instrumentação médica 9 - uminho

Instrumentação Médica– 9. 1

Aula 9 - 2005imlebiom2006

Licenciatura em Engenharia Biomédica

3º Ano/ 2º Sem.-

Paulo Mendes

http://dei-s1.dei.uminho.pt/pessoas/pmendes/IMLEBIOM

2005/2006

Instrumentação Médica


• Sinais biomédicos - 1• Aquisição e análise de sinais biomédicos - 2• Sensores biomédicos - 3• Eléctrodos para biopotenciais, micro-eléctrodos - 4• Espectrofotómetros e métodos ópticos- 5 • Biopotenciais - 6• Aquisição de Biopotenciais – 6a)• Amplificadores e filtros para biopotenciais - 7• Dispositivos cardiovasculares e neurofisiológicos - 8• Sistemas médicos de imagem (Radiografia, TAC, PET, MRI,)

com destaque para a ultrasonografia - 9• Microcontroladores em instrumentação médica/ Filtros ADC -10• Telemetria biomédica – 11


Câmaras• Raios-x, Ultra-sons, televisão, infravermelhos• Limitados por:

• Resolução• Escala de amplitude• Ruído

• Imagem estudada independentemente da câmara que a produz


Resolução

Figure 12.1 Scanning lines and round objects (a) Each object

represents 1 pixel, but each cycle of output signal represents 2 pixels. (b)

For 2n scanning lines, n vertical objects are required. (c) If objects

are located between scanning lines, 2n lines are insufficient. (d) For

adequate resolution, 2n√2 lines are required.

•lp/mm•pixel/mm

•Dimensão de meio ciclo da largura de banda•Na vertical é igual, embora sobre-amostrado

•Igual à dimensão mínimaa resolver


Sistemas de televisão

Figure 12.5 The vidicon has a cathode and a series of grids to form, shape, and control and electron beam. Magnetic deflection (not shown) scans the beam over

the target, which is mounted on the interior of the glass face plate. From the target, light-modulated signal current flows through the load resistor and is amplified.

• Câmaras de televisão

• Foto-resistência, junção fotocondutora• CCD

• Fotodíodo, circuito de carga, condensador, circuito de transferência de carga


Radiografia• Raio-X – radiação electromagnética

• 20 – 150 keV (104 x energia luz)• Radiação ionizante (proporcional à quantidade e frequência)

Figure 12.6 The x-ray tube generates x rays that are restricted

by the aperture in the collimator. The Al filter removes low-energy x rays that would not penetrate the body. Scattered secondary radiation is

trapped by the grid, whereas primary radiation strikes the screen phosphor. The resulting light exposes the film.

•6 Sv -> dose letal (600 rem)


Atenuação raios-x

Figure 12.7 The lowest-energy x rays are absorbed in the anode metal and the tube

glass envelope. An Al filter further reduces the low-energy x rays that do not

pass through the body and would just increase the patient dose. Only the

highest-energy x rays are capable of penetrating the

body and contributing to the film darkening required for a

picture. Note that the average energy increases with the

amount of filtration.


Detecção digital


Tomografia computadorizada

Figure 12.10 Basic coordinates and geometry for computed tomography The projection rays shown represent those measured at some angle θ. The source and detector pair are rotated

together through a small angle, and a new set of rays measured. The process is repeated through a total angle of 180°. (From R. A. Brooks and G. Di Chiro, "Theory of image

reconstruction in computed tomography." Radiology, 1975, 177, 561-572.)


Tomografia computadorizada

Figure 12.14 512 × 512 pixel CT image of the brain Note that the increased number of pixels yields improved images (Photo Courtesy of Philips Medical Systems.)


• MRI• Radiação não

ionizante• Campo magnético

a oscilar na ordem dos MHz

• Medicina Nuclear• PET


Ultra-sons• Ondas acústicas

• Energia térmica, magnética, eléctrica-> mecânica

• Efeito piezoeléctrico


Ultra-sons


Ultra-sons

Figure 12.26 A-mode scan of the brain midline


Figure 12.27 Time-motion ultrasound scan of the mitral valve of the heart The central trace follows the motions of the mitral valve (MV) over a 3 s period,

encompassing three cardiac cycles. The other traces correspond to other relatively static structures, such as the interventricular septum (IVS) and the walls of the left

atrium (LA).


Figure 12.28 (a) B-mode ultrasonic imaging shows the two-dimensional shape and reflectivity of objects by using multiple-scan paths. (b) This B-mode ultrasonic image, which corresponds to (a), shows the skin of the belly at the

top right, the liver at the left center, the gall bladder at the right

above center, and the kidney at the right below center. The bright areas within the kidney are the

collecting ducts.


Figure 12.29 Different types of ultrasonic transducers range in frequency from 12 MHz for ophthalmic devices to 4 MHz for transducers equipped with

a spinning head. (Photo courtesy of ATL.)


Figure 12.30Ultrasound scan heads. (a) Rotating mechanical

device. (b) Linear phased array which scans an area of the

same width as the scan head. (c) Curved linear

array can sweep a sector. (d) Phasing the

excitation of the crystals can steer the beam so that a small transducer can sweep a large area.

Transducers

Beam axis

Directionof sweep

Directionof sweep

Pulses toindividualelements

Directionof sweep

Directionof sweep

Beamaxis

(b)

(d)(c)

(a)

Beamaxis


Focagem e varrimento


•Array linear •Array curvilíneo

•Phased array linear •Array 1.5D

•Array 2D


Transdutor


• Transdutor• Elevada sensibilidade (SNR), boa resolução

espacial, imune a artefactos• Elementos individuais

• Boa resposta angular, baixo acoplamento cruzado, impedância eléctrica adaptada

•Resoluçãoaxial


Diagrama de radiação• Resolução lateral


Imagiologia com ultra-sons• f> 20 kHz • 1MHz -> resolução 1.5mm

• 1.5 MHz -> resolução 1mm• cardiologia, abdominal, obstetrícia-> 2- to 5-MHz• oftalmologia, vascular periférico -> 20 MHz. • Intra-arterial-resolução sub-milímetro ->20 to 50

MHz• Aplicações laboratoriais -> 100 ou 200 MHz para

examinar células individuais.


Equações

• c=1500 m/s, 1.5mm/υs

•recebido

•enviado

•piezo

•atenuação

•interface


• A-Mode (linha de vista)• M-Mode (movimento)• B-Mode (2D)


Efeito Doppler• Desvio na frequência


Efeito Doppler

instrumentação médica 9 - uminho

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