Kalina Jordanova

All Publications

• Paramagnetic salt and agarose recipes for phantoms with desired T1 and T2 values for low-field MRI. NMR in biomedicine Jordanova, K. V., Fraenza, C. C., Martin, M. N., Tian, Y., Shen, S., Vaughn, C. E., Walsh, K. J., Walsh, C., Sappo, C. R., Ogier, S. E., Poorman, M. E., Teixeira, R. P., Grissom, W. A., Nayak, K. S., Rosen, M. S., Webb, A. G., Greenbaum, S. G., Witherspoon, V. J., Keenan, K. E. 2024: e5281

  Abstract

  Tissue-mimicking reference phantoms are indispensable for the development and optimization of magnetic resonance (MR) measurement sequences. Phantoms have greatest utility when they mimic the MR signals arising from tissue physiology; however, many of the properties underlying these signals, including tissue relaxation characteristics, can vary as a function of magnetic field strength. There has been renewed interest in magnetic resonance imaging (MRI) at field strengths less than 1 T, and phantoms developed for higher field strengths may not be physiologically relevant at these lower fields. This work focuses on developing materials with specific relaxation properties for lower magnetic field strengths. Specifically, we developed recipes that can be used to create synthetic samples for target nuclear magnetic resonance relaxation values for fields between 0.0065 and 0.55 T. T 1 $$ {T}_1 $$ and T 2 $$ {T}_2 $$ mixing models for agarose-based gels doped with a paramagnetic salt (one of CuSO4, GdCl3, MnCl2, or NiCl2) were created using relaxation measurements of synthetic gel samples at 0.0065, 0.064, and 0.55 T. Measurements were evaluated for variability with respect to measurement repeatability and changing synthesis protocol or laboratory temperature. The mixing models were used to identify formulations of agarose and salt composition to approximately mimic the relaxation times of five neurological tissues (blood, cerebrospinal fluid, fat, gray matter, and white matter) at 0.0065, 0.0475, 0.05, 0.064, and 0.55 T. These mimic sample formulations were measured at each field strength. Of these samples, the GdCl3 and NiCl2 measurements were closest to the target tissue relaxation times. The GdCl3 or NiCl2 mixing model recipes are recommended for creating target relaxation samples below 0.55 T. This work can help development of MRI methods and applications for low-field systems and applications.

  View details for DOI 10.1002/nbm.5281

  View details for PubMedID 39552017

• Iron oxide nanoparticles as positive T1 contrast agents for low-field magnetic resonance imaging at 64 mT. Scientific reports Oberdick, S. D., Jordanova, K. V., Lundstrom, J. T., Parigi, G., Poorman, M. E., Zabow, G., Keenan, K. E. 2023; 13 (1): 11520

  Abstract

  We have investigated the efficacy of superparamagnetic iron oxide nanoparticles (SPIONs) as positive T1 contrast agents for low-field magnetic resonance imaging (MRI) at 64 millitesla (mT). Iron oxide-based agents, such as the FDA-approved ferumoxytol, were measured using a variety of techniques to evaluate T1 contrast at 64 mT. Additionally, we characterized monodispersed carboxylic acid-coated SPIONs with a range of diameters (4.9-15.7 nm) in order to understand size-dependent properties of T1 contrast at low-field. MRI contrast properties were measured using 64 mT MRI, magnetometry, and nuclear magnetic resonance dispersion (NMRD). We also measured MRI contrast at 3 T to provide comparison to a standard clinical field strength. SPIONs have the capacity to perform well as T1 contrast agents at 64 mT, with measured longitudinal relaxivity (r1) values of up to 67 L mmol-1 s-1, more than an order of magnitude higher than corresponding r1 values at 3 T. The particles exhibit size-dependent longitudinal relaxivities and outperform a commercial Gd-based agent (gadobenate dimeglumine) by more than eight-fold at physiological temperatures. Additionally, we characterize the ratio of transverse to longitudinal relaxivity, r2/r1 and find that it is ~ 1 for the SPION based agents at 64 mT, indicating a favorable balance of relaxivities for T1-weighted contrast imaging. We also correlate the magnetic and structural properties of the particles with models of nanoparticle relaxivity to understand generation of T1 contrast. These experiments show that SPIONs, at low fields being targeted for point-of-care low-field MRI systems, have a unique combination of magnetic and structural properties that produce large T1 relaxivities.

  View details for DOI 10.1038/s41598-023-38222-6

  View details for PubMedID 37460669

  View details for PubMedCentralID PMC10352268

• In vivo quantitative MRI: T1 and T2 measurements of the human brain at 0.064 T. Magma (New York, N.Y.) Jordanova, K. V., Martin, M. N., Ogier, S. E., Poorman, M. E., Keenan, K. E. 2023; 36 (3): 487-498

  Abstract

  To measure healthy brain [Formula: see text] and [Formula: see text] relaxation times at 0.064 T.[Formula: see text] and [Formula: see text] relaxation times were measured in vivo for 10 healthy volunteers using a 0.064 T magnetic resonance imaging (MRI) system and for 10 test samples on both the MRI and a separate 0.064 T nuclear magnetic resonance (NMR) system. In vivo [Formula: see text] and [Formula: see text] values are reported for white matter (WM), gray matter (GM), and cerebrospinal fluid (CSF) for automatic segmentation regions and manual regions of interest (ROIs).[Formula: see text] sample measurements on the MRI system were within 10% of the NMR measurement for 9 samples, and one sample was within 11%. Eight [Formula: see text] sample MRI measurements were within 25% of the NMR measurement, and the two longest [Formula: see text] samples had more than 25% variation. Automatic segmentations generally resulted in larger [Formula: see text] and [Formula: see text] estimates than manual ROIs.[Formula: see text] and [Formula: see text] times for brain tissue were measured at 0.064 T. Test samples demonstrated accuracy in WM and GM ranges of values but underestimated long [Formula: see text] in the CSF range. This work contributes to measuring quantitative MRI properties of the human body at a range of field strengths.

  View details for DOI 10.1007/s10334-023-01095-x

  View details for PubMedID 37208553

  View details for PubMedCentralID PMC10386946

• 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

• Unfolding-synthesis technique for digital pulse processing, Part 2: Synthesis NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT Jordanov, V. T., Jordanova, K. V. 2022; 1044

  View details for DOI 10.1016/j.nima.2022.167421

  View details for Web of Science ID 000877200500011

• 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