General Bio Medical Engineering

Prof. Dr. Markolf Niemz - Lecture notes - Exam preparation -

Introduction / literature Chap. 1: Biomaterials Chap. 2: Biosensors Chap. 3: Ultrasound Chap. 4: Radiology Chap. 5: Magnetic resonance

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Biomaterials natural

cell tissue organ

smallest unit of life capable of independent existence group of similar cells plus extracellular material group of tissues with a common function

natural (artifically put in place)

transplant

transfer of natural tissue or organ

artificial

implant prosthesis

assistance to natural tissue or organ replacement of natural tissue by substitute

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Natural biomaterial cell

example: human skin Epidermis

tissue

O R

Dermis

cell

tissue

G A

Subcutis

cell

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tissue

N

Biological tissue type

class

function

connective epithelial muscular nervous

proper, cartilage, bone, blood covering and lining, glandular skeletal, cardiac, smooth Aα, Aβ, Aγ, Aδ, B, C

binding, support, protection, transport protection, filtration, secretion contraction, movement monitoring, carrier of information

connective

epithelial, muscular, nervous

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Organ systems type

organs

function

circulatory respiratory digestive urinary musculoskeletal immune nervous endocrine reproductive integumentary

heart, blood vessels, blood nose, pharynx, trachea, bronchi, lungs mouth, esophagus, stomach, intestines kidneys, ureters, bladder, urethrae bone, cartilage, tendon, skeletal muscle thymus, lymphoid tissues brain, spinal cord, nerves all glands secreting hormones testes, penis, ovaries, uterus skin

transport of blood exchange of O2 and CO2 digestion of nutrients regulation of plasma composition support and movement of body defense against foreign invaders coordination of activities, consciousness regulation of activities reproduction protection, control of temperature

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Transplants, implants, prostheses transplant

• still natural tissue or organ, transferred from same patient or from donor • to recover function of diseased or removed tissue or organ • e.g. blood, bypass, heart, liver, skin

implant

• artificial tissue, alloy, glass, metal, or electronics • to assist function of diseased tissue or organ • e.g. contact lens, hearing aid, hernial mesh, inlay, pacemaker, stent

prosthesis

• artificial tissue, alloy, glass, or metal • to replace diseased tissue • e.g. denture, hip, joint, knee, leg

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Artificial biomaterials material

advantage

disadvantage

application

polymer nylon polyester silicone

ductile light easy to fabricate

not strong prone to creep degradable

suture vascular prosthesis breast prosthesis

metal Ti, Ti alloy, Co-Cr alloy stainless steel Au, Ag, Pt

partly ductile strong tough

prone to corrosion release of ions

artificial joint bone plate, screw dental root implant

ceramic carbon aluminum oxide hydroxyapatite

biocompatible inert stiff

brittle, fragile weak in tension

inlay denture orthopedic prosthesis

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Artificial biomaterials – part II material

advantage

disadvantage

application

composite carbon polymer metal-PMMA

strong customized

difficult to fabricate high cost

heart valve bone cement

directly bonds to human bone

brittle, fragile

middle ear device jaw repair

directly bonds to human bone

brittle, fragile

spine surgery hip surgery

bioactive glass Bioglass R

bioactive glass-ceramic Cerabone R

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Biomechanics Hooke‘s law for elastic solids:

σ = E ε with stress σ (Pa), modulus of elasticity E (Pa), and strain ε

tissue L σ/2

σ/2 tissue L+∆L ε = ∆L/L

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Biomechanics – part II stress–strain curves for brittle and ductile materials

Stress σ (Pa)

Hooke‘s law: σ= E ε

Material failure

Brittle Ductile

toughness: ∫ σ dε Toughness

slope: modulus of elasticity E (Pa) Strain ε

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Biosensors

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Thermosensors

Hg thermometer expansion: 1.82 ml / oC

RTD resistive temp. detector

thermistor semiconductor

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thermocouple two metals

Thermosensors - part II

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ECG: Limb leads

standard limb leads

augmented limb leads

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ECG: Precordial leads

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ECG waves

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ECG: Normal criteria of normal ECG: • P and T waves upright in lead I • q < 20 ms in leads I and aVL • QT interval < 0.44 s • PR interval < 0.2 s

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ECG: Myocardial infarction criteria of myocardial infarction: • R wave absent in leads I or V2−V5 • ST segment elevated in V2−V5 • T wave inversed in V2−V5

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EEG: Standard waves

type

frequency (Hz)

location

normal adult

normal child

alpha

7.5 − 13

posterior

eyes closed

eyes closed

beta

> 14

anterior

alert

alert

theta

3 − 7.5

all leads

asleep

< 13 years

delta

<3

anterior

asleep

< 1 year

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EMG: Electromyography

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EOG: Electrooculography • • • •

provides measure of retinal function voltage Uint corresponds to illumination Uint is estimated by measuring Uext Uext is measured when eye looks from side to side

Arden ratio:

maximum voltage under light adaption minimum voltage under dark adaption

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Ultrasound ultrasound: > 20 kHz

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Ultrasonic transducer

piezoelectric effect: electric field mechanical force

electric field: mechanical force:

mechanical force electric field

voltage contraction, strain

piezoelectric materials: e.g. quartz, polyvinyldifluoride (PVDF)

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Ultrasound: Reflection and refraction c λ f Z ρ

velocity wavelength frequency impedance density

velocity:

c = λf

impedance:

Z = ρc

law of reflection:

θi = θr

law of refraction:

sin θi c1 λ1 = = c2 sin θt λ2

reflection:

R =

Z2 cos θi − Z1 cos θt Z2 cos θi + Z1 cos θt

transmission:

T =

2 Z2 cos θi Z2 cos θi + Z1 cos θt

normal incidence:

R =

Z2 − Z1 Z2 + Z1

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T =

2 Z2 Z2 + Z1

Ultrasound imaging: A-mode and B-mode

signal: display:

voltage amplitudes

signal: display:

voltage brightness

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Doppler ultrasound

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Radiology

• computed tomography (CT): x-ray

• nuclear medicine: α, β, γ, neutron, heavy ion

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Electromagnetic spectrum

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X-rays type

transition

Kα Kβ Kγ ... Lα Lβ Lγ ... Mα Mβ Mγ ...

L → M → N → ... M → N → O → ... N → O → P → ...

K K K L L L M M M

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CT scanner

rotation: 360o

aperture of gantry: 60 − 70 cm

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Medical x-ray applications

organ

indication

blood vessel bone brain intestines liver lung lymphoid tissue spine tooth

bleeding complicated fracture hematoma, tumor tumor, metastases cyst, tumor, metastases tuberculosis, tumor, metastases metastases herniated disc caries

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Nuclear medicine A Z N:

nucleus

A: number of protons and neutrons Z: number of protons

type of decay

Z

A

example

α β− β+ γ e− capture

−2 +1 −1 ±0 −1

−4 ±0 ±0 ±0 ±0

226Ra

→ 222Rn + α 32P → 32S + β− 11C → 11B + β+ 99Tc → 99Tc + γ p + e− → n

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Radiation safety

activity absorbed dose dose equivalent

traditional units

SI units

Curie (Ci) = 3.7E10 dps Rad = 0.01 J/kg Rem = Rad × Q

Becquerel (Bq) = 1 dps Gray (Gy) = 1 J/kg Sievert (Sv) = Gy × Q

dps = disintegrations per second Q = quality factor

target

exposure limit

public radiation controller radiation worker

1.5 mSv/year 5.0 mSv/year 50 mSv/year

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Radiation safety - part II

quality factor Q 20 1 1

10

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Magnetism

e.g. iron, nickel, cobalt µ >> 0 (magnetic susceptibility) able to maintain magnetization

e.g. oxygen, magnesium, gadolinum µ >0 unable to maintain magnetization

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e.g. water, most tissues µ <0 no intrinsic magnetization

Spin and magnetic moment nucleons (protons and neutrons) have a quantum property known as spin spin L is analogue of momentum p torque θ = δL/δt is analogue of force F = δp/δt

spinning nucleon causes magnetic moment µ

spinning nucleons cause magnetization M = Σ µ

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MR active elements in tissues

half integer spins: odd mass number

integer spins: even mass number and odd atomic number

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T1 images vs. T2 images signal

T1 image

T2 image

bright middle dark

fat muscle, cartilage, marrow water, blood, liquor, edema, bone, calcification

water, blood, liquor, edema fat, marrow muscle, bone, calcification

tissue

T1 (ms)

T2 (ms)

fat white matter (brain) gray matter (brain) water, edema malignant tumor

160 380 520 600 800

100 85 95 150 200

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Gradient echo sequence

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Spin echo sequence

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MR instruments

B ≅ 1 − 2 Tesla 1 Tesla = 10 000 Gauss earth: 0.5 Gauss

MR scanner with superconductive magnets

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University of Heidelberg

Mannheim Technical University Medical Center of Mannheim

Biomedical engineering:

characterization and processing of biomaterials internet database for tissue parameters

Medical physics:

design of medical applicators and sensors bioelectrical multichannel measurement devices

Laser medicine:

laser-tissue interactions medical applications of ultrashort laser pulses

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