M. Oudkerk

Magnetic resonance imaging of the coronary arteries: clinical results from three dimensional evaluation of a respiratory gated technique

BACKGROUND Magnetic resonance coronary angiography is challenging because of the motion of the vessels during cardiac contraction and respiration. Additional challenges are the small calibre of the arteries and their complex three dimensional course. Respiratory gating, turboflash acquisition, and volume rendering techniques may meet the necessary requirements for appropriate visualisation. OBJECTIVE To determine the diagnostic accuracy of respiratory gated magnetic resonance imaging (MRI) for the detection of significant coronary artery stenoses evaluated with three dimensional postprocessing software. METHODS 32 patients referred for elective coronary angiography were studied with a retrospective respiratory gated three dimensional gradient echo MRI technique. Resolution was 1.9 × 1.25 × 2 mm. After manual segmentation three dimensional evaluation was performed with a volume rendering technique. RESULTS Overall 74% (range 50% to 90%) of the proximal and mid coronary artery segments were visualised with an image quality suitable for further analysis. Sensitivity and specificity for the detection of significant stenoses were 50% and 91%, respectively. CONCLUSIONS Volume rendering of respiratory gated MRI techniques allows adequate visualisation of the coronary arteries in patients with a regular breathing pattern. Significant lesions in the major coronary artery branches can be identified with a moderate sensitivity and a high specificity.

Informatics in Radiology: Postprocessing Pitfalls in Using CT for Automatic and Semiautomatic Determination of Global Left Ventricular Function

Recent advances in technical capabilities of computed tomographic (CT) scanners, including an increasing number of detector rows, improved spatial and temporal resolution, and the development of retrospective gating, have allowed the acquisition of four-dimensional (4D) datasets of the beating heart. As a result, the heart can be visualized in different phases and CT datasets can be used to assess cardiac function. Many software packages currently exist that allow automatic or semiautomatic evaluation of left ventricular function on the basis of 4D CT datasets. The level of automation varies from extensive, completely manual segmentation by the user to fully automatic evaluation of left ventricular function without any user interaction. Although the reproducibility of functional parameter assessment is reported to be high and intersoftware variability low for larger groups of patients, significant differences can exist among measurements obtained with different software tools from the same dataset. Thus, careful review of automatically or semiautomatically obtained results is required.

Magnetic resonance imaging of the coronary arteries : anatomy of the coronary arteries and veins in three-dimensional imaging

Magnetic resonance imaging of coronary arteries will visualize, besides the arteries, the myocardium, blood in the cavities and cardiac veins. This will hamper the application of projectional visualization techniques such as those used in conventional coronary angiography. Volume rendering, a different visualization technique, can be used to create a three-dimensional impression of a magnetic resonance data set on a two-dimensional surface. In this article, we will review the volume-rendering technique and anatomy of the coronary arteries and veins in the obtained images. Also we will discuss the relation between arteries and veins and the possible sites of confusion.

Influence of the Choice of Software Package on the Outcome of Semiquantitative MR Myocardial Perfusion Analysis

PURPOSEnTo assess the repeatability and reproducibility of semiquantitative magnetic resonance (MR) perfusion analysis performed by using different software packages.nnnMATERIALS AND METHODSnThe study protocol was approved by the institutional ethics committee. Informed consent was obtained from each patient. Semiquantitative perfusion analysis was performed twice by two independent observers using four dedicated software packages. MR perfusion datasets originated from eight patients with known single-vessel disease who were scheduled for percutaneous coronary intervention (PCI) on the basis of coronary angiography findings. Each patient underwent two examinations: 1 day before and 1 day after PCI. Repeatability (intra- and interobserver agreements) and reproducibility (intersoftware agreement) were evaluated for perfusion upslope and myocardial perfusion reserve index with Student t test and Bland-Altman analyses.nnnRESULTSnIntra- and interobserver agreements were good and comparable for repeated measurements within each individual software platform (mean differences < 6%, intraclass correlation coefficient [ICC] ≥ 0.68). However, the intersoftware variability was significant (limits of agreement ≥ 65%, ICC ≤ 0.67) such that the values produced with the different software packages are not interchangeable.nnnCONCLUSIONnThe results indicate high repeatability within individual software but low reproducibility between different software packages, suggesting that within-group and/or sequential observation of semiquantitative perfusion parameters must be performed with the same software platform. Before semiquantitative perfusion analysis can be incorporated reliably into clinical studies, it is important to resolve the differences between the software packages.

Respiratory level tracking with visual biofeedback for consistent breath-hold level with potential application in image-guided interventions

BackgroundTo present and evaluate a new respiratory level biofeedback system that aids the patient to return to a consistent breath-hold level with potential application in image-guided interventions.MethodsThe study was approved by the local ethics committee and written informed consent was waived. Respiratory motion was recorded in eight healthy volunteers in the supine and prone positions, using a depth camera that measures the mean distance to thorax, abdomen and back. Volunteers were provided with real-time visual biofeedback on a screen, as a ball moving up and down with respiratory motion. For validation purposes, a conversion factor from mean distance (in mm) to relative lung volume (in mL) was determined using spirometry. Subsequently, without spirometry, volunteers were given breathing instructions and were asked to return to their initial breath-hold level at expiration ten times, in both positions, with and without visual biofeedback. For both positions, the median and interquartile range (IQR) of the absolute error in lung volume from initial breath-hold were determined with and without biofeedback and compared using Wilcoxon signed rank tests.ResultsWithout visual biofeedback, the median difference from initial breath-hold was 124.6xa0mL (IQR 55.7–259.7 mL) for the supine position and 156.3xa0mL (IQR 90.9–334.7 mL) for the prone position. With the biofeedback, the difference was significantly decreased to 32.7xa0mL (IQR 12.8–59.6 mL) (pu2009<u20090.001) and 22.3xa0mL (IQR 7.7–47.0 mL) (pu2009<u20090.001), respectively.ConclusionsThe use of a depth camera to provide visual biofeedback increased the reproducibility of breath-hold expiration level in healthy volunteers, with a potential to eliminate targeting errors caused by respiratory movement during lung image-guided procedures.

The influence of beam-pitch, reconstruction slice-thickness, and kernel on 3D visualisation of 16-MSCT data

Abstract The latest technology 16-MSCT enables shorter rotation times of less than 500 ms and has therefore a much faster scan time than the previous ones. Although many studies on this topic have been done, evaluation and, more importantly, quantification of this MSCT from signal processing perspective, however, are still lacking. This paper presents quantification of the influence of the most important parameters of MSCT, namely the beam-pitch, reconstruction slice-thickness, and kernels on the 3D reconstruction and visualisation. The results of our phantom study recommend the use of a beam-pitch of approximately 1 and a reconstruction slice-thickness of 1.65 mm to obtain optimal 3D reconstructions. Moreover, vessels smaller than 3 mm will be highly affected by any kernel and, therefore, become unreliable.

Demonstration of three-dimensional visualization techniques for coronary artery evaluation using EBCT - a case study

A variety of visualization techniques, both established and recently developed, can be used for evaluation of the coronary arteries and identification of stenotic lesions. Using a single contrast enhanced electron beam computed tomography (EBCT) scan the results and drawbacks of these techniques will be shown.