Magnetic Resonance Imaging on Soft Tissue 1 Jiten K. Mistry Calvin Gan
Outline Background of Medical Imaging Introduction to MRI How MRI works MRI of Soft Tissue Benefits & Risks Recent Advances 2
The Need for Medical Imaging A method required to view and diagnose the human body noninvasively Could aid and lead to surgery and treatment of the patient Cause and Effect Cause Internal Tissue Effect Received signal 3
History of Medical Imaging The Medical Imaging industry was said to be conceived by Wilhelm Conrad Roentgen in 1895 His discovery of X-rays began to allow physicians to use primitive x-ray machines to view broken bones and contrast-enhanced structures in the body such as the GI system. Further development of Medical Imaging was fairly insignificant until the later half of the 20th century, when computer technology was beginning to play a large role in the instruments developed Clarity of the image created as well as the speed at which the image is rendered have been the two properties pulling development in the industry 4 1896 X ray of Roentgen s wife s hand
Computed Tomography (CT) Scan Developed during the late 1960 s Uses X-ray images to re-create a cross sectional (axial) image of the body, in part or whole Body is bombarded with low intensity x-rays and sensors detect the amount of x-rays that rebound Study blood vessels Identify masses and tumors, including cancer Guide a surgeon to the right area during a biopsy 5
Ultrasound First introduced in the 1960 s A probe is used to send sound waves into the body Sounds waves reflect off of internal organs and tissues Probe records reflected waves machine then calculates distance of tissue from probe based on echo return time and speed of sound in tissue (5,005 ft/s) 6
Where do these techniques fall short? CT scan Can only provide axial plane image Unable to distinguish between different types of tissues Ultrasound Also unable to distinguish between different tissues Why do previous methods have this problem? Provide images that show the density of the object Tissues in the human body have a fairly uniform density, Very difficult to distinguish between different types of tissues 7
Different Types of Tissues Deep vs. Superficial tissue Ligaments vs. Tendons Organs vs. surrounding tissue How do we identify these tissues separately? 8
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Why MRI? Unlike other more common Medical Imaging Techniques, MRI creates images from signals received from resonating protons within the matter The data range we can have for signals from protons is quite large, allowing us to more easily differentiate between different matter which are closely related 10
Soft Tissue MRI is excellent for imaging of soft tissue Why? Rather then using the different densities for different tissues (which does not work) we instead look at the vastly different magnetic properties of the proton in the tissue we are observing, which can allow us to determine other properties of the 11 tissue
Magnetic Properties of Soft Tissue T1 (ms) T2 (ms) Putamen 747 ± 33 71 ± 4 Caudate nucleus 822 ± 16 76 ± 4 Thalamus 703 ± 34 75 ± 4 Cortical gray matter 871 ± 73 87 ± 2 Corpus callosum 509 ± 39 69 ± 8 White matter 515 ± 27 74 ± 5 Cerebrospinal fluid 1900 ± 353 250 ± 3 Artery 1205 ± 58 224.5 ± 5.3 Vein 1335 ± 49 189.4 ± 10.0 12
Magnetic Properties of Soft Tissue 13
What is MRI? A noninvasive diagnostic technique to produce images of inside the human body Ability to provide functional as well as anatomical information 14
What is MRI? Equipment: MRI scanner 1. Magnet: largest and most expensive part i) Is superconducting, liquid helium is cooled to 4K 2. RF System: transmitting and receiving of signals 3. Gradients: Spatial encoding, determine plane for imaging Computer: Configures gradients Input from RF system is sent to a monitor 15
16 Image courtesy of Dr. Noseworthy
17 Image courtesy of Dr. Noseworthy
Magnetic Fields Region of space Produced in the presence of a magnet or moving electric current The direction of a magnetic field at any point is towards the south pole of a bar magnet Positive particles follow the path of magnetic field The direction in which a compass needle points 18
Magnetic Fields Nikola Tesla (July 10, 1856 January 7, 1943) Tesla: SI unit for measuring the magnetic field (B) Source Superconducting (laboratory) magnet Strong conventional (laboratory) magnet Field Magnitude (T) 30 2 MRI scanners use fields ranging from 1.5 3 T can operate up to 9.4 teslas World s largest MRI machine Bar magnet & surface of the sun 1e-2 Surface of the earth 30 60 µ Inside the human brain (nerve impulses) 1e-13 19 Serway & Beichner, 2000
How MRI Works 1. A strong magnetic field align protons 2. i) RF pulses excite these protons ii) Upon realignment, each proton emits distinct signals 3. The signals are then detected and read, producing an image of inside the body Video: http://www.radiologyinfo.org/en/video/index.cfm?filename=mr&larger=1 20
21 1. A strong magnetic field align protons
How MRI Works 2 i) RF pulses excite these proton 22
How MRI Works What are the time constants T1 and T2? 2 ii) Upon realignment, each proton emits distinct signals T1 and T2 are magnetic timing parameters which differ from tissue to tissue 23
How MRI Works T1-Weighted T2-Weighted 24
How MRI Works 25
How MRI Works 3. The signals are then detected and read, producing an image of inside the body, using K space 26 Burger et al., 2001
Case Studies Rotator Cuff Tear - These muscles keep the humeral head centered on the glenoid cavity - traumatic injury and wearing down may lead to the tear - the white arrow points to the supraspinatus tendon
Case Studies The rotator cuff tear is identified as loose, degenerated, and frayed tissue around the cuff edge Pain occurs over the deltoid muscle and when the arm is raised The red arrow points to the torn edge of the rotator cuff 28
Case Studies Pituitary Tumour The Pituitary gland is a small endocrine/hormone gland which is located at the base of the brain. Growths or tumours in the pituitary can secrete excessive amounts of hormone Symptoms: Headache, visual disturbance, clinical effects of excessive hormone secretion. 29
Case Studies Multiple Sclerosis Demyelinating disease that affects the CNS MRI reveals plagues in the white matter of the brain and spinal cord. 30
Case Studies 31 T1-Weighted
Case Studies Normal vs Torn ACL 32
Case Studies This image is an axial section of the head of an elderly man. What has caused the abnormality shown? 33
Case Studies young female patient had experienced amenorrhoea What can you conclude from this MRI image? 34
MRI Disadvantages High Initial cost, translates to a high examination cost Metallic orthopedic hardware cause distortions in images as they interfere with magnetic field Require patient to hold still for up to 90 minutes Could cause distortion in images 35
MRI Disadvantages cont. Individuals with pacemakers or large non stainless steel implants are unsafe to use MRI machine Creates a large noise during operation 36
Future of MRI Ultra Low Field MRI 37 MRI machine which uses a Magnetic Field of a few microtesla to create an image Signals are measured by SQUIDS (superconducting quantum interference devices) the most sensitive detectors of magnetic flux Allows paramedics to obtain quick MRI images on the go (crappy quality but can easily diagnose injury)
References http://www.medphys.ucl.ac.uk/teaching/undergrad/projects/2002/group_02/magfield.htm http://www.liv.ac.uk/mariarc/research/mrs.htm http://en.wikipedia.org/wiki/medical_imaging#medical_imaging_service http://www.imaginghss.org/patient-information/mri.htm http://open-mri.com/whatis.html http://en.wikipedia.org/wiki/mri http://www.emedicine.com/radio/topic420.htm http://www.cancer.org/docroot/cri/content/cri_2_4_1x_what_is_sarcoma_38.asp http://www.cancerhelp.org.uk/help/default.asp?page=4559 http://en.wikipedia.org/wiki/medical_imaging Bister, Jeffrey. Clinical Applications of Medical Imaging. Plenum Press. New York, New York, 1986 Young, Stuart W. Nuclear Magnetic Resonance Imaging. Basic Principles. Raven Press Books, Ltd. New York, New York, 1984 38