All Publications

  • Relaxation measurements of an MRI system phantom at low magnetic field strengths MAGNETIC RESONANCE MATERIALS IN PHYSICS BIOLOGY AND MEDICINE Martin, M. N., Jordanova, K. V., Kos, A. B., Russek, S. E., Keenan, K. E., Stupic, K. F. 2023; 36 (3): 477-485

    Abstract

    Temperature controlled T1 and T2 relaxation times are measured on NiCl2 and MnCl2 solutions from the ISMRM/NIST system phantom at low magnetic field strengths of 6.5 mT, 64 mT and 550 mT.The T1 and T2 were measured of five samples with increasing concentrations of NiCl2 and five samples with increasing concentrations of MnCl2. All samples were scanned at 6.5 mT, 64 mT and 550 mT, at sample temperatures ranging from 10 °C to 37 °C.The NiCl2 solutions showed little change in T1 and T2 with magnetic field strength, and both relaxation times decreased with increasing temperature. The MnCl2 solutions showed an increase in T1 and a decrease in T2 with increasing magnetic field strength, and both T1 and T2 increased with increasing temperature.The low field relaxation rates of the NiCl2 and MnCl2 arrays in the ISMRM/NIST system phantom are investigated and compared to results from clinical field strengths of 1.5 T and 3.0 T. The measurements can be used as a benchmark for MRI system functionality and stability, especially when MRI systems are taken out of the radiology suite or laboratory and into less traditional environments.

    View details for DOI 10.1007/s10334-023-01086-y

    View details for Web of Science ID 000991167800001

    View details for PubMedID 37209233

    View details for PubMedCentralID PMC10386925

  • Challenges in ensuring the generalizability of image quantitation methods for MRI. Medical physics Keenan, K. E., Delfino, J. G., Jordanova, K. V., Poorman, M. E., Chirra, P., Chaudhari, A. S., Baessler, B., Winfield, J., Viswanath, S. E., deSouza, N. M. 2021

    Abstract

    Image quantitation methods including quantitative MRI, multiparametric MRI, and radiomics, offer great promise for clinical use. However, many of these methods have limited clinical adoption, in part due to issues of generalizability, i.e., the ability to translate methods and models across institutions. Researchers can assess generalizability through measurement of repeatability and reproducibility, thus quantifying different aspects of measurement variance. In this article, we review the challenges to ensuring repeatability and reproducibility of image quantitation methods as well as present strategies to minimize their variance to enable wider clinical implementation. We present possible solutions for achieving clinically acceptable performance of image quantitation methods and briefly discuss the impact of minimizing variance and achieving generalizability towards clinical implementation and adoption. This article is protected by copyright. All rights reserved.

    View details for DOI 10.1002/mp.15195

    View details for PubMedID 34455593

  • Measuring B-1 distributions by B-1 phase encoding MAGNETIC RESONANCE IN MEDICINE Jordanova, K. V., Nishimura, D. G., Kerr, A. B. 2017; 77 (1): 229-236

    Abstract

    We propose a method to acquire B1 distribution plots by encoding in B1 instead of image space. Using this method, B1 data is acquired in a different way from traditional spatial B1 mapping, and allows for quick measurement of high dynamic range B1 data.To encode in B1, we acquire multiple projections of a slice, each along the same direction, but using a different phase sensitivity to B1. Using a convex optimization formulation, we reconstruct histograms of the B1 distribution estimates of the slice.We verify in vivo B1 distribution measurements by comparing measured distributions to distributions calculated from reference spatial B1 maps using the Earth Mover's Distance. Phantom measurements using a surface coil show that for increased spatial B1 variations, measured B1 distributions using the proposed method more accurately estimate the distribution than a low-resolution spatial B1 map, resulting in a 37% Earth Mover's Distance decrease while using fewer measurements.We propose and validate the performance of a method to acquire B1 distribution information directly without acquiring a spatial B1 map. The method may provide faster estimates of a B1 field for applications that do not require spatial B1 localization, such as the transmit gain calibration of the scanner, particularly for high dynamic B1 ranges. Magn Reson Med 77:229-236, 2017. © 2016 Wiley Periodicals, Inc.

    View details for DOI 10.1002/mrm.26114

    View details for Web of Science ID 000391038800024

    View details for PubMedCentralID PMC4947573

  • Lowering the B1 threshold for improved BEAR B1 mapping. Magnetic resonance in medicine Jordanova, K. V., Nishimura, D. G., Kerr, A. B. 2016; 75 (3): 1262-1268

    Abstract

    Accurate measurement of the nonuniform transmit radiofrequency field is necessary for magnetic resonance imaging applications. The radiofrequency field excitation amplitude (B1 ) is often obtained by acquiring a B1 map. We modify the B1 estimation using adiabatic refocusing (BEAR) method to extend its range to lower B1 magnitudes.The BEAR method is a phase-based B1 mapping method, wherein hyperbolic secant pulses induce a phase sensitivity to B1 . The measurable B1 range is limited due to the adiabatic threshold of the pulses. We redesign the method to use flattened hyperbolic secant pulses, which have lower adiabatic thresholds. We optimize the flattened hyperbolic secant parameters to minimize phase sensitivity to frequency variations.We validate the performance of the new method via simulation and in vivo at 3T, and show that for n≤8, accurate B1 maps can be acquired using reduced nominal peak B1 values.The adiabatic threshold for the BEAR method is reduced with flattened hyperbolic secant pulses, which are optimized for accurate phase-to-B1 mapping over a frequency range, and allow for lower nominal B1 values. At 3T, the nominal B1 is decreased by 52% and the sensitivity to B1 is increased by a factor of 3.8. This can improve the method's applicability for measurement of low B1 . Magn Reson Med 75:1262-1268, 2016. © 2015 Wiley Periodicals, Inc.

    View details for DOI 10.1002/mrm.25711

    View details for PubMedID 25846905

  • B-1 Estimation Using Adiabatic Refocusing: BEAR MAGNETIC RESONANCE IN MEDICINE Jordanova, K. V., Nishimura, D. G., Kerr, A. B. 2014; 72 (5): 1302-1310

    Abstract

    Accurate measurement of the nonuniform transmit radiofrequency field is useful for many applications in magnetic resonance imaging, such as calibrating the scanner transmit system, evaluating coil performance, and improving image quality and quantitation. The radiofrequency field excitation amplitude (B(1)) is often obtained by acquiring a B(1) map. In this study, a new B(1) mapping method is proposed.The use of two adiabatic full passage pulses with different magnitudes applied as successive refocusing pulses results in a linear relationship between phase and B(1) field strength that is insensitive to the repetition time, off-resonance effects, T(1), and T(2). Using this method, B(1) mapping can be localized to a slice or three-dimensional (3D) volume, with a spin-echo acquisition that is appropriate for fast projection measurements.This new method is shown to agree well with the Bloch-Siegert B(1) mapping method for both phantom and in vivo B(1) measurements at 1.5T, 3T, and 7T. The method's ability to acquire accurate projection B(1) measurements is also demonstrated.This method's high dynamic range, ability to make fast projection measurements, and linear quantitative relationship between phase and B1 make it an ideal candidate for use in robust transmitter gain calibration.

    View details for DOI 10.1002/mrm.25049

    View details for Web of Science ID 000343873900012

    View details for PubMedCentralID PMC4031300

https://orcid.org/0000-0002-9097-3863