grey white and black in xray

1. WHITE ,GREY, BLACK- WHY AND
WHEREFORES??????
RADIOGRAPHY

2. • X RAYS USED IN MEDICAL DIAGNOSIS ARE
PRODUCED WITHIN THE XRAY TUBE WHEN
EXPOSURE IS MADE
• DIFFERENT TISSUES IN OUR BODY
ATTENUATES XRAYS AT DIFFERENT EXTENTS
• ATTENUATION IS THE REDUCTION IN THE
INTENSITY OF AN X-RAY BEAM AS IT
TRAVERSES MATTER BY EITHER THE
ABSORPTION OR DEFLECTION OF PHOTONS
FROM THE BEAM

3. • EXPONENTIAL ATTENUATION : When the number
of photons remaining in the beam decreases by
the same percentage with each increment of
absorber, as with monochromatic radiation
• Attenuation coefficient : Measure of the quantity
of radiation attenuated by the given thickness of
an absorber

4. • Linear attenuation coefficient: most
important for diagnostic radiology
• Quantitative measure of attenuation per
centimeter of the absorber
• Is for monochromatic radiation and is specific
for both the energy of the x-ray and type of
absorber
• When the energy of the radiation is increased
the number of xrays that are attenuated
decreases,and does the linear attenuation
coefficient

5. HALF VALUE LAYER
• The Absorber thickness required to reduce the
intensity of orginal beam by one half
• Common method for expressiong the quality of
an xray beam
• A beam with high HVL is a more penetrating
beam than one with low Hvl
• Hvl of a typical diagnostic beam is
• 30mm : tissue
• 12mm :bone
• 0.15mm : lead

6. Mass attenuation coefficient
• Quantitates the attenuation of materials
independent of their physical state
• Obtained by dividing the linear attenuation
coefficient by the density
• Mass attenuation coefficient is independent of
the density of the absorber

7. Factors affecting Attenuation
• ENERGY
• DENSITY
• ATOMIC NUMBER
• ELECTRONS PER GRAM

8. Density and atomic number
• Elements with higher atomic number are
denser than elements with lower atomic
number
• No relationship between atomic number and
density when different physical states of
matter are involved
• Water – effective atomic number -7.4 (but
density varies in ice,liquid,vapour )

9. Density and electrons per gram
• Density depends on volume ,hence there is no
relationship between density and electrons
per gram

10. Effect of energy and atomic number
• With extremely low energy radiation(20kev)
photoelectric attenuation predominates
irrespective of the atomic number of the
absorber
• Attenuation is always greater when the
photoelectric effect predominates
• As the radiation energy increases Compton
scattering predominates and replace
photoelectric effect

11. • ABSORPTION OF XRAYS IS BASED ON THE
1.ATOMIC NUMBER
2.DENSITY
3.THICKNESS OF THE TISSUES
• TISSUES WITH HIGHER ATOMIC NUMBER WILL
ABSORB MORE RADIATION THAN TISSUE WITH
LOWER ATOMIC NUMBER

13. • DENSITY– AIR AND SOFT TISSUE HAVE SAME
ATOMIC NUMBER BUT DENSITY IS LESS FOR
AIR SO LESS ABSORPTION
• THICKER TISSUES WILL ABSORB MORE XRAYS
THAN THINNER TISSUE OF SIMILAR
COMPOSITION
• GREATER THE AMOUNT OF TISSUE
ABSORPTION FEWER XRAYS REACH THE FILM
AND WHITER THE IMAGE ON THE FILM
• RADIOPAQUE TISSUES APPEAR MORE WHITE
AND RADIOLUCENT TISSUES APPEAR MORE
BLACK

14. BASIC TISSUE RADIOGRAPHIC
OPACITIES
1. GAS - BLACK
• MOST RADIOLUCENT MATERIAL VISIBLE ON
XRAY

15. FAT -GREY
• MORE LUCENT THAN BONE AND SOFT TISSUES
BUT IS MORE OPAQUE THAN AIR

16. SOFT TISSUE /FLUID- LIGHT WHITE
• BOTH SOFT TISSUE AND FLUID HAVE SAME
RADIOLUCENCY. VARIATION IN VOLUME ,
THICKNESS AND DEGREE OF COMPACTNESS
OF SOFT TISSUE CREATES A PATTERN OF
VARIOUS DENSITIES ON THE RADIOGRAPH

18. BONES & MINERAL- WHITE
• BONE IS COMPOSED PRIMARLY OF CALCIUM
AND PHOSPHOROUS
• NORMAL VARIATION IN THE RADIOPACITY
WITHN THE BONE AND BETWEEN BONES
BECOZ OF DIFFERENCE IN RADIOPACITY OF
COMPACT V/S SPONGY BONE ,CORTICAL V/S
MEDULLARY CANAL

20. METAL –BRIGHT WHITE
• MOST OPAQUE SHADOW SEEN ON
RADIOGRAPH