clinical aspects of US, x-ray, CT

Question 1

advantages of the US examination

Answer 1

• no ionising radiation
• good accessibility
• low cost
• portable -> examination at bed-side, ER, ICU, operating theatre

Question 2

disadvantages of US

Answer 2

• not usable in gas or bone covered territories (mainly: chest, skull)
• poos visualisation in obese patients
• operator dependent
• moderately useful in some postoperative conditions -> not good skin contact, difficulties with catheters, bandages

Question 3

physical theory of US

Answer 3

Vibration of piezoelectric crystals. Very small ceramic parcels which, after electronic vibration, produce mechanical vibration. These piezoelectric crystals work as a transmitter and receiver of US, alternatively.

Question 4

echogenicity Vs echodensity

Answer 4

• echogenicity: the reflection of different tissues

- echodensity: the strength of reflection

Question 5

different US modes

Answer 5

• A mode: measurement of reflected US -> distance measurement. eg) ophthalmology
• M mode: motion
• B mode: brightness
• Doppler US
• color Doppler US
• Power Doppler US

Question 6

US probes

Answer 6

a) convex:
- 3.5-5.5 MHz
- deep penetration
- poorer resolution

b) linear:
- 8-10 (or more) MHz
- superficial penetration
- better resolution

Question 7

indications of chest x-ray

Answer 7

• high fever
• respiratory symptoms
• physical disorder
• primary tumor
• traumatic injury
• abdominal emergency
• pre-, post- operative condition
• chest screening

Question 8

indications of abdominal x-ray

Answer 8

• abdominal emergency
• perforation
• ileus
• crampy pain (gall-stone, renal stone)
• inflammation: appendicitis, pancreatitis, diverticulitis, extrauterine gravidity, adnexitis
• mesenterial thrombo-embolism
• peritonitis
• paralytic ileus
• for free abdominal gas -> need to do a chest x-ray!

Question 9

ileus

Answer 9

• small or large bowel
• mechanical obstruction
• stenosis - stricture - obstruction
• congenital: atresia, stenosis, anal imperforation
• acquired: inflammation, tumors, obstruction, adhesion, strangulation, hernia, volvulus, intussusception

Question 10

ileus caused by inflammatory processes

Answer 10

• regional enteritis (Crohn’s disease)
• ulcerative colitis
• diverticulitis
• tuberculosis
• actinomycosis

Question 11

ileus caused by obstruction

Answer 11

• gall-stone
• foreign body
• helminthiasis
• stercolith
• tumor

Question 12

CT - what are we measuring?

Answer 12

The average linear attenuation coefficient, μ, between tube and detectors. Attenuation coefficient reflects the degree to which the x-ray intensity is reduced by a material

Question 13

tissue densities

Answer 13

• vacuum: - 1000 HU
• lipid: - 100 HU
• water: 0 HU
• dens liquid: 20 HU
• soft tissues: 20-80 HU
• fresh bleeding: 70-100 HU
• contrast medium, calcium: 100-1000 HU

Question 14

CT - windowing techniques

Answer 14

• soft tissue window
• lung window
• brain window
• bone window

Question 15

dynamic CT scan

Answer 15

• iodinated contrast medium: IV injection
• one or more scans from the same region, following contrast medium injection
• the time-course of contrast-enhacement is detected

Question 16

HRCT = high resolution CT

Answer 16

• slim slices
• high resolution images
• larger x-ray does
• longer scan time

Question 17

dual source / dual energy CT

Answer 17

• two x-ray tubes and two detectors are used simultaneously
• the two tubes are perpendicular to each other
• dual source: same kV in both tubes
• dual energy: x-ray voltage in 80 kV and 140 kV, rotation of the tubes are 180 degrees
• attenuation of the two x-rays will be different, making fine tissue specification possible

Question 18

advantages of dual source CT scan

Answer 18

• better resolution
• lower x-ray dose
• better tissue differentiation
• direct vessels or bone subtraction
• staging of oncology patients
• characterisation of vascular plaques
• differentiation of fluids in emergency medicine