Case 2 Diagnostics Flashcards
What does MRI stand for?
Magnetic Resonance Imaging
How does an MRI work?
Powerful magnet releases a burst of electromagnetic energy causing the hydrogen atoms in the patient to be in their high energy state. As some hydrogen atoms return to their low energy state, they release energy which is detected.
What are some advantages of MRI?
Good for soft tissues, CNS and PNS; no ionising radiation; usable in pregnant women; excellent quality of detail
What are some disadvantages of MRI?
not good for areas without much water; presence of metallic objects in prohibited; expensive; resource heavy; claustrophobic; patient needs to be as still as possible
How does an ultrasound work?
Probe emits ultrasound, reflect various amounts from different surfaces (eg they pass through air and reflect lots from bone) and reflected waves are picked up by receiver.
What is the Doppler effect?
Objects moving away or closer changes the frequency of a wave
Why is the Doppler effect useful in ultrasonography
It can show arterial and venous blood flow.
What are the advantages of ultrasound?
cheap, portable, no ionising radiation
What are the disadvantages of ultrasound?
user dependent; limited by patient BMI; not good if the surrounding or superficial tissues are of a high echogenicity (bone)
How does plain radiography work?
X-rays are generated by electrons colliding with the end of a tube. X-rays penetrate through the body to varying degrees. X-rays are detected (used to be by a photographic film or plate, now by a digital detector)
What are the advantages of plain radiography?
cheap, quick, good for when there is an air background (eg near the lungs)
What are the disadvantages of plain radiography?
ionising radiation, 2D (pathologies could be hidden or missed), not good for soft tissues/hollow organs or neurological system
What does CT stand for?
Computed Tomography
How do CT scans work?
X-rays at different levels. Plain films are fed into a processor to generate a 3D image.
What are the advantages of CT scans?
3D, relatively simple, quick, less resource heavy
What are the disadvantages of CT scans?
difficulty in producing accurate images of soft tissue, lots of ionising radiation
How does echocardiology work?
Ultrasound of the heart, with the probe placed between the patient’s ribs or down the oesophagus.
What are the advantages of echocardiology?
Can see the heart in real time, and can use Doppler effect to visualise blood flow so good for assessing valvular disease.
How does coronary angiography work?
Peripheral artery is punctured with a hollow needle. Coronary catheter wire is then passed through into the artery, up to the aortic root and into the coronary vasculature. Radioplaque dye in injected into each coronary root. The dye is a dense liquid which blocks X-rays. Plain radiography is then used to image blockages in the coronary vasculature can be visualised.
How do you place the electrodes for a lead I ECG?
+ve electrode on left arm
-ve electrode on right arm
ground on right foot
How do you place the electrodes for a lead II ECG?
+ve electrode on left foot
-ve electrode on right arm
ground on right foot
How do you place the electrodes for a lead III ECG?
+ve electrode on left foot
-ve electrode on left arm
ground on right foot
How do you place the electrodes for an aVF ECG?
+ve electrode on left foot
-ve electrodes on left and right arms
How do you place the electrodes for an aVL ECG?
+ve electrode on left arm
-ve electrodes on right arm and left foot
