Understanding MRI: basic MR physics for physicians

Currie, Stuart; Hoggard, Nigel; Craven, Ian; Hadjivassiliou, Marios; Wilkinson, Iain D.

doi:10.1136/postgradmedj-2012-131342

Cited by 92 publications

(68 citation statements)

References 25 publications

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“…Within the magnet, protons spinning parallel to the magnetic field cancel each other out in all directions other than those spinning along the z axis. 2 This is known as longitudinal magnetisation.…”

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confidence: 99%

Radiological investigations in neuroanaesthesia and neurocritical care, part 2: magnetic resonance imaging

2018

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By reading this article, you should be able to:Describe the basic physical principles behind the formation of a magnetic resonance image. Identify the common contraindications to MRI. Discuss some of the more common clinical indications for MRI. Explain with clinical cases and accompanying images the advantages of MRI over CT.After its advent in the late 1970s, MRI has achieved widespread acceptance as an imaging technique that is an alternative to CT and is free from ionising radiation. MRI has other significant advantages over CT, particularly regarding brain imaging. Because of its greater contrast resolution, MRI depicts anatomy in far greater detail than CT, and the range of imaging sequences available allows for greater sensitivity and specificity in identifying pathology. With the increase in the number of MRI examinations performed and the accessibility of images by clinicians via the picture archive and communication system, images are often reviewed before a formal report is issued by a specialist radiologist. Therefore, a basic understanding of the physics behind the creation of a magnetic resonance (MR) image is required to aid in image interpretation by the general clinician. This article also highlights the main indications and contraindications to MRI in the field of neuroscience, and using cases from our institutions, demonstrates the more common pathologies and associated imaging findings. Physics of MRIThe MRI physics is complex, and an in-depth explanation of the various techniques used to create the wide range of sequences available is beyond the scope of this article.Nick Skipper FRCR EDiNR is a consultant neuroradiologist at Brighton and Sussex University Hospitals NHS Trust. He completed a fellowship in adult and paediatric neuroradiology in Sheffield.Mark Igra FRCR EDiNR is a consultant neuroradiologist at Leeds General Infirmary. He completed his neuroradiology fellowship in Sheffield, and has a subspecialty interest in neuro-oncology and spinal intervention.Andrew Davidson FRCA FFICM is a consultant in neuroanaesthesia and neurointensive care at the Royal Hallamshire Hospital, Sheffield. Key pointsMRI provides greater anatomical detail than CT scanning, and the range of sequences available to the radiologist allows for greater detection of pathology.A basic understanding of the physics behind the creation of a magnetic resonance image is useful in facilitating image interpretation. An understanding of MRI safety issues is essential, because strong magnetic fields, radio-frequency pulses, and i.v. contrast agents are used.

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Radiological investigations in neuroanaesthesia and neurocritical care, part 2: magnetic resonance imaging

2018

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“…Functional MRI refers to techniques that aim to measure or visualize physiological variables in the kidney, whereas non-functional MRI renders images of kidney anatomy. Conventional imaging of the kidney (through T 1 , T 2 and proton density weighted imaging) (Currie et al, 2013) can identify morphological abnormalities, for instance with magnetic resonance urography and angiography, and a sensitive, though non-specific loss of corticomedullary differentiation with increased T 1 relaxation times can be observed in kidneys with impaired function (Huang et al, 2011). Since T 1 imaging cannot identify the cause of kidney function impairment given its lack of specificity, this technique is probably of little value in evaluation of allograft function in transplantation patients.…”

Section: Conventional Vs Functional Mri For the Assessment Of Subclimentioning

confidence: 99%

Innovative Perspective: Gadolinium-Free Magnetic Resonance Imaging in Long-Term Follow-Up after Kidney Transplantation

et al. 2017

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Since the mid-1980s magnetic resonance imaging (MRI) has been investigated as a non- or minimally invasive tool to probe kidney allograft function. Despite this long-standing interest, MRI still plays a subordinate role in daily practice of transplantation nephrology. With the introduction of new functional MRI techniques, administration of exogenous gadolinium-based contrast agents has often become unnecessary and true non-invasive assessment of allograft function has become possible. This raises the question why application of MRI in the follow-up of kidney transplantation remains restricted, despite promising results. Current literature on kidney allograft MRI is mainly focused on assessment of (sub) acute kidney injury after transplantation. The aim of this review is to survey whether MRI can provide valuable diagnostic information beyond 1 year after kidney transplantation from a mechanistic point of view. The driving force behind chronic allograft nephropathy is believed to be chronic hypoxia. Based on this, techniques that visualize kidney perfusion and oxygenation, scarring, and parenchymal inflammation deserve special interest. We propose that functional MRI mechanistically provides tools for diagnostic work-up in long-term follow-up of kidney allografts.

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“…An oscillating RF wave is then used to generate an excitation pulse that aligns a proportion of the magnetization perpendicular to the direction of the main field, forming transverse magnetization. The transverse magnetization precesses around the main magnetic field, which generates the signals used for imaging . The excited protons then return (i.e., “relax”) to the equilibrium state along the main magnetic field.…”

Section: Basics Of Mrimentioning

confidence: 99%

“…The transverse magnetization precesses around the main magnetic field, which generates the signals used for imaging. 1 The excited protons then return (i.e., ''relax'') to the equilibrium state along the main magnetic field.…”

Section: Basics Of Mrimentioning

confidence: 99%