2. Table of Content
● What is macroradiography ?
● Principles of macroradiography
● Magnification factor
● Factors affecting image quality
○ Geometric unsharpness
○ X-ray tube rating
○ Photographic unsharpness
○ Scattered radiation
● Aim & applications of macroradiography
● References
● Questions
3. What is Macroradiography ?
● Macroradiography is a radiographic
imaging technique used to increase
the size of the image relative to the
object.
● In 1982 an Italian doctor named
Alessandro Vallebone proposed this
technique.
4. Principles of Macroradiography.
● A technique of producing an image by
direct magnification using an x-ray
tube with very fine focal spot.
● Focal spot-object distance will be
adequatly changed in accordance with
the change in accordance with the
change in magnification.
5. [Cotd…]
● Magnified image can be produced by increasing the object to film
distance from the point source.
● The required magnification is obtained by moving the object away from
the film.
6. [Cotd…]
● However, the geometric unsharpness increases with the increase of
magnification.
7. Magnification Factor
● The ratio of image size to object size is known as magnification factor. Its
value is normally assessed by measuring the focus - film distance (FFD)
and the object - film distance (OFD). the focus - object distance (FOD) is
then obtained by subtraction:
FOD = FFD - OFD
● Thus ,
Magnification factor = FFD/FFD-OFD=FFD/FOD
8. [Cotd…]
● For a routine examination of the hand (dorsipalmar projection), the
relevant dimensions are typically: FFD = I 00 cm, OFD = I cm. This gives
a magnification factor of 100/99 = 1.01. Thus, a 10 cm long finger gives an
image which is 10.1 cm in length.
● For a lateral projection of the lumbar spine, the relevant dimensions arc
typically: FFD = I 00 cm, OFD = 25 cm (spine-table-top distance + table-
top-film distance). This gives a magnification factor of 100/75 = 1.3. A true
measurement of 10 cm in the spine is reproduced as 13 cm in the image
9. [Cotd…]
● For macroradiography, it is usual to arrange the FFD and OFD to give a
magnification factor of at least 1.5. Typically, a magnification factor of2.0
is achieved by positioning the structure under examination half-way
between the X-ray tube focus and the film, i.e. FFD = FOD x 2 (sec Fig.
26.2). In practice, the FOD is often maintained at its normal value but the
FFD is increased, i.e. the X-ray tube and patient are positioned normally
hut the film is moved further from the patient.
10.
11. Factors affecting Image Quality
● The quality of the magnified image is also an important consideration,
which may be affected by modifications to the FFD, FOD and OFD.
● Geometrical factors involves,
○ Geometric Unsharpness
○ X-Ray tube rating
○ Photographic Unsharpness
○ Scattered radiation
12. Geometric Unsharpness
● Geometric unsharpness refers to the loss of sharpness of feature on
radiograph that correspond to the boundaries from thickness that result
of geometric factor of the radiographic equipment and setup.
● To reduce this the the point source focal spot used.
13. ● In the 1st image, radiation
originates at a very small
source, so very little geometric
unsharpness is produced in the
image.
● In the 2nd image, the source is
large & different path the rays
of radiation can take from their
point of origin in source that
cause the edges of the notch to
be less defined.
Source
Film
Film density
plot
14. Formulae of Geometric Unsharpness
● When the detector is not placed next to
sample, such as when the geometric
magnification is used then,
Ug = f . b/a
f = Source focal spot
a = Subject - Source distance
b = Subject - detector distance
Source focal spot
Subject
Detector
Penumbra
{Ug}
15. X_Ray Tube rating
● To limit geometric unsharpness and still achieve substantial
magnification requires the use of an ultrafine focus. Such a small focus
sets serious constraints on the output of the X-ray tube.
● This may well be manifested as a reduction in maximum tube current e.g.
from over 1000 mA on broad focus to less than 400 mA when fine focus
is selected, and consequently, exposure times become longer than
desirable. Unless great care is taken, motional unsharpness is the result.
Motional unsharpness problems can be alleviated by:
○ Taking positive measures to immobilize the patient;
○ Using fast film-screen systems, if necessary
16. [Contd…]
● Extremities is often highly successful because the required X-ray exposure
is small and effective immobilization is possible: thus, high-resolution
screens can be used.
● Macroradiography may prove impossible, e.g. for many abdominal
structures the large exposures necessary and the problems of involuntary
movement may exclude macroradiography as a viable technique.
● minimizing the FFD may ease rating problems but the radiographer must
be alert to the increased radiation dose to the patient associated with a
short focus-skin distance.
17. Photographic Unsharpness
● The resolution of the film or film-screen system is not normally a critical
limiting factor in carrying out macroradiography.
● Photographic unsharpness ( Up) remains constant because it is not the
recorded image that is magnified.
18. Scattered Radiation
● The large object-film distance used in macroradiography reduces the
amount of forward-scattered radiation reaching the film from the patient.
● It is not necessary to use a secondary-radiation grid, even for regions such
as the skull or spine where a grid would be essential.
● Collimation of the X-ray beam and provision of backscatter protection for
the film help to maintain optimum contrast on the macroradiograph.
19. Aim of Macroradiography.
● Aimed to improve the study of the bony structures and the
pulmonary designs.
● Allows the small detail obvious in the image.
Application of Macroradiography
● Carpal bones of the wrist (especially the scaphoid bone)
● Bones of hand, e.g., early detection of metabolic bone disease.
● Temporal bone.
● The lacrimal system during Dacryocystography.
● Nodular pattern in chest radiographs.
● Cerebral Angiography.
21. Questions ?
1. Whats are the 2 requirements of successful macroradiography ?
2. How is macroradiography is achieved ?
3. What is the main disadvantage of macroradiography ?
4. What is the formulae of geometric unsharpness ?
5. Who proposed macroradiography ?
