Faculty Bibliography

Sodium magnetic resonance imaging (MRI) is highly sensitive to cellular ionic balance due to tenfold difference in sodium concentration across membranes, actively maintained by the sodium-potassium (Na⁺-K⁺) pump. Disruptions in this pump or membrane integrity, as seen in neurological disorders like epilepsy, multiple sclerosis, bipolar disease, and mild traumatic brain injury, lead to increased intracellular sodium. However, this cellular-level alteration is often masked by the dominant extracellular sodium signal, making it challenging to distinguish sodium populations with mono- vs. bi-exponential transverse (T₂) decays-especially given the low signal-to-noise ratio (SNR) even at an advanced clinical field of 3 Tesla. Here, we propose a novel technique that leverages intrinsic difference in T₂ decays by acquiring single-quantum images at multiple echo times (TEs) and applying voxel-wise matrix inversion for accurate signal separation. Using numerical models, agar phantoms, and human subjects, we achieved high separation accuracy in phantoms (95.8% for mono-T₂ and 72.5-80.4% for bi-T₂) and demonstrated clinical feasibility in humans. This approach may enable early detection of neurological disorders and early assessment of treatment responses at the cellular level using sodium MRI at 3 T.

PURPOSE/OBJECTIVE:Na images. METHODS:Na TPI brain datasets of healthy controls acquired on a 3T Siemens Prisma system were reconstructed using conventional reconstruction, AGR and AGRdm. RESULTS:Our simulations show that compared to conventional reconstructions, AGR and AGRdm show improved bias-noise characteristics in several regions of the brain. Moreover, AGR and AGRdm images show more anatomical detail and less noise in the reconstructions of the experimental data sets. Compared to AGR and the conventional reconstruction, AGRdm shows higher contrast in the sodium concentration ratio between gray and white matter and between gray matter and the brain stem. CONCLUSION/CONCLUSIONS:Na MR imaging at 3T.

BACKGROUND: THE PURPOSE OF THE STUDY/OBJECTIVE:Na MRI dual echo relative to TSC imaging. METHODS:Na MRI) were assessed. RESULTS:Na MRI suppressed the sodium signal within both CSF and necrotic foci. CONCLUSION/CONCLUSIONS:Na MRI of BCS improves tissue conspicuity relative to TSC imaging.

Osteoarthritis (OA) is a leading cause of pain and disability for which disease-modifying treatments remain lacking. This is because the symptoms and radiographic changes of OA occur after the onset of likely irreversible changes. Defining and treating earlier disease states are therefore needed to delay or to halt OA progression. Taking this concept a step further, studying OA pathogenesis before disease onset by characterizing potentially reversible markers of increased OA risk to identify a state of "pre-osteoarthritis (pre-OA)" shifts the paradigm towards OA prevention. The purpose of this review is to summarize the 42 studies comprising the 2019 Kappa Delta Elizabeth Lanier Award where conceptualization of a systems-based definition for "pre-osteoarthritis (pre-OA)" was followed by demonstration of potentially reversible markers of heightened OA risk in patients after anterior cruciate ligament (ACL) injury and reconstruction. In the process, these efforts contributed a new magnetic resonance imaging method of ultrashort echo time (UTE) enhanced T2* mapping to visualize joint tissue damage before the development of irreversible changes. The studies presented here support a transformative approach to OA that accounts for interactions between mechanical, biological, and structural markers of OA risk to develop and evaluate new treatment strategies that can delay or prevent the onset of clinical disease. This body of work was inspired by and performed for patients. Shifting the paradigm from attempting to modify symptomatic radiographic OA towards monitoring and reversing markers of "pre-OA" opens the door for transforming the clinical approach to OA from palliation to prevention.

BACKGROUND:The necessity of the inferior pulmonary ligament (IPL) dissection after an upper lobectomy remains controversial. This meta-analysis aimed to evaluate whether this accessional procedure could reduce the postoperative complications and improve outcomes. METHODS:PubMed, Embase, Ovid, Cochrane Library, CBM, and CNKI databases were searched for the relevant studies which compared the dissection with preservation of IPL during the upper lobectomy. The Review Manager 5.3 software was used for this meta-analysis. RESULTS:Three RCTs and five CCTs were included in this meta-analysis. These studies contained a total of 610 patients, in which 315 patients received a pulmonary ligament dissection (group D) after the upper lobectomy, while the other 295 patients preserved the pulmonary ligament (group P). No significant difference was demonstrated between the group D and group P in terms of drainage time after surgery (MD 0.14, 95%CI - 0.05 to 0.33, P = 0.15), rate of postoperative dead space (OR 1.33, 95%CI 0.72 to 2.46, P = 0.36), rate of postoperative complications (OR 1.20, 95%CI 0.66 to 2.19, P = 0.56). However, the pooled comparison revealed a greater change of the right main bronchial angle (MD 5.00, 95%CI 1.68 to 8.33, P = 0.003) in group D compared with group P, indicated that the dissection of IPL may lead to a greater distortion of bronchus. CONCLUSIONS:This meta-analysis confirmed that the dissection of IPL do not effectively reduce the postoperative complications and improve the prognosis. Therefore, it is not necessary to dissect the IPL after an upper lobectomy.

PURPOSE:To demonstrate a circular EPI (CEPI) sequence as well as a generalized EPI reconstruction for fast fMRI with parallel imaging acceleration. METHODS:The CEPI acquisition was constructed using variable readout lengths and maximum ramp sampling as well as blipped-CAIPI z-gradient encoding for simultaneous multislice (SMS) and 3D volumetric imaging. A signal equation model with constant and linear phase terms was used to iteratively reconstruct images with low ghosting. Simulation, phantom, and human imaging experiments including audio/visual fMRI were performed at 3T using a 52-channel coil. RESULTS:Application of CEPI gradients with duration of 27 ms covering a 22-cm FOV at a 64 × 64 pixel resolution in SMS and 3D acquisitions resulted in images with comparable quality to those of standard Cartesian EPI. With parallel imaging techniques robust detection of BOLD fMRI activation with temporal sampling down to 275 ms was possible. The high temporal resolution enabled higher activation statistics at a penalty in increased noise and residual aliasing. The un-accelerated 3D acquisition showed large temporal instability compared with a standard 2D acquisition. CONCLUSION:Nonuniform sampling and generalized image reconstructions can be applied to EPI acquisitions including those with blipped-CAIPI z gradients. The same gradients can be used for either SMS or 3D acquisitions providing identical coverage.

The purpose of this work is to illustrate a new coil decoupling strategy and its application to a transmit/receive sodium/proton phased array for magnetic resonance imaging (MRI) of the human brain. We implemented an array of eight triangular coils that encircled the head. The ensemble of coils was arranged to form a modified degenerate mode birdcage whose eight shared rungs were offset from the z-axis at interleaved angles of ±30°. This key geometric modification resulted in triangular elements whose vertices were shared between next-nearest neighbors, which provided a convenient location for counter-wound decoupling inductors, whilst nearest-neighbor decoupling was addressed with shared capacitors along the rungs. This decoupling strategy alleviated the strong interaction that is characteristic of array coils at low frequency (32.6 MHz in this case) and allowed the coil to operate efficiently in transceive mode. The sodium array provided a 1.6-fold signal-to-noise ratio advantage over a dual-nuclei birdcage coil in the center of the head and up to 2.3-fold gain in the periphery. The array enabled sodium MRI of the brain with 5-mm isotropic resolution in approximately 13 min, thus helping to overcome low sodium MR sensitivity and improving quantification in neurological studies. An eight-channel proton array was integrated into the sodium array to enable anatomical imaging.

The ability to assess tumor apoptotic response to therapy could provide a direct and prompt measure of therapeutic efficacy. ¹⁸F-labeled 2-(5-fluoro-pentyl)-2-methyl-malonic acid ([¹⁸F]ML-10) is proposed as a positron emission tomography (PET) apoptosis imaging radiotracer. This manuscript presents initial experience using [¹⁸F]ML-10 PET to predict therapeutic response in 4 patients with human glioblastoma multiforme. Each patient underwent [¹⁸F]ML-10 PET and contrast-enhanced magnetic resonance imaging (MRI) before (baseline) and at ∼2-3 weeks after therapy (early-therapy assessment). All PET and MRI data were acquired using a Siemens BioGraph mMR integrated PET/MRI scanner. PET acquisitions commenced 120 minutes after injection with 10 mCi of [¹⁸F]ML-10. Changes in [¹⁸F]ML-10 standard uptake values were assessed in conjunction with MRI changes. Time-to-progression was used as the outcome measure. One patient, ML-10 #4, underwent additional sodium-23 (²³Na) MRI at baseline and early-therapy assessment. Siemens 3 T Magnetom Tim Trio scanner with a dual-tuned (¹H-²³Na) head coil was used for ²³Na-MRI, acquiring two three-dimensional single-quantum sodium images at two echo times (TE). Volume-fraction-weighted bound sodium concentration was quantified through pixel-by-pixel subtraction of the two single-quantum sodium images. In the cases presented, [¹⁸F]ML-10 uptake changes were not clearly related to time-to-progression. We suggest that this may be because the tumors are undergoing varying rates of cell death and growth. Acquisition of complementary measures of tumor cell proliferation or viability may aid in the interpretation of PET apoptosis imaging.

PURPOSE: This work intends to demonstrate a new method for quantifying concentration of sodium (23 Na) of bi-exponential T2 relaxation in patients on MRI scanners at 3.0 Tesla. THEORY AND METHODS: Two single-quantum (SQ) sodium images acquired at very-short and short echo times (TE = 0.5 and 5.0 ms) are subtracted to produce an image of the short-T2 component of the bi-exponential (or bound) sodium. An integrated calibration on the SQ and short-T2 images quantifies both total and bound sodium concentrations. Numerical models were used to evaluate signal response of the proposed method to the short-T2 components. MRI scans on agar phantoms and brain tumor patients were performed to assess accuracy and performance of the proposed method, in comparison with a conventional method of triple-quantum filtering. RESULTS: A good linear relation (R2 = 0.98) was attained between the short-T2 image intensity and concentration of bound sodium. A reduced total scan time of 22 min was achieved under the SAR restriction for human studies in quantifying both total and bound sodium concentrations. CONCLUSION: The proposed method is feasible for quantifying bound sodium concentration in routine clinical settings at 3.0 Tesla. Magn Reson Med, 2014. (c) 2014 Wiley Periodicals, Inc.