventional CT), which minimizes motion artifacts, or routine-pitch, dual-energy acquisitions (routine-pitch conventional DECT), which maximize iodine signal. We compared iodine signal, radiation dose, and motion artifacts of pulmonary CTA between these conventional CT modalities and dual-source photon-counting detector CT with high-pitch, multienergy acquisitions (high-pitch photon-counting CT). Consecutive clinically indicated pulmonary CTA exams were collected. CT number/noise was measured from the main to right lower lobe segmental pulmonary arteries using 120 kV threshold low, 120 kV, and mixed kV (0.6 linear blend) images. Three radiologists reviewed anonymized, randomized exams, rating them using a 4- or 5-point Likert scale (1 = worst, and 4/5 = best) for contrast enhancement in pulmonary arteries, motion artifacts in aortic root to subsegmental pulmonary arteries, lung image quality; pulmonary blood volume (PBV) map image quality (for multienergy or dual-energy exams), and contribution to reader confidence. One hundred fifty patients underwent high-pitch photon-counting CT (n = 50), high-pitch conventional CT (n = 50), and routine-pitch conventional DECT (n = 50). High-pitch photon-counting CT had lower radiation dose (CTDIvol: 8.1 ± 2.5 vs 9.6 ± 6.8 and 16.2 ± 8.5 mGy, respectively; P < 0.001), and routine-pitch conventional DECT had significantly less contrast (P < 0.009). CT number and CNR measurements were significantly greater at high-pitch photon-counting CT (P < 0.001). Across readers, high-pitch photon-counting CT demonstrated significantly higher subjective contrast enhancement in the pulmonary arteries compared to the other modalities (4.7 ± 0.6 vs 4.4 ± 0.7 vs 4.3 ± 0.7; P = 0.011) and lung image quality (3.4 ± 0.5 vs 3.1 ± 0.5 vs 3.1 ± 0.5; P = 0.013). High-pitch photon-counting CT and high-pitch conventional CT had fewer motion artifacts at all levels compared to DECT (P < 0.001). High-pitch photon-counting CT PBV maps had superior image quality (P < 0.001) and contribution to reader confidence (P < 0.001) compared to routine-pitch conventional DECT. High-pitch photon-counting pulmonary CTA demonstrated higher contrast in pulmonary arteries at lower radiation doses with improved lung image quality and fewer motion artifacts compared to high-pitch conventional CT and routine-pitch conventional dual-energy CT.

3D printed heterogeneous paediatric head and adult thorax phantoms for linear accelerator radiotherapy quality assurance: from fabrication to treatment delivery.

This study aims to design and fabricate a 3D printed heterogeneous paediatric head phantom and to customize a thorax phantom for radiotherapy dosimetry. &#xD;Approach: This study designed, fabricated, and tested 3D printed radiotherapy phantoms that can simulate soft tissue, lung, brain, and bone. Various polymers were considered in designing the phantoms. Polylactic acid+, nylon, and plaster were used in simulating different tissue equivalence. Dimensional accuracy, and CT number were investigated. The phantoms were subjected to a complete radiotherapy clinical workflow. Several treatment plans were delivered in both the head and the thorax phantom from a simple single 6 MV beam, parallel opposed beams, and five-field intensity modulated radiotherapy (IMRT) beams. Dose measurements using an ionization chamber and radiochromic films were compared with the calculated doses of the Varian Eclipse treatment planning system (TPS). &#xD;Main results: The fabricated heterogeneous phantoms represent paediatric human head and adult thorax based on its radiation attenuation and anatomy. The measured CT number ranges are within -786.23 ± 10.55, 0.98 ± 3.86, 129.51 ± 12.83, and 651.14 ± 47.76 HU for lung, water/brain, soft tissue, and bone, respectively. It has a good radiological imaging visual similarity relative to a real human head and thorax depicting soft tissue, lung, bone, and brain. The accumulated dose readings for both conformal radiotherapy and IMRT match with the TPS calculated dose within ±2% and ±4% for head and thorax phantom, respectively. The mean pass rate for all the plans delivered are above 90% for gamma analysis criterion of 3% / 3 mm.&#xD;Significance and conclusion: The fabricated heterogeneous paediatric head and thorax phantoms are useful in Linac end-to-end radiotherapy quality assurance based on its CT image and measured radiation dose. The manufacturing and dosimetry workflow of this study can be utilized by other institutions for dosimetry and trainings. &#xD.

Exploration of the pulse pileup effects in a clinical CdTe-based photon-counting computed tomography.

High tube current generates a high flux of x-rays to photon counting detectors (PCDs) that can potentially result in the piling up of pulses formed by concurrent photons, which can cause count loss and energy resolution degradation. To evaluate the performance of clinical photon-counting CT (PCCT) systems in high flux, potentially influenced by pulse pileup effects, in terms of task-generic image quality metrics. A clinical phantom was scanned on a commercial PCCT scanner (NAEOTOM Alpha, Siemens) at 120kV under fourteen different tube current levels (40-1000mA) with a rotation time of 0.25 s and a pitch of 1. The dose levels corresponded to CTDIvol (32cm phantom) of 0.79-19.8mGy. CT sinograms were reconstructed using QIR-off mode (noniterative reconstruction algorithm), Br44 kernel, and a voxel size of . imQuest, an open-source MATLAB-based software package was used to calculate noise power spectrum (NPS), task transfer function (TTF), contrast-to-noise ratio (CNR), and CT number according to AAPM Task Group 233 metrology. The 50% cut-off frequency of TTF (f50 ) remained mostly constant across all higher tube currents for all inserts, namely polyethylene, bone, air, and acrylic. Using the lowest two data points (40 and 80mA), the expected relationship between noise magnitude and tube current was determined to be noise mA-0.47 . The measured noise magnitude were up to 11.1% higher than the expected value at the highest tube current. The average frequency of NPS (fav ) decreased from 0.32 to 0.29mm-1 as tube current increased from 40 to 1000mA. No considerable effects were observed in CT number measurement of any insert; however, CT numbers for air and bone changed almost monotonically as tube current increased. Absolute CNR increased monotonically for all inserts; however, the difference between measured and expected CNRs were approximately -6% to 12% across all tube currents. Increasing tube currents did not affect the spatial resolution, but slightly affected the CT number and noise measurements of the clinical PCCT system. However, the effects were only considerable at clinically irrelevant tube currents used on a small 20-cm phantom. In general clinical practices, automatic exposure control techniques are used to decrease the variation of flux on the detector, which alleviates the chances of detector saturation due to high count rates. The observed effects could be due to pulse pileup, signal-dependent filtration of the system, or nonlinearities in the reconstruction algorithm. In conclusion, either the deadtime of the detector used in the photon-counting CT system is shorter such that count losses due to pulse pileup are negligible, or pulse pileup has inconsiderable effects on the image quality of clinical photon-counting CT systems in routine clinical practice due to possible corrections applied on the system.

Comparing CT and MR Properties of Artificial Thrombi According to Their Composition.

This study aims to determine whether and to what extent the structure and composition of thrombi can be assessed using NMR and CT measurements. Seven different thrombus models, namely, six RBC thrombi with hematocrit levels (HTs) of 0%, 20%, 40%, 60%, 80% and 100% and one platelet thrombus model, were analyzed using proton NMR at 100 MHz and 400 MHz, with measurements of T1 and T2 NMR relaxation times and measurements of the apparent diffusion coefficient (ADC). In addition, the thrombus models were CT-scanned in a dual-energy mode (80 kV and 140 kV) and in a single-energy mode (80 kV) to measure their CT numbers. The results confirmed that RBC thrombi can be distinguished from platelet thrombi by using ADC and CT number measurements in all three settings, while they cannot be distinguished by using T1 and T2 measurements. All measured parameters allowed for the differentiation of RBC thrombi according to their HT values, but the best sensitivity to HT was obtained with ADC and single-energy CT measurements. The importance of this study also lies in the potential application of its results for the characterization of actual thrombi in vivo.

Rapid and one-step mechanochemical ligand exchange of Yb3+/Er3+ co-doped NaGdF4 upconversion nanoparticles for efficient MR and CT imaging

Abstract Upconversion nanoparticles possess the ability to convert low energy photons to high energy photons, with the advantages of no autofluorescence, reduced photodamage, deeper tissue penetration, and extended photostability. Therefore, upconversion nanoparticles are considered ideal probes for framing potential theranostic agents. Generally, oleic acid has been used as a capping agent to fabricate high-quality upconversion nanoparticles. However, the hydrophobic oleic acid ligands on the surface of the nanoparticles continue to be a barrier when used in biological applications. Herein, we modified the surface of oleic acid coated upconversion (OA-NaGdF4:Yb/Er) nanoparticles to be hydrophilic using a novel one-step solvent assisted mechanochemical (SAM) milling ligand exchange strategy. Normal ligand exchange processes are tedious and take one to two days to complete, but the SAM ligand exchange strategy presented here is facile, rapid, and takes less than 1 h. This surface modified citric acid coated upconversion (CA-NaGdF4:Yb/Er) nanoparticles further ensures dispersibility in water and good biocompatibility, as revealed by electron microscopy, ATR-FTIR spectroscopy, zeta potential measurement, upconversion luminescence studies, and cytotoxicity assessment. Besides, the size and shape of the nanoparticles were retained after surface modification. Moreover, the monodispersed CA-NaGdF4:Yb/Er nanoparticles exhibit intrinsic paramagnetic behavior which makes them suitable to be used as a contrast enhancer for T 1-weighted MRI. In addition, the measured CT numbers (in HU) increased linearly with increasing the concentration of the surface modified CA-NaGdF4:Yb/Er nanoparticles, indicating their plausibility as a CT contrast agent. The current findings suggest that the SAM ligand exchange strategy could be used to fabricate hydrophilic and biocompatible upconversion nanoparticles for bioimaging applications.

The first mobile photon-counting detector CT: the human images and technical performance study

Objective. The purpose of this study is to assess its human images and its unique capabilities such as the ‘on demand’ higher spatial resolution and multi-spectral imaging of photon-counting-detector (PCD)-CT. Approach. In this study, the FDA 510(k) cleared mobile PCD-CT (OmniTom Elite) was used. To this end, we imaged internationally certified CT phantoms and a human cadaver head to evaluate the feasibility of high resolution (HR) and multi-energy imaging. We also demonstrate the performance of PCD-CT via first-in-human imaging by scanning three human volunteers. Main results. At the 5 mm slice thickness, routinely used in diagnostic head CT, the first human PCD-CT images were diagnostically equivalent to the EID-CT scanner. The HR acquisition mode of PCD-CT achieved a resolution of 11 line-pairs (lp)/cm as compared to 7 lp cm−1 using the same kernel (posterior fossa-kernel) in the standard acquisition mode of EID-CT. For the quantitative multi-energy CT performance, the measured CT numbers in virtual mono-energetic images (VMI) of iodine inserts in the Gammex Multi-Energy CT phantom (model 1492, Sun Nuclear Corporation, USA) matched the manufacturer reference values with mean percent error of 3.25%. Multi-energy decomposition with PCD-CT demonstrated the separation and quantification of iodine, calcium, and water. Significance. PCD-CT can achieve multi-resolution acquisition modes without physically changing the CT detector. It can provide superior spatial resolution compared with the standard acquisition mode the conventional mobile EID-CT. Quantitative spectral capability of PCD-CT can provide accurate, simultaneous multi-energy images for material decomposition and VMI generation using a single exposure.

Comparison of lung CT number and airway dimension evaluation capabilities of ultra-high-resolution CT, using different scan modes and reconstruction methods including deep learning reconstruction, with those of multi-detector CT in a QIBA phantom study.

Ultra-high-resolution CT (UHR-CT), which can be applied normal resolution (NR), high-resolution (HR), and super-high-resolution (SHR) modes, has become available as in conjunction with multi-detector CT (MDCT). Moreover, deep learning reconstruction (DLR) method, as well as filtered back projection (FBP), hybrid-type iterative reconstruction (IR), and model-based IR methods, has been clinically used. The purpose of this study was to directly compare lung CT number and airway dimension evaluation capabilities of UHR-CT using different scan modes with those of MDCT with different reconstruction methods as investigated in a lung density and airway phantom design recommended by QIBA. Lung CT number, inner diameter (ID), inner area (IA), and wall thickness (WT) were measured, and mean differences between measured CT number, ID, IA, WT, and standard reference were compared by means of Tukey's HSD test between all UHR-CT data and MDCT reconstructed with FBP as 1.0-mm section thickness. For each reconstruction method, mean differences in lung CT numbers and all airway parameters on 0.5-mm and 1-mm section thickness CTs obtained with SHR and HR modes showed significant differences with those obtained with the NR mode on UHR-CT and MDCT (p < 0.05). Moreover, the mean differences on all UHR-CTs obtained with SHR, HR, or NR modes were significantly different from those of 1.0-mm section thickness MDCTs reconstructed with FBP (p < 0.05). Scan modes and reconstruction methods used for UHR-CT were found to significantly affect lung CT number and airway dimension evaluations as did reconstruction methods used for MDCT. • Scan and reconstruction methods used for UHR-CT showed significantly higher CT numbers and smaller airway dimension evaluations as did those for MDCT in a QIBA phantom study (p < 0.05). • Mean differences in lung CT number for 0.25-mm, 0.5-mm, and 1.0-mm section thickness CT images obtained with SHR and HR modes were significantly larger than those for CT images at 1.0-mm section thickness obtained with MDCT and reconstructed with FBP (p < 0.05). • Mean differences in inner diameter (ID), inner area (IA), and wall thickness (WT) measured with SHR and HR modes on 0.5- and 1.0-mm section thickness CT images were significantly smaller than those obtained with NR mode on UHR-CT and MDCT (p < 0.05).

Coronary calcium scores on dual-source photon-counting computed tomography: an adapted Agatston methodology aimed at radiation dose reduction

ObjectivesThe aim of this study was to determine mono-energetic (monoE) level–specific photon-counting CT (PCCT) Agatston thresholds, to yield monoE level independent Agatston scores validated with a dynamic cardiac phantom. Also, we examined the potential of dose reduction for PCCT coronary artery calcium (CAC) studies, when reconstructed at low monoE levels.MethodsTheoretical CAC monoE thresholds were calculated with data from the National Institute of Standards and Technology (NIST) database. Artificial CAC with three densities were moved in an anthropomorphic thorax phantom at 0 and 60–75 bpm, and scanned at full and 50% dose on a first-generation dual-source PCCT. For all densities, Agatston scores and maximum CT numbers were determined. Agatston scores were compared with the reference at full dose and 70 keV monoE level; deviations (95% confidence interval) < 10% were deemed to be clinically not-relevant.ResultsAveraged over all monoE levels, measured CT numbers deviated from theoretical CT numbers by 6%, 13%, and − 4% for low-, medium-, and high-density CAC, respectively. At 50% reduced dose and 60–75 bpm, Agatston score deviations were non-relevant for 60 to 100 keV and 60 to 120 keV for medium- and high-density CAC, respectively.ConclusionMonoE level–specific Agatston score thresholds resulted in similar scores as in standard reconstructions at 70 keV. PCCT allows for a potential dose reduction of 50% for CAC scoring using low monoE reconstructions for medium- and high-density CAC.Key Points• Mono-energy level–specific Agatston thresholds allow for reproducible coronary artery calcium quantification on mono-energetic images.• Increased calcium contrast-to-noise ratio at reduced mono-energy levels allows for coronary artery calcium quantification at 50% reduced radiation dose for medium- and high-density calcifications.

Differentiating total from subtotal arterial occlusion in lower extremities by using reverse attenuation gradient sign in CT angiography.

To investigate the use of reverse attenuation gradient sign (RAGS) in CT angiography (CTA) to differentiate total from subtotal occlusion in lower extremities which poses different challenges for the procedure and carries different prognoses. Eighty patients with 91 lesions in the lower extremities were divided into total occlusion (TO) group and subtotal occlusion (SO) group confirmed by digital subtraction angiography. The CT numbers of vascular lumen at the end of lesion (proximal, P) and at the first entrance (distal, D) of the lateral branch were measured and their difference (CT(PD) = CT(P) - CT(D)) of each lesion was calculated. The CT number gradient (G(DP) = 2 * CT(PD)/[CT(P) + CT(D)]) was calculated by dividing the CT number difference by the average CT number of the two points. The existence of RAGS where the CT number at the distal point is higher than that at the proximal point (CT(PD) and G(PD) < 0) was determined and the diagnostic efficacy of using RAGS in CTA for differentiating total from subtotal occlusive lesions in lower extremities was calculated. The SO group had higher CT numbers than the TO group (p < 0.001). More importantly, the SO group had positive CT number gradient (G(PD) > 0), while the gradient was negative (G(PD) < 0) in the TO group. The specificity and sensitivity of using RAGS (G(PD) < 0) in images for diagnosing TO of lower extremity were 97.6% and 92.0%, respectively, and 87.8% and 88.0% using the standard CTA images. The use of RAGS in CTA images has high diagnostic accuracy to differentiate TO from SO in lower extremities. • Total occlusions often exhibit higher CT number at distal point than at proximal point to the occlusion. • The reverse attenuation gradient sign (RAGS) may be determined using the CT number measurements between the proximal and distal points after occlusion. • RAGS can be used to improve the diagnostic efficiency in CTA to differentiate between total and subtotal occlusions of lower extremity arteries.

Fabrication of a pediatric torso phantom with multiple tissues represented using a dual nozzle thermoplastic 3D printer.

PurposeTo demonstrate an on‐demand and nearly automatic method for fabricating tissue‐equivalent physical anthropomorphic phantoms for imaging and dosimetry applications using a dual nozzle thermoplastic three‐dimensional (3D) printer and two types of plastic.MethodsTwo 3D printing plastics were investigated: (a) Normal polylactic acid (PLA) as a soft tissue simulant and (b) Iron PLA (PLA‐Fe), a composite of PLA and iron powder, as a bone simulant. The plastics and geometry of a 1‐yr‐old computational phantom were combined with a dual extrusion 3D printer to fabricate an anthropomorphic imaging phantom. The volumetric fill density of the 3D‐printed parts was varied to approximate tissues of different radiographic density using a calibration curve relating the printer infill density setting to measured CT number. As a demonstration of our method we printed a 10 cm axial cross‐section of the computational phantom’s torso at full scale. We imaged the phantom on a CT scanner and compared HU values to those of a 1‐yr‐old patient and a commercial 5‐yr‐old physical phantom.ResultsThe phantom was printed in six parts over the course of a week. The printed phantom included 30 separate anatomical regions including soft tissue remainder, lungs (left and right), heart, esophagus, rib cage (left and right ribs 1 to 10), clavicles (left and right), scapulae (left and right), thoracic vertebrae (one solid object defining thoracic vertebrae T1 to T9). CT scanning of the phantom showed five distinct radiographic regions (heart, lung, soft tissue remainder, bone, and air cavity) despite using only two types of plastic. The 3D‐printed phantom demonstrated excellent similarity to commercially available phantoms, although key limitations in the printer and printing materials leave opportunity for improvement.ConclusionPatient‐specific anthropomorphic phantoms can be 3D printed and assembled in sections for imaging and dosimetry applications. Such phantoms will be useful for dose verification purposes when commercial phantoms are unavailable for purchase in the specific anatomies of interest.

Body size and tube voltage dependent corrections for Hounsfield Unit in medical X-ray computed tomography: theory and experiments

The purpose of this work is to present a body size and tube voltage dependent correction scheme for the Hounsfield Unit, HU, in medical X-ray Computed Tomography imaging. Boltzmann photon transport equation was employed to study X-ray interaction with bulk water in CT imaging. Experimentally measured X-ray output in body of phantoms and attenuation cross sections of water were employed in the derivation of beam intensity in X-ray imaging. A Somatom Emotion CT scanner from Siemens and electron density phantoms from CIRS were employed to acquire CT images of different body sizes and different tissue materials located at different depths from body’s surface. Tube voltage and depth dependent effective attenuation of bulk water was found from theoretical analysis in agreement with measured size-specific correction factors for CTDIvol under different tube voltages. A size and tube voltage dependent correction scheme for the Hounsfield Unit is established. For the same tissue material, body size has much larger impact on the CT number variations than that of depth from the body surface in phantom measurements. Good results were achieved by applying the established correction scheme on the experimentally measured CT number variations under different tube voltages and body sizes.

Effects of acquisition method and reconstruction algorithm for CT number measurement on standard-dose CT and reduced-dose CT: a QIBA phantom study.

To compare the effect of different acquisition and reconstruction methods on the radiation dose and accuracy of CT number measurements, using a 320-detector row CT and a Quantitative Imaging Biomarker Alliance (QIBA) recommended phantom. Acquisitions were performed on a 320-detector row CT, as 64- and 80-detector row helical and wide detector step-and-shoot (i.e., wide volume) acquisitions with tube currents of 400mA, 100mA, 50mA, 20mA, and 10mA. Image was reconstructed with the filtered back projection (FBP), adaptive iterative dose reduction using 3D processing (AIDR 3D), and forward projected model-based iterative reconstruction (FIRST) methods. The difference between measured CT numbers and the actual -856HU value of the phantom insert was determined by each CT acquisition protocol. Differences in actual and measured CT numbers were compared among acquisitions and among reconstruction methods by means of Tukey's HSD test. The CT number obtained with 64-detector row helical acquisition was significantly larger than that obtained with others (p < 0.0001). At each tube current, the CT number reconstructed with FIRST was significantly smaller than that with others (p < 0.0001). Acquisition and reconstruction methods are significantly affecting radiation dose reduction and accuracy of CT number measurements on a phantom study.

Radiopaque and biodegradable beads fabricated with Lipiodol and polycaprolactone for transarterial chemoembolization

AbstractEmbolic beads for transarterial chemoembolization (TACE) should possess radiopacity and biodegradability at the same time, to be visualized in a body under fluoroscopy and CT scanning to avoid complicating disease. In this study, we fabricated radiopaque and biodegradable beads composed of Lipiodol (LPD) (ethiodized oil) and polycaprolactone (PCL), a biocompatible and biodegradable polymer. LPD/PCL beads were first fabricated with a home-made microfluidic device. By changing the flow-rate ratio in the microfluidic device, the mean diameter of LPD/PCL beads could be well controlled. The radiopacity was evaluated by the fluoroscopic imaging and the CT number measurements. Furthermore, the biodegradability was evaluated by collecting the weight loss data of LPD/PCL immersed in lipase/PBS solution and PBS. The results showed that LPD/PCL beads obtained in this study had sufficient radiopacity and biodegradability, which would be an alternative embolic agent for TACE.

100 days with scans of the same Catphan phantom on the same CT scanner.

Quality control (QC) of CT scanners is important to evaluate image quality and radiation dose. Different QC phantoms for testing image quality parameters on CT are commercially available, and Catphan phantoms are widely used for this purpose. More data from measured image quality parameters on CT are necessary to assess test methods, tolerance levels, and test frequencies. The aim of this study was to evaluate the stability of essential image quality parameters for axial and helical scans on one CT scanner over time. A Catphan 600 phantom was scanned on a Philips Ingenuity CT scanner for 100 days over a period of 6 months. At each day of testing, one helical scan covering the entire phantom and four axial scans covering four different modules in the phantom were performed. All images were uploaded into Image Owl for automatic analysis of CT numbers, modular transfer function (MTF), low‐contrast resolution, noise, and uniformity. In general, the different image quality parameters for both scan techniques were stable over time compared to given tolerance levels. Average measured CT numbers differed between axial and helical scans, while MTF was almost identical for helical and axial scans. Axial scans had better low‐contrast resolution and less noise than helical scans. The uniformity was relatively similar for axial and helical scans. Most standard deviations of measured values were larger for helical scans compared to axial scans. Test results in this study were stable over time for both scan techniques, but further studies on different CT scanners are required to confirm that this also holds true for other systems.

Development of a thresholding algorithm for calcium classification at multiple CT energies

The objective of this study was to develop a thresholding method for calcium classification with different concentration using single-energy computed tomography. Five different concentrations of calcium chloride were filled in PMMA tubes and placed inside a water-filled PMMA phantom (diameter 10 cm). The phantom was scanned at 70, 80, 100, 120 and 140 kV using a SECT. CARE DOSE 4D was used and the slice thickness was set to 1 mm for all energies. ImageJ software inspired by the National Institute of Health (NIH) was used to measure the CT numbers for each calcium concentration from the CT images. The results were compared with a developed algorithm for verification. The percentage differences between the measured CT numbers obtained from the developed algorithm and the ImageJ show similar results. The multi-thresholding algorithm was found to be able to distinguish different concentrations of calcium chloride. However, it was unable to detect low concentrations of calcium chloride and iron (III) nitrate with CT numbers between 25 HU and 65 HU. The developed thresholding method used in this study may help to differentiate between calcium plaques and other types of plaques in blood vessels as it is proven to have a good ability to detect the high concentration of the calcium chloride. However, the algorithm needs to be improved to solve the limitations of detecting calcium chloride solution which has a similar CT number with iron (III) nitrate solution.

Variation in CT Number and Image Noise Uniformity According to Patient Positioning in MDCT.

Many algorithms for clinical decision making rely on assessment of the CT number (expressed as Hounsfield units); however, to our knowledge, few, if any, studies have addressed how CT numbers change as a function of patient positioning within the scanner. An anthropomorphic phantom underwent imaging with varying amounts of vertical orientation misalignment with respect to isocenter. CT number and noise were measured using ROIs in the upper thorax, mid thorax, and abdomen. The degree of noise nonuniformity and changes in the CT number were assessed by comparing values obtained in the anterior versus posterior ROIs. To add clinical relevance, data on vertical mispositioning were collected from 20,316 clinical abdominal CT scans. Box-and-whisker plot analysis was used to identify the range of patient positioning. Absolute CT number changes of more than 20 HU were observed for some ROIs at phantom positions of 10 cm from isocenter, with important differences noted between the thoracic and abdominal regions. Noise uniformity varied by more than twofold for all regions at 10 cm below isocenter. On clinical CT examinations, off-centering of more than 1, 2, 4, and 6 cm occurred for 41%, 19%, 1.9%, and 0.3% of patients, respectively. Radiologists should treat CT number measurements with caution when patients are grossly mispositioned in the scanner. The substantial changes in attenuation values shown in the present study are large enough to warrant further investigation.

Evaluation of 3D printing materials for fabrication of a novel multi-functional 3D thyroid phantom for medical dosimetry and image quality

Recently, the three-dimensional printer has started to be utilized strongly in medical industries. In the human body, many parts or organs can be printed from 3D images to meet accurate organ geometries.In this study, five common 3D printing materials were evaluated in terms of their elementary composition and the mass attenuation coefficients. The online version of XCOM photon cross-section database was used to obtain the attenuation values of each material. The results were compared with the attenuation values of the thyroid listed in the International Commission on Radiation Units and Measurements - ICRU 44.Two original thyroid models (hollow-inside and solid-inside) were designed from scratch to be used in nuclear medicine, diagnostic radiology and radiotherapy for dosimetry and image quality purposes. Both designs have three holes for installation of radiation dosimeters. The hollow-inside model has more two holes in the top for injection the radioactive materials.The attenuation properties of the Polylactic Acid (PLA) material showed a very good match with the thyroid tissue, which it was selected to 3D print the phantom using open source RepRap, Prusa i3 3D printer.The scintigraphy images show that the phantom simulates a real healthy thyroid gland and thus it can be used for image quality purposes. The measured CT numbers of the PA material after the 3D printing show a close match with the human thyroid CT numbers. Furthermore, the phantom shows a good accommodation of the TLD dosimeters inside the holes.The 3D fabricated thyroid phantom simulates the real shape of the human thyroid gland with a changeable geometrical shape-size feature to fit different age groups.By using 3D printing technology, the time required to fabricate the 3D phantom was considerably shortened compared to the longer conventional methods, where it took only 30min to print out the model. The 3D printing material used in this study is commercially available and cost-effective compared to current commercial tissue-equivalent materials.

Accessory spleen versus lymph node: Value of iodine quantification with dual-energy computed tomography

ObjectivesTo evaluate whether iodine quantification with Dual-Energy Computed Tomography (DECT) improves the differentiation of accessory spleens (AS) from lymph nodes (LN) compared to CT number measurements. MethodsAbdominal DECT images of 75 patients with either AS (n=35) or LN (n=48) (benign entity) were retrospectively evaluated. Hounsfield Units (HU) and iodine concentrations of AS, LN and the main spleen were measured. Receiver operating characteristics (ROC) were performed to calculate an optimal threshold for distinguishing AS from LN. Sensitivity, specificity, and accuracy were calculated for distinguishing AS from LN by iodine concentration measurements. ResultsMean CT numbers and iodine concentrations were higher for AS (148±29 HU and 48.2±11×100μg/cc) than LN (83±19 HU and 31.5±6.2×100μg/cc, respectively, P<0.001 each). Mean CT numbers were lower for AS compared to the main spleen (161±29HU, P<0.01), whereas mean iodine concentrations (47.7±10×100μg/cc) were not significantly different (P=0.095). An iodine concentration greater than 38×100μg/cc suggested AS with a sensitivity, specificity and accuracy of 91%, 85%, and 88%, respectively (Area under ROC curve 0.941). ConclusionsIodine measurements might contribute to the differentiation of AS from LN. Iodine concentrations similar to that of the main spleen may help to confirm the diagnosis of AS.