Anatomy – Imaging
Learning Objectives
1. Describe the uses of, and the differences between,
a. plain (X-ray) films;
b. computerised tomography (CT);
c. Magnetic resonance imaging (MRI).
2. Discuss why knowledge of anatomy is vital to appreciate the applications of imaging to medicine.
3. Discuss the use of contrast: Barium, iodine, gadolinium.
X-ray (plain radiograph)
• Useful for visualising the skeletal system and some disease processes in soft tissue.
o Large static machines
o Able to move
• A heterogeneous beam of x-rays
• Based on the density and composition of the structure a proportion of the x-rays
will be absorbed
o Put out gamma radiation waves and the detector picks up X rays
• The x-rays that pass through are detected as black and less dense tissues
• Grey/white areas are denser tissues that have absorbed more x-rays
o Blacker the image means more X rays pass through
o That’s why bone shows up as white
Advantages of plain radiographs Disadvantages of plain radiographs
Cheap Limited range of densities
Air = black
Fat = lighter grey than air
Soft tissue/fluid
Calcium = most dense naturally occurring tissue [in
bone]
Metal = white
Readily available 2D representation of a 3D object
Uses ionising radiation → can cause mutations in DNA
Remember - Stomach is filled with gas.
Chest X-Rays
Skeletal system – normally taken anterior to
posterior view → Sensor is at the back, x rays at the
front
X rays hit the heart first and meaning the heart
appears enlarged as the X rays spread out
So for chest x rays: use posterior to
anterior view
, o Heart is closer to the sensor and so the heart doesn’t appear enlarged as this would
obscure everything else
o Most chest x rays are taken in this manner unless patient is unable to stand up or if the
patient is a child
o PA view gives you a more anatomically correct view and things are a bit clearer
PA view- AP view-
1. Clavicle in lung field 1. Clavicle remains at top of lung field
2. Ribs slanted 2. Ribs lie more horizontal
3. Scapula outwards from lung field 3. Scapula comes in the lung field
4. Heart shadow smaller 4. Heart shadow looks larger
5. Usual view for the chest 5. Usually bedridden and infants
Learning Objectives
1. Describe the uses of, and the differences between,
a. plain (X-ray) films;
b. computerised tomography (CT);
c. Magnetic resonance imaging (MRI).
2. Discuss why knowledge of anatomy is vital to appreciate the applications of imaging to medicine.
3. Discuss the use of contrast: Barium, iodine, gadolinium.
X-ray (plain radiograph)
• Useful for visualising the skeletal system and some disease processes in soft tissue.
o Large static machines
o Able to move
• A heterogeneous beam of x-rays
• Based on the density and composition of the structure a proportion of the x-rays
will be absorbed
o Put out gamma radiation waves and the detector picks up X rays
• The x-rays that pass through are detected as black and less dense tissues
• Grey/white areas are denser tissues that have absorbed more x-rays
o Blacker the image means more X rays pass through
o That’s why bone shows up as white
Advantages of plain radiographs Disadvantages of plain radiographs
Cheap Limited range of densities
Air = black
Fat = lighter grey than air
Soft tissue/fluid
Calcium = most dense naturally occurring tissue [in
bone]
Metal = white
Readily available 2D representation of a 3D object
Uses ionising radiation → can cause mutations in DNA
Remember - Stomach is filled with gas.
Chest X-Rays
Skeletal system – normally taken anterior to
posterior view → Sensor is at the back, x rays at the
front
X rays hit the heart first and meaning the heart
appears enlarged as the X rays spread out
So for chest x rays: use posterior to
anterior view
, o Heart is closer to the sensor and so the heart doesn’t appear enlarged as this would
obscure everything else
o Most chest x rays are taken in this manner unless patient is unable to stand up or if the
patient is a child
o PA view gives you a more anatomically correct view and things are a bit clearer
PA view- AP view-
1. Clavicle in lung field 1. Clavicle remains at top of lung field
2. Ribs slanted 2. Ribs lie more horizontal
3. Scapula outwards from lung field 3. Scapula comes in the lung field
4. Heart shadow smaller 4. Heart shadow looks larger
5. Usual view for the chest 5. Usually bedridden and infants
