Ultrasound_L4

Disabilities and Therapeutic Procedures PT 1211

  • Instructor: Prof Enrique Amador

Therapeutic Heat/Thermotherapy

  • Heat Agents:

    • Categories:

      • Superficial: Affects skin and subcutaneous tissues, with limited effect beyond 2 cm (e.g., Hot Packs, Fluidotherapy, Paraffin).

      • Deep: Affects deeper tissues, goes about 3-5 cm (e.g., Short Wave Diathermy and Ultrasound).

    • Literature Discrepancy: There are varying numbers regarding the depth of effect.

Ultrasound

  • Historical Background:

    • Therapeutic ultrasound began in the early 20th century, originally developed from military applications using sonar.

    • Initial focus was on heating properties, using continuous mode at intensities of 0.5-1.5 watts/cm², primarily studied by scientists rather than clinicians treating patients.

Importance of Understanding Ultrasound

  • Relevance of Material: Not all chapter content is crucial for practical application in patient care.

  • Focus: Lecture will emphasize basic physical principles, crucial for understanding clinical applications for thermal and non-thermal effects in both superficial and deep tissues.

Physics of Sound and Ultrasound

  • Sound Properties:

    • Sound is a mechanical wave characterized by pressure oscillation in solids, liquids, or gases that can be heard.

    • Ultrasound operates at frequencies beyond human hearing ranges.

  • Frequency Range:

    • Audible Sound: 30-20,000 cycles/second.

    • Therapeutic Ultrasound: 1-3 million cycles/second (1-3 MHz).

Functionality of Ultrasound

  • Wave Effects:

    • When waves travel through media, they cause effects such as vibrations and energy transfer, shifting mechanical energy to thermal energy.

  • Machine Mechanics:

    • Ultrasound machines convert electrical currents into mechanical vibrations through crystals in the transducer to produce ultrasound waves.

Variables in Ultrasound Therapy

  • Key Characteristics:

    • Frequency, Duty Cycle/Duty Factor, Intensity, Duration.

Frequency in Ultrasound

  • Impact on Tissue Depth:

    • Higher frequencies (3 MHz) target superficial tissues, while lower frequencies (1 MHz) penetrate deeper.

Duty Cycle / Duty Factor

  • Delivery Modes:

    • Continuous Ultrasound: 100% duty factor, generates thermal effects.

    • Pulsed Ultrasound: Intermittent intensity (20-50% duty factor), results in non-thermal effects.

  • Clinical Application: Continuous mode for heating, pulsed mode for inflammation.

Wave Characteristics

  • Ultrasound Properties: Absorption, Penetration, Reflection, Refraction.

Absorption and Penetration

  • Tissue Absorption: Different tissues absorb ultrasound energy variably: Bone > Muscle > Blood.

  • Inverse Relation: Higher absorption correlates with lower penetration.

Reflection

  • Sound waves may reflect from boundaries, diminishing power as they enter tissues.

  • Coupling Agent Importance: Essential to mitigate reflection at the transducer-skin interface.

Refraction

  • Wave Bending: Occurs at angled boundaries, risking standing waves that may increase energy and cause tissue damage.

  • Movement Precaution: Keeping the ultrasound head in motion avoids damage.

Cavitation

  • Definition: Expansion and contraction of gas bubbles in tissues exposed to ultrasound.

  • Types: Stable cavitation increases cell permeability, while unstable cavitation can harm tissues - mitigate by moving the transducer head.

Beam Quality Parameters

  • BNR (Beam Nonuniformity Ratio): Indicates quality; recommended ratios are 5:1 or 6:1.

  • ERA (Effective Radiating Area): Refers to the size of the effective ultrasound delivery.

Biomedical Engineering Metrics

  • Assessment: BNR and ERA determined using hydrophones; periodic safety checks ensure effective delivery and compliance.

Thermal Effects of Ultrasound

  • Benefits:

    • Increases nerve conduction velocity, modulation of pain, improved circulation, metabolic rate, reduction of muscle spasms, increases soft tissue extensibility, decreased joint stiffness.

Non-Thermal Effects of Ultrasound

  • Benefits:

    • Enhancement of cell membrane permeability, increased intracellular calcium, facilitation of tissue repair, and promotion of normal cell functions.

Indications for Ultrasound Use

  • Determining the required thermal vs. non-thermal effects based on conditions—recognizing variations in treatment for acute versus chronic issues.

  • Specific Conditions:

    • Examples include (non-thermal): Acute conditions, calcium deposits, chronic inflammation, etc.

Contraindications for Ultrasound Therapy

  • Conditions:

    • Includes decreased circulation, DVT, active malignancy, and pregnancy. Important for clinicians to remember key contraindications (e.g., pacemaker, pregnancy, cancer).

Technique Application of Ultrasound

  • Transducer Sizes: Commonly from 1-10 cm², with 5 cm² being the most used.

    • Direct Coupling: Apply a coupling agent before treatment;

    • Indirect Coupling: Includes using water or gel pads in specific scenarios.

Effective Application Techniques

  • Transducer movement should overlap at a speed of 3-4 cm/s, at 90-degree angles to tissues.

  • Treatment area should be approximately 2-3 times the ERA, avoiding ultrasound for over 4 times the ERA size.

Treatment Frequency and Duration

  • Determine based on size, depth, and desired effects. Research supports 5 minutes for an area of 2-3 times the ERA, but billing practices necessitate a minimum of 8 minutes.

  • Non-thermal effects applied early in healing, while thermal effects focus on later recovery stages.

Safety in Ultrasound Therapy

  • Requires annual inspections, understanding contraindications, ongoing patient assessments, and clear documentation among care personnel.

Phonophoresis

  • Definition: Ultrasound used for the transdermal delivery of medications (e.g., anti-inflammatories, analgesics).

  • Application Modes: Either pulsed or continuous, tailored to minimize tissue heating.

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