Curt Corum

Dental Magnetic Resonance Imaging: Making the Invisible Visible

INTRODUCTION Clinical dentistry is in need of noninvasive and accurate diagnostic methods to better evaluate dental pathosis. The purpose of this work was to assess the feasibility of a recently developed magnetic resonance imaging (MRI) technique, called SWeep Imaging with Fourier Transform (SWIFT), to visualize dental tissues. METHODS Three in vitro teeth, representing a limited range of clinical conditions of interest, imaged using a 9.4T system with scanning times ranging from 100 seconds to 25 minutes. In vivo imaging of a subject was performed using a 4T system with a 10-minute scanning time. SWIFT images were compared with traditional two-dimensional radiographs, three-dimensional cone-beam computed tomography (CBCT) scanning, gradient-echo MRI technique, and histological sections. RESULTS A resolution of 100 μm was obtained from in vitro teeth. SWIFT also identified the presence and extent of dental caries and fine structures of the teeth, including cracks and accessory canals, which are not visible with existing clinical radiography techniques. Intraoral positioning of the radiofrequency coil produced initial images of multiple adjacent teeth at a resolution of 400 μm. CONCLUSIONS SWIFT MRI offers simultaneous three-dimensional hard- and soft-tissue imaging of teeth without the use of ionizing radiation. Furthermore, it has the potential to image minute dental structures within clinically relevant scanning times. This technology has implications for endodontists because it offers a potential method to longitudinally evaluate teeth where pulp and root structures have been regenerated.

RASER: A new ultrafast magnetic resonance imaging method

A new MRI method is described to acquire a T2‐weighted image from a single slice in a single shot. The technique is based on rapid acquisition by sequential excitation and refocusing (RASER). RASER avoids relaxation‐related blurring because the magnetization is sequentially refocused in a manner that effectively creates a series of spin echoes with a constant echo time. RASER uses the quadratic phase produced by a frequency‐swept chirp pulse to time‐encode one dimension of the image. In another implementation the pulse can be used to excite multiple slices with phase‐encoding and frequency‐encoding in the other two dimensions. The RASER imaging sequence is presented along with single‐shot and multislice images, and is compared to conventional spin‐echo and echo‐planar imaging sequences. A theoretical and empirical analysis of the spatial resolution is presented, and factors in choosing the spatial resolution for different applications are discussed. RASER produces high‐quality single‐shot images that are expected to be advantageous for a wide range of applications. Magn Reson Med 58:794–799, 2007.

Dental magnetic resonance imaging

INTRODUCTION Clinical dentistry is in need of noninvasive and accurate diagnostic methods to better evaluate dental pathosis. The purpose of this work was to assess the feasibility of a recently developed magnetic resonance imaging (MRI) technique, called SWeep Imaging with Fourier Transform (SWIFT), to visualize dental tissues. METHODS Three in vitro teeth, representing a limited range of clinical conditions of interest, imaged using a 9.4T system with scanning times ranging from 100 seconds to 25 minutes. In vivo imaging of a subject was performed using a 4T system with a 10-minute scanning time. SWIFT images were compared with traditional two-dimensional radiographs, three-dimensional cone-beam computed tomography (CBCT) scanning, gradient-echo MRI technique, and histological sections. RESULTS A resolution of 100 μm was obtained from in vitro teeth. SWIFT also identified the presence and extent of dental caries and fine structures of the teeth, including cracks and accessory canals, which are not visible with existing clinical radiography techniques. Intraoral positioning of the radiofrequency coil produced initial images of multiple adjacent teeth at a resolution of 400 μm. CONCLUSIONS SWIFT MRI offers simultaneous three-dimensional hard- and soft-tissue imaging of teeth without the use of ionizing radiation. Furthermore, it has the potential to image minute dental structures within clinically relevant scanning times. This technology has implications for endodontists because it offers a potential method to longitudinally evaluate teeth where pulp and root structures have been regenerated.

SWIFT Detection of SPIO Labeled Stem Cells Grafted in the Myocardium

We report initial results from studies using sweep imaging with Fourier transformation (SWIFT) to detect superparamagnetic iron oxide (SPIO) particle–labeled stem cells in the rat heart. In experiments performed on phantoms containing titanium balls or SPIO–labeled cells, frequency‐shifted signals surrounding the paramagnetic objects produced a pileup artifact visualized by SWIFT. Total signal intensity was retained to a much greater extent by SWIFT as compared to gradient echo imaging. SWIFT imaging of excised and in vivo hearts showed (a) reduced blooming artifact as compared with gradient echo imaging, which helped reduce ambiguity in the detection of SPIO–labeled cells; (b) enhancement of off‐resonance signals relative to the background in the imaginary component of images; and (c) detailed myocardial anatomy in magnitude images, which provided anatomic reference. These features suggest SWIFT can facilitate the detection of SPIO–laden cells in the cardiovascular system. Magn Reson Med 63:1154–1161, 2010.

SWIFT MRI Enhances Detection of Breast Cancer Metastasis to the Lung

To evaluate the capability of longitudinal MR scans using sweep imaging with Fourier transformation (SWIFT) to detect breast cancer metastasis to the lung in mice.

Rapid ex vivo imaging of PAIII prostate to bone tumor with SWIFT-MRI

The limiting factor for MRI of skeletal/mineralized tissue is fast transverse relaxation. A recent advancement in MRI technology, SWIFT (Sweep Imaging with Fourier Transform), is emerging as a new approach to overcome this difficulty. Among other techniques like UTE, ZTE, and WASPI, the application of SWIFT technology has the strong potential to impact preclinical and clinical imaging, particularly in the context of primary or metastatic bone cancers because it has the added advantage of imaging water in mineralized tissues of bone allowing MRI images to be obtained of tissues previously visible only with modalities such as computed tomography (CT). The goal of the current study is to examine the feasibility of SWIFT for the assessment of the prostate cancer induced changes in bone formation (osteogenesis) and destruction (osteolysis) in ex vivo specimens.

Exact and stable interior ROI reconstruction for radial MRI

MRI applications often require high spatial and/or temporal resolution within a region of interest (ROI) such as for perfusion studies. In theory, both spatial resolution and temporal resolution can be significantly improved using a ROI-focused MRI data acquisition scheme. However, in radial MRI, there is no such acquisition-based solution available. Traditional reconstruction methods to image the ROI by reducing the field of view produce aliasing artifacts when the dataset becomes truncated. Here we propose an interior MRI methodology to perform ROI reconstruction without artifacts. Methods: In contrast to the conventional wisdom that the interior problem does not have a unique solution, interior tomography has been recently proposed as an exact and stable solution to this longstanding problem. In this project, a ROI-focused radial MRI data acquisition scheme was developed, aided by a dedicated digital filter. We implemented this method in a 4T 90 cm bore Oxford magnet with a GE phantom and a transceiver TEM head coil. The parameters were 4 gauss/cm sonata gradients, 5 mm slice thickness, TE=30 ms, TR=200 ms, FOVs of 40 cm and 12 cm respectively. Results: Both numerical simulation and phantom experiments have demonstrated that the proposed interior MRI method can exactly reconstruct a ROI with increased spatial resolution (~4 fold) while keeping the same temporal resolution. The image artifacts from truncated projections are effectively eliminated. No crosstalk with the outside ROI region is involved using the proposed method. Conclusions: Our interior radial MRI method can be used for zoomed-in and fast

Introduction to SWIFT (Sweep Imaging with Fourier Transformation) for Magnetic Resonance Imaging of Materials

A novel, fast, and quiet method of magnetic resonance imaging (MRI), called SWIFT (sweep imaging with Fourier transformation) has recently been introduced. In addition to SWIFTs potential for in-vivo MRI, it creates new opportunities for MRI of materials. SWIFT currently operates in 3d radial acquisition mode. A series of segmented hyperbolic secant excitation pulses is accompanied by acquisition in the gaps. Each excitation, after correlation with the pulse results in a free induction decay (FID). The spectrum corresponding to the FID is a projection. There is very little “dead time” between excitation and acquisition, making SWIFT useful for imaging of short T 2 materials, but in total imaging times comparable to fast gradient echo sequences.