Curtis A. Corum

Detection of calcifications in vivo and ex vivo after brain injury in rat using SWIFT

Calcifications represent one component of pathology in many brain diseases. With MRI, they are most often detected by exploiting negative contrast in magnitude images. Calcifications are more diamagnetic than tissue, leading to a magnetic field disturbance that can be seen in phase MR images. Most phase imaging studies use gradient recalled echo based pulse sequences. Here, the phase component of SWIFT, a virtually zero acquisition delay sequence, was used to detect calcifications ex vivo and in vivo in rat models of status epilepticus and traumatic brain injury. Calcifications were detected in phase and imaginary SWIFT images based on their dipole like magnetic field disturbances. In magnitude SWIFT images, calcifications were distinguished as hypointense and hyperintense. Hypointense calcifications showed large crystallized granules with few surrounding inflammatory cells, while hyperintense calcifications contained small granules with the presence of more inflammatory cells. The size of the calcifications in SWIFT magnitude images correlated with that in Alizarin stained histological sections. Our data indicate that SWIFT is likely to better preserve signal in the proximity of a calcification or other field perturber in comparison to gradient echo due to its short acquisition delay and broad excitation bandwidth. Furthermore, a quantitative description for the phase contrast near dipole magnetic field inhomogeneities for the SWIFT pulse sequence is given. In vivo detection of calcifications provides a tool to probe the progression of pathology in neurodegenerative diseases. In particular, it appears to provide a surrogate marker for inflammatory cells around the calcifications after brain injury.

Quantifying iron‐oxide nanoparticles at high concentration based on longitudinal relaxation using a three‐dimensional SWIFT look‐locker sequence

Iron‐oxide nanoparticles (IONPs) have proven utility as contrast agents in many MRI applications. Previous quantitative IONP mapping has been performed using mainly T2* mapping methods. However, in applications requiring high IONP concentrations, such as magnetic nanoparticles based thermal therapies, conventional pulse sequences are unable to map T2* because the signal decays too rapidly. In this article, sweep imaging with Fourier transformation (SWIFT) sequence is combined with the Look‐Locker method to map T1 of IONPs in high concentrations.

T1 estimation for aqueous iron oxide nanoparticle suspensions using a variable flip angle SWIFT sequence

T1 quantification of contrast agents, such as super‐paramagnetic iron oxide nanoparticles, is a challenging but important task inherent to many in vivo applications in magnetic resonance imaging. In this work, a sweep imaging with Fourier transformation using variable flip angles (VFAs‐SWIFT) method was proposed to measure T1 of aqueous super‐paramagnetic iron oxide nanoparticle suspensions.

Transformation in mandibular imaging with sweep imaging with fourier transform magnetic resonance imaging

OBJECTIVE Current imaging techniques are often suboptimal for the detection of mandibular invasion by squamous cell carcinoma. The aim of this study was to determine the feasibility of a magnetic resonance imaging (MRI)-based technique known as sweep imaging with Fourier transform (SWIFT) to visualize the structural changes of intramandibular anatomy during invasion. DESIGN Descriptive case study. SETTING Tertiary academic institution. PATIENTS Patients with oral carcinoma who underwent segmental mandibulectomy. INTERVENTIONS Two specimens from each patient were imaged using a 9.4-T Varian MRI system. The SWIFT images were correlated with histologic sections. RESULTS The SWIFT technique with in vitro specimens produced images with sufficient resolution (156-273 μm) and contrast to allow accurate depiction of tumor invasion of cortical and medullary bone. Both specimens had histopathologic evidence of mandibular invasion with tumor. A high degree of correlation was found between magnetic resonance images and histopathologic findings. CONCLUSIONS The SWIFT MRI offers 3-dimensional assessment of cortical and medullary bone in fine detail and excellent qualitative agreement with histopathologic findings. Imaging with the SWIFT MRI technique demonstrates great potential to identify mandibular invasion by oral carcinoma.

Intraoral approach for imaging teeth using the transverse B1 field components of an occlusally oriented loop coil

The signal‐to‐noise ratio and resolution are two competing parameters for dental MRI and are highly dependent on the radiofrequency coil configuration and performance. The purpose of this work is to describe an intraoral approach for imaging teeth with the radiofrequency coil plane oriented orthogonally to the Zeeman field to use the transverse components of the B1 field for transmitting and receiving the NMR signal.

Multi-Band-SWIFT

A useful extension to SWIFT (SWeep Imaging with Fourier Transformation) utilizing sidebands of the excitation pulse is introduced. This MRI method, called Multi-Band-SWIFT, achieves much higher bandwidth than standard SWIFT by using multiple segmented excitations (bands) of the field of view. A description of the general idea and variants of the pulse sequence are presented. From simulations and semi-phenomenological theory, estimations of power deposition and signal-to-noise ratio are made. MB-SWIFT and ZTE (zero-TE) sequences are compared based on images of a phantom and human mandible. Multi-Band-SWIFT provides a bridge between SWIFT and ZTE sequences and allows greatly increased excitation and acquisition bandwidths relative to standard SWIFT for the same hardware switching parameters and requires less peak amplitude of the radiofrequency field (or greater flip angle at same peak amplitude) as compared to ZTE. Multi-Band-SWIFT appears to be an attractive extension of SWIFT for certain musculoskeletal and other medical imaging applications, as well as for imaging materials.

MRI by steering resonance through space

This work introduces a technique to excite MR signals locally and to steer this localized region over the object in a spatiotemporal manner. The purpose is to demonstrate the feasibility of MRI with multidimensional spatiotemporal‐encoding in a way that provides the ability to compensate extreme field inhomogeneity.

Gradient-modulated SWIFT

Methods designed to image fast‐relaxing spins, such as sweep imaging with Fourier transformation (SWIFT), often utilize high excitation bandwidth and duty cycle, and in some applications the optimal flip angle cannot be used without exceeding safe specific absorption rate (SAR) levels. The aim is to reduce SAR and increase the flexibility of SWIFT by applying time‐varying gradient‐modulation (GM). The modified sequence is called GM‐SWIFT.

Feasibility of single-voxel MRS measurement of apparent diffusion coefficient of water in breast tumors.

We report initial results with single voxel spectroscopy (SVS) using diffusion weighting and localization by adiabatic selective refocusing (LASER) in breast tumors to measure the apparent diffusion coefficient of water (ADCw). This is a quick (30 s) and relatively easy method to implement compared with image‐based diffusion measurements, and is insensitive to lipid signal contamination. The ADCw and concentration of total choline containing compounds [tCho] were evaluated for associations with each other and final pathologic diagnosis in 25 subjects. The average (± SD) ADCw in benign and malignant lesions was 1.96 ± 0.47 mm2/s and 1.26 ± 0.29 × 10−3 mm2/s, respectively, P< 0.001. Receiver operating characteristic curve analysis showed an area under the curve of 0.92. Analysis of the single voxel (SV) ADCw and [tCho] showed significant correlation with a R2 of 0.56, P< 0.001. Compared with more commonly used image‐based methods of measuring water ADC, SV‐ADCw is faster, more robust, insensitive to fat, and potentially easier to implement on standard clinical systems. Magn Reson Med, 2009.

Measurement of T1 relaxation time of osteochondral specimens using VFA-SWIFT

To evaluate the feasibility of SWIFT with variable flip angle (VFA) for measurement of T1 relaxation time in Gd‐agarose‐phantoms and osteochondral specimens, including regions of very short T2*, and compare with T1 measured using standard methods