Evaluation of acoustic noise in magnetic resonance imaging

Magnetic resonance imaging (MRI) is a technique in which strong static and dynamic magnetic fields are used to create virtual slices of the human body. The process of MR imaging is associated with several health and safety issues which may negatively affect patient and radiological health workers. Potentially hazardous are biological effects of both the static and dynamic magnetic fields, the torques of the magnetic fields acting on ferromagnetic objects, thermal effects, and the negative effects of high acoustic sound pressures. The subject of this dissertation is the evaluation and modification of acoustic noise generated during MRI

Interventional MR imaging at 1.5 T: quantification of sound exposure

Sound pressure levels (SPLs) during interventional magnetic resonance (MR) imaging may create an occupational hazard for the interventional radiologist (ie, the potential risk of hearing impairment). Therefore, A-weighted and linear continuous-equivalent SPLs were measured at the entrance of a 1.5-T MR imager during cardiovascular and real-time pulse sequences. The SPLs ranged from 81.5 to 99.3 dB (A-weighted scale), and frequencies were from 1 to 3 kHz. SPLs for the interventional radiologist exceeded a safe SPL of 80 dB (A-weighted scale) for all sequences; therefore, hearing protection is recommended

Evaluation of a Semi-automatic Right Ventricle Segmentation Method on Short-Axis MR Images

The purpose of this study was to evaluate a semi-automatic right ventricle segmentation method on short-axis cardiac cine MR images which segment all right ventricle contours in a cardiac phase using one seed contour. Twenty-eight consecutive short-axis, four-chamber, and tricuspid valve view cardiac cine MRI examinations of healthy volunteers were used. Two independent observers performed the manual and automatic segmentations of the right ventricles. Analyses were based on the ventricular volume and ejection fraction of the right heart chamber. Reproducibility of the manual and semi-automatic segmentations was assessed using intra- and inter-observer variability. Validity of the semi-automatic segmentations was analyzed with reference to the manual segmentations. The inter- and intra-observer variability of manual segmentations were between 0.8 and 3.2%. The semi-automatic segmentations were highly correlated with the manual segmentations (R2 0.79–0.98), with median difference of 0.9–4.8% and of 3.3% for volume and ejection fraction parameters, respectively. In comparison to the manual segmentation, the semi-automatic segmentation produced contours with median dice metrics of 0.95 and 0.87 and median Hausdorff distance of 5.05 and 7.35 mm for contours at end-diastolic and end-systolic phases, respectively. The inter- and intra-observer variability of the semi-automatic segmentations were lower than observed in the manual segmentations. Both manual and semi-automatic segmentations performed better at the end-diastolic phase than at the end-systolic phase. The investigated semi-automatic segmentation method managed to produce a valid and reproducible alternative to manual right ventricle segmentation

Continuous roadmapping in liver TACE procedures using 2D–3D catheter-based registration

PURPOSE: Fusion of pre/perioperative images and intra-operative images may add relevant information during image-guided procedures. In abdominal procedures, respiratory motion changes the position of organs, and thus accurate image guidance requires a continuous update of the spatial alignment of the (pre/perioperative) information with the organ position during the intervention. METHODS: In this paper, we propose a method to register in real time perioperative 3D rotational angiography images (3DRA) to intra-operative single-plane 2D fluoroscopic images for improved guidance in TACE interventions. The method uses the shape of 3D vessels extracted from the 3DRA and the 2D catheter shape extracted from fluoroscopy. First, the appropriate 3D vessel is selected from the complete vascular tree using a shape similarity metric. Subsequently, the catheter is registered to this vessel, and the 3DRA is visualized based on the registration results. The method is evaluated on simulated data and clinical data. RESULTS: The first selected vessel, ranked with the shape similarity metric, is used more than 39 % in the final registration and the second more than 21 %. The median of the closest corresponding points distance between 2D angiography vessels and projected 3D vessels is 4.7–5.4 mm when using the brute force optimizer and 5.2–6.6 mm when using the Powell optimizer. CONCLUSION: We present a catheter-based registration method to continuously fuse a 3DRA roadmap arterial tree onto 2D fluoroscopic images with an efficient shape similarity

Non-rigid registration of liver ct images for ct-guided ablation of liver tumors

CT-guided percutaneous ablation for liver cancer treatment is a relevant technique for patients not eligible for surgery and with tumors that are inconspicuous on US imaging. The lack of real-time imaging and the use of a limited amount of CT contrast agent make targeting the tumor with the needle challenging. In this study, we evaluate a registration framework that allows the integration of diagnostic pre-operative contrast enhanced CT images and intra-operative non-contrast enhanced CT images to improve image guidance in the intervention. The liver and tumor are segmented in the pre-operative contrast enhanced CT images. Next, the contrast enhanced image is registered to the intra-operative CT images in a two-stage approach. First, the contrast-enhanced diagnostic image is non-rigidly registered to a non-contrast enhanced image that is conventionally acquired at the start of the intervention. In case the initial registration is not sufficiently accurate, a refinement step is applied using non-rigid registration method with a local rigidity term. In the second stage, the intra-operative CT-images that are used to check the needle position, which often consist of only a few slices, are registered rigidly to the intra-operative image that was acquired at the start of the intervention. Subsequently, the diagnostic image is registered to the current intra-operative image, using both transformations, this allows the visualization of the tumor region extracted from pre-operative data in the intra-operative CT images containing needle. The method is evaluated on imaging data of 19 patients at the Erasmus MC. Quantitative evaluation is performed using the Dice metric, mean surface distance of the liver border and corresponding landmarks in the diagnostic and the intra-operative images. The registration of the diagnostic CT image to the initial intra-operative CT image did not require a refinement step in 13 cases. For those cases, the resulting registration had a Dice coefficient for the livers of 91.4%, a mean surface distance of 4.4 mm and a mean distance between corresponding landmarks of 4.7 mm. For the three cases with a refinement step, the registration result significantly improved (p<0.05) compared to the result of the initial non rigid registration method (DICE of 90.3% vs 71.3% and mean surface distance of 5.1 mm vs 11.3 mm and mean distanc

Diagnostic performance of stress myocardial perfusion imaging for coronary artery disease: A systematic review and meta-analysis

Objectives To determine and compare the diagnostic performance of stress myocardial perfusion imaging (MPI) for the diagnosis of obstructive coronary artery disease (CAD), using conventional coronary angiography (CCA) as the reference standard. Methods We searched Medline and Embase for literature that evaluated stress MPI for the diagnosis of obstructive CAD using magnetic resonance imaging (MRI), contrastenhanced echocardiography (ECHO), single-photon emission computed tomography (SPECT) and positron emission tomography (PET). Results All pooled analyses were based on random effects models. Articles on MRI yielded a total of 2,970 patients from 28 studies, articles on ECHO yielded a sample size of 795 from 10 studies, articles on SPECT yielded 1,323 from 13 studies. For CAD defined as either at least 50 %, at least 70 % or at least 75 % lumen diameter reduction on CCA, the natural logarithms of the diagnostic odds ratio (lnDOR) for MRI (3.63; 95 % CI 3.26-4.00) was significantly higher compared to that of SPECT (2.76; 95 % CI 2.28-3.25; P=0.006) and that of ECHO (2.83; 95 % CI 2.29-3.37; P=0.02). There was no significant difference between the lnDOR of SPECT and ECHO (P=0.52). Conclusion Our results suggest that MRI is superior for the diagnosis of obstructive CAD compared with ECHO and SPECT. ECHO and SPECT demonstrated similar diagnostic performance. Key Points ̇ MRI can assess myocardial perfusion. ̇ MR perfusion diagnoses coronary artery disease better than echocardiography or SPECT. ̇ Echocardiography and SPECT have similar diagnostic performance. ̇ MRI can save coronary artery disease patients from more invasive tests. ̇ MRI and SPECT show evidence of publication bias, implying possible overestimation

Antegrade balloon dilatation as a treatment option for posttransplant ureteral strictures: Case series of 50 patients

Objectives: The aim of this study was to investigate the effects of antegrade balloon dilatation on ureteral strictures that developed after kidney transplant. Materials and Methods: The hospital databases of the Erasmus Medical Center (Rotterdam, The Netherlands) and the Academic Medical Center (Amsterdam, The Netherlands) were retrospectively screened for patients who underwent balloon dilatation after kidney transplant. Balloon dilatation was technically successful whenever it was able to pass the strictured segment with the guidewire followed by balloon inflation; the procedure was clinically successful if no further interventions (for example, surgical revision of the ureteroneocystostomy or prolonged double J placement) were necessary. Results: Fifty patients (2.4%) of 2075 kidney transplant recipients underwent antegrade balloon dilatation because of urinary outflow obstruction. Median time between transplant and balloon dilatation was 3 months (range, 0-139 mo). In 43 patients (86%), balloon dilatation was technically successful. In the remaining 7 patients (14%), it was impossible to pass the strictured segment with the guidewire. In 20 of 43 patients (47%) having a technically successful procedure, the procedure was also clinically successful, with median follow-up after balloon dilatation of 35.5 months (range, 0-102 mo). We did not identify any patient o

Percutaneous transhepatic biliary drainage in patients with postsurgical bile leakage and nondilated intrahepatic bile ducts

Objective and Background: Bile leakage is a serious postoperative complication and percutaneous transhepatic biliary drainage (PTBD) may be an option when endoscopic treatment is not feasible. In this retrospective study, we established technical and clinical success rates as well as the complication rates of PTBD in a large group of patients with postoperative bile leakage. Methods: Data on all patients with nondilated intrahepatic bile ducts who underwent a PTBD procedure for the treatment of bile leakage between January 2000 and August 2012 were retrospectively assessed. Data included type of surgery, site of bile leak, previous attempts of bile leak repair, interval between surgery and PTBD placement. Outcome measures were the technical and clinical success rates, the procedure-related complications, and mortality rate. Results: A total of 63 patients were identified; PTBD placement was technically successful in 90.5% (57/63) after one to three attempts. The clinical success rate was 69.8% (44/63). Four major complications were documented (4/63; 6.3%): liver laceration, pneumothorax, pleural empyema, and prolonged hemobilia. One minor complication involved pain. Conclusion