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Ultrasound technique

Probe manipulation techniques:

get comfortable:

  • operator should be positioned so that forearm & hand are gently resting on the patient, with spine erect & eyes at the level of the system monitor
  • adjust the height of the patient's bed to match your position

initialise scanner:

  • patient ID info including your initials as suffix to ID code
  • choose the correct transducer for the job:
    • examples:
      • aorta/FAST: curved linear transducer - 5MHz if slim; 3.5MHz if fat; 
      • heart: phased array or TV transducer - 3.5-5MHz
      • 9MHz if paediatric, TV or foreign body
  • select appropriate presets eg. “abdominal”

apply plenty of ultrasound gel:

  • too much gel is far better than not enough!
  • spread out the gel over the proposed scanning area

hold transducer correctly:

  • probe should be held with operator's fingers close to the transducer face & with the little finger resting on the patient's skin so that maximal control is exerted & the transducer will not slide off the scan plan needed & can be kept steady on the patient's skin at the correct angle

orientate the transducer correctly:

  • marker on transducer should always be either to the patient's head or to their right
  • use the US beam as a torch

perform a survey scan:

  • always perform a swift survey of the area in question before focussing on the point of clinical question
  • this will help you orient yourself to the anatomy & identify good sonographic windows

consider using a sonographic window to reach the organ in question:

  • use right lobe of liver to view R kidney or GB lumen
  • use GB lumen to view the CBD
  • use distended urinary bladder to view pelvic organs
  • use spleen to view L. kidney, adrenal or tail of pancreas
  • use left lobe of liver to view pancreas, central abdominal vasculature or the heart
  • use intercostal spaces to view liver & spleen

optimise scanner settings in order:

  • adjust depth of view to only include region required
  • adjust focal zone so that target structure is at or just superficial to the focal zone (ie. within Fresnel zone)
    • this increases the beam intensity at this region as well as resolution whilst reducing beam width
  • adjust total 2D gain aiming for:
    • structures that should be anechoic such as bladder, cysts & blood vessels should as much as possible appear anechoic
  • adequate brightness of soft tissue organs
  • consider adjusting TGC aiming for equal brightness across display such that an organ appears as uniform as possible from top to bottom
    • inappropriate TGC may cause:
      • hypo-echoic horizontal regions suggestive of free fluid, etc
      • hyper-echoic horizontal regions that may hide presence of free fluid, etc

moving the transducer:

  • this should be smooth, free flowing, allowing time for the operator to view the real time image on the monitor without constantly checking the position of the transducer
  • once target found, movements should be slow & small, made in one plane at a time to avoid becoming confused & losing sight of the target
  • movements include:
    • rotate:
      • to move from one plane (eg. transverse) to another (eg. longitudinal)
      • to re-align to direction of axis of target organ or to get between ribs by aligning parallel with rib
    • rock heel-to-toe:
      • esp. to change orientation eg. to make a longitudinal view of aorta look more horizontal
      • to view other structures through the same window such as bladder window
    • roll:
      • to get best view of target eg. longitudinal aorta
      • to view other structures through same window such as bladder window
    • slide up or down , side to side:
      • to get a different window or avoid a rib or navel

consider moving the patient:

  • where organs are obscured by bowel gas or are difficult to visualise, moving the patient may shift the bowel gas away or alter the positions of organs to make target more readily visualised.
  • examples:
    • if GB is positioned high in the liver & obscured by hepatic flexure gas, move pt to left lateral decubitus position which may allow GB to become more dependent & easier to view subcostally

consider using graded compression:

  • use of gradually increasing & decreasing pressure on the transducer is usually well tolerated by patients, even those experiencing significant pain
  • advantages:
    • decreases distance to target thus may:
      • bring target into main focal area of the beam
      • allow use of higher frequency transducers
    • may push gas filled bowel out of the field
    • improve skin/transducer contact & minimise some artefacts
    • allow better angle of incidence on target eg. endometrial line where may need to compress and angle to visualise it
    • helps distinguish hollow from solid as the hollow target will also compress eg. veins

use multiple scan planes:

  • structures should always be viewed in at least two different scan planes, with longitudinal & transverse sections being the minimum
  • it is preferable to view from two different approaches as well eg. anterior & coronal
  • this can easily resolve confusion concerning the nature of some structures
    • eg. cyst vs tube; aorta vs IVC
  • it is also essential in many cases to exclude the echoes visualised as being artefacts

respiratory techniques:

  • holding the transducer steady & watching organs move in & out of field during respiration can often tell you which best respiratory technique to use
  • commonly, suspended respiration at the correct part of the cycle will suffice
  • examples:
    • to view liver, GB, portal system, pancreas & mid-abdominal structures:
      • deep inspiration
      • protrusion of anterior abdominal wall
    • to view spleen, tail of pancreas & L. kidney:
      • deep expiration
      • deep inspiration
      • protrusion of anterior abdominal wall
    • to view fluid in pelvis:
      • consider asking pt to do Valsalvre and push down so that fluid goes into pelvis

transducer as a palpation tool:

  • use of the transducer face to gently palpate an area of pain will often give clinically useful information
  • examples:
    • acute pain on direct palpation of the GB fundus - positive ultrasound Murphy's sign
    • transvaginal - adnexal tenderness

consider using colour Doppler mode as well:

  • helpful in confirming target is a blood vessel and that there is flow within it
  • ensure B-mode image is optimised 1st!
  • use smallest colour Doppler box possible to reduce colour Doppler artefacts
  • create a good Doppler beam angle (remember no Doppler effect if perpendicular to moving interface's direction of motion)
  • optimise colour Doppler settings such as scale (low velocity range vs high velocity range)

consider developing & using standardised examination protocols

us_techniques.txt · Last modified: 2008/11/19 23:56 (external edit)