August 5, 2015 - Introduction to Radiology Flashcards
Risk of X-Rays
Because X-rays use ionizing radiation, there is a small but real risk of causing cancer in the patient.
X-Ray Densities
- Air is Black
- Fat is Dark Grey
- Soft Tissue is Light Gray –> this is the downfall of X-rays. Light gray does not give much discerning power as many things appear this colour and it makes it very difficult to determine what things are.
- Bone and Metal is White.
CT Scan
Computed Tomography
Uses a similar technology to X-rays, but basically on steroids. This gives you significantly more information, but unfortunately requires a lot more radiation to your patient. This is very quick and easy to perform, however.
Ultrasound
Utilizes high-frequency sound waves to formulate an image.
A significant benefit from this is that it does not utilize radiation. Another benefit is that it is in real-time, so it can also be utilized for procedures.
Unfortunately, it cannot see deep into bone or gas and will create white “shadows” that indicate a point you cannot see past.
White “Shadows” on Ultrasound
Indicate a point where you cannot see past, often due to calcification. For example, gallstones in the gall bladder will cast a white shadow.
MRI
Magnetic resonance imaging.
Does not involve radiation. This utilizes an enormous magnet which rotates around your body and causes the protons to allign. It then disrupts the field, allows protons to go back, and re-initiate the magnetic field. Protons behave differently depending on the tissue, which allows excellent images to be formed.
This test takes much longer to perform and is much more uncomfortable, causing it to be more difficult for the elderly or acutely ill.
Indications for Ordering Abdominal X-Rays
- Obstruction
- Perforation
- Pain
The Abdominal Series
Always order the abdominal series when you send a patient for abdominal X-rays. This includes…
- Upright chest
- Upright abdomen
- Supine abdomen
ABCS of X-Ray Interpretation
A - Air
B - Bone
C - Calcifications
S - Soft Tissue
Interpretation - Air
Pneumoperitoneum occurs when free air is in the abdomen. This is extremely bad and needs emergency surgical intervention. This occurs under the right hemidiaphram which will appear black if air is present.
Air is normally present in the fundus of the stomache, but NOT in the hemidiaphram.
Pneumoperitoneum
The presence of air or gas in the abdominal (peritoneal) cavity. This requires emergency surgical intervention. This is very difficult to spot on the abdominal pictures, but very easy on the chest. This is why the abdominal series are always ordered.
Large Bowel on X-Ray
Takes up the periphery and acts as a “picture frame”.
Small Bowel on X-Ray
Is centrally located within the large bowel on the X-Ray.
Obstruction in Bowel
Can cause a sharp line in the X-ray which is caused by fluid and gas seperation. This is viewed as a meniscus on the X-ray.
Colon Distension in X-Ray
Causes enormous distension of 6-9cm because of air fluid levels. Looks like a giant coffee bean on the X-ray.
Mural Edema
Look for “thumbprinting”. This is causes by large chunks of soft tissue projecting into the bowel. This is caused by edema on the wall of the colon. These look like many individual thumb prints.
Calcifications / Clips on X-Ray
Will show up as solid white. You need to know anatomy and understand where different organs live within your body to make a good diagnosis. For example, seeing solid lumps in the area that contains your kidney is a good indication of a kidney stone.
See below for gallstones…
