Reading x-rays

• Wilhelm Conrad Roentgen, a german physicist, discovered x rays on November 8,1895.

• Roentgen was investigating the behavior of cathode rays in high energy cathode ray tube which was enclosed in black card board to prevent escape of light.

• On passing high voltage discharge through tube, he noticed a faint light glowing on a workbench about 3 feet away.

• He discovered that the source of light was the fluorescence of a small piece of paper coated with barium platinocyanide.

• Because electrons could not escape the glass envelope to produce fluorescence, & because

card board permitted no light to escape from tube, he concluded that some unknown type of ray (X) was produced when the tube was energised.

• He called them X-RAYS.

• X - rays is a form of electromagnetic radiation.

• They are produced by the X-ray tube, using the high voltage to accelerate the electrons produced by the cathode.

• The produced electrons interact with the anode, thus producing X-rays. 

• Less than 1% of energy is converted into X-ray production.

• Anode is made of tungsten disc in ordinary diagnostic x ray tube.

• X-ray film displays the radiographic image and consists of emulsion (single or double) of silver halide (AgBr is most common) which when exposed to light, produces silver ion (Ag+) and electron.

• The total thickness of the film is about 0.25 mm.

Advantages

• Cost

• Availability

Disadvantages

• Ionising radiation

• 2D information - overlap

Radiographic positioning terminology

• Anterior • Posterior • Superior • Inferior • Medial • Lateral • Proximal • Distal • Superficial • Deep • Ipsilateral • Contralateral 

Body positions

• erect: either standing or sitting

• decubitus: lying down

• supine: lying on back

• prone: lying face-down

• lateral decubitus: lying on one side– right lateral: right side touches the cassette– left lateral: left side touches the cassette

Projections

• antero-posterior: central ray passes from anterior to posterior

• postero-anterior: central ray passes from posterior to anterior 

• lateral: central ray passes from one side of body to the other through the axial plane

• oblique: central ray passes through the body/body part through a plane which is at an angle to the transverse plane/coronal plane

Different tissues in our body absorb X-rays at different extents:

• Bone- high absorption (white)

• Tissue- somewhere in the middle absorption (grey)

• Air- low absorption (black)

• Technically adequate chest x-ray

• Penetration

• Inspiration

• Rotation

• Angulation

Penetration

Under penetration

See the spine through the heart

Inspiration

• 10 anterior ribs are visualised

• Anterior ribs – harder to see

• Posterior ribs – horizontal

Anterior vs posterior ribs

Poor inspiration

• Poor inspiration – crowd lung markings – disease in lung bases

Disease in lung bases

Rotation

• Spinous process equidistant to the medial ends of the clavicles

• Spinous process closer to right clavicle – patient rotated to his left

• Spinous process closer to left clavicle – patient rotated to his right

Marked rotation

AP vs. PA

• PA film – heart close to film – less magnified

– Standard film

• AP film – heart away from film – more magnified

– Portable films

Angulation

• Apical lordotic view – beam angulated toward the head

• Anterior structures projected higher than the posterior structures

Angulation

Factors

• See spine through heart

• At least 9 – 10 ribs

• Spinous process between clavicles

• Clavicle over 3rd rib