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