Medical Imaging on Soft Tissue Presented by Sam, Xiu Ting Li Eric, Yuan Zhang
Medical Imaging on Soft Tissue
Presented by
Sam, Xiu Ting LiEric, Yuan Zhang
About soft tissue
Muscle, fat, fibrous tissue, blood vessels, or other supporting tissue of the body. Ligaments, tendons, cartilages and muscles in the musculoskeletal system.
Soft Tissue Problems
Orthopaedic injuriesSarcoma Some need to be imaged to process diagnosis
Medical imaging today
3 most commonly used modalities: Conventional X-rayComputerized tomography (CT)Magnetic resonance Imaging (MRI)Give different soft tissue image quality
Conventional X-ray
High energy, short wavelength x-rays pass through bodyDenser tissue attenuate morePoor on soft tissue imaging Contrast agent—improve image details, i.e. blood vessels Risk of radiation exposure http://www.nbmdi.com/products/idb/html%20for%20each%20modality/Film
%20X-ray%20Radiography.html
CT scanningBase on x-ray principleBack projection to generate datacould be reconstructed to show 3-D details Give good contrast between tissues Not common in orthopaedic use http://www.imaginis.com/ct-scan/how_ct.asp
MRI
MRI (magnetic resonance imaging) since the beginning of the 1980s. use magnetic and radio wavesno exposure to any damaging forms of radiation. More detailed difference between normal and abnormal tissueBest soft tissue image so far
MRI (magnetic resonance imaging) and Soft tissue
*A typical kind of homographic emission imaging *Source of energy: photonic energy (electromagnetic waves)-determined by the magnetic field gradient-for soft tissue, the local magnetic property is the key factor. fundamental-- Spatial localization
An example of Spatial localization
Pulse sequence of a simplified MRI experiment Spatial coding is obtained via the use of magnetic field gradients.
Figure: Pulse sequence of a simplified MRI experiment.
Major types of gradients in localization
Magnetic field gradient Slice select gradientFrequency encoding gradientPhase encoding gradient
Spin
Positive charge hydrogen spinsgenerates magnetic dipole along the spin axisMagnetic dipoles orientate in random directionsApply magnetic field, dipoles line up
Detecting hydrogen
Origin of most MRI signals (water molecules)Signal variation (the way water bounded)-among tissues-among different health condition
Types of images
T1 weighted films- fat has a bright signal e.g. bone marrow. T2 weighted films- fluid has a bright signal. Those tissues with little fat or water e.g. cortical bone, tendons, ligaments-dark in both types.
White No change Grey Scar tissue in disc surgery pts
Grey/black White Grey Recurrent disc herniation
White No change Grey Normal Intervertebraldisc central
Grey No change Black Normal Intervertebraldisc peripheral
Grey No change Grey Muscle
Black Black No change Black Calcium/cortical bone
Grey/ black Grey / black No change Grey/black Scarring And ligaments
White/black White White Grey Fibrosis
White White White rim grey centre Grey Infection
White White White Grey Inflammation
White White White Grey Tumour
White White White Grey Trauma/ Haemmorhage
White White No change Grey Water
Black Grey No change White Fat ,inc bone marrow
T2 with STIR (fat suppression)
T2 T1 and Gadolinium T1
How to choose sequences
For screeningFor diagnosisThese two types of examination do not need to be tailored to the individual If MR scan is being performed for decisions on precise management then a more specialized examination must take place, with various sequences.
MRI scan: Musculoskeletal System
Most frequently to image spine, knee and shoulder.Sometimes hips, wrists, and hands.Locate and identify even very small tears and injuries to tendons, ligaments and muscles.
Related image
Related image con’t
Why MRI is not enough?
Time factor-X-ray, fast in general-MRI, might last up to an hourThe cost-X-ray machine is around 30,000-MRI machine, starts from million-cost per procedure ratio 1:20
Diffraction Enhanced Imaging (DEI)--basic physics
Account for attenuation, diffractionand refractionBase on phase contrast Radiation treated as a wave fieldRequired lower dose of x-ray
Basic physics con’tRefractive index:a) n = 1 − δ(RI decrement) − iβ(absoption index) b) 4πβ/λρ = μPhase change and attenuation on propagating a distance x
-Io, incident intensity-I, the final intensity-λ, the wavelength.
Phase shift and the absorption of an x-ray beam propagating through a patient are dependent upon both the δ and β of the particular tissues being traversed.
Mass absorption coefficients
The DEI system
Two perfect silicon crystals-detect the ultra-small-angle scattering & refraction of objectAnalyzer (3rd crystal) -diffracts x-rays onto image plate detectorLow and high rocking curve(-1/+1) Base of rocking curve(-2/+2)
DEI system con’t
The greater toe
Taken at +1 of the rocking curve
Image of foot ankle
Taken at +2 of the rocking curveShow bones and soft tissues of the ankle and proximal foot of a right lower extremity.Two dorsal tendons are apparent.
Practical considerations
Synchrotron cannot be provided by the clinical deviceHigher resolution but longer imaging timeOverlapping structures-interpetation difficulties
Referenceshttp://www.hyperdictionary.com/search.aspx?define=soft-tissuehttp://www.umm.edu/orthopaedics/soft.htmhttp://www.netdoctor.co.uk/health_advice/examinations/mriscan.htmhttp://www.vh.org/adult/provider/radiology/NormalRadAnatomy/Images/LowerEx/LAtKneeLwrEx9.htmlhttp://ric.uthscsa.edu/personalpages/lancaste/DI-II_Chapters/DI_chap4.pdfhttp://www.ajronline.org/cgi/content/full/175/3/575http://dutnsic.tn.tudelft.nl:8080/c59_to_html/node45.htmlhttp://www.radiologyinfo.org/content/diagnostic/diagnostic.htm
Referencehttp://www.orthoteers.co.uk/Nrujp~ij33lm/Orthimaging.htmhttp://www.blackwellsynergy.com.libaccess.lib.mcmaster.ca/links/doi/10.1046/j.1469-7580.2003.00175.x/full/http://ej.iop.org.libaccess.lib.mcmaster.ca/links/q69/CJppUK,o63gS4+D8wkKPJA/pmb4_16_005.pdfJ. T. Bushberg, J. A. Seibert, E. M. Leidholdt and J. M. Boone, "The Essential Physics of Medical Imaging," 2nd Edition, Lippincott Williams & Wilkins, 2001.David Sutton, “A Textbook of Radiology and imaging,” 4th edition, Volume 2, Churchhill Livingstone, 1987. “List of charges”, McMaster University Department of Diagnostic Imaging, pers. Comm. 2004