Metal artefact reduction in CT imaging of hip prostheses­an evaluation of commercial techniques provided by four vendors.

OBJECTIVE: The aim of this study was to evaluate commercial metal artefact reduction (MAR) techniques in X-ray CT imaging of hip prostheses. METHODS: Monoenergetic reconstructions of dual-energy CT (DECT) data and several different MAR algorithms, combined with single-energy CT or DECT, were evaluated by imaging a bilateral hip prosthesis phantom. The MAR images were compared with uncorrected images based on CT number accuracy and noise in different regions of interest. RESULTS: The three MAR algorithms studied implied a general noise reduction (up to 67%, 74% and 77%) and an improvement in CT number accuracy, both in regions close to the prostheses and between the two prostheses. The application of monoenergetic reconstruction, without any MAR algorithm, did not decrease the noise in the regions close to the prostheses to the same extent as did the MAR algorithms and even increased the noise in the region between the prostheses. CONCLUSION: The MAR algorithms evaluated generally improved CT number accuracy and substantially reduced the noise in the hip prostheses phantom images, both close to the prostheses and between the two prostheses. The study showed that the monoenergetic reconstructions evaluated did not sufficiently reduce the severe metal artefact caused by large orthopaedic implants. ADVANCES IN KNOWLEDGE: This study evaluates several commercially available MAR techniques in CT imaging of large orthopaedic implants.

Estimation of ejection fraction and stroke volume using single- and biplane magnetic resonance imaging of the left cardiac ventricle.

BACKGROUND: In cardiac magnetic resonance imaging (MRI), left ventricular stroke volume (SV) and ejection fractions (EF) are occasionally calculated using single-plane and biplane ellipsoid models. In previous studies, the calculated SV and EF using single- and biplane ellipsoid models have been compared to reference values calculated from short-axis (SA) images. In these studies, however, it has been emphasized that through-plane motion of the basal SA images represents an important source of error, which may result in incorrect reference values. PURPOSE: To compare the calculated SV and EF using single-plane and biplane ellipsoid models with SV and EF calculated from SA images in which compensation was made for through-plane motion. MATERIAL AND METHODS: A group of 20 patients who underwent MRI examination were included in the study. SV and EF were calculated using the stack of SA images (which had been compensated for through-plane motion) and compared to the SV and EF calculated according to the single- and biplane ellipsoid models. RESULTS: The mean difference between the single-plane model and the reference was -0.3+/-6.5 for EF and 7.2+/-17.1 ml for SV. Corresponding comparison between the biplane method and the reference resulted in a mean difference of 0.3+/-6.1 for EF and 11.8+/-14.9 ml for SV. CONCLUSION: The results from this study show that left ventricular EF can be adequately estimated using the single- and biplane ellipsoid models, while SV tends to be overestimated using both geometrical models.

Outer contour and radial changes of the cardiac left ventricle: a magnetic resonance imaging study.

Earlier studies have shown a +/-5% end-systolic decrease in the volume encompassed by the pericardial sack, manifesting as a radial diminution of the pericardial/epicardial contour of the left ventricle (LV). The aim of this study was to measure this radial displacement at different segmental levels of the LV and try to find out were it is as greatest and to calculate regional myocardial volume changes as a reference in healthy subjects. Eleven healthy subjects were examined by magnetic resonance imaging. Images were acquired using an ECG-triggered balanced fast field echo pulse sequence. The epicardial borders of the LV wall were delineated in end-diastole (ED) and end-systole (ES). Regional changes of the LV wall were analysed at three different levels (base, mid and apex) by dividing the myocardium into segments. The volumes obtained as the differences between the outer volume of the left ventricle at ED and ES at different slice levels were found to be greatest at the base of the heart and lowest at apex. The relative inward motion, that is the motion in short-axis direction of the epicardial border of the myocardium from ED to ES towards the centre of the LV, was greatest at the base and lowest at the mid level, something that has to be taken into account when measuring the LV during clinical exams. There was a significant difference in the relative inward motion between the segments at apex (p < 0.0001), mid (p = 0.036) and at base level (p < 0.0001).

Correction for acceleration-induced displacement artifacts in phase contrast imaging.

The acceleration-induced displacement artifact impairs the accuracy of MR velocity measurements. This study proposes a post processing method for correction of this artifact. Velocity measurements were performed in a flow phantom containing a constriction. Velocity curves were obtained from streamlines parallel to the frequency, phase, and slice directions, respectively. The acceleration-induced displacement artifact was most prominent when the frequency encoding direction was aligned with the flow direction. After correction, velocity assignment improved and a more accurate description of the flow was obtained. In vivo measurements were performed in the aorta in a patient with a repaired aortic coarctation. The correction method was applied to velocity data along a streamline parallel to the frequency encoding direction. The result after correction was a new location of the peak velocity and improved estimates of the velocity gradients.

Intraperitoneal interferon in the management of malignant ascites.

BACKGROUND: Ascites secondary to malignancy is a major cause of recurring morbidity in patients with ovarian cancer. In patients previously treated with cisplatin, other chemotherapeutic agents are not likely to be effective in relieving symptoms. METHODS: A pilot group of ten patients was treated with intraperitoneal alpha-2B-interferon (alpha-2B-IFN) in an effort to provide symptomatic relief of their ascites. All patients had advanced epithelial ovarian cancer at the time of therapy and were receiving treatment for palliation only. Symptoms included abdominal distention (100% of patients), nausea and vomiting in the absence of mechanical intestinal obstruction (60%), and dyspepsia (40%). RESULTS: At a dose of 10 M units/m2 given intraperitoneally every 2 weeks for one to four treatments, the toxicity was low, but the benefits were minimal. Five (50%) patients reported symptomatic improvement of 2-7 weeks' duration. The most common side effects included fever (temperature of more than 38.5 degrees C) and abdominal pain. CONCLUSIONS: At the dose of 10 M units/m2 of intraperitoneal alpha-2B-IFN, this regimen did not appear to produce clinically significant palliation of the ascites in most patients.