Charles A Mckenzie

Charles A Mckenzie
The University of Western Ontario | UWO · Department of Medical Biophysics

PhD

About

172
Publications
12,421
Reads
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6,940
Citations
Citations since 2016
37 Research Items
3024 Citations
20162017201820192020202120220100200300400
20162017201820192020202120220100200300400
20162017201820192020202120220100200300400
20162017201820192020202120220100200300400
Additional affiliations
January 2008 - present
July 2007 - present
The University of Western Ontario
July 2007 - June 2016
The University of Western Ontario
Position
  • Professor (Associate)
Education
May 1993 - March 1999
The University of Western Ontario
Field of study
  • Medical Biophysics
September 1987 - April 1993

Publications

Publications (172)
Article
Full-text available
Background Volumetric measurements of fetal brain maturation in the third trimester of pregnancy are key predictors of developmental outcomes. Improved understanding of fetal brain development trajectories may aid in identifying and clinically managing at-risk fetuses. Currently, fetal brain structures in magnetic resonance images (MRI) are often m...
Article
Background: Fetal myelination assessment is important for understanding neurodevelopment and neurodegeneration. Myelin water imaging (MWI) quantifies myelin water fraction (MWF), a validated marker for myelin content, and has been used to assess brain myelin in children and neonates. Purpose: To demonstrate that MWI can quantify MWF in fetal gui...
Preprint
Full-text available
Template-based segmentation techniques have been used for targeting deep brain structures in fetal MR images. In this study, two registration algorithms were compared to determine the optimal strategy of segmenting subcortical structures in T2-weighted images acquired during the third trimester of pregnancy. Adult women with singleton pregnancies (...
Article
Full-text available
Background Assessment of fetal adipose tissue gives information about the future metabolic health of an individual, with evidence that the development of this tissue has regional heterogeneity.Objective To assess differences in the proton density fat fraction (PDFF) between fetal adipose tissue compartments in the third trimester using water-fat ma...
Article
Purpose To demonstrate and validate electric field (E-field) calculation and peripheral nerve stimulation (PNS) prediction methods that are accurate, computationally efficient, and that could be used to inform regulatory standards. Methods We describe a simplified method for calculating the spatial distribution of induced E-field over the volume o...
Conference Paper
Full-text available
Computationally effcient methods are presented which allow calculation of switched-gradient-induced electric field distributions on realistically sized body model with uniform interior properties (compatible with regulatory IEC standards). Electric fields were calculated for three classes of gradient coils (asymmetric head, symmetric head and body...
Article
Background Alterations in glycolysis are central to the increasing incidence of non‐alcoholic fatty liver disease (NAFLD), highlighting a need for in vivo, non‐invasive technologies to understand the development of hepatic metabolic aberrations. Purpose To use hyperpolarized magnetic resonance spectroscopy (MRS) and proton density fat fraction (PD...
Article
Full-text available
Background: Despite its many advantages, experience with fetal magnetic resonance imaging (MRI) is limited, as is knowledge of how fetal tissue relaxation times change with gestational age (GA). Quantification of fetal tissue relaxation times as a function of GA provides insight into tissue changes during fetal development and facilitates comparis...
Preprint
Full-text available
BACKGROUND Alterations in glycolysis and oxidative pathways are central to the increasing incidence of non-alcoholic fatty liver disease (NAFLD), highlighting a need for in vivo , non-invasive technologies to understand the development of hepatic metabolic aberrations in lean NAFLD. PURPOSE/HYPOTHESIS To use hyperpolarized magnetic resonance spect...
Preprint
Full-text available
Purpose: To demonstrate and validate E-field calculation and PNS prediction methods that are accurate, computationally efficient and largely consistent with regulatory standards. Methods: We describe a simplified yet accurate method for calculating the spatial distribution of induced E-field over the volume of a body model given a gradient coil vec...
Article
Full-text available
Observing fetal development in utero is vital to further the understanding of later-life diseases. Magnetic resonance imaging (MRI) offers a tool for obtaining a wealth of information about fetal growth, development, and programming not previously available using other methods. This review provides an overview of MRI techniques used to investigate...
Article
Advanced imaging techniques are enhancing research capacity focussed on the developmental origins of adult health and disease (DOHaD) hypothesis, and consequently increasing awareness of future health risks across various subareas of DOHaD research themes. Understanding how these advanced imaging techniques in animal models and human population stu...
Article
Introduction: Nonalcoholic fatty liver disease (NAFLD) is an obesity-related disorder that is rapidly increasing in incidence and is considered the hepatic manifestation of the metabolic syndrome. The gut microbiome plays a role in metabolism and maintaining gut barrier integrity. Studies have found differences in the microbiota between NAFLD and...
Article
Full-text available
Purpose: To improve the SNR of hyperpolarized carbon-13 MRI of [1-13 C]pyruvate using a multispectral variable flip angle (msVFA) scheme in which the spectral profile and flip angle vary dynamically with time. Methods: Each image acquisition in a time-resolved imaging experiment used a unique spectrally varying RF pulse shape for msVFA. Therefor...
Article
Background: Functional MRI (fMRI) is a noninvasive method to investigate the neural correlates of brain development. Insight into the rapidly developing brain in utero is limited, and fetal fMRI can be used to gain a greater understanding of the developmental process. Fetal brain fMRI is typically limited to resting-state fMRI due to the difficult...
Article
More than 100 attendees from Australia, Austria, Belgium, Canada, China, Germany, Hong Kong, Indonesia, Japan, Malaysia, the Netherlands, the Philippines, Republic of Korea, Singapore, Sweden, Switzerland, the United Kingdom, and the United States convened in Singapore for the 2019 ISMRM‐sponsored workshop on MRI of Obesity and Metabolic Disorders....
Article
Hibernators survive challenging winters by entering torpor, which lowers body temperature (Tb) to ∼5 °C for 12-14 days, followed by spontaneous arousals where Tb increases to ∼37 °C for 10-12 h before entering another torpor bout. This Tb cycle is accompanied by significant fluctuations in metabolic rate. Little is known about the role of the liver...
Article
We discovered a previously undescribed orbital lipid depot in the 13-lined ground squirrel during the first ever magnetic resonance image (MRI) of this common experimental model of mammalian hibernation. In animals housed at constant ambient temperatures (5°C or 25°C, 12h L:12h D photoperiod) the volume of this depot increased in the autumn and dec...
Article
Obligate hibernators express circannual patterns of body mass and hibernation, which persist under constant laboratory conditions. Brown adipose tissue (BAT) is important for thermogenesis during arousals from hibernation, whereas white adipose tissue (WAT) serves as energy storage and thermal insulation. The goal of this study was to investigate t...
Article
Full-text available
Background The hepatic circulation is involved in adaptive systemic responses to circulatory stress. However, it is vulnerable to both chronic hypervolemia and cardiac dysfunction. The influence of hemodialysis (HD) and ultrafiltration (UF) upon liver water content has been understudied. We conducted a detailed pilot study to characterize the effec...
Article
Purpose: Analysis of fetal adipose tissue volumes may provide useful insight towards assessment of overall fetal health, especially in cases with abnormal fetal growth. Here, we assess whether fetal adipose tissue volume can be reliably measured using 3D water-fat MRI, using a quantitative assessment of the lipid content of tissues. Materials and m...
Article
Abnormal maternal lipid profiles, a hallmark of increased maternal adiposity, are associated with pregnancy complications such as preeclampsia and gestational diabetes, and offspring long-term metabolic health is impacted as the consequence of altered fetal growth, physiology and often iatrogenic prematurity. The metabolic changes associated with m...
Article
Full-text available
Purpose To examine the feasibility of using MRI to identify differences in liver size and fat deposition in fetal guinea pigs exposed to an in utero environment influenced by maternal consumption of a Western diet. Materials and methods Female guinea pigs fed either an energy-dense Western Diet (WD), comprised of increased saturated fats and simpl...
Data
Example adipose tissue segmentation images. Example images showing fetal TAT segmentation (left) and maternal TAT segmentation (right). (TIF)
Article
BACKGROUND Fetal fat is indicative of the energy balance within the fetus, which may be disrupted in pregnancy complications such as fetal growth restriction, macrosomia, and gestational diabetes. Water‐fat separated MRI is a technique sensitive to tissue lipid content, measured as fat fraction (FF), and can be used to accurately measure fat volume...
Article
Full-text available
Obligate hibernators, such as ground squirrels, display circannual patterns which persist even under constant laboratory conditions, suggesting that they are regulated by endogenous rhythms. Brown adipose tissue (BAT) is important for thermogenesis during periodic arousals from hibernation when core body temperature rises spontaneously from 5 to 37...
Article
Workshops are an important part of the IFPA annual meeting as they allow for discussion of specialized topics. At IFPA meeting 2016 there were twelve themed workshops, four of which are summarized in this report. These workshops covered innovative technologies applied to new and traditional areas of placental research: 1) genomic communication; 2)...
Article
Aim: To evaluate the effect of sitagliptin vs placebo on histologic and non-histologic parameters of non-alcoholic steatohepatitis (NASH). Methods: Twelve patients with biopsy-proven NASH were randomized to sitagliptin (100 mg daily) (n = 6) or placebo (n = 6) for 24 wk. The primary outcome was improvement in liver fibrosis after 24 wk. Secondar...
Article
Purpose: To accurately analyze vibroacoustics in MR head gradient coils. Theory and methods: A detailed theoretical model for gradient coil vibroacoustics, including the first description and modeling of Lorentz damping, is introduced and implemented in a multiphysics software package. Numerical finite-element method simulations were used to est...
Article
Purpose: To assess the feasibility of hyperpolarized (HP) (129)Xe MRI for detection of early stage radiation-induced lung injury (RILI) in a rat model involving unilateral irradiation by assessing differences in gas exchange dynamics between irradiated and unirradiated lungs. Methods: The dynamics of gas exchange between alveolar air space and p...
Article
Full-text available
Aims . Nonalcoholic fatty liver disease (NAFLD) is a chronic liver disease that can progress to cirrhosis and hepatocellular carcinoma. This retrospective chart review investigated the incidence of hepatic steatosis in London, Ontario, Canada. Methods . A retrospective chart review was performed on emergency room (ER) patients undergoing nonschedul...
Article
To implement and optimize a single-shot spiral encoding strategy for rapid 2D IDEAL projection imaging of hyperpolarized (Hp) (129) Xe in the gas phase, and in the pulmonary tissue (PT) and red blood cells (RBCs) compartments of the rat lung, respectively. A theoretical and experimental point spread function analysis was used to optimize the spiral...
Article
To test the feasibility of hyperpolarized [1-(13) C]pyruvate magnetic resonance imaging (MRI) for noninvasive examination of guinea pig fetoplacental metabolism and nutrient transport. Seven pregnant guinea pigs with a total of 30 placentae and fetuses were anesthetized and scanned at 3T. T1 -weighted (1) H images were obtained from the maternal ab...
Article
To demonstrate a new multigradient echo bipolar acquisition sequence for fat quantification. A multiecho bipolar acquisition is used such that the even echoes have opposite polarity to the odd echoes. In addition, the readout gradients alternate their polarities every other phase-encode line. Each echo, therefore, consists of phase-encode lines wit...
Article
To validate a fully automated adipose segmentation method with magnetic resonance imaging (MRI) fat fraction abdominal imaging. We hypothesized that this method is suitable for segmentation of subcutaneous adipose tissue (SAT) and intra-abdominal adipose tissue (IAAT) in a wide population range, easy to use, works with a variety of hardware setups,...
Article
In addition to coil sensitivity data (parallel imaging), sparsity constraints are often used as an additional lp-penalty for under-sampled MRI reconstruction (compressed sensing). Penalizing the traditional decimated wavelet transform (DWT) coefficients, however, results in visual pseudo-Gibbs artifacts, some of which are attributed to the lack of...
Article
Purpose: To demonstrate a reconstruction technique for separating signal from different hyperpolarized carbon-13 metabolites. Methods: A reconstruction method is described for chemical shift encoded separation of the signal from pyruvate and its downstream metabolites. This method uses consistency of the data with the signal model rather than an...
Article
A specialized kinetic analysis of real-time hyperpolarized [1,1,2,2-D4, 1-13C]choline 13C-magnetic resonance spectroscopy, enabled determination of initial rates of metabolic enzyme activity (choline oxidase), enzyme-substrate affinity (Km), and inhibition. In a clinical MRI scanner, metabolite levels lower than 16 µM were detected at a temporal re...
Article
To propose a novel approach to water/fat separation using a unique smoothness constraint. Chemical-shift based water/fat separation is an established noninvasive imaging tool for the visualization of body fat in various anatomies. Nevertheless, B0 magnetic field inhomogeneities can hamper the water/fat separation process. In this work, B0 variation...
Conference Paper
We present a new wave-based framework for understanding acoustic noise in MR gradient coils, and propose two new concepts for acoustic noise reduction. Results of this wave-based coupled structural-acoustic modeling, as well as experimental measurements, demonstrate that the addition of an impedance matching “horn” and an absorbing end cap both act...
Article
PurposeTo assess the feasibility of choline MRI using a new choline molecular probe for dynamic nuclear polarization (DNP) hyperpolarized MRI.Materials and Methods Male Sprague-Dawley rats with an average weight of 400 ± 20 g (n = 5), were anesthetized and injection tubing was placed in the tail vein. [1,1,2,2-D4, 1-13C]choline chloride (CMP1) was...
Conference Paper
Purpose: T2 weighted and diffusion weighted magnetic resonance imaging (MRI) show promise in isolating prostate tumours. Dynamic contrast enhanced (DCE)-MRI has also been employed as a component in multi-parametric tumour detection schemes. Model-based parameters such as Ktrans are conventionally used to characterize DCE images and require arterial...
Article
Purpose: A new approach to mapping the flip angle quickly and efficiently in 3D based on the Look-Locker technique is presented. Methods: We modified the accelerated 3D Look-Locker T1 measurement technique to allow rapid measurement of flip angle. By removing the inversion pulses and interleaving two radio frequency pulses with different amplitu...
Article
Purpose: To demonstrate an approach to water-fat separation with R2* correction using compressed sensing and parallel imaging. Methods: Acquisition times for chemical shift based water-fat separation imaging are lengthy, and many applications rely on image acceleration techniques. In this study, we present an integrated compressed sensing, paral...
Article
Purpose: To develop a new method of reducing T1 bias in proton density fat fraction (PDFF) measured with iterative decomposition of water and fat with echo asymmetry and least-squares estimation (IDEAL). Materials and methods: PDFF maps reconstructed from high flip angle IDEAL measurements were simulated and acquired from phantoms and volunteer...
Article
Full-text available
Visceral adiposity is increased in those with Metabolic Syndrome (MetS) and atherosclerotic disease burden. In this study we evaluate for associations between intra-thoracic fat volume (ITFV) and myocardial infarction (MI) in patients with MetS. Ninety-four patients with MetS, MI or both were identified from a cardiovascular CMR clinical registry....
Article
A new noninvasive, nonradioactive approach for glucose imaging using spin hyperpolarization technology and stable isotope labeling is presented. A glucose analog labeled with (13) C at all six positions increased the overall hyperpolarized imaging signal; deuteration at all seven directly bonded proton positions prolonged the spin-lattice relaxatio...
Conference Paper
PURPOSE To image choline distribution and metabolism in the live rat by MRI, non-invasively and non-radioactively. METHOD AND MATERIALS The animal study protocol was approved by the Institutional Animal Use Subcommittee. Anesthetized male Sprague-Dawley rats, 400+/-20 g (n=6), underwent MRI and MRS in a 3T clinical MRI scanner. Coronal projection...
Conference Paper
While Magnetic Resonance Imaging is capable of separating water and fat components in the body, mapping of magnetic field inhomogeneities is essential for the successful application of this process. In this study, we address the problem of field map estimation using a convex-relaxed max-flow method. We propose a novel two-stage approach that leads...
Article
Dynamic nuclear polarisation (DNP) of carbon-13 ((13)C) enriched endogenous compounds provides a novel means for magnetic resonance imaging and spectroscopy of biological processes. Adding small amounts of gadolinium-based contrast agents (GBCAs) to the (13)C-enriched substrate matrix increases the amount of hyperpolarisation that can be achieved,...
Article
The purposes of this study were to determine 1) whether sex differences in quadriceps torque and isotonic power persist when controlling for muscle volume (i. e., torque/muscle volume and power/muscle volume) in participants with knee osteoarthritis (OA) and 2) the factors responsible for potential sex differences. Isometric torque, isotonic power...
Article
Full-text available
The purposes of this study were to determine 1) the relationships of self-reported function scores in patients with knee osteoarthritis (OA) to both maximal isometric torque and to isotonic power at a variety of loads, and 2) the degree to which muscle volume (MV) or voluntary activation (VA) are associated with torque and power measures in this po...
Article
To develop a robust T(2) -weighted volumetric imaging technique with uniform water-silicone separation and simultaneous fat suppression for rapid assessment of breast implants in a single acquisition. A three-dimensional (3D) fast spin echo sequence that uses variable refocusing flip angles was combined with a three-point chemical-shift technique (...
Article
To develop and evaluate a technique for the registration of in vivo prostate magnetic resonance (MR) images to digital histopathologic images by using image-guided specimen slicing based on strand-shaped fiducial markers relating specimen imaging to histopathologic examination. The study was approved by the institutional review board (the Universit...
Article
Fat suppression is an essential part of routine MRI scanning. Multiecho chemical-shift based water-fat separation methods estimate and correct for Bo field inhomogeneity. However, they must contend with the intrinsic challenge of water-fat ambiguity that can result in water-fat swapping. This problem arises because the signals from two chemical spe...
Article
The utilization of parallel imaging permits increased MR acquisition speed and efficiency; however, parallel MRI usually leads to a deterioration in the signal-to-noise ratio when compared with otherwise equivalent unaccelerated acquisitions. At high accelerations, the parallel image reconstruction matrix tends to become dominated by one principal...
Article
Measuring signal-to-noise ratio (SNR) for parallel MRI reconstructions is difficult due to spatially dependent noise amplification. Existing approaches for measuring parallel MRI SNR are limited because they are not applicable to all reconstructions, require significant computation time, or rely on repeated image acquisitions. A new SNR estimation...
Article
To validate iterative decomposition of water and fat with echo asymmetry and least-squares estimation (IDEAL) for adipose tissue volume quantification. IDEAL allows MRI images to be produced only from adipose-containing tissues; hence, quantifying adipose tissue should be simpler and more accurate than with current methods. Ten healthy controls wer...
Article
Multipoint water-fat separation techniques rely on different water-fat phase shifts generated at multiple echo times to decompose water and fat. Therefore, these methods require complex source images and allow unambiguous separation of water and fat signals. However, complex-based water-fat separation methods are sensitive to phase errors in the so...