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Ultrasound Diagnostic MethodsB Mode--Alfred Vivek DSouza4VV13LSP03ContentsIntroductionA mode disadvantagesB Mode IntroductionStatic B Mode ScannerStatic B Mode Scanner DisadvantagesReal Time B ScannersLinear Array ScannersApplications

IntroductionUltrasound is a category of sound waves which are not audible by humans.

Ultrasounds are longitudinal waves.

Diagnostic ultrasounds are usually in the range of 1 12 MHz.

The concept of ultrasound imaging is based on the fact that different types of tissues echoes different amount of incident ultrasound .

A Mode - DisadvantagesAmplitude mode displays the amplitude information of the reflected waves not the image of the underlying tissues or organs.

B Mode IntroductionB mode stands for Brightness mode. Echo amplitude is used to modulate the electron beam intensity of a cathode ray tube or Z-axis of CRT instead of Y axis. Two types of B mode display areBi-static B mode display : Electron beam has only two states based on thresholdGreyscale B mode display: Electron beam strength is made proportional to amplitude of echo2D image of structure can be obtained by either rotating or linearly translating the proble.Static B Mode Scanner

Static B Mode ScannerEchoes from the tissues are amplified by preamplifier and variable gain amplifierAmplified signals are logarithmically compressedCompressed signals are demodulated and envelope is detected. Scan converter is used to convert envelope detected signal to standard TV format.Output of scan converter can be smoothed, filtered or even thresholding can be performedStatic B Scanning Illustration

Tissue2D Image

TransducerStatic B Scanning Illustration

Tissue2D ImageStatic B Mode Scanner DisadvantagesSeveral minutes are required to construct the image.Reflection from flat interfaces is directional, different types of motions of probe may have to be combined to produce a better image. This kind of scanning is called compound B scan.Image quality depends on operator skills.Real Time B ScannersBeams are automatically steered.Fast image production enables to visualize motions of organs.One acoustic pulse travels in field of interest at any instant of time Constraint on real time scanners.Typical frame rate is 30/sec with 128 lines and depth of maximum 19.5 cm.

Real Time B ScannersHuman hand is replaced by mechanically driven device.Transducer is housed in plastic dome and bathed in a fluid.Transducer is rocked back and forth at a rate more than 30 times/sec.Uncomfortable for patients due to vibrations.Also causes motion artifacts.

Real Time B Scanners

A rotating wheel consisting four transducers are used.Transducers are placed in sealed, oil filled plastic housing.Can generate a 90 degree sector scan of four frames per revolution.

Real Time B Scanners In Action

Linear Array ScannersThere are 3 different types of electronic scannersLinear arrayLinear phased arrayAnnular array

Linear Array ScannersPulser excite groups of piezoelectric elements sequentially.Switching network controls the sequencing and is activated by pulses.Fast ramp Sweeps electron beam of CRT vertically.Slow ramp Drives horizontal axis of CRTDisadvantagesLarge appertureProduces poor quality images near far fieldApplications2 to 10 MHz frequencies are used. High frequency scanners can only be used for imaging smaller organs like thyroid, testicles etc.Used in fetal monitoring in obstetrics. Diagnosing masses in abdominal organs such as liver and kidney.Assessing cardiac condition.THANK YOU18QUERIES?