Biomedical subjects

V Rasche

Publications and source records attributed to V Rasche.

16 recordsLinked to original sources

PubMed2001

Projection reconstruction balanced fast field echo for interactive real-time cardiac imaging.

A balanced fast field echo (FFE) sequence (also referred to as true fast imaging with steady precession (true FISP)), based on projection reconstruction (PR) is evaluated in combination with real-time reconstruction and interactive scanning capabilities for cardiac function studies. Cardiac image sequences obtained with the balanced PR-FFE method are compared with images obtained with a spin-warp (2D Fourier transform (2DFT)) technique. In particular, the representation of motion artifacts in both techniques is investigated. Balanced PR-FFE provides a similar contrast to spin-warp-related techniques, but is less sensitive to motion artifacts. The use of angular undersampling within balanced PR-FFE is examined as a means to increase temporal resolution while causing only minor artifacts. Furthermore, a modification of the profile order allows the reconstruction of PR images at different spatial and temporal resolution levels from the same data. This study shows that balanced PR-FFE is a robust tool for cardiac function studies.

Artifacts↗

PubMed2001

Interactive reduced FOV imaging for projection reconstruction and spiral acquisition.

MR fluoroscopy is likely to gain increasing importance for the visualization of dynamic processes such as cardiac function and for the guidance of interventional procedures. In many applications the dynamic processes are restricted to a part of the object under study making reduced field of view (rFOV) imaging desirable. The restriction to a smaller FOV can either be used to increase the spatial or the temporal resolution. In projection reconstruction (PR) and spiral imaging severe backfolding artifacts occur if a rFOV is used. In this paper efficient suppression schemes are proposed for PR- and spiral imaging to avoid backfolding artifacts. Evaluation of the proposed schemes was done on an interactive real-time MR-scanner. Cardiac function studies clearly showed the potential of this technique for PR- and spiral imaging.

Angioplasty, Balloon, Coronary↗

PubMed2001

Real-time MR Guidance for inferior vena cava filter placement in an animal model.

It was the aim of this study to examine the feasibility of real-time magnetic resonance (MR) imaging for MR-guided placement of inferior vena cava (IVC) filters, which were placed in five pigs via a femoral approach. The introducer sheath and dilator were marked with Dysprosium rings. The procedures were performed under MR guidance with use of a 1.5-T ACS-NT imager. Radial filling of k-space in conjunction with the sliding window reconstruction technique achieved real-time MR imaging with a frame rate of 20 images/sec. Simultaneous real-time visualization of the vascular anatomy and interventional instruments was achieved under real-time conditions and allowed correct placement of IVC filters in all five cases as confirmed by radiographic angiography.

Animals↗

PubMed2000

Real-time MR fluoroscopy for MR-guided iliac artery stent placement.

The purpose of this study was to test the feasibility of real-time magnetic resonance (MR) guidance of iliac artery stent placement. Radial scanning together with the sliding window reconstruction technique was implemented on a 1.5 T magnet, yielding a frame rate of 20 images per second. Seven prototype nitinol ZA stents were deployed in iliac arteries of living pigs under MR control. All stents were well visualized on the radial MR images, allowing depiction of the mounted stents as well as stent deployment without anatomy-obscuring artifacts. Stent placement was sucessful in all cases and took 6 minutes on average. The position of the stents was correctly visualized by real-time radial MR scanning, as proved by digital subtraction X-ray angiography. Combined radial scanning and the sliding window reconstruction technique allow real-time MR-guided stent placement in iliac arteries.

Alloys↗

PubMed2000

[Value of fine needle puncture cytology in neoplasms of the parotid gland].

BACKGROUND: In many parts of Germany fine-needle aspiration biopsy (FNAB) is still not part of the routine preoperative diagnostic evaluation of salivary gland neoplasms. Most opponents consider the study unnecessary and recommend that all salivary gland neoplasms should be excised. OBJECTIVE: Because of this an evaluated the ability of FNAB to provide an accurate diagnosis of parotid gland neoplasms. PATIENTS AND METHOD: Between January 1992 and October 1995, 336 patients referred for operative therapy of salivary gland neoplasms underwent retrospective analysis of preoperative FNAB compared with the excised tumor histology. RESULTS: Results showed that the FNAB had a sensitivity of 93.1%, a specificity of 99.2%, a positive predictive value of 93.1%, a negative predictive value of 99.2% and an accuracy of 98.6%. Complications were observed in less than 1%. DISCUSSION: Our findings demonstrated that the FNAB is a safe diagnostic tool that has a reliable sensitivity and high specificity for the assessment of salivary gland pathology. Since many malignant salivary gland neoplasms present with a virtual lack of symptoms indicating actual malignancy we believe that there is need for FNAB in routine preoperative diagnostic testing.

Adolescent↗

PubMed1999

Motion compensated projection reconstruction.

Over recent years, MRI has shown the capability for real-time applications. Although the acquisition times of fast MRI methods have been reduced significantly, patient motion during a magnetic resonance imaging (MRI) examination still causes artifacts in the image. In this paper, the effects of motion in MRI using a radial acquisition scheme are examined. It is shown that motion can be estimated without the use of additional measurement, based on the acquired projections only. A new reconstruction technique is introduced that integrates a motion compensation algorithm into the MR-reconstruction process, resulting in a significant reduction of blurring artifacts in the reconstructed images. The proposed method is applied to different kinds of motion such as kinetic joint studies.

Algorithms↗

PubMed1999

MR fluoroscopy using projection reconstruction multi-gradient-echo (prMGE) MRI.

A projection reconstruction multi-gradient-echo (prMGE) technique is presented. The introduced technique is an extension of a standard projection reconstruction steady-state gradient-echo technique allowing for the acquisition of several gradient echoes after each excitation of the spin system. Each echo train is used for acquiring data of a certain angular segment of k-space. By use of echo trains consisting of up to four echoes, the overall acquisition time for a 128(2) image can be reduced to 150 ms without sacrificing image quality. Results are presented for cardiac fluoroscopy, for the visualization of swallowing, and for the visualization of joint motion. For all investigated applications promising results have been obtained. Especially in parts of the body where motion on an even shorter time scale than the acquisition process or significant in-plane or through-plane flow are within the field of view, the introduced technique appears to be a promising technique for MR fluoroscopy. Magn Reson Med 42:324-334, 1999.

Deglutition↗

PubMed1999

Projection-reconstruction reduced [correction of reduces] FOV imaging.

Reduced field-of-view (rFOV) imaging was introduced recently as a rapid imaging technique that improves temporal resolution while maintaining spatial resolution. It is based on undersampling in k-space and utilizes the fact that the dynamics of an evolving process are often confined to a local area within the full FOV. In the work presented here the reduced FOV approach is applied to projection-reconstruction MRI and compared to the original spin-warp implementation. Results are presented that clearly demonstrate the increased robustness of the projection-reconstruction version of rFOV imaging. The technique is successfully applied to an MR-guided biopsy scenario (ex-vivo) and to cine cardiac imaging. Finally an algorithm is proposed that uses the intrinsic advantages of radial k-space sampling to evaluate the projection data to control the adjustment of position and size of the reduced FOV window.

Algorithms↗

PubMed1999

Resampling of data between arbitrary grids using convolution interpolation.

For certain medical applications resampling of data is required. In magnetic resonance tomography (MRT) or computer tomography (CT), e.g., data may be sampled on nonrectilinear grids in the Fourier domain. For the image reconstruction a convolution-interpolation algorithm, often called gridding, can be applied for resampling of the data onto a rectilinear grid. Resampling of data from a rectilinear onto a nonrectilinear grid are needed, e.g., if projections of a given rectilinear data set are to be obtained. In this paper we introduce the application of the convolution interpolation for resampling of data from one arbitrary grid onto another. The basic algorithm can be split into two steps. First, the data are resampled from the arbitrary input grid onto a rectilinear grid and second, the rectilinear data is resampled onto the arbitrary output grid. Furthermore, we like to introduce a new technique to derive the sampling density function needed for the first step of our algorithm. For fast, sampling-pattern-independent determination of the sampling density function the Voronoi diagram of the sample distribution is calculated. The volume of the Voronoi cell around each sample is used as a measure for the sampling density. It is shown that the introduced resampling technique allows fast resampling of data between arbitrary grids. Furthermore, it is shown that the suggested approach to derive the sampling density function is suitable even for arbitrary sampling patterns. Examples are given in which the proposed technique has been applied for the reconstruction of data acquired along spiral, radial, and arbitrary trajectories and for the fast calculation of projections of a given rectilinearly sampled image.

Algorithms↗

PubMed1999

[Experimental MRI-controlled cryotherapy of the brain with almost real-time imaging by radial k-space scanning].

PURPOSE: To test radial k-space scanning by MR fluoroscopy to guide and control MR-guided interstitial cryotherapy of the healthy pig brain. METHODS: After MR tomographic planning of the approach, an MR-compatible experimental cryotherapy probe of 2.7 mm diameter was introduced through a 5 mm burr hole into the right frontal brain of five healthy pigs. The freeze-thaw cycles were imaged using a T1-weighted gradient echo sequence with radial k-Space scanning in coronal, sagittal, and axial directions. RESULTS: The high temporal resolution of the chosen sequence permits a continuous representation of the freezing process with good image quality and high contrast between ice and unfrozen brain parenchyma. Because of the interactive conception of the sequence the layer plane could be chosen as desired during the measurement. Ice formation was sharply demarcated, spherically configurated, and was free of signals. Its maximum diameter was 13 mm. CONCLUSIONS: With use of the novel, interactively controllable gradient echo sequence with radial k-space scanning, guidance of the intervention under fluoroscopic conditions with the advantages of MRT is possible. MR-guided cryotherapy allows a minimally-invasive, precisely dosable focal tissue ablation.

Animals↗

PubMed1998

[MR-micturating cystourethrography using radical k-space sampling].

PURPOSE: To investigate the feasibility of micturating cystourethrography (MCU) by means of real-time MR imaging with radial k-space sampling. METHODS: The MR-MCU was performed in 7 adult male patients subsequent to a gadolinium(Gd)-DTPA-enhanced excretory MR-urography. The Gd-enhancement of the urethra was visualized by MR-fluoroscopy using a T1-weighted gradient-echo-sequence with radial k-space sampling and a slice thickness of 10 mm. RESULTS: The proposed technique allowed in all 7 patients a dynamic realtime imaging of the Gd-flow inside the urethra during micturition. The normal anatomy of the entire course of the urethra was demonstrated in each patient, while simultaneously the relation to the prostate and pelvic floor became visible. Furthermore, the urinary bladder could be assessed by interactive repositioning of the slice orientation in any preferred direction. The ureters could also be visualized due to the persisting Gd-enhancement of the upper urinary tract after the preceding MR-urography. CONCLUSIONS: MR-MCU using Gd-DTPA and radial k-space data acquisition is a novel imaging modality for a real-time visualization of the urethra during micturition without radiation exposure. This method also allows the assessment of the bladder, the pelvic floor, and the Gd-filled upper urinary tract which suggests a potential for the diagnosis of vesicoureteral reflux and urinary incontinence.

Adult↗

PubMed1998

[Real-time MRI with radial k-radial scanning technique for control of angiographic interventions].

PURPOSE: To test the feasibility of real-time MR controlled guidance of field-inhomogeneity catheters in vitro and in vivo as a first step to MR-guided angiographic interventions. METHODS: Applying a combination of radial scanning with the sliding window reconstruction technique, a frame rate of 23 low resolution images per second was achieved. Field inhomogeneity catheters were steered through a flow phantom and into the renal arteries of a pig. RESULTS: It was possible to visualize flow or, respectively, vessels and to depict catheter movements. This enabled real-time MR-guidance of the catheter into the renal arteries of the flow phantom and into those of the pig. CONCLUSIONS: The new technique yields a sufficiently high temporal resolution for MR-guidance of catheters through vessels.

Angiography↗

PubMed1998

[Stent placement with real time MRI guidance: initial animal experiment experiences].

PURPOSE: The aim of this study was to test the feasibility of iliac artery stent placement under MR guidance with real-time MR radial scanning in an animal model. MATERIALS AND METHODS: The experiments were performed on three pigs in a 1.5 T scanner. Radial scanning with a gradient echo technique (TR 8.4 ms, TE 3.6 ms, flip angle 10 degrees) was used. A dedicated backprojector performed the reconstruction of the raw data in real-time. The resulting MR-images were displayed on LCD screens beside the magnet. The sliding window reconstruction technique allowed image acquisition at a frame rate of 16 images per second. MR-compatible self-expanding stents with a diameter of 8 mm and a length of 3 cm were placed into the left iliac artery. Their positions were verified by digital subtraction angiography (DSA) and compared to MRI. RESULTS: All stents were successfully placed. Stent positions as monitored by real-time MR were identical to those seen on DSA images. The time needed for exact positioning of the scan plane ranged from 15 to 30 minutes. Stent placement itself took 8 minutes on average. CONCLUSION: Radial scanning applied together with the sliding window reconstruction technique allows placement of stents in iliac arteries under real-time MR control.

Angioplasty, Balloon↗

PubMed1997

Catheter tracking using continuous radial MRI.

The guidance of minimally invasive procedures may become a very important future application of MRI. The guidance of interventions requires images of the anatomy as well as the information of the position of invasive devices used. This paper introduces continuous radial MRI for the simultaneous acquisition of the anatomic MR image and the position of one or more small RF-coils (mu-coils), which can be mounted on invasive devices such as catheters or biopsy needles. This approach allows the in-plane tracking of an invasive device without any prolongation of the overall acquisition time. The extension to three-dimensional position tracking is described. Phantom studies are presented demonstrating the capability of this technique for real-time automatic adjustment of the slice position to the current catheter position with a temporal resolution of 100 ms. Simultaneously the in-plane catheter position is depicted in the actually acquired MR image during continuous scanning.

Catheterization↗

PubMed1995

Continuous radial data acquisition for dynamic MRI.

Since image acquisition times in MRI have been reduced considerably over recent years, several new important application areas of MRI have appeared. In addition to pure static anatomic information, the evolution of a dynamic process may be visualized by a sequence of temporal snapshots of the process acquired within a short time period. This makes applications like interactive or interventional MRI as well as the acquisition of additional functional information feasible. For high temporal resolution, all these applications require a quasi real-time image acquisition during the time the interaction or dynamic process evolves. We present an approach to real-time imaging using a continuous radial acquisition scheme. The intrinsic advantages of radial or projection reconstruction (PR) techniques are used to minimize motion-related image distortions. Modifications of the acquisition scheme as well as dedicated reconstruction techniques are used to further reduce the temporal blurring due to the finite acquisition time of one entire data set in our approach. So far we have used this technique for the visualization of active joint motion.

Artifacts↗

PubMed1994

Radial turbo spin echo imaging.

Fast MR imaging methods should provide a familiar contrast behavior at a reduced scan time. The multi-spin echo approach (TSE) is one of the most promising techniques satisfying this condition. Although the data acquisition time is significantly reduced, image quality may still suffer from artifacts due to patient motion and flow. The radial turbo spin echo (rTSE) approach combines TSE methods and projection reconstruction (PR) techniques. In PR images, artifacts induced by patient motion or flow are known to have a different appearance with lower level of intensity. The contrast and artifact behavior of the rTSE approach has been investigated. The new technique has been applied to abdominal imaging with acquisition times shorter than 30 s and to heart imaging in combination with cardiac triggering.

Abdomen↗