Macroradiography Flashcards
Why is PA preferred over AP for CXR?
In AP Chest, the heart size is exaggerated and can be mistaken for cardiac enlargement on a PA image.
Objects further away from the detector are magnified.
What is the principle of Macroradiography?
It is a technique which a magnified image is produced by the relative positions of the x-ray source, object and the image receptor.
What is the purpose of Image Magnification?
Magnification enhances the visualization of fine anatomical details better than the original, enabling more accurate diagnosis.
How is the image magnified?
By increasing the object to image receptor distance (OID)
Source Object Distance (SOD) is usually fixed.
How do you find the Magnification Factor, M?
M = SID/SOD
Where is the Source Object Distance (SOD) taken from?
Mid-level of the anatomical part or the lesion
How do you find OID?
OID = SOD (M-1)
Why is SOD kept at 100cm?
So that skin dose can be minimized.
How to obtain the required magnification?
By moving the image receptor away from the object.
How do we maintain the dose to the IR in macroradiography?
By increasing the mAs
How do reduce movement unsharpness with increased magnification?
Complete immobilization of the patient using devices whenever possible e.g. supports, sandbags and pads.
Instruct patients to remain still.
How do reduce geometrical unsharpness?
Choose a smaller focal spot size.
The smaller the focal spot size, the greater the possible magnification while still retaining acceptable image quality.
What is the formula for Geometrical Unsharpness (Ug)?
Ug = f(M-1)
f= focal spot
M = magnification factor
What are some considerations to note for macroradiography?
Need for immobilization
Requires precise centering
Tight collimation
Exposure increased about 2-4 times the mAs
Decrease in SOD increases skin dose
What are some clinical applications of Macroradiography?
Imaging the carpal bones in cases of suspected fracture of scaphoid
Mammography
Dental Imaging
Angiography (localized areas such as Cerebral Angiography)
