Wouter J. H. Veldkamp

Development and validation of segmentation and interpolation techniques in sinograms for metal artifact suppression in CT.

PURPOSE Metal prostheses cause artifacts in computed tomography (CT) images. The purpose of this work was to design an efficient and accurate metal segmentation in raw data to achieve artifact suppression and to improve CT image quality for patients with metal hip or shoulder prostheses. METHODS The artifact suppression technique incorporates two steps: metal object segmentation in raw data and replacement of the segmented region by new values using an interpolation scheme, followed by addition of the scaled metal signal intensity. Segmentation of metal is performed directly in sinograms, making it efficient and different from current methods that perform segmentation in reconstructed images in combination with Radon transformations. Metal signal segmentation is achieved by using a Markov random field model (MRF). Three interpolation methods are applied and investigated. To provide a proof of concept, CT data of five patients with metal implants were included in the study, as well as CT data of a PMMA phantom with Teflon, PVC, and titanium inserts. Accuracy was determined quantitatively by comparing mean Hounsfield (HU) values and standard deviation (SD) as a measure of distortion in phantom images with titanium (original and suppressed) and without titanium insert. Qualitative improvement was assessed by comparing uncorrected clinical images with artifact suppressed images. RESULTS Artifacts in CT data of a phantom and five patients were automatically suppressed. The general visibility of structures clearly improved. In phantom images, the technique showed reduced SD close to the SD for the case where titanium was not inserted, indicating improved image quality. HU values in corrected images were different from expected values for all interpolation methods. Subtle differences between interpolation methods were found. CONCLUSIONS The new artifact suppression design is efficient, for instance, in terms of preserving spatial resolution, as it is applied directly to original raw data. It successfully reduced artifacts in CT images of five patients and in phantom images. Sophisticated interpolation methods are needed to obtain reliable HU values close to the prosthesis.

Automated analysis of neuronal morphology, synapse number and synaptic recruitment

The shape, structure and connectivity of nerve cells are important aspects of neuronal function. Genetic and epigenetic factors that alter neuronal morphology or synaptic localization of pre- and post-synaptic proteins contribute significantly to neuronal output and may underlie clinical states. To assess the impact of individual genes and disease-causing mutations on neuronal morphology, reliable methods are needed. Unfortunately, manual analysis of immuno-fluorescence images of neurons to quantify neuronal shape and synapse number, size and distribution is labor-intensive, time-consuming and subject to human bias and error. We have developed an automated image analysis routine using steerable filters and deconvolutions to automatically analyze dendrite and synapse characteristics in immuno-fluorescence images. Our approach reports dendrite morphology, synapse size and number but also synaptic vesicle density and synaptic accumulation of proteins as a function of distance from the soma as consistent as expert observers while reducing analysis time considerably. In addition, the routine can be used to detect and quantify a wide range of neuronal organelles and is capable of batch analysis of a large number of images enabling high-throughput analysis.

Dose and perceived image quality in chest radiography.

Chest radiography is the most commonly performed diagnostic X-ray examination. The radiation dose to the patient for this examination is relatively low but because of its frequent use, the contribution to the collective dose is considerable. Consequently, optimization of dose and image quality offers a challenging area of research. In this article studies on dose reduction, different detector technologies, optimization of image acquisition and new technical developments in image acquisition and post processing will be reviewed. Studies indicate that dose reduction in PA chest images to at least 50% of commonly applied dose levels does not affect diagnosis in the lung fields; however, dose reduction in the mediastinum, upper abdomen and retrocardiac areas appears to directly deteriorate diagnosis. In addition to patient dose, also the design of the various digital detectors seems to have an effect on image quality. With respect to image acquisition, studies showed that using a lower tube voltage improves visibility of anatomical structures and lesions in digital chest radiographs but also increases the disturbing appearance of ribs. New techniques that are currently being evaluated are dual energy, tomosynthesis, temporal subtraction and rib suppression. These technologies may improve diagnostic chest X-ray further. They may for example reduce the negative influence of over projection of ribs, referred to as anatomic noise. In chest X-ray this type of noise may be the dominating factor in the detection of nodules. In conclusion, optimization and new developments will enlarge the value of chest X-ray as a mainstay in the diagnosis of chest diseases.

Metal artifact reduction for CT: development, implementation, and clinical comparison of a generic and a scanner-specific technique.

PURPOSE To develop, implement, and compare two metal artifact reduction methods for CT. METHODS Two methods for metal artifact reduction were developed. The first is based on applying corrections in a Radon transformation of the CT images. The second method is based on a forward projection of the CT images and applying corrections in the scanners original raw data. The first method is generic since it does not depend on the scanner specifications. For the second method, detailed information on the design of the CT scanner and the raw data of the study is required. Clinical implementation and evaluation were performed using pre- and post-operative CT scans of four patients with shoulder prosthesis. For comparison of these methods, the authors developed a quantitative technique that compares improvement in image quality for the two metal artifact reduction techniques with the image quality of the uncorrected images. RESULTS Metal artifact reduction using either of the two methods yields a decrease of noise and artifacts in CT scans of patients with shoulder prostheses. Artifacts that appeared as bright and dark streaks were reduced or eliminated and as a result image quality improved. Quantitative assessment of clinical images showed improved image quality for both techniques of metal artifact reduction, but the method based on correction in original raw data performed better in all comparisons. CONCLUSION Both methods are effective for metal artifact reduction, but better performance was observed for the method that is based on correcting the original raw data. The used evaluation technique provides an objective way of evaluating the metal artifacts in clinical CT images.

Cochlear coordinates in regard to cochlear implantation: a clinically individually applicable 3 dimensional CT-based method.

Setting: Cochlear implant (CI)/tertiary referral center. Subjects: Twenty-five patients implanted with an Advanced Bionics HiRes90K HiFocus1J CI. Study Design/Main Outcome Measures: A 3-dimensional cylindrical coordinate system is introduced using the basal turn of the cochlea as the x and y planes and the center of the modiolus as the z axis. The 0-degree angle is defined by the most lateral point of the horizontal semicircular canal. It is applied to both preoperative and postoperative computed tomographies in 25 patients. The angular position of the round window is examined. Interobserver reproducibility is tested by localization of all electrode contacts within the coordinate system. To observe realignment over time, electrode coordinates in postoperative images were projected on preoperative images. Additionally, comparison to existing imaging-related coordinate systems was made. Results: The angular position of the center of the round window is 34.6 ± 0.4 degrees (standard deviation) with an intraclass coefficient of 1.00. The intraclass coefficient for interobserver reproducibility of the 16 electrode contacts ranged from 0.74 to 1 for the rotational angle (&phgr;) and 0.77 to 1 for the distance to the modiolus (&rgr;). In 21 of 25 patients, a perfect match or minimal displacement of up to 3 electrode contacts was seen. Comparison to existing systems showed good correlation. Conclusion: A 3-dimensional cochlear coordinate system easily applicable in clinical patients is described, which fulfills the requirements set by an international consensus.

Evaluation of 4 multisection CT systems in postoperative imaging of a cochlear implant: a human cadaver and phantom study.

BACKGROUND AND PURPOSE: Postoperative imaging of cochlear implants (CIs) needs to provide detailed information on localization of the electrode array. We evaluated visualization of a HiFocus1J array and accuracy of measurements of electrode positions for acquisitions with 64-section CT scanners of 4 major CT systems (Toshiba Aquilion-64, Philips Brilliance-64, GE LightSpeed-64, and Siemens Sensation-64). MATERIALS AND METHODS: An implanted human cadaver temporal bone, a polymethylmethacrylate (PMMA) phantom containing a CI, and a point spread function (PSF) phantom were scanned. In the human cadaver temporal bone, the visibility of cochlear structures and electrode array were assessed by using a visual analog scale (VAS). Statistical analysis was performed with a paired 2-tailed Student t test with significant level set to .008 after Bonferroni correction. Distinction of individual electrode contacts was quantitatively evaluated. Quantitative assessment of electrode contact positions was achieved with the PMMA phantom by measurement of the displacement. In addition, PSF was measured to evaluate spatial resolution performance of the CT scanners. RESULTS: VAS scores were significantly lower for Brilliance-64 and LightSpeed-64 compared with Aquilion-64 and Sensation-64. Displacement of electrode contacts ranged from 0.05 to 0.14 mm on Aquilion-64, 0.07 to 0.16 mm on Brilliance-64, 0.07 to 0.61 mm on LightSpeed-64, and 0.03 to 0.13 mm on Sensation-64. PSF measurements show an in-plane and longitudinal resolution varying from 0.48 to 0.68 mm and 0.70 to 0.98 mm, respectively, over the 4 scanners. CONCLUSION: According to PSF results, electrode contacts of the studied CI can be visualized separately on all of the studied scanners unless curvature causes intercontact spacing narrowing. Assessment of visibility of CI and electrode contact positions, however, varies between scanners.

A Technique for Simulating the Effect of Dose Reduction on Image Quality in Digital Chest Radiography

Purpose: The purpose of this study is to provide a pragmatic tool for studying the relationship between dose and image quality in clinical chest images. To achieve this, we developed a technique for simulating the effect of dose reduction on image quality of digital chest images. Materials and Methods: The technique was developed for a digital charge-coupled-device (CCD) chest unit with slot-scan acquisition. Raw pixel values were scaled to a lower dose level, and a random number representing noise to each specific pixel value was added. After adding noise, raw images were post processed in the standard way. Validation was performed by comparing pixel standard deviation, as a measure of noise, in simulated images with images acquired at actual lower doses. To achieve this, a uniform test object and an anthropomorphic phantom were used. Additionally, noise power spectra of simulated and actual images were compared. Also, detectability of simulated lesions was investigated using a model observer. Results: The mean difference in noise values between simulated and real lower-dose phantom images was smaller than 5% for relevant clinical settings. Noise power spectra appeared to be comparable on average but simulated images showed slightly higher noise levels for higher spatial frequencies and slightly lower noise levels for lower spatial frequencies. Comparable detection performance was shown in simulated and actual images with slightly worse detectability for simulated lower dose images. Conclusion: We have developed and validated a method for simulating dose reduction. Our method seems an acceptable pragmatic tool for studying the relationship between dose and image quality.

Adaptive Iterative Dose Reduction 3D Versus Filtered Back Projection in CT: Evaluation of Image Quality

OBJECTIVE The purpose of this study was to evaluate image quality with filtered back projection (FBP) and adaptive iterative dose reduction 3D (AIDR 3D). MATERIALS AND METHODS Phantom acquisitions were performed at six dose levels to assess spatial resolution, noise, and low-contrast detectability (LCD). Spatial resolution was assessed with the modulation transfer function at high and low contrast levels. Noise power spectrum and SD of attenuation were assessed. LCD was calculated with a mathematic model observer applied to phantom CT images. The subjective image quality of clinical CT scans was assessed by five radiologists. RESULTS Compared with FBP, AIDR 3D resulted in substantial noise reduction at all frequencies with a similar shape of the noise power spectrum. Spatial resolution was similar for AIDR 3D and FBP. LCD improved with AIDR 3D, which was associated with a potential average dose reduction of 36% (range, 9-86%). The observer study showed that overall image quality improved and artifacts decreased with AIDR 3D. CONCLUSION AIDR 3D performs better than FBP with regard to noise and LCD, resulting in better image quality, and performs similarly with respect to spatial resolution. The evaluation of image quality of clinical CT scans was consistent with the objective assessment of image quality with a phantom. The amount of dose reduction should be investigated for each clinical indication in studies with larger numbers of patients.

Comparison of a flexible versus a rigid breast compression paddle: pain experience, projected breast area, radiation dose and technical image quality

AbstractPurposeTo compare pain, projected breast area, radiation dose and image quality between flexible (FP) and rigid (RP) breast compression paddles.MethodsThe study was conducted in a Dutch mammographic screening unit (288 women). To compare both paddles one additional image with RP was made, consisting of either a mediolateral-oblique (MLO) or craniocaudal-view (CC). Pain experience was scored using the Numeric Rating Scale (NRS). Projected breast area was estimated using computer software. Radiation dose was estimated using the model by Dance. Image quality was reviewed by three radiologists and three radiographers.ResultsThere was no difference in pain experience between both paddles (mean difference NRS: 0.08 ± 0.08, p = 0.32). Mean radiation dose was 4.5 % lower with FP (0.09 ± 0.01 p = 0.00). On MLO-images, the projected breast area was 0.79 % larger with FP. Paired evaluation of image quality indicated that FP removed fibroglandular tissue from the image area and reduced contrast in the clinically relevant retroglandular area at chest wall side.ConclusionsAlthough FP performed slightly better in the projected breast area, it moved breast tissue from the image area at chest wall side. RP showed better contrast, especially in the retroglandular area. We therefore recommend the use of RP for standard MLO and CC views.Key points• Pain experience showed no difference between flexible and rigid breast compression paddles. • Flexible paddles do not depict clinically relevant retroglandular areas as well. • Flexible paddles move breast tissue from image area at the chest wall side. • Rigid paddles depict more breast tissue and shows better contrast. • Rigid breast compression paddles are recommended for standard mediolateral-oblique and craniocaudal views.

Automated Cardiac Phase Selection with 64-MDCT Coronary Angiography

OBJECTIVE The aim of this study was to assess three different phase-selection methods for obtaining optimal CT coronary artery image quality. MATERIALS AND METHODS ECG-gated CT coronary angiography scans of 40 patients (23 men, 17 women; mean age, 56 years) were retrieved. The patient group was composed of 20 consecutive patients with heart rates < or = 65 beats per minute (bpm) and 20 consecutive patients with heart rates > 65 bpm. Three phase-selection methods were evaluated: fixed phase selection, manual phase selection, and automated phase selection. Two scoring systems were used to evaluate diagnostic quality: scoring of axial images on a 5-point scale and scoring of multiplanar reconstructions (MPRs) on a forced-choice 3-point preference scale. Differences were tested by Wilcoxons signed rank test for the entire patient group and the two subgroups including patients with heart rates < or = 65 bpm and those with heart rates > 65 bpm. RESULTS Axial image evaluation of the entire patient group showed statistically significant superior image quality for the manual phase-selection method compared with the predefined phase-selection method and no statistically significant differences were found for the other comparisons. Analysis at heart rates < or = 65 bpm showed no significant differences between phase-selection methods. Analysis at heart rates > 65 bpm showed the best results for the automated phase-selection method, and image quality was significantly better for the automated and manual phase-selection methods than for the predefined phase-selection method. CONCLUSION The automated phase-selection method accurately detects the optimal diagnostic phase for CT coronary artery evaluation and has the potential to reduce operator time needed for image reconstruction.