• “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
• Roentgen’s discovery of X-rays in 1895.
• Plain X ray
• Computerized Axial Tomography
• Magnetic Resonance Imaging
• Others PET, Bone scan.
• EM spectrum ranges from cosmic waves to radio
• 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.
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-density depends on the composition, and
thickness a given object.
How is a X-ray image taken?
• Summation of shadow layers.
• Negative of the true image commonly used
• Shows structures closest to the film with the best
• Clear anatomical knowledge is essential to
interpret a X ray.
• Should be obtained prior to any other imaging
• Is basically glorified Roentgenography, which
shows the anatomy much superiorly than a plain
X ray with the drawback of increased radiation
• 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 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
• 3D reformations are possible
• Best imaging tech to detect
• Radiation effectiveness (100-
200 times a plain X ray)
• Cost effectiveness
• Requires contrast to visualize
• 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 ; TE
Time of repetition ; TR
• T1 short TE + Short TR
• T2 short TE + Short TR
• Still ????
• T1 weighted images depict Normal anatomy at
• T2 weighted images picks up “pathology” better
MR in Orthopedics
• THE BEST method to detect soft tissue
• Not of much use in cortical bone studies, as bone
cortex contains minimal H+ ions.
Pros and cons
• Best soft tissue detailing,
• No ionizing rad:
• Possibility of creating infinite
no: of virtual planes
• Virtual arthroscopy +
• Procuring time is high
resulting in more movement
• Claustrophobia/ magnetic
• Bone cortex poorly visualized
• USG useful in detecting joint pathology like
• New generation high frequency probes can
detect hair line cracks which are not picked on X
• X ray absolute necessity in Ortho invest:
• CT currently the best modality for cortical
• MRI best to detect soft tissue pathology.
• None of these have a complete dominance over
• Cost Pelvis Xray = Rs 135/-
CT = Rs 2000/-
MRI = Rs 6000/-