Imaging Of Musculo-Skeletal System

Introduction

•“Imaging” excludes direct visualization of the body… for e.g. arthroscopy.

•For all the right reasons Plain Roentgenography is termed the mother of imaging in medical science.

•Roentgen’s discovery of X-rays in 1895.

Imaging modalities

•Plain X ray

•Computerized Axial Tomography

•Magnetic Resonance Imaging

•Others PET, Bone scan.

•EM spectrum ranges from cosmic waves to radio waves.

•Visible spectrum VIBGYOR•Principle of vision interpretation of

chemical reaction induced by visible light on retina.

•Possibility to expand the visible spectrum???

•“See” the effects of the non-visible spectrum.

Roengenography

Plain X ray imaging

•Principle based on a particular property of electromagnetic waves Penetrance.

•Penetration potential of EM waves α frequency.

•Objects which absorb/reflect EMW are termed radio-dense objects.

•Radio-density depends on the composition, and thickness a given object.

Pb

BaSO4

Bone

Muscle

Blood

Liver

Butter

Fat

Air

EMW

Object

EMW

How is a X-ray image taken?

Film

X Ray

source

Object

X ray…

•Summation of shadow layers.•Negative of the true image commonly

used•Shows structures closest to the film with

the best clarity.•Clear anatomical knowledge is essential

to interpret a X ray.•Should be obtained prior to any other

imaging techniques.

Tomography

•Is basically glorified Roentgenography, which shows the anatomy much superiorly than a plain X ray with the drawback of increased radiation exposure.

•Conventional Tomography is a technique by which an image is procured with the use of X rays emphasizing a particular plane of interest and blurring the rest. (obsolete)

CAT

•CAT focuses on multiple planes of pre-specified thickness around a particular pivot line, usually the Axis being the pivot.

Advantages of CAT Disadvantages of CAT

• Excellent image resolution

• Faster procuring time (v/s

MRI)

• 3D reformations are

possible

• Best imaging tech to

detect cortical pathology

• Radiation effectiveness

(100-200 times a plain X

ray)

• Cost effectiveness

• Requires contrast to

visualize vessels.

MRI

Introduction

•Unlike the yet discussed techniques, it doesn’t use ionizing radiations.

•As the name suggests, MRI incorporates two physical principles, Magnetism and resonance.

•Magnets in discussion H+ ions in our body and the external magnetic field source.

•Resonance b/w the magnetic moment of the H+ ions and the magnetic impulse produced by the external magnet.

The external magnetic field

•Strengths range from 0.3 – 1.5 Tesla•1 Tesla = 10,000 Gauss

•Earth’s magnetic field = 0.5 Gauss

“Outline” of the technique

•H+ ions in random rotation and alignment external magnetic field aligns them to a vector.

•Energy as radio wave pulse applied to such a setting, certain number of H+ ions knocked out of their alignment eventually return back as the ext energy wades off.

•Return phase H+ ions emit energy final phase, resonates together pattern picked up by electronic devices and visualized.

T1 and T2????

•Time intervals pertaining MR scan include

Time of echo ; TETime of repetition ; TR•T1 short TE + Short TR•T2 short TE + Short TR

•Still ????

Practical purpose

•T1 weighted images depict Normal

anatomy at its best.

•T2 weighted images picks up “pathology”

better than T1.

Other differencesT1 T2

• Fat• Marrow• Brain WM• Liver, pancreas• Brain GM• Kidney• Spleen• CSF• Water, lung• Bone, air, flowing blood

• CSF, water• IVD• Brain, GM• Spleen• Brain, WM• Liver• Fat• Iron in basal ganglia• Bone, air, flowing blood

MR in Orthopedics

•THE BEST method to detect soft tissue

pathology.

•Not of much use in cortical bone studies,

as bone cortex contains minimal H+ ions.

Pros and consPros Cons

• Best soft tissue detailing,

contrast

• No ionizing rad:

• Possibility of creating

infinite no: of virtual

planes

• Virtual arthroscopy +

• Cost

• Procuring time is high

resulting in more

movement blur

• Claustrophobia/ magnetic

implants

• Bone cortex poorly

visualized

Other investigations

•USG useful in detecting joint pathology like effusion

•New generation high frequency probes can detect hair line cracks which are not picked on X rays.

Summarize

•X ray absolute necessity in Ortho invest:•CT currently the best modality for

cortical studies.•MRI best to detect soft tissue pathology.•None of these have a complete dominance

over the other.•Cost Pelvis Xray = Rs 135/- CT = Rs 2000/- MRI = Rs 6000/-

Thank You