Biomedical subjects

Houchun H Hu

Publications and source records attributed to Houchun H Hu.

13 recordsLinked to original sources

PubMed2006

Undersampled elliptical centric view-order for improved spatial resolution in contrast-enhanced MR angiography.

Although contrast-enhanced MR angiography (CE-MRA) has been successfully developed into a routine clinical imaging technique, there is still need for improved spatial resolution in a given acquisition time. Undersampled projection reconstruction (PR) techniques maintain spatial resolution with reduced scan times, and the elliptical centric (EC) view order provides high quality arterial phase images without venous contamination. In this work, we present a hybrid elliptical centric-projection reconstruction (EC-PR) technique to provide spatial resolution improvement over standard EC in a given time. The k-space sampling was performed by undersampling the periphery of the k(Y)-k(Z) phase encoding plane of an EC view order in a PR like manner. The sampled views were maintained on a rectilinear grid, and thus reconstructed by standard 3DFT. The non-sampled views were compensated either by zero-filling or performing a 2D homodyne reconstruction. Compared to a fully sampled k-space, the EC-PR sequence acquired in the same scan time provides a resolution improvement of about two, as shown by point spread function analysis and phantom experiments. The hypothesis that EC-PR provides improved resolution while retaining diagnostically adequate SNR was tested in 11 CE-MRA studies of the popliteal and carotid arteries and shown to be true (P < 0.03).

Carotid Arteries↗

PubMed2006

Combination of 2D sensitivity encoding and 2D partial fourier techniques for improved acceleration in 3D contrast-enhanced MR angiography.

Sensitivity encoding (SENSE) and partial Fourier (PF) techniques both reduce MRI acquisition time. Two-dimensional SENSE uses coil sensitivities to unfold aliasing in the phase/slice-encoding plane. One-dimensional PF and homodyne reconstruction are routinely applied in the frequency/phase-encoding plane to compensate for nonsampled k-space of the presumed real magnetization. Recently, a modified 3D elliptical centric acquisition was proposed to facilitate 2D-PF and homodyne reconstruction on an undersampled phase/slice-encoding plane. In this work we hypothesized that this 2D-PF technique can be combined with 2D-SENSE to achieve a greater acceleration factor than what each method can provide separately. Reconstruction of data whereby SENSE and PF are applied along the same axes is described. Contrast-enhanced MR angiography (CE-MRA) results from experiments using four receiver coils in phantom and volunteer studies are shown. In 11 volunteer studies, the SENSE-PF-homodyne technique using sevenfold acceleration (4x SENSE, 1.7x PF) consistently provided high-diagnostic-quality images with near 1-mm isotropic resolution in acquisition times of <20 s.

Contrast Media↗

PubMed2006

Numerical equilibration of signal intensity and spatial resolution in time-resolved continuously moving table imaging.

Time-resolved continuously moving table imaging techniques have been previously developed to observe a dynamically changing phenomenon over an extended field-of-view. The acquisition involves differential k-space sampling and view sharing. Since the table is continuously moving during data acquisition, the k-space for any longitudinal position is sampled only sparsely for the first reconstruction timeframe and is progressively more fully sampled for subsequent frames. Consequently, the signal intensity increases and the lateral spatial resolution improves from frame to frame even for static materials, which can mask true dynamically changing phenomena. This work provides a description of this effect and a means for signal correction in the early reconstruction frames, thus permitting any residual variation in signal intensity to be primarily attributed to true dynamic processes. The method is tested experimentally on a static phantom and in a peripheral vascular study designed to observe the leading edge of the contrast bolus.

Humans↗

PubMed2006

Contrast-enhanced MR angiography of the peripheral vasculature with a continuously moving table and modified elliptical centric acquisition.

This study was approved by the institutional review board and was HIPAA compliant. All subjects provided written informed consent, and subject confidentiality was protected. The purpose of this study was to prospectively evaluate the feasibility of integrating a modified elliptical centric (EC) acquisition with a continuously moving table technique to acquire high-spatial-resolution contrast material-enhanced magnetic resonance (MR) angiograms of the peripheral vasculature. Incorporation of two-dimensional homodyne reconstruction modified the EC view order, allowing improved spatial resolution per unit time while retaining the advantage of venous suppression intrinsic to the EC technique. Spatial resolution was dynamically improved when the table reached the distal-most station. The modified view order provided improved spatial resolution in phantom examinations compared with that in standard examinations. Peripheral MR angiograms were generated in a group of 13 volunteers (eight women; five men; age range, 51-72 years; mean age, 58.5 years +/- 7.9 [standard deviation]) at 1.5 T. Four arterial regions were evaluated on a five-point scale (scores ranged from 0 to 4; a score of 4 was considered excellent); venous suppression was also evaluated. The mean arterial scores exceeded 3.0 for all regions. There was no venous signal or only superficial venous signal in 10 of the 13 cases.

Aged↗

PubMed2005

Dual-velocity continuously moving table acquisition for contrast-enhanced peripheral magnetic resonance angiography.

Acquisition of MR angiographic data of the peripheral vasculature during continuous table motion offers certain advantages over fixed station approaches, such as the elimination of wasted time moving between stations and the ability to form a seamless image of the extended field of view. However, it has recently been demonstrated that there is an approximate twofold reduction in contrast bolus velocity as it moves from the thighs to the calves. This can potentially cause a mismatch of the moving table with the contrast peak, resulting in the table outpacing the contrast bolus distally. In this work we describe a modification to the continuous table motion technique allowing two table velocities: a high (ca. 3.6 cm/sec) velocity from the abdomen to the thighs and a low (ca. 1.6 cm/sec) velocity distally. Implications of the nonconstant velocity on k-space sampling are described, and it is shown that lateral resolution is improved for the low-velocity region. Correction for table deceleration during the transition time between high and low velocities is demonstrated. Contrast-enhanced studies in 15 volunteers are free of table-motion-related artifact and suggest improved depiction of the contrast bolus distally.

Aged↗

PubMed2005

Variable field of view for spatial resolution improvement in continuously moving table magnetic resonance imaging.

An approach is described in which the field of view (FOV) along the Y (right/left) phase encoding direction can be dynamically altered during a continuously moving table (CMT) coronal acquisition for extended FOV MRI. We hypothesize that with this method, regions of the anatomy exhibiting significantly different lateral widths can be imaged with a matching local FOV(Y), thereby improving local lateral spatial resolution. k-space raw data from the variable-FOV CMT acquisition do not allow simple Fourier reconstruction due to the presence of a mixture of phase encodes sampled at different Deltak(Y) intervals. In this work, we employ spline interpolation to reregister the mixed data set onto a uniformly sampled k-space grid. Using this interpolation scheme, we present phantom and peripheral contrast-enhanced MR angiography results demonstrating an approximate 45% improvement in local lateral spatial resolution for continuously moving table acquisitions.

Algorithms↗

PubMed2005

Recovery of phase inconsistencies in continuously moving table extended field of view magnetic resonance imaging acquisitions.

MR images formed using extended FOV continuously moving table data acquisition can have signal falloff and loss of lateral spatial resolution at localized, periodic positions along the direction of table motion. In this work we identify the origin of these artifacts and provide a means for correction. The artifacts are due to a mismatch of the phase of signals acquired from contiguous sampling fields of view and are most pronounced when the central k-space views are being sampled. Correction can be performed using the phase information from a periodically sampled central view to adjust the phase of all other views of that view cycle, making the net phase uniform across each axial plane. Results from experimental phantom and contrast-enhanced peripheral MRA studies show that the correction technique substantially eliminates the artifact for a variety of phase encode orders.

Artifacts↗

PubMed2005

Continuously moving table MRI with SENSE: application in peripheral contrast enhanced MR angiography.

An integration of SENSitivity Encoding (SENSE) with continuously moving table (CMT) MRI for extended field-of-view (FOV) acquisitions is described. In this work, the approach in which receiver coils are attached to the object and move in synchrony with the scanner table is considered. Technical issues dealing with the implementation of SENSE-CMT are addressed, including coil calibration, correction for non-uniform magnetic gradients, and specific reconstruction steps. An explanation of combining SENSE with gradient non-linearity correction is given, as the latter becomes necessary in CMT acquisitions where a large sampling FOV is used. It is hypothesized that SENSE can provide at least a 2-fold improvement in lateral spatial resolution compared to non-accelerated CMT acquisitions. The hypothesis is tested in phantoms, where the effectiveness of both SENSE and gradient non-linearity correction to improve spatial resolution is shown. The SENSE-CMT technique is further demonstrated in vivo with contrast-enhanced MR angiography of the peripheral vasculature.

Equipment Design↗

PubMed2005

CT fluoroscopy-guided biopsy of the lung or upper abdomen with a breath-hold monitoring and feedback system: a prospective randomized controlled clinical trial.

PURPOSE: To prospectively determine the clinical effectiveness of a breath-hold monitoring and feedback system in computed tomographic (CT) fluoroscopy-guided biopsies in which respiratory motion is a problem. MATERIALS AND METHODS: Institutional review board approval and oral and written informed consent were obtained. This study was HIPAA compliant. A bellows-based system was used to monitor respiration and provide patient feedback. A randomized controlled clinical trial compared intermittent mode CT fluoroscopy-guided biopsies of the lung or upper abdomen performed with (n = 56) and without (n = 57) the bellows system. Inclusion criteria for 113 patients were lesions 6 cm or smaller in maximum dimension that were not affixed to the chest or abdominal wall. Primary outcome measurements were CT fluoroscopy exposure time and patient dose. Wilcoxon rank sum, chi(2), and Fisher exact tests were used for statistical analysis. RESULTS: Median CT fluoroscopy exposure time was 12.6 seconds (range, 2.4-44.4 seconds) for the bellows group and 18.0 seconds (range, 6.0-118.0 seconds) for the nonbellows group (P = .004). Patient dose was decreased in the bellows group (median dose, 29.5 mGy; range, 4.7-135.8 mGy) versus the nonbellows group (median, 41.3 mGy; range, 11.8-155.9 mGy) (P = .01). Lesions were accessed successfully with one needle puncture attempt in 43 of 56 patients (77%) in the bellows group and 30 of 57 patients (53%) in the nonbellows group (P = .007). Pneumothorax developed in 11 of 50 patients (22%) in the bellows group who underwent lung biopsy compared with 16 of 50 (32%) patients in the nonbellows group. CONCLUSION: A breath-hold monitoring and feedback system allows depiction of mobile target lesions throughout CT fluoroscopy-guided biopsy of the lung and upper abdomen.

Abdomen↗

PubMed2004

Time-resolved 3D contrast-enhanced MRA of an extended FOV using continuous table motion.

A method is presented for acquiring 3D time-resolved MR images of an extended (>100 cm) longitudinal field of view (FOV), as used for peripheral MR angiographic runoff studies. Previous techniques for long-FOV peripheral MRA have generally provided a single image (i.e., with no time resolution). The technique presented here generates a time series of 3D images of the FOV that lies within the homogeneous volume of the magnet. This is achieved by differential sampling of 3D k-space during continuous motion of the patient table. Each point in the object is interrogated in five consecutive 3D image sets generated at 2.5-s intervals. The method was tested experimentally in eight human subjects, and the leading edge of the bolus was observed in real time and maintained within the imaging FOV. The data revealed differential bolus velocities along the vasculature of the legs.

Algorithms↗

PubMed2004

Improved venous suppression and spatial resolution with SENSE in elliptical centric 3D contrast-enhanced MR angiography.

The elliptical centric (EC) view order samples a 3DFT acquisition from the center of k-space outward, and when applied to contrast-enhanced MR angiography (CE-MRA) provides intrinsic venous suppression. This is because the veins enhance several seconds after the scan is initiated, and are thus encoded solely by noncentral k-space frequencies. A separate method, sensitivity encoding (SENSE), accelerates the k-space sampling rate by reducing the phase FOV or, equivalently, by increasing the k-space sampling interval, and has been used to increase spatiotemporal resolution. We hypothesized that by combining SENSE with EC, sampling of central k-space would be accelerated and the k-space radius at which the veins first showed contrast enhancement would be increased over a reference scan, thus providing improved venous suppression and spatial resolution without additional scan time. This hypothesis was studied with the use of phantom and carotid CE-MRA experiments, and the results demonstrated an approximate 25% reduction in venous signal when SENSE was used.

Blood Flow Velocity↗

PubMed2003

Intermittent-mode CT fluoroscopy-guided biopsy of the lung or upper abdomen with breath-hold monitoring and feedback: system development and feasibility.

A bellows-based breath-hold monitoring and feedback system was developed and evaluated for use in intermittent-mode computed tomographic (CT) fluoroscopy-guided biopsy procedures in the lung or upper abdomen. The bellows system is described, and its feasibility is demonstrated in studies with a respiratory phantom and human volunteers. Results are reported for seven patients who underwent bellows-assisted biopsy. Breath-hold monitoring and feedback with the bellows system allow the patient to perform reliable breath holding at a preselected level. This optimizes intermittent-mode CT fluoroscopy-guided biopsies by allowing consistent visualization of the target lesion throughout the procedure.

Abdomen↗

PubMedDate not supplied

Parallel MR imaging: a user's guide.

Parallel imaging is a recently developed family of techniques that take advantage of the spatial information inherent in phased-array radiofrequency coils to reduce acquisition times in magnetic resonance imaging. In parallel imaging, the number of sampled k-space lines is reduced, often by a factor of two or greater, thereby significantly shortening the acquisition time. Parallel imaging techniques have only recently become commercially available, and the wide range of clinical applications is just beginning to be explored. The potential clinical applications primarily involve reduction in acquisition time, improved spatial resolution, or a combination of the two. Improvements in image quality can be achieved by reducing the echo train lengths of fast spin-echo and single-shot fast spin-echo sequences. Parallel imaging is particularly attractive for cardiac and vascular applications and will likely prove valuable as 3-T body and cardiovascular imaging becomes part of standard clinical practice. Limitations of parallel imaging include reduced signal-to-noise ratio and reconstruction artifacts. It is important to consider these limitations when deciding when to use these techniques.

Artifacts↗