MRI Part 1 24th Oct 23.pptx

MAGNETIC RESONANCE IMAGING INTRODUCTION TO THE UNIT - 2023 REVIEW OF IMAGE GENERATION 24TH OCTOBER PART 1 – 10AM TO 12PM - LECTURE THEATRE C 24TH OCTOBER PART 2 – 1PM TO 3PM - LECTURE THEATRE A QUESTIONS AND ANSWERS SESSION 31ST OCTOBER 10AM TO...

MAGNETIC RESONANCE IMAGING INTRODUCTION TO THE UNIT - 2023 REVIEW OF IMAGE GENERATION 24TH OCTOBER PART 1 – 10AM TO 12PM - LECTURE THEATRE C 24TH OCTOBER PART 2 – 1PM TO 3PM - LECTURE THEATRE A QUESTIONS AND ANSWERS SESSION 31ST OCTOBER 10AM TO 12PM - LECTURE THEATRE F MRI REVISION SESSION 30TH JANUARY 2024 10AM TO 12.00PM - LECTURE THEATRE C INTRODUCING THE UNIT PRESENTER Dr Marcus Thomas Jackson Professional Lead Diagnostic Radiography MRI Radiographer  The unit will be delivered onsite over 4 sessions Addition learning resources available on CANVAS The principles of image generation will be presented in two sessions with summary points on the 24th October UNIT DELIVERY A Question and Answer session on the 31 st October will underpin the sessions delivered on the 24th October. A revision session will be facilitated on the 30th January 2024 LEARNING OUTCOMES FOR THIS UNIT At the end of this unit the student will be …. 1. Differentiate between MRI and Computed Tomography or CT 2. Able to describe the basics of image generation in MRI 3. Able to correctly identify, view and orientate an MR image 4. Able to identify common pulse sequences used in MRI  MAGNETIC RESONANCE IMAGING GENERATING THE MRI SIGNAL PHYSICAL PRINCIPLES – PART 1 24TH OCTOBER 2023 DR MARCUS THOMAS JACKSON Reviewed and revised 17th October 2023 MAGNETIC RESONANCE IMAGING (MRI) / COMPUTED TOMOGRAPHY (CT) Physical Differences? Different Sounds? Measures different things? DIFFERENT SOUNDS MEASURES DIFFERENT THINGS MRI Sounds HERE CT Sounds HERE MRI – THE BASICS  Developed into an important imaging modality from 1978  Utilises the fact that magnetic nuclei in a static magnetic field exhibit a characteristic resonance frequency that is proportional to the field strength  Primarily MR images map the distribution of hydrogen nuclei within the body  The medical imaging community have recognised MRI’s unique ability to image soft tissue & differentiate between benign and malignant tissue/ multiplanar capabilities/morphology & physiology (DWI)/ molecular imaging MRI ?  Stands for:  Magnetic  Involves magnetic fields  Resonance  Involves resonance – frequency has to be matched to a natural process  Imaging  Produces images Generating the MR signal rf B0 0 =   B0 NMV SOME OTHER TERMS  MR  MRS  Any MRI exam  MR Spectroscopy –  MRA chemical composition of the  MR Angiography – brain blood vessels  fMRI  MRV  Functional MRI –  MR Venography – how the brain works veins only  iMRI  MRA  Interventional MRI –  MR Arthrography – real-time image joints guided surgery MRI HARDWARE MRI HARDWARE MRI HARDWARE GRADIENT COILS HAVE EVOLVED INSIDE AN MRI SCANNER https://www.bing.com/videos/search?q=MRI+sound+&view=detail& mid=92182A9C1F50EED7817392182A9C1F50EED78173&FORM=VI RE MRI FIELD STRENGTHS High field systems Low field systems Standard clinical (At some clinical sites (usually systems but mainly research interventional) or spectroscopy) 1.0 to 3.0 Tesla 0.2 – 0.5 Tesla Up to 7 Tesla  MRI relies on the principles of magnetism and resonance to produce an image that we recognise as a ‘brain’, ‘liver’ , knee etc. MRI targets the hydrogen proton because of its abundance in the body (attached to both fat and water) SUMMARY 1 A spinning proton (in the nucleus of an atom) produces a magnetic charge (well an electromagnetic change actually) Outside of the strong magnetic field of the MR machine these tiny magnetic fields are randomly distributed and cancel each other out resulting zero magnetisation SUMMARY 2  When a patient is placed in a strong magnetic field i.e. the MRI scanner two things happen (i) the magnetic fields of the individual hydrogen atoms begin to align with the magnetic field of the scanner (ii) the magnetic field generated by the proton adopts an additional movement known as precession (a wobbling movement)  In order to read the magnetism from the patient it needs to be separated from the magnetism from the MR scanner. This is achieved by the physical principle of resonance  Once separated the signal can be read by an MR receiver coil. we will look at these processes in more detail ….. ATOMIC STRUCTURE Atoms are made up of: electrons orbiting a central nucleus, which contains protons and neutrons NUCLEAR SPIN As well as orbiting the nucleus, electrons spin on their own axis Protons and neutrons also have this property of spin In most nuclei they cancel each other out, leaving no net spin  HYDROGEN ATOMS In MRI we are primarily concerned with hydrogen atoms: 1. they are abundant in the human body 2. they have a strong magnetic moment Nucleus of hydrogen is a single positively-charged proton which spins on its axis MAGNETIC MOMENT A moving (or rotating) particle with electric charge has an associated magnetic field (basic electromagnetism) Protons may be thought of as a tiny bar magnet MAGNETIC DISTRIBUTION MAGNETIC MOMENT IN AN EXTERNAL FIELD MDM in external magnetic field becomes aligned with field Alignment is not exact because of proton’s spin Precesses around field with tip of magnetic vector tracing out a circle ENERGY STATES Hydrogen atoms have 2 stable orientations spin up (lower energy) spin down (higher energy) MAGNETIC DISTRIBUTION IN B0 Always small excess of spins in lower energy state (spin up) Produces net magnetization M0 parallel to direction of B0 M0 (aka “net magnetization vector” NMV) represents average behavior of all protons, and can be NET MAGNETISATION VECTOR Random Random Axes Axes Net Net Vector Vector Aligned Aligned with with Magnetic Magnetic Field Field VECTOR COMPONENTS – A FRAMEWORK FOR EXPLAINING MRI z In MR, z direction is defined by direction of B0 (longitudinal) mz m No difference between x and y B0 (both are y perpendicular to B0) - called transverse x plane REVIEW MRI  Hydrogen atoms have their own magnetism caused by nuclear spin  They interact with a magnetic field  MDM precess around the magnetic field at a particular frequency WHAT IS MRI? – WATCH THE TWO INTRODUCTORY VIDEOS BELOW https://www.youtube.com/watch?v=nFkBhUYynUw https://www.bing.com/videos/search?q=Example+MRI+Audio+Noise+ Level&&view=detail&mid=0A69D819FD88DE6B451C0A69D819FD88D E6B451C&rvsmid=5EC5D528ACBBB7F2C34D5EC5D528ACBBB7F2C34 D&FORM=VDQVAP