Patrick W Hales

Patrick W Hales
University College London | UCL · Institute of Child Health

PhD Physics

About

42
Publications
5,192
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889
Citations
Additional affiliations
May 2010 - present
University College London
Position
  • PostDoc Position
June 2007 - May 2010
University of Oxford
Position
  • PostDoc Position

Publications

Publications (42)
Article
Full-text available
Previous studies have pointed to a role for regional cerebral hemodynamic stress in neurological complications in patients with sickle cell anemia (SCA), with watershed regions identified as particularly at risk of ischemic tissue injury. Using single- and multi-inflow time (TI) arterial spin labeling sequences (ASL) in 94 patients with SCA and 42...
Article
Full-text available
Prior studies have described high venous signal qualitatively using arterial spin labelling (ASL) in patients with sickle cell anemia (SCA), consistent with arteriovenous shunting. We aimed to quantify the effect and explored cross-sectional associations with arterial oxygen content (CaO 2 ), disease-modifying treatments, silent cerebral infarction...
Article
Full-text available
Purpose Several neurological conditions are associated with microstructural changes in the hippocampus that can be observed using DWI. Imaging studies often use protocols with whole-brain coverage, imposing limits on image resolution and worsening partial-volume effects. Also, conventional single-diffusion-encoding methods confound microscopic diff...
Article
Full-text available
To determine if apparent diffusion coefficients (ADC) can discriminate between posterior fossa brain tumours on a multicentre basis. A total of 124 paediatric patients with posterior fossa tumours (including 55 Medulloblastomas, 36 Pilocytic Astrocytomas and 26 Ependymomas) were scanned using diffusion weighted imaging across 12 different hospitals...
Article
The dentato-rubro-thalamo-cortical tract (DRTC) is the main outflow pathway of the cerebellum, contributing to a finely balanced corticocerebellar loop involved in cognitive and sensorimotor functions. Damage to the DRTC has been implicated in cerebellar mutism syndrome seen in up to 25% of children after cerebellar tumor resection. Multi-shell dif...
Article
Full-text available
Introduction Tractography derived from diffusion MRI can provide important insights into human brain microstructure in vivo. Neurosurgeons were quick to adopt the technique at the turn of the century, but it remains plagued by technical fallibilities. This study aims to describe how tractography is deployed clinically in a modern-day, public health...
Article
Full-text available
Background The subventricular zone of the third ventricle (TVZ) is a germinal stem cell niche, identified as the possible location of optic pathway glioma (OPG) cell origin. Paediatric OPGs are predominantly diagnosed as low-grade astrocytomas, which are either sporadic or are associated with neurofibromatosis type-1 (NF1). These tumours often caus...
Article
Full-text available
Objective: ADC (Apparent Diffusion Coefficient) derived from Diffusion-Weighted Imaging (DWI) has shown promise as a non-invasive quantitative imaging biomarker in Wilms' tumours. However, many non-Gaussian models could be applied to DWI. This study aimed to compare the suitability of four diffusion models (mono exponential, IVIM [Intravoxel Incoh...
Article
Full-text available
Background Arterial spin labeling (ASL) is a useful tool for measuring cerebral blood flow (CBF). However, due to the low signal‐to‐noise ratio (SNR) of the technique, multiple repetitions are required, which results in prolonged scan times and increased susceptibility to artifacts. Purpose To develop a deep‐learning‐based algorithm for simultaneo...
Conference Paper
In 15 homozygous sickle-cell disease patients (SCD; hemoglobin-SS) and 12 healthy controls (HC; 10 Hb-AA, 2 Hb-AS), we compared a quantitative susceptibility mapping (QSM)-based estimate of venous oxygen saturation (Yv) with T2-relaxation-under-spin-tagging (TRUST)-based estimates using bovine-hemoglobin (TRUST-HbBV), hemoglobin-S (TRUST-HbS), or h...
Article
Full-text available
Background Diffusion- and perfusion-weighted MRI are valuable tools for measuring the cellular and vascular properties of brain tumours. This has been well studied in adult patients, however, the biological features of childhood brain tumours are unique, and paediatric-focused studies are less common. We aimed to assess the diagnostic utility of ap...
Article
Full-text available
Purpose: We report a retrospective comparison between bi-dimensional RANO criteria and manual volumetric segmentation (MVS) in pediatric low-grade gliomas. Methods: MRI FLAIR or T1 post contrast images were used for assessment of tumor response. Seventy patients were included in this single center study, for each patient two scans were assessed...
Conference Paper
Full-text available
Background The aim of this study was to perform a comparison between bi-dimensional measurement of tumour diameter based on RANO and manual volumetric segmentation of paediatric low grade gliomas to determine response assessment. Methods MR FLAIR images were used for assessment of tumour response with the exception of those patients in whom comple...
Conference Paper
Background The aim of this study was to perform a comparison between bi-dimensional measurement of tumour diameter based on RANO and manual volumetric segmentation of paediatric low grade gliomas to determine response assessment. Methods MR FLAIR images were used for assessment of tumour response with the exception of those patients in whom comple...
Article
Full-text available
Background: Radiological biomarkers which correlate with visual function are needed to improve the clinical management of optic pathway glioma (OPG) patients. Currently, these are not available using conventional magnetic resonance imaging (MRI) sequences. The aim of this study was to determine whether diffusion MRI could be used to delineate the e...
Article
Many MRI techniques require prior knowledge of the T1-relaxation time of blood (T1bl). An assumed/fixed value is often used; however, T1bl is sensitive to magnetic field (B0), haematocrit (Hct), and oxygen saturation (Y). We aimed to combine data from previous in vitro measurements into a mathematical model, to estimate T1bl as a function of B0, Hc...
Article
Wilms' tumours (WTs) are large heterogeneous tumours, which typically consist of a mixture of histological cell types, together with regions of chemotherapy-induced regressive change and necrosis. The predominant cell type in a WT is assessed histologically following nephrectomy, and used to assess the tumour subtype and potential risk. The purpose...
Article
The purpose of this work was to assess the reproducibility of diffusion imaging, and in particular the apparent diffusion coefficient (ADC), intra-voxel incoherent motion (IVIM) parameters and diffusion tensor imaging (DTI) parameters, across multiple centres using clinically available protocols with limited harmonization between sequences. An ice-...
Article
Full-text available
Diffusion tensor magnetic resonance imaging (MRI) reveals valuable insights into tissue histo-anatomy and microstructure, and has steadily gained traction in the cardiac community. Its wider use in small animal cardiac imaging in vivo has been constrained by its extreme sensitivity to motion, exaggerated by the high heart rates usually seen in rode...
Article
To investigate the reproducibility of arterial spin labelling (ASL) and dynamic contrast-enhanced (DCE) magnetic resonance imaging (MRI) and quantitatively compare these techniques for the measurement of renal blood flow (RBF). Sixteen healthy volunteers were examined on two different occasions. ASL was performed using a multi-TI FAIR labelling sch...
Article
Full-text available
The human brain changes structurally and functionally during adolescence, with associated alterations in cerebral perfusion. We performed dynamic arterial spin labeling (ASL) magnetic resonance imaging in healthy subjects between 8 and 32 years of age, to investigate changes in cerebral hemodynamics during normal development. In addition, an invers...
Article
Full-text available
The ability to assess brain tumor perfusion and abnormalities in the vascular structure in vivo could provide significant benefits in terms of lesion diagnosis and assessment of treatment response. Arterial spin labeling (ASL) has emerged as an increasingly viable methodology for non-invasive assessment of perfusion. Although kinetic models have be...
Article
Full-text available
The human coronary tree is commonly assumed to have two roots: the left and right coronary arteries (LCA and RCA, respectively). However, a third coronary artery (TCA) has been observed in humans and animals, usually arising from the right anterior aortic sinus near the RCA. Using high-resolution magnetic resonance imaging, we identified TCA preval...
Article
Full-text available
A number of two-compartment models have been developed for the analysis of arterial spin labeling (ASL) data, from which both cerebral blood flow (CBF) and capillary permeability-surface product (PS) can be estimated. To derive values of PS, the volume fraction of the ASL signal arising from the intravascular space (v(bw)) must be known a priori. W...
Article
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Deformation and wall-thickening of ventricular myocardium are essential for cardiac pump function. However, insight into the histo-anatomical basis for cardiac tissue re-arrangement during contraction is limited. In this report, we describe dynamic changes in regionally prevailing cardiomyocyte (fibre) and myolaminar (sheet) orientations, using Dif...
Article
Chemical tissue fixation, followed by embedding in either agarose or Fomblin, is common practice in time-intensive MRI studies of ex vivo biological samples, and is required to prevent tissue autolysis and sample motion. However, the combined effect of fixation and sample embedding may alter tissue structure and MRI properties. We investigated the...
Conference Paper
Full-text available
Mathematical models of ventricular cardiomyocyte orientation provide a simple description of histo-anatomical arrangements that are important for cardiac mechano-electric behaviour. They can be used to analyse interspecies differences, to explore dynamic remodelling such as during development or disease, and they are key for building realistic comp...
Conference Paper
Full-text available
Increased resolution in cardiac Magnetic Resonance Imaging (MRI) and growing interest in the effect of small structures in electrophysiology of the heart pose new challenges for cardiac atlases. In this paper we discuss the limitations of current atlas-building models when trying to incorporate cardiac small structure and argue for the need of deve...
Article
The ordered electrical stimulation of the ventricles is achieved by a specialized network of fibres known as the Purkinje system. The gross anatomy and basic functional role of the Purkinje system is well understood. However, very little is known about the detailed anatomy of the Purkinje system, its inter-individual variability and the implication...
Article
Full-text available
Annulus manual segmentation is an important tool for the study of valve anatomy and physiology, for the four main valves of the heart (mitral, tricuspid, aortic and pulmonary). In this paper we review two traditional manual segmentation approaches: slice-by-slice and interpolating a sparse set of landmarks with a spline curve. We propose a new Spli...
Article
Full-text available
This paper presents methods to build histo-anatomically detailed individualized cardiac models. The models are based on high-resolution three-dimensional anatomical and/or diffusion tensor magnetic resonance images, combined with serial histological sectioning data, and are used to investigate individualized cardiac function. The current state of t...
Article
We present a description of the design, construction and operation of a magnet system comprising of 2 HTS coils separated by 164 mm, that can encompass a plasma coating module. The coil system comprises of two winding packages of 3 pancake pairs of BSCCO (bismuth strontium calcium copper oxide)/Ag tape. These are mounted such that they are in optim...
Article
A small high-temperature superconducting (HTS) magnet has been produced as part of a magnetohydrodynamic (MHD) propulsion unit to power a model boat. The magnet is wound from 6 pancake coils of Bi-Sr-Ca-Cu-O HTS tape (BSCCO-2223), and is conduction cooled using an onboard "thermal battery", containing 3 liters of solid nitrogen. The magnet is racet...
Article
The design of a portable, “stand-alone” cooling system, for use with a high-temperature superconducting (HTS) magnet, is discussed. The HTS magnet is used to propel a magnetohydrodynamically powered model boat (approximately 120 cm × 60 cm). The aim of this investigation was to establish the suitability of solid nitrogen for use in the stand-alone...
Article
Full-text available
The human brain changes structurally and functionally during adolescence, with associated alterations in cerebral perfusion. We performed dynamic arterial spin labeling (ASL) magnetic resonance imaging in healthy subjects between 8 and 32 years of age, to investigate changes in cerebral hemodynamics during normal development. In addition, an invers...
Conference Paper
The anisotropic electrical conduction within myocardial tissue due to preferential cardiac myocyte orientation (‘fibre orientation) is known to impact strongly in electrical wavefront dynamics, particularly during arrhythmogenesis. Faithful representation of cardiac fibre architecture within computational cardiac models which seek to investigate su...