{[ promptMessage ]}

Bookmark it

{[ promptMessage ]}

ultrasound4 prelim

ultrasound4 prelim - 11.0 Ultrasound Imaging Systems After...

Info icon This preview shows pages 1–11. Sign up to view the full content.

View Full Document Right Arrow Icon
11.0 Ultrasound Imaging Systems After plane film x-ray, ultrasound is one of the most widely used medical imaging system due to low risk, low cost and portability. Most systems use a single transducer in the so-called pulse-echo format, where the transducer is coupled to the body with an “acoustic gel”. Block Diagram Transducer variations and considerations Single elements, mechanical scanners, electronic scanners, phased arrays Pulse-echo imaging, envelope detection Transducer motion, estimation of reflector distribution Resolution cell, speckle A-mode, M-mode, B-mode scanning Beam steering and focusing Dynamic beamforming and focusing
Image of page 1

Info icon This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Important points from Ultrasound 3 Lecture Transducer materials: Quartz, Barium Titanate, PZT The basic concept of the piezoelectric effect Transmit and Receive constants d (m/V), g (V-m/N) Resonant frequency f T =c T /2d T Q of a transducer (losses, f/ Δ f), need for damping Typical impulse waveform (modulation & envelope): 5MHz, 4-5cycles, 0.9mm Transmit/Receive switching, diode switches Single transducer, sector scanners, linear arrays Used knowledge of narrowness of pulse to simplify r(t) (received signal) to identify compensatable signal loss vs “z” (depth), using range equation: z=ct/2 TGC, Time Gain Compensation Key reflectivity equation: Resolution cell, speckle A-mode, M-mode, B-mode
Image of page 2
Bushberg, Essential Physics of Medical Imaging, 2 nd Ed,2002.
Image of page 3

Info icon This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Bushberg, Essential Physics of Medical Imaging, 2 nd Ed,2002.
Image of page 4
B-Mode Scan Makes an image by displaying R(x,y,z) using knowledge of the position and angle of the transducer at each pulse-echo. -manual modes >linear scanning moves the transducer in one direction >compound scanning allows angling the transducer while moving to see behind specular reflectors, building up an image from several directions -mechanical modes >linear array >mechanical sector scanner >phased array -sector scanners and compound scanning require conversion from polar to rectangular coordinates scan conversion
Image of page 5

Info icon This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Bushberg, Essential Physics of Medical Imaging, 2 nd Ed,2002.
Image of page 6