This guy Reading Ultrasound Imaging from Bjørn A.J. Angelsen (III)

Posted on July 4, 2009. Filed under: Ultrasound |

My note will include the following content:

Important concept.

Factors affecting image quality.

Pulse echo amplitude imaging VS. Doppler imaging and color flow imaging, requirement and application.

Distinguishing and comparing PW/CW, LPRF/HPRF, different transducer arrays.

Ultrasound scanline processing.

Some problems according to the book and my confusing.

Distinguishing and comparing PW/CW, LPRF/HPRF, different transducer arrays.

Pulsed Wave (PW) Doppler – one transducer	Continous Wave (CW) Doppler – two transducers
+ spatial resolution - limited maximum velocity detection -? posible range ambiguity (in HPRF)	+ no limit on maximum velocity detection - no range resolution - poor sensitivity because of smaller transducers.

LPRF	HPRF
+ less or no range ambiguity - lower maximum velocity detection	+ higher maximum velocity detection - multi range ambiguity

Phased linear array	Switched linear arrays	Curvilinear arrays	Annlar arrays
an array composed of a set of thin bars (typically 64-128) where the signal from each element can be put through a delay of up to 6-10 usec to steer the beam within a sector.	an array composed of a set of piezoelectric bars, usually wider than for the phased linear array, where linear scanning of the beam is obtained by switching between the elements used. Focusing is obtained with smaller delays of the signals for the individual elements.	a linear array that is curved to steer the beam in a sector	an array of concentric rings
- large delay with large steering angle	+ less delay - large - steering is still a problem at the edge	+ easy steering	+ symmetric focus - need mechanical steering

Ultrasound scanline processing.

amplitude imaging of tissue:

Receiver: Duplexer—> DGC (Depth Variable Gain) Amplifier –> Depth Swept Filter –> Compression Amplifier –> Detection (Rectification) –> Anti Aliasing Filter –> A/D Converter –> to Instrument Bus

PW/CW Doppler

Receiver: Duplexer—>RF Amplifier –> Mixer –> Range Gating –> Highpass Lowpass Filter –> A/D Converter –> Spectrum Analyzer –> to Instrument Bus

Color flow imaging: (Milti Range Gated (MRG) PW Doppler

Receiver: Duplexer—>RF Amplifier –> Mixer –> Multiple Range Gating –> Highpass filter or slow target canceller (Analog Highpass Filter –> A/D Converter –> Digital Filtering) –> Estimator –> to Instrument Bus

Detail with figures can be refer to the book. Here just know the general idea of different scanline processing for each kind of US application.