BME Exam 2

Biomechanics:

• What is Biomechanics?

  • Apply principles from classical mechanics to study the movement of living systems

  • From your muscles and bones to your tendons and ligaments – Biomechanics analyzes how different body parts work together to produce movement. 

• Kinetics: deals with forces that cause motion only

• Kinematics: deals objects solely in terms of their position, velocity, and acceleration

• Kinetics quantities: force, torque (Moment of force), power, and work

• Kinematics quantities: time, position, displacement (distance), velocity (speed), and acceleration 

• Applications of biomechanics:

  • Musculoskeletal disorders: Assessing joint forces and mechanics in conditions like osteoarthritis to understand pain mechanisms and design appropriate treatment strategies.

  • Gait analysis: Studying walking patterns to identify imbalances or abnormalities in patients with neurological conditions, joint pain, or musculoskeletal disorders, allowing for tailored interventions.

  • Prosthetics design: Utilizing biomechanical principles to design prosthetic limbs that mimic natural movement patterns and optimize function.

  • Sports medicine: Evaluating athletic movements to identify biomechanical factors contributing to injuries and optimize performance. 

  • Cardiovascular disease: Studying blood flow dynamics in arteries to assess the risk of cardiovascular events and design interventions for conditions like atherosclerosis. 

Bioinstrumentation:

• Bioinstrumentation is the application of electronics and measurement principles to develop devices used in diagnosis and treatment of disease

• What do biomedical engineers do in bioinstrumentation?

  • Invent, design, build, and test devices for use in medicine, provide training to use such devices, overseeing maintenance, and take measurements + give data for diagnosis

• Measurement Systems: 

  • Input → Sensor → Processor → Receiver → Output

  • Clinic Input: Temperature, oxygen saturation, blood pressure, biopotentials

  • Lab input: pH, glucose, light absorbance, blood cell counts, fluorescence 

    • Sensor: detects the physiological parameter and converts the input parameter into a signal, usually an electrical voltage or current, varies in a predictable and reliable way with changes in the input

    • Processor: modify the received signal, eg; signal amplification; filter to remove unwanted information; comparison to signals from previous measurements or control signals

    • Receiver: display, store or communicate the signal in interpretable way (usually a digital readout)

• Type of Sensors:

  • Thermal | Sensing element: Thermocouple, thermistor

  • Mechanical | Strain gauge, piezoelectric sensor

  • Electrical | Electrode

  • Chemical | Electrode

  • Optical | Photoiodide, photomultiplier

• Ohm’s Law: I = ΔV/R or ΔV = iR

  • ΔV = potential difference or voltage drop across an ideal conductor

  • I = current, amperes (amp)

  • R = resistance of the conductor (ohm, 1V/amp)

• Circuit analysis:

  • For a circuit consisting of a single resistor and voltage source, Ohm’s law can be applied

  • For analyzing circuits containing multiple sensors: use Kirchoff’s current and voltage law (Sum of N|n-1 i = 0 and Sum of N|n-1 V = 0)

• Thermal Sensors:

  • Thermocouple: fusing two dissimilar metals to produce two junctions, records voltage difference depends on temperature

  • Thermistors: Homogeneous composites of dissimilar metals; records resistance difference as temperature varies

  • Use electric resistance formula: Rt = Ro*e^B(1/T - 1/To)

• Mechanical Sensors:

  • Measures: Force, pressure (force over an area), strain

  • Eg Gait analysis, pulse detection, voice + blood pressure monitoring etc

  • Strain gauge: a sensor whose resistance varies with applied force

    • Tension causes resistance increase, while compression causes decrease

    • It converts force, pressure, tension, weight, etc., into a change in electrical resistance which can then be measured

    • Uses piezoelectric materials (pressure), when a piezoelectric element is placed under pressure, polarized ions within the crystal deform and generate electric charge

• Electrical Sensors:

  • In biological applications, electrodes are often used to detect the electric potential generated by cellular ionic currents.

  • The electrodes can range in size from micro-sized probes to larger adhesive pads

  • All cells have resting membrane potential caused by the difference in ion concentrations

• Bioelectric signals: the electric potential generated by cell membrane potential, ( called action potential), mainly generated by muscle and nerve cells (ionic conductor Na, K, Cl)

  • E.g. action potentials in excitable cells such as neurons and muscle cells; electrocardiograph (ECG) measures the electrical activity of cardiac muscle cells; measure brain activity

  • Types of signals: 

    • Electrocardiogram (ECG) in Heart 0.5-4mV and 0.05-150Hz

    • Electroencephalogram (EEG) in Brain 5-300uV and 0.5-150Hz

    • Electromyogram (EMG) in Muscles 1-10mV and 0-10 kHz

• Chemical sensors: measure the presence and concentration of specific chemicals: ions/gasses, chemical/biochemical agents

  • ISE: Ion selective electrode

    • ISE acquires specificity from membranes that are permeable to a particular ion species. For eg. Glass ISEs selective to H+, used in pH meters

    • A working cell consists of an ISE, reference electrode and a voltmeter

    • These sensors produce a potential or voltage, that is proportional to ion concentration, also called as potentiometric sensors

  • Amperometric sensor: current is proportional to the concentration of the species generating the current (Use a Clark O2 sensor)

• Optical Sensor: able to detect light in the visible, infrared, or ultraviolet regions of the electromagnetic spectrum, wavelengths from 10 nanometers to 1 millimeter

  • Photodiodes: –a light-sensitive semiconductor diode. It produces current when it absorbs photons. Made of semiconductor materials such as silicon (Si) or gallium arsenide (GaAs), like a finger pulse oximeter

  • Photomultiplier: amplify weak light signals through a series of processes involving a photocathode, dynodes, and an anode; offer high sensitivity

  • Commonly found in UV spectrometers in research labs

Bioimaging:

• Bioimaging relates to methods that non-invasively visualize structures and biological processes, examples: ultrasound, CT using x-rays, OCT, and MRI

• Ultrasound:

  • Ultrasound is based on the propagation of high-frequency sound waves through tissue

  • Ultrasound imaging is fast:  structure and function can be recorded from rapidly moving tissues and provide real-time imaging  (e.g. heart beat; internal bleeding; localize internal injuries)

• Ultrasound imaging:

  • 1. Producing a sound wave by piezoelectric transducer

    • Piezoelectric crystals: convert the electrical pulses from the transmitter to acoustic pulses and reconvert received echoes from targets into electrical signals.

  • 2. Receiving the echoes

  • 3. Image display

    • The magnitude of the transduced voltages indicates the strength of echoes

  • The spatial location of each echo is determined by the time of flight (the time it takes between the generation of the pulse and reception of the echo

    • T = 2d/c (d = travel distance, c= speed of pulse, t = time of flight)

• X-Rays:

  • Were discovered by Wilhelm Conrad Rontgen in 1895, a form of electromagnetic radiation with wavelength of 0.1 nm

  • They have high energy and can pass through most objects, including the body

  • E = hv = hc/wavelength

  • Two properties made x-ray useful for imaging

    • Human body is translucent to x-rays of correct wavelength and energy

    • X-rays can expose photographic film to be recorded

• Formation of medical x-ray image:

  • X-ray intensity is decreased as x ray passes the body structure. Form like a shadow

  • During development of the film, silver halide particles in the film will absorb the transmitted light, convert to silver and appear as black gains.

  • Lighter film where body is denser; darker film when body is light

• Attenuation of x-rays

  • Beer’s Law: I = Io e^-μx

  • X = thickness of the material, μ = linear attenuation coefficient, Io = Intensity input, I = intensity output

  • HLV: thickness of a given tissue that attenuates 50% of incident x-ray = ln2/μ

• Applications of x-rays:

  • Provide good contrast when there is a difference in density between two materials, like soft tissue and air, bone and soft tissue etc

  • How about a digestive system that is composed of structures that do not vary greatly in  x-ray absorption?

    • Swallow a dense element such as barium to generate more brighter x-ray; or introduce air bubble to make the tract black

• CT (Computed tomography)

  • Algorithmic method applied to x-ray imaging: take x-ray images at many different angles and use these images to construct 3-D image of the body

  • Whereas contrast of CT is limited in soft tissue, CT is quite versatile for imaging the head, lungs, abdomen, pelvis, and extremities

• Magnetic Resonance Imaging (MRI):

  • MRI is a type of diagnostic test that can create detailed images of nearly every structure and organ inside the body, including the organs, bones, muscles and blood vessels. 

  • MRI scanners create images of the body using a large magnet and radio waves.

  • To produce ‘signal’, the MRI scanner interacts with protons in water and fat in the body. 

  • No ionizing radiation is produced during an MRI exam, unlike X-rays.

• Physics of MRI:

  • Free protons within molecules of the body are randomly oriented, spinning on a North-South magnetic field

  • Protons aligned in scanner with the axis of the magnetic field within the bore

  • A radiofrequency pulse is applied to excite the protons, aligning them at an angle to the magnetic field and spin in phase with each other, creating resonance

  • After a few milliseconds and removal of radiofrequency pulse, the excited protons relax, giving off radiofrequency signals

    • Two kinds of relaxing occur:

      • Realignment of protons with the magnetic field

      • Dephasing of spinning protons (loss of resonance)

    • Two types of signal can be detected

      • T1 signal relates to the speed of realignment with the magnetic field, the more quickly the protons realign, the greater the signal

      • T2 signal relates to the speed of proton spin dephasing - the slower the dephasing the greater the T2 signal

  • Tissue differentiation - Fat vs Water

    • Protons in fat realign quickly with high energy to produce high T1 signal, which would highlight fat tissues in the body

    • Protons in water dephase slowly, used to produce T2 weighted images that highlight water in tissues of the body

• Comparison between imaging modalities:

  • X-rays:

    • Main characteristics: A photograph or image obtained through x-rays

    • Advantages: Fast and easy method of imaging

    • Disadvantages: Superposition of structures creates difficulties for interpretation, it cannot pass from the bone

    • Spatial Resolution: High

    • Contrast: Low

    • Application: Anatomical

    • Cost: Low cost

    • Radiation source and type: X-rays (ionizing)

  • CT:

    • Main characteristics: A method of examining body organs by scanning them with x-rays and using a computer to construct series of cross-sectional images

    • Advantages: Tomographic acquisition eliminates the superposition of images of overlapping structures

    • Disadvantages: high dose per examination

    • Spatial Resolution: High

    • Contrast: High

    • Application: Anatomical, Functional

    • Cost: Intermediate cost

    • Radiation source and type: x-rays (ionizing)

  • MRI:

    • Main characteristics: A method which uses magnetic signals to create image “slices” of the human body

    • Advantages: No short term effects are observed and variable thickness of any plane

    • Disadvantages: Strong magnetic field disturb activated implants, patients exists large time in B so claustrophobia disease may occur

    • Spatial Resolution: High

    • Contrast: High

    • Application: Anatomical, Functional

    • Cost: Intermediate Cost

    • Radiation source and type: Electric and Magnetic fields (Non-ionizing)

  • Ultrasound:

    • Main characteristics: A method which use of high-frequency sound to make image internal structures by signals from different densities tissues

    • Advantages: ultrasound scanning is noninvasive (no needles or injections) and ultrasound is widely available, easy-to-use

    • Disadvantages: Operator dependent and imaging limited to vascular compartment, difficult image of bone and lungs

    • Spatial Resolution: High 

    • Contrast: N/A

    • Application: Anatomical, Functional

    • Cost: Low cost

    • Radiation source and type: Sound waves (Non-ionizing)