Ultrasound guided procedures and investigations

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Slide 1 : Ultrasound Chapter 4
Slide 2 : Biophysics of Ultrasound Absorption & Penetration Fluid elements, such as blood and water are poor absorbers of ultrasound Bone (most dense tissue), scar tissue, joint capsule, ligament & tendon are good absorbers of ultrasound Refraction At tissue-air boundary, wave changes direction at 90 , if not perpendicular to surface
Slide 3 : Biophysics cont. Frequency: Influences amount of energy absorbed by tissue Describes the number of complete wave cycles generated each second Ultrasound available between 0.75-3.3 MHZ (million cycles/sec) The higher the MHZ, the more superficial the Rx Intensity: Describes the magnitude of the force in a sound wave Measure in watts per square centimeter (W/cm2) Most significant factor in determining tissue response in US Rx
Slide 4 : Generators & Transducers US machines generate a pressure wave by causing a crystal to vibrate Crystal made of natural quartz or synthetic material that alternates current rapidly (vibrating) Crystal housed inside transducer that has a metal plate Air gap between transducer & skin will prevent pressure wave from leaving transducer, resulting in overheating & potentially damaging crystal Couplant agent (gel) used to improve continuity Transducer size 1cm – 10 cm
Slide 5 : Distribution of energy Continuous: Set intensity level remains constant throughout Rx period Pulsed: Average intensity over the Rx time is less than peak intensity that occurs during pulse Pulse ratio: relationship between on/off periods; 1:1 ratio = on 1ms & off 1 ms Duty factor (cycle): % of time that US is on in each on/off period; 1:1 ratio = 50 % 1:4 ratio = 20%
Slide 6 : Heating tissue with continuous-wave US Area of tissue that can be treated is approximately 2x size of transducer Water-immersion techniques diminish skin & subcutaneous heating, because water quickly absorbs heat; Effective deep heating still occurs Pt will report little to no sensation of warmth during underwater Rx At 1MHz & 1.0 W/cm2, a change in temp of 7-10 F can be anticipated close to bone Therapeutic temps are achieved with 8 – 15 min US at 1 – 1.5 W/cm2
Slide 7 : US to facilitate tissue repair Lower dosages of 0.2 & 0.3 W/cm2, pulsed in 20% duty cycle, are beneficial for tissue healing (ex. Open wound, tendon repair, closed trauma, bone healing) Brief Rx: 30 – 60 sec per area of the transducer Rx repeated daily or every 48 hours
Slide 8 : Phonophoresis Practice of applying ultrasound through a medicated couplant The ultrasound pressure drives the drug into the skin Examples of drugs: corticosteroids, local anesthetics, and nonsteroidal anti-inflammatory drugs (NSAIDS)
Slide 9 : Indications for treatment For low-intensity pulsed ultrasound/ tissue repair: Inflammation from strains & sprains Bruising Muscle tears Burns Superficial & deep skin wounds Crush injuries For high-intensity continuous-mode ultrasound: Restriction of movement Muscle spasms Chronic edema Fibrosis Connective tissue contracture Adhesions Unresolved hematoma
Slide 10 : Precautions Discomfort should not be experienced during Rx Pain is sign of too much periosteal heating Transducer must constantly be moving Stationary transducer can cause hot spots & burn pt.
Slide 11 : Contraindications Over or close to site of abnormal growth (cancer) Over tissue being Rx’d with radiation therapy Over lower back or abdomen of pregnant women Over orbits of the eyes Over a DVT Directly over pacemaker Where uncontrolled bleeding exists
Slide 12 : Therapeutic Application Sequence of ultrasound in a Rx plan: With thermal Rx, stretch must immediately follow US Ice and continuous US have contradictory effects However, Ice can be used for pain control at end of Rx session
Slide 13 : Ultrasound Treatment Procedures Preparation for Rx: Collect all necessary items – gel, towels, container (plastic or rubber if using water) Pt education & consent to treat: Explain sensations & purpose to pt Pulsed US – no sensation Continuous US – possible mild skin heating Preparation of Equipment: Clinicians should be seated so they can see both pt and dials of the equipment Time and intensity dials should be at zero before power switched on.
Slide 14 : US Treatment Procedures cont. Patient position Patient should be comfortable with part to be treated exposed Technique: Apply gel to skin approximately 1-2 mm layer Soundhead moved in overlapping circles Rate of transducer movement is slow, approximately 3 to 4 cm/sec Soundhead should be parallel to tissue surface Water-immersion techniques, Rx applied 1-2 cm from skin If pt reports pain during Rx, immediately lower intensity No limit on # of US Rx’s that can be safely applied

 


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