Alain Vlassenbroek

Phantom-less QCT BMD system as screening tool for osteoporosis without additional radiation

PURPOSE Phantom-less bone mineral density (PLBMD) systems are easily integrated into the CT workflow for non-dedicated Quantitative CT (QCT) BMD measurements in thoracic and abdominal scans. This in vivo retrospective study aims to determine accuracy and precision of the PLBMD option located on the Extended Brilliance Workspace (Philips Medical Systems, Cleveland, OH, US) from both cross-sectional and longitudinal image data. MATERIALS AND METHODS The cross-sectional comparison with phantom-based QCT BMD was performed for 82 patients (61 female, 21 male) with a mean age of (63.0±11.8 SD) years on 197 vertebrae. This was followed by an interobserver variability analysis on 71 vertebrae. The longitudinal PLBMD study was carried out on 45 vertebrae from 10 patients (5 female, 5 male) with a mean age of (64.4±11.5 SD) years. They were re-scanned with standardized scan and contrast-injection protocols within a mean and median of (33±41 SD) and 8 days, respectively. All CT scans were acquired on an Mx8000 Quad (Philips) at Florence-Nightingale Hospital, Kaiserswerth, Germany, in a spiral acquisition mode. RESULTS A negligible BMD bias of -0.9mg/cm(3) for the PLBMD option was observed with respect to phantom-based QCT BMD. Applying CT number matching of muscle and fat ROIs, the analysis of cross-sectional interobserver and of longitudinal variability yielded precision values of 3.1mg/cm(3) (CV%=4.0) and 4.2mg/cm(3) (CV%=5.3), respectively. CONCLUSION Although the precision is inferior to phantom-based BMD systems, PLBMD is a robust clinical utility for the detection of lowered BMD in a large patient population. This can be achieved without additional radiation exposure from non-contrasted CT scans, to perform an ancillary diagnosis of osteopenia or osteoporosis.

Prevalence and determinants of coronary and aortic calcifications assessed by chest CT in renal transplant recipients.

Background: Coronary artery calcifications independently predict cardiovascular events (CVE) in the general population. We assessed the prevalence and determinants of coronary (CAC) and thoracic aorta (AoC) calcifications in renal transplant recipients (RTR). Methods: Consecutive RTR living in Belgium, with an isolated kidney graft functioning for more than 1 year, were asked to participate. They underwent a 16-slice spiral computerized tomography in order to measure calcium mass. Demographic, clinical, biochemical and urinary parameters were recorded. Results: We included 281 patients. CAC and AoC were detected in 81 and 85%, with geometric means (SD) of 52.2 (4.9) and 99.3 (8.2) mg, respectively. By multiple linear regression, independent predictors of both types of calcifications included older age, longer time on dialysis, a history of CVE, of multiple transplantations and of smoking. Other determinants of CAC were male gender, current statin use and history of parathyroidectomy, and other determinants of AoC included higher pulse pressure, shorter time under mycophenolate mofetil and current use of anti-vitamin-K. Conclusion: The prevalence of both CAC and AoC is substantial in RTR. We delineate independent determinants either common to both CAC and AoC or specific to one, and known as classic or chronic kidney disease related risk factors.

Dual Layer CT

Dual-energy CT enables improvement of material and possibly tissue separation when compared to regular CT. Philips Healthcare has been successfully operating a dual-layer detector system in a modified Brilliance 64 CT scanner installed since 2005 in Hadassah University Medical Center, Israel. The dual-layer detector acquires single x-ray source CT data using two scintillation layers on top of each other with which two energy datasets are acquired simultaneously. The results of the two reconstructions are mapped into a plane created from the Hounsfield units (HU) of the upper-layer image versus the HU of the lower-layer image. We find that different materials end up in different definable regions in the HU-plane, so material separation can be performed. Application of a special correction on the reconstructed images achieves stability on the HU-plane despite beam-hardening effects on this image-based dual energy CT. We describe the material separation capabilities and algorithms with such a configuration and conclude that the combination of the dual-layer CT with the classification analysis in the HU-plane is a practical and robust method that may improve clinical applications, in particular those involving Iodine-Calcium.

Quantifying metal artefact reduction using virtual monochromatic dual-layer detector spectral CT imaging in unilateral and bilateral total hip prostheses

PURPOSE To quantify the impact of prosthesis material and design on the reduction of metal artefacts in total hip arthroplasties using virtual monochromatic dual-layer detector Spectral CT imaging. METHODS The water-filled total hip arthroplasty phantom was scanned on a novel 128-slice Philips IQon dual-layer detector Spectral CT scanner at 120-kVp and 140-kVp at a standard computed tomography dose index of 20.0mGy. Several unilateral and bilateral hip prostheses consisting of different metal alloys were inserted and combined which were surrounded by 18 hydroxyapatite calcium carbonate pellets representing bone. Images were reconstructed with iterative reconstruction and analysed at monochromatic energies ranging from 40 to 200keV. CT numbers in Hounsfield Units (HU), noise measured as the standard deviation in HU, signal-to-noise-ratios (SNRs) and contrast-to-noise-ratios (CNRs) were analysed within fixed regions-of-interests placed in and around the pellets. RESULTS In 70 and 74keV virtual monochromatic images the CT numbers of the pellets were similar to 120-kVp and 140-kVp polychromatic results, therefore serving as reference. A separation into three categories of metal artefacts was made (no, mild/moderate and severe) where pellets were categorized based on HU deviations. At high keV values overall image contrast was reduced. For mild/moderate artefacts, the highest average CNRs were attained with virtual monochromatic 130keV images, acquired at 140-kVp. Severe metal artefacts were not reduced. In 130keV images, only mild/moderate metal artefacts were significantly reduced compared to 70 and 74keV images. Deviations in CT numbers, noise, SNRs and CNRs due to metal artefacts were decreased with respectively 64%, 57%, 62% and 63% (p<0.001) compared to unaffected pellets. Optimal keVs, based on CNRs, for different unilateral and bilateral metal hip prostheses consisting of different metal alloys varied from 74 to 150keV. The Titanium alloy resulted in less severe artefacts and were reduced more effectively compared to the Cobalt alloy. CONCLUSIONS Virtual monochromatic dual-layer Spectral CT imaging results in a significant reduction of streak artefacts produced by beam-hardening in mild and moderate artefacts by improving CT number accuracy, SNRs and CNRs, while decreasing noise values in a total hip arthroplasty phantom. An optimal monochromatic energy of 130keV was found ranging from 74keV to 150keV for different unilateral and bilateral hip prostheses consisting of different metal alloys.

Quantitative right and left ventricular functional analysis during gated whole-chest MDCT: A feasibility study comparing automatic segmentation to semi-manual contouring

PURPOSE To evaluate the feasibility of an automatic, whole-heart segmentation algorithm for measuring global heart function from gated, whole-chest MDCT images. MATERIAL AND METHODS 15 patients with suspicion of PE underwent whole-chest contrast-enhanced MDCT with retrospective ECG synchronization. Two observers computed right and left ventricular functional indices using a semi-manual and an automatic whole-heart segmentation algorithm. The two techniques were compared using Bland-Altman analysis and paired Students t-test. Measurement reproducibility was calculated using intraclass correlation coefficient. RESULTS Ventricular analysis with automatic segmentation was successful in 13/15 (86%) and in 15/15 (100%) patients for the right ventricle and left ventricle, respectively. Reproducibility of measurements for both ventricles was perfect (ICC: 1.00) and very good for automatic and semi-manual measurements, respectively. Ventricular volumes and functional indices except right ventricular ejection fraction obtained from the automatic method were significantly higher for the RV compared to the semi-manual methods. CONCLUSIONS The automatic, whole-heart segmentation algorithm enabled highly reproducible global heart function to be rapidly obtained in patients undergoing gated whole-chest MDCT for assessment of acute chest pain with suspicion of pulmonary embolism.

Review of an initial experience with an experimental spectral photon-counting computed tomography system

Abstract Spectral photon-counting CT (SPCCT) is an emerging X-ray imaging technology that extends the scope of available diagnostic imaging tools. The main advantage of photon-counting CT technology is better sampling of the spectral information from the transmitted spectrum in order to benefit from additional physical information being produced during matter interaction, including photo-electric and Compton effects, and the K-edge effect. The K-edge, which is specific for a given element, is the increase in X-ray absorption of the element above the binding energy between its inner electronic shell and the nucleus. Hence, the spectral information contributes to better characterization of tissues and materials of interest, explaining the excitement surrounding this area of X-ray imaging. Other improvements of SPCCT compared with conventional CT, such as higher spatial resolution, lower radiation exposure and lower noise are also expected to provide benefits for diagnostic imaging. In this review, we describe multi-energy CT imaging, from dual energy to photon counting technology, and our initial experience results using a clinical-scale spectral photon counting CT (SPCCT) prototype system in vitro and in vivo. In addition, possible clinical applications are introduced.

Computed Tomography Imaging of a Hip Prosthesis Using Iterative Model-Based Reconstruction and Orthopaedic Metal Artefact Reduction: A Quantitative Analysis.

Objectives To quantify the combined use of iterative model-based reconstruction (IMR) and orthopaedic metal artefact reduction (O-MAR) in reducing metal artefacts and improving image quality in a total hip arthroplasty phantom. Methods Scans acquired at several dose levels and kVps were reconstructed with filtered back-projection (FBP), iterative reconstruction (iDose4) and IMR, with and without O-MAR. Computed tomography (CT) numbers, noise levels, signal-to-noise-ratios and contrast-to-noise-ratios were analysed. Results Iterative model-based reconstruction results in overall improved image quality compared to iDose4 and FBP (P < 0.001). Orthopaedic metal artefact reduction is most effective in reducing severe metal artefacts improving CT number accuracy by 50%, 60%, and 63% (P < 0.05) and reducing noise by 1%, 62%, and 85% (P < 0.001) whereas improving signal-to-noise-ratios by 27%, 47%, and 46% (P < 0.001) and contrast-to-noise-ratios by 16%, 25%, and 19% (P < 0.001) with FBP, iDose4, and IMR, respectively. Conclusions The combined use of IMR and O-MAR strongly improves overall image quality and strongly reduces metal artefacts in the CT imaging of a total hip arthroplasty phantom.

Evaluation of a method for improving the detection of hepatocellular carcinoma

ObjectiveTo improve the detection of liver lesions in patients with hepatocellular carcinoma (HCC) via an iodine contrast enhancement tool.MethodsThirty-two patients with clinically proven HCCs underwent imaging with a three-phase protocol on a 256-slice MDCT. The contrast enhancement in the reconstructed slices was improved via a post-processing tool. Mean image noise was measured in four different regions: liver lesion, healthy liver, subcutaneous fat and bone. For each image set the image noise and contrast-to-noise ratio (CNR) were assessed. For subjective image assessment, four experienced radiologists evaluated the diagnostic quality.ResultsWhile employing the post-processing algorithm, CNR between the liver lesion and healthy liver tissue improves significantly by a factor of 1.78 (CNRwithout vC = 2.30 ± 1.92/CNRwith vC = 4.11 ± 3.05) (P* = 0.01). All results could be achieved without a strengthening of artefacts; mean HU values of subcutaneous fat and bone did not significantly change. Subjective image analysis illustrated a significant improvement when employing post-processing for clinically relevant criteria such as diagnostic confidence.ConclusionWith post-processing we see a significantly improved detection of arterial uptake in hepatic lesions compared with non-processed data. The improvement in CNR was confirmed by subjective image assessment for small lesions and for lesions with limited uptake.Key Points• Enhancement with iodine-based contrast agents is an essential part of CT.• A new post-processing tool significantly improves the diagnostics of hepatocellular carcinoma.• It also improves detection of small lesions with limited iodine uptake.

The Use of Isotropic Imaging and Computed Tomography Reconstructions

With modern multislice computed tomography (CT) scanners, which combine ultrafast acquisition with high spatial resolution, isotropic imaging of the chest can be performed during a short breathold. Adapting the slice thickness, the reconstruction increment, filter, and matrix enable an optimal isotropic visualization of each organ. The very large high-quality 3-dimensional datasets that are then generated require the use of various postprocessing techniques for an improved diagnostic. These tools have become a vital component for the visualization and the interpretation of the large volumetric data and to present the results to the clinicians. New dynamic modes of visualization have recently been introduced to reduce the storage capacity and to improve the workflow and the image quality for any organ interpreted by the user. Despite this gain in information obtained with modern multislice CT scanners, the patient’s dose has not been increased. On the contrary, it has been reduced thanks to the use of automatic dose modulation which adapts the X-ray tube output to maintain adequate dose and image quality when moving to different body regions.

Could new reconstruction CT techniques challenge MRI for the detection of brain metastases in the context of initial lung cancer staging

AbstractObjectivesTo evaluate the diagnostic performance of brain CT images reconstructed with a model-based iterative algorithm performed at usual and reduced dose.Methods115 patients with histologically proven lung cancer were prospectively included over 15 months. Patients underwent two CT acquisitions at the initial staging, performed on a 256-slice MDCT, at standard (CTDIvol: 41.4 mGy) and half dose (CTDIvol: 20.7 mGy). Both image datasets were reconstructed with filtered back projection (FBP) and iterative model-based reconstruction (IMR) algorithms. Brain MRI was considered as the reference. Two blinded independent readers analysed the images.ResultsNinety-three patients underwent all examinations. At the standard dose, eight patients presented 17 and 15 lesions on IMR and FBP CT images, respectively. At half-dose, seven patients presented 15 and 13 lesions on IMR and FBP CT images, respectively. The test could not highlight any significant difference between the standard dose IMR and the half-dose FBP techniques (p-value = 0.12). MRI showed 46 metastases on 11 patients. Specificity, negative and positive predictive values were calculated (98.9–100 %, 93.6–94.6 %, 75–100 %, respectively, for all CT techniques).ConclusionNo significant difference could be demonstrated between the two CT reconstruction techniques.Key points• No significant difference between IMR100 and FBP50 was shown. • Compared to FBP, IMR increased the image quality without diagnostic impairment. • A 50 % dose reduction combined with IMR reconstructions could be achieved. • Brain MRI remains the best tool in lung cancer staging.