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.