Slice Orientation Research Articles

Automatic 3D Registration for Interventional MRI-Guided Treatment of Prostate Cancer

The goal of this research is to register real-time interventional magnetic resonance imaging (iMRI) slice images with a previously obtained high-resolution MRI image volume, which in turn can be registered with functional images such as those Urom SPECT. The immediate application is in iMRI-guided treatment of prostate cancer, where additional images are desired to improve tumor targeting. In this article, simulation experiments are performed to demonstrate the feasibility of slice-to-volume registration for this application. We acquired 3D volume images from a 1.5-T MRI system and simulated low-field iMRI image slices by creating thick slices and adding noise. We created a slice-to-volume mutual information registration algorithm with special features to improve robustness. Features included a multiresolution approach, two similarity measures, and automatic restarting to avoid local minima. To assess the quality of registration, we calculated 3D displacements on a voxel-by-voxel basis over a volume of interest between slice-to-volume registration and volume-to-volume registration, which was previously shown to be quite accurate. More than 800 registration experiments were performed on MR images of three volunteers. The slice-to-volume registration algorithm was very robust and accurate for transverse slice images covering the prostate, with a registration error of only 0.4 ± 0.2 mm. Error was greater at other slice orientations and positions. The automatic slice-to-volume mutual information registration algorithm is robust and probably sufficiently accurate to aid in iMRI-guided treatment of prostate cancer.

Centroid-based maximum intensity projections.

Maximum intensity projection (MIP) is a three-dimensional visualization technique for tomographic angiograms. While conventional MIPs display contralateral vascular anatomy, this study uses centroid calculations to remove this information. It is necessary to provide accurate, unambiguous vessel depiction and identical projections regardless of slice orientation. A mathematical model was formed using parameters from clinical images of the head. The vessel widths from the resulting projections were measured and compared with the model. To test the consistency of the projection process, a clinical image set was reformatted and projections of the same view were compared. The vessel widths were smaller than in the model while varying interpolation and noise. Similar projection views were generated for all slice orientations, but some misalignment was present. Vessel width is affected by the ray's path length and interpolation method. Some slight misalignment is present because the reformatting process alters the centroid calculations.

Effect of slice orientation on reproducibility of fMRI motor activation at 3 Tesla

The effect of slice orientation on reproducibility and sensitivity of 3T fMRI activation using a motor task has been investigated in six normal volunteers. Four slice orientations were used; axial, oblique axial, coronal and sagittal. We applied analysis of variance (ANOVA) to suprathreshold voxel statistics to quantify variability in activation between orientations and between subjects. We also assessed signal detection accuracy in voxels across the whole brain by using a finite mixture model to fit receiver operating characteristic (ROC) curves to the data. Preliminary findings suggest that suprathreshold cluster characteristics demonstrate high motor reproducibility across subjects and orientations, although a significant difference between slice orientations in number of activated voxels was demonstrated in left motor cortex but not cerebellum. Subtle inter-orientation differences are highlighted in the ROC analyses, which are not obvious by ANOVA; the oblique axial slice orientation offers the highest signal detection accuracy, whereas coronal slices give the lowest.

Time-course magnetic resonance imaging of rat pancreatic cyst after experimental pancreatitis

Fast magnetic resonance (MR) imaging of the rat pancreas was carried out using a snapshot method to observe three-dimensional (3D) and temporal development of the pancreatic cyst after experimental pancreatitis. Acute pancreatitis was induced by a retrograde infusion of the trypsin-taurocholate solution into the pancreatic duct in 23 rats, of which seven survived for one month. Under 2% enflurane anesthesia, 1H images of the rat abdomen were taken by a 4.7 T magnetic resonance spectrometer under spontaneous breathing. 3D images of the pancreas and cyst were reconstructed from the axial, sagittal and coronal images taken before, 24 h, 7 days, 14 days, 21 days and 28 days after the induction of pancreatitis. The 3D images reconstructed from different slice orientations at each time point showed good agreement with each other. The calculated volumes of the cyst on 7th, 14th, 21st, and 28th day were 0.3 ± 0.1, 0.8 ± 0.3, 2.1 ± 0.6, 6.5 ± 1.3 mL, respectively. The cystic fluid volume on 28th day was 6.4 ± 1.4 mL, which confirmed reliability of volume measurement by MR imaging. Fast MR imaging (snapshot) together with 3D reconstruction allows us to understand the detailed chronological and spatial development of pancreatic cyst after acute pancreatitis in rats.

WS01‐09Diagnostically critical fetal imaging artifacts: identification and management

The purpose of this project was to identify sources and clinical significance of 3DUS artifacts on patient diagnosis and to increase clinician and sonographer awareness to reduce misdiagnosis in 3DUS studies. To accomplish this 3DUS data were acquired and reviewed interactively. Artifacts were cataloged according to origin: B‐mode, color/power Doppler or unique to 3DUS (acquisition, rendering or volume editing). Original scan planes, re‐sliced planes and rendered images were evaluated. Overall our results showed a variety of artifacts. B‐mode artifacts included drop‐out, shadowing, etc. and depending on relationships between slice and imaging plane orientation. Color/power Doppler artifacts were related to gain, aliasing, and flash and could add apparent structure or confusion to the volume images. Rendering artifacts were due to parameter adjustment, shadowing and motion.Important structures could be removed by improper editing. In conclusion 3DUS and 2DUS are prone to similar artifacts plus others unique to 3DUS. Diagnostically significant artifacts can mimick abnormal development, masses, or missing structures thus requiring careful study before reaching a diagnosis.

Sources and impact of artifacts on clinical three‐dimensional ultrasound imaging

The purpose of this paper is to investigate, identify and discuss artifacts and their sources arising in three-dimensional ultrasound (3D US) in clinical practice in order to increase the awareness of clinicians and sonographers with respect to common 3D US artifacts and to use this increased awareness to avoid or reduce the occurrence of misdiagnosis in 3D US studies. Patient 3D US data were acquired using several different scanners and reviewed interactively on the scanner and graphics workstations. Artifacts were catalogued according to artifact origin. Two-dimensional ultrasound (2D US) artifacts were classified whether they were of a B-mode or color/power Doppler origin and their presentation in the original scan planes and the resulting volume re-sliced planes and rendered images was identified. Artifacts unique to 3D US were observed, noted and catalogued on the basis of whether they arose during acquisition, rendering or volume editing operations. Acoustic artifacts identified included drop-out, shadowing, etc. whose presentation depended on the relationship between slice and imaging plane orientation. Color/power Doppler artifacts were related to gain, aliasing, and flash which could add apparent structure or confusion to the volume images. Rendered images also demonstrated artifacts due to shadowing and motion of adjacent structures, cardiac motion or pulsatility of the cardiac septum or vessel walls. Editing artifacts potentially removed important structures. Three-dimensional ultrasound is prone to the same types of artifacts encountered in 2D US imaging plus others unique to volume acquisition and visualization. The consequences of these diagnostically significant artifacts include mimicking of abnormal development, masses, or missing structures thus requiring careful study before reaching a diagnosis.

MAGNETIC RESONANCE IMAGING OF THE NORMAL AND DISEASED FELINE MIDDLE EAR

The magnetic resonance imaging appearance of the feline middle ear is described in three healthy cats and in five cats with middle ear disease. Owing to the good spatial resolution, multiplanar slice orientation as well as display high contrast resolution of soft tissue, in particular fluids, MR imaging was helpful prior to surgery. It is superior to radiography which failed to allow identification of the abnormality in two of our five cats. MR imaging for middle ear disease should include dorsal and transverse plane images using T1‐ and T2‐ weighted sequences. In the presence of a mass within the bulla or the external ear canal application of contrast medium is helpful.

Improved phase-contrast flow quantification by three-dimensional vessel localization

In this paper, a method of three-dimensional (3D) vessel localization is presented to allow the identification of a vessel of interest, the selection of a vessel segment, and the determination of a slice orientation to improve the accuracy of phase-contrast magnetic resonance (PCMR) angiography. A marching-cube surface-rendering algorithm was used to reconstruct the 3D vasculature. Surface-rendering was obtained using an iso-surface value determined from a maximum intensity projection (MIP) image. This 3D vasculature was used to find a vessel of interest, select a vessel segment, and to determine the slice orientation perpendicular to the vessel axis. Volumetric flow rate (VFR) was obtained in a phantom model and in vivo using 3D localization with double oblique cine PCMR scanning. PCMR flow measurements in the phantom showed 5.2% maximum error and a standard deviation of 9 mL/min during steady flow, 7.9% maximum error and a standard deviation of 13 mL/min during pulsatile flow compared with measurements using an ultrasonic transit-time flowmeter. PCMR VFR measurement error increased with misalignment at 10, 20, and 30 degrees oblique to the perpendicular slice in vitro and in vivo. The 3D localization technique allowed precise localization of the vessel of interest and optimal placement of the slice orientation for minimum error in flow measurements.

Effect of slice orientation on conspicuity and reproducibility of 3T fMRI activation using a motor task

Effect of slice orientation on conspicuity and reproducibility of 3T fMRI activation using a motor task

Quantification of fMRI artifact reduction by a novel plaster cast head holder.

In light of artifact-induced high variability of activation in fMRI repeat studies, we developed and tested a clinically useful plaster cast head holder (PCH) with improved immobilization, repositioning, and comfort. With PCH, there were considerably lower levels of translational and rotational head motion components compared to head fixation with conventional restraining straps (CRS). Rotational components cannot be fully compensated by realignment and lead to "false activations." In addition, task-correlated head motion, which highly increases the risk of artifacts, was considerably reduced with PCH, especially in a motion prone subject. Compared with PCH, head motion was 133% larger with CRS in a highly cooperative subject. With a motion prone subject, head motion range was increased by 769% (PCH: 0.9 mm, CRS: 7.8 mm), which may indicate the usefulness of PCH for restless patients. In functional activation maps, PCH alone yielded fewer residual motion artifacts than CRS + image registration. Subject tolerance of the head holder during the long measurement times of up to 2.5 hr was good, and slice orientation on different days confirmed the quality of repositioning.

Advantages and limitations of whole-body bone marrow MRI using turbo-STIR sequences in comparison to planar bone scans

At modern MRI tomographs the whole body can be screened for bone marrow metastases within 45 min. AIM of this study was to evaluate the diagnostic advantages and disadvantages of a whole-body bone marrow MRI protocol using Turbo Short Tau Inversion Recovery [STIR] sequences in comparison to planar bone scintigraphy (SZ). In order to screen for bone metastases within two weeks SZ and whole-body MRI with Turbo-STIR-sequences were performed in 20 patients with known breast cancer. For further evaluation five regions were defined: skull, spine including the pelvis, femora, humeri and ribs including scapulae and sternum. In 9/20 patients neither with SZ nor with MRI bone metastases were detected (staging M0). Among the remaining 11 patients SZ detected 109 and MRI 150 lesions which were typical for bone metastases. All of these 11 patients were staged M1 correspondingly with both methods. Within the thorax (ribs, sternum, scapulae) MRI discovered only 6/17 and within the skull 0/6 lesions which were suspicious for metastases in SZ. Inversely MRI identified much more metastatic lesions than SZ within the femora (20/16), the humeri (14/12) and the spine including the pelvis (110/58). Susceptibility-, truncation-, chemical-shift-, third arm- and particularly pulsation artifacts along with the impossibility to chose slice orientation equally advantageous for all regions of the body cause impaired image quality of MRI whole body scanning. Therefore, concerning the detection rate of bone metastases within the thorax (ribs, sternum and scapulae) and the skull, conventional Turbo-STIR-MRI whole-body scans are even less accurate than conventional planar bone scintigraphy in those regions.

PRINCIPLES OF CONTRAST-ENHANCED MR ANGIOGRAPHY: Basic and Clinical Applications

Contrast-enhanced MR angiography has several advantages in the clinical setting. One advantage is the shortening of T1 because the source of signal increase is resistant to signal losses caused by blood saturation, especially for in-plane flow as encountered in TOF MR angiography and PC MR angiography. This T1 reduction is clearly advantageous in obtaining images of tortuous vessels and stenotic regions. Because the contrast agent Gd-DTPA is well-tolerated and has no nephrotoxic effect, its use in patients with impaired renal function is widely accepted. It is also reported in the literature that the depiction of large aneurysms is markedly more simple with CE-MR angiography than with digital subtraction angiography because filling and subsequent washout of contrast material can be followed over a longer period of time. The main intrinsic advantage of CE-MR angiography compared with TOF and PC-MR angiography is its acquisition speed (because of ultra-short TRs) with comparable gradient performance. Also, the slice orientation can be chosen as the clinical situation dictates and needs rather than being uniformly perpendicular to blood flow, as was often necessary previously. The author considers CE-MR angiography a valuable development for vascular MR imaging. It is currently being compared with alternative methods in studies at several centers.

Use of single-slice thick slab phase-contrast angiography for the diagnosis of dural venous sinus thrombosis.

The aim of this study was to examine the reliability of single-slice phase-contrast angiography (SSPCA) as a rapid technique for the investigation of suspected dural venous sinus occlusion. Images were obtained on 25 normal volunteers to document the accuracy of SSPCA in the demonstration of slow flow states. Normal volunteers were imaged using sagittal and coronal SSPCA (slice thickness 13 cm, matrix 256 x 256, TR 14 ms, TE 7 ms, flip angle 20 degrees, peak velocity encoding rate 30 cm/s). Sinus patency and flow rate were confirmed by measurement of flow in the superior sagittal and transverse sinuses using quantified single-slice phase difference images. Imaging was performed in 50 patients undergoing routine brain scans in order to determine the optimal slice orientation for clinical use. Twenty-one patients with suspected dural venous sinus thrombosis were also investigated with SSPCA and the diagnosis confirmed by one or more alternative imaging techniques. Imaging time was 29 s per acquisition and image quality was good in all cases. Variations in dural sinus patency and flow in normal volunteers were accurately predicted by SSPCA (kappa = 0.92). Use of a single angulated slice (130 mm thick, para-sagittal image angled 30 degrees towards coronal and 30 degrees towards transverse) provided sufficient separation of right- and left-sided venous structures to allow use of a single projection. The presence and extent of sinus occlusions in 14 patients and the absence of thrombosis in 7 were accurately identified by SSPCA. Sensitivity and specificity in this limited study were both 100%. The SSPCA technique takes less than 30 s and provides a reliable and rapid technique for the diagnosis of dural venous sinus thrombosis.

An Optimized Pulse Sequence for Isotropically Weighted Diffusion Imaging

Single-shot echo-planar imaging is becoming the most widely used technique for magnetic resonance diffusion imaging, since it enables measurement of diffusion coefficients in human brain without motion artifacts. However, its reliability is limited by geometrical distortions due to eddy currents. In this report, an isotropically weighted echo-planar pulse sequence, optimized to give the maximum signal-to-noise ratio in the computed trace image and designed to produce inherently low distortions, is presented. It is also shown how the residual translational distortion can be easily characterized and removed by postprocessing. A full characterization of the distortion artifact involves a few measurements on a phantom, in order to estimate the distortion as a function of slice orientation, which can then be used to correct any slice orientation. Results of applying the image translation correction to data collected from a patient are presented.

A tunable focusing beamline for desktop x-ray microtomography

In this article a desktop x-ray microtomography (μXCT) instrument is presented, which utilizes conventional diffraction tubes and tunable focusing optics. The beamline is based on an elastically bent cylindrical multilayer mirror, given by a coated and rhombic shaped Si wafer, which is placed on bearings with two of its tips and is actuated by a single transverse center force to a desired curvature and herewith focal length. This optical element is used in a grazing incidence reflection geometry, demagnifying the tube focal spot into an image line with width (w) and position following from a classical imaging equation (magnification ratio M). While the tube and the image (“focal”) position are kept fixed, the curvature and axial position of the mirror are adaptively controlled for different M values and Bragg angles θ̄ (i.e., pass-energies Ē), which results in a one-dimensional zoom-optical system. The specimen is placed in the high-depth focal region of the condensed beam for the CT-scanning procedure with the slice orientation given by the focusing direction. Minor modifications of the fundamental rhombic mirror shape also enable the establishment of imaging geometries with elliptical and parabolic cylindrical-type optical figures. Multilayer reflection inherently results in a small bandpass of photon energies (ΔE/Ē). Pass-energy Ē is preferably tuned to characteristic lines of the tubes in use (Cr, Cu, Mo target) with the option of also using the white x-ray spectrum. Numerical values of beamline specifications are characterized by: 0.1⩽M⩽1.0, 10⩽w⩽100 μm, 0.5⩽θ̄⩽2°, 5⩽Ē⩽30 keV, ΔE/Ē≲0.1. Photon intensity along the focal line is given by 106<N<2×107 (s mm)−1, depending on the type of tube, mirror reflectivity and M setting. The fundamental principles, the experimental setup and major components of the beamline are described and the theoretical and experimental performance in terms of photon flux, pass-energy bandwidth and beam geometry are evaluated. Examples of μXCT scanning are also given. In the current configuration, a fast scintillation counter behind an object slice collimator is used for photon detection, although the sheet-like geometry of the focused x-ray beam can be further used for parallel projection data acquisition along the nonfocusing direction of the optical system (i.e., for different object slices) by application of a suitable charge coupled device-type detector.

Phase-contrast MR angiography of peripheral arteries: technique and clinical application.

This articles describes Phase-Contrast-MRA (PC-MRA) techniques and their current clinical applications for peripheral arteries based on more than 250 clinical MRA studies performed at two institutions. PC-MRA depends on phase shifts caused by blood flow and thus this technique permits the use of coronal or sagittal slice orientations with large FOV's along the direction of the vessel of interest. Clinical applications focus on patients with peripheral arterial occlusive disease (PAOD) describing the role and limitations of PC-MRA for the work-up of stenoses, occlusions, aneurysms, and postsurgical follow-up. Recommendations for clinical routine are provided. A combined MR angiographic approach with various MRA techniques depending on the vessel segment to be imaged, PC-flow velocity measurements, and high-resolution scans of the vessel wall may turn out to be diagnostically effective and provide a comprehensive test for PAOD within the near future.

Analysis of right ventricular areas to assess the severity of ascites syndrome in broiler chickens

Ascites syndrome in broiler chickens is defined as a condition associated with pulmonary hypertension leading to right heart failure, increased central venous pressure, passive congestion of the liver, and accumulations of serous fluids in body cavities. The syndrome is currently seen in fast-growing broiler chickens associated with an increase in the weight, volume, and area of the right ventricle of the heart. The ratio of the right ventricle weight to the total heart mass has been used to assess the consequences of increased blood pressure. The right ventricle area (RVA) can be quantified using image analysis technology. Hearts were removed from 719 male broilers at slaughter (42 d). All birds were visually scored for the incidence of ascites. A score of 0 or 1 represented slight hydropericardium, slight right heart hypertrophy, and slight edema. A score of 4 was assigned to birds with marked accumulation of ascitic fluid in one or more ceolomic cavities, pronounced dilation of the right heart, and prominent liver lesions. A cross-sectional image of each heart slice (a 4-mm-thick slice of the ventricles) was digitally recorded. Using image analysis software, the RVA, left ventricular area (LVA), and total heart area (HA) were determined. Because a slice of the heart was used in image analysis, the importance of maintaining the original shape was determined. Twenty hearts in five ranges of RVA size were scanned in four different positions, which have differing heart slice orientations and differing RVA shapes, for a comparison of positioning technique (placement) relating to the RVA. The shape of the heart slice for image analysis was observed not to be critical for the small RVA. For heart slices with large RVA values, it was found to be critical to analyze the heart slice in a standardized placement.

MRI-guided treatment of degenerative spinal diseases

SummaryIn the treatment of degenerative spinal diseases, CT-guided local injections, RF or ethanol denervation of facet joints and laser decompression of herniated intervertebral disks offer a precisely aimed and effective option in cases of back pain and sciatica. As CT involves significant exposure of the patient to ionising radiation, we evaluated the feasibility of MR-guided therapy. MRI offers a variety of advantages, such as excellent soft-tissue contrast, high flow and temperature sensitivity, and arbitrary slice orientation within a 3D data set. The recently-introduced low-field open magnets, though of compromising imaging capabilities, have considerably facilitated access to the patient. The use of instruments and ancillary equipment, however, is made difficult by the high magnetic field and sensitive RF system of the MRI scanner. The techniques of MR-guided injection and using MR-compatible cannulae were developed and tested with ex vivo specimens of the spine and animal phantoms. 184 patients were treated with periradicular corticoid injections, six patients with laser decompression, 21 patients with neurolysis of facet joints and 16 patients underwent chemical lumbar sympathectomy. MR-guidance is feasible and the early clinical results are promising and comparable to those of CT-guided pain therapy. Further technical improvement of MR technology are required to facilitate the procedures.

Pulmonary veins: Magnetic resonance angiography anatomy

to optimize magnetic resonance angiography technique for the selective study of the anatomy of pulmonary veins. twenty consecutive patients (13 males and seven females; mean age 30.5 years) prospectively studied were enrolled. Magnetic resonance angiography was performed using a 1 T superconductive magnet and three dimensional time of flight technique (3D TOF). Imaging with steady-state free precession sequence during intravenous infusion of contrast medium (Gd DTPA 0.2 mmol kg(-1)) administration was employed using the following parameters: FA 20 degrees, TR 58 ms, TE 6 ms, MA 192 x 256, NEX 1, slice thickness 4 mm and slice orientation on the Z and Y planes. in the right lung magnetic resonance angiography well visualized 124 venous vessels on the coronal plane versus 106 venous vessels on the sagittal plane, whereas in the left lung magnetic resonance angiography visualized 96 vessels on the coronal plane versus 44 visualized on the sagittal plane. Our data suggest that 3D time of flight with contrast medium is a promising evaluation technique for pulmonary veins, and that combined evaluation of acquisitions on coronal and sagittal planes allows the visualization of a higher number of venous vessels. 3D time of flight with contrast medium and without breath-hold permits to visualize a venous vascular map of the lungs.

Pulmonary veins: Magnetic resonance angiography anatomy

Objective: to optimize magnetic resonance angiography technique for the selective study of the anatomy of pulmonary veins. Materials and methods: twenty consecutive patients (13 males and seven females; mean age 30.5 years) prospectively studied were enrolled. Magnetic resonance angiography was performed using a 1 T superconductive magnet and three dimensional time of flight technique (3D TOF). Imaging with steady-state free precession sequence during intravenous infusion of contrast medium (Gd DTPA 0.2 mmol kg −1) administration was employed using the following parameters: FA 20°, TR 58 ms, TE 6 ms, MA 192×256, NEX 1, slice thickness 4 mm and slice orientation on the Z and Y planes. Results: in the right lung magnetic resonance angiography well visualized 124 venous vessels on the coronal plane versus 106 venous vessels on the sagittal plane, whereas in the left lung magnetic resonance angiography visualized 96 vessels on the coronal plane versus 44 visualized on the sagittal plane. Our data suggest that 3D time of flight with contrast medium is a promising evaluation technique for pulmonary veins, and that combined evaluation of acquisitions on coronal and sagittal planes allows the visualization of a higher number of venous vessels. Conclusion: 3D time of flight with contrast medium and without breath-hold permits to visualize a venous vascular map of the lungs.