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AAPM/RSNA Physics Tutorial for Residents: Topics in US

B-mode US: Basic Concepts and New Technology¹

¹ From the Department of Radiology, East-2, Mayo Clinic, 200 First St SW, Rochester, MN 55905. From the AAPM/RSNA Physics Tutorial at the 2002 RSNA scientific assembly. Received February 19, 2003; revision requested March 28 and received April 17; accepted April 21. The author received a loan of equipment and research funding from Siemens Medical Solutions, Issaquah, Wash. Address correspondence to the author (e-mail: hangiandreou@mayo.edu).

View larger version (97K): [in a new window]   Figure 1.  Sequence of diagrams shows the propagation of an ultrasound pulse (yellow arrow) along one particular beam line (dotted line). Echoes (blue arrows) are generated by reflections of the pulse from structures in the tissue medium all along this path, and the echoes travel back to the transducer (not shown).

View larger version (62K): [in a new window]   Figure 2.  Sequence of diagrams shows the sweeping of the ultrasound beam through a planar FOV in the patient. Echo signals from all of the beam lines are detected by the transducer and are processed and reconstructed into a complete B-mode image.

View larger version (16K): [in a new window]   Figure 3a.  (a) Diagram shows an ultrasound pulse that was generated by a transducer and consists of two wave cycles. The spatial pulse length (SPL) in this case is equal to twice the ultrasound wavelength. (b) Diagram shows tall "elements" of the tissue medium along with the regions that are compressed and rarefied by the pressure oscillations of the ultrasound pulse (dashed line). Regions beyond the extent of the ultrasound pulse are at ambient pressure.

View larger version (33K): [in a new window]   Figure 3b.  (a) Diagram shows an ultrasound pulse that was generated by a transducer and consists of two wave cycles. The spatial pulse length (SPL) in this case is equal to twice the ultrasound wavelength. (b) Diagram shows tall "elements" of the tissue medium along with the regions that are compressed and rarefied by the pressure oscillations of the ultrasound pulse (dashed line). Regions beyond the extent of the ultrasound pulse are at ambient pressure.

View larger version (17K): [in a new window]   Figure 4.  Diagram shows specular reflection with 90° incidence on an interface between two tissues with acoustic impedances of Z1 and Z2.

View larger version (18K): [in a new window]   Figure 5.  Diagram shows scattering of the ultrasound pulse by a tiny reflective structure. The scattered echo is shown soon after the scattering event (solid lines) and after it has propagated far enough to reach the transducer (dotted lines).

View larger version (183K): [in a new window]   Figure 6.  US image shows variation in the appearance of scatter according to the dimensions (regions a and b) and beam line direction (regions c and d) of the ultrasound pulse.

View larger version (22K): [in a new window]   Figure 7.  Diagram shows the effects of attenuation on echo intensity from three equally reflective structures. The graphs show echo intensity detected by the transducer (represented by the pulse heights) as a function of reflector depth. Deeper reflectors produce weaker echoes (solid lines) due to increased attenuation over longer path lengths. In addition, attenuation increases (and echo intensity decreases) in proportion to the ultrasound frequency. The dotted lines represent the processed echo signals that result from time-gain compensation (arrows). In this case, all of the signals have the same strength, thus indicating equal reflectivity for the three interfaces, as desired.

View larger version (13K): [in a new window]   Figure 8a.  Diagrams show the ultrasound beam profiles from an unfocused transducer (a), a mechanically focused transducer with a curved piezoelectric element (b), and a mechanically focused transducer with an acoustic lens (c). Side lobes are also present for each of the transducers but are shown only for the unfocused transducer (a).

View larger version (7K): [in a new window]   Figure 8b.  Diagrams show the ultrasound beam profiles from an unfocused transducer (a), a mechanically focused transducer with a curved piezoelectric element (b), and a mechanically focused transducer with an acoustic lens (c). Side lobes are also present for each of the transducers but are shown only for the unfocused transducer (a).

View larger version (8K): [in a new window]   Figure 8c.  Diagrams show the ultrasound beam profiles from an unfocused transducer (a), a mechanically focused transducer with a curved piezoelectric element (b), and a mechanically focused transducer with an acoustic lens (c). Side lobes are also present for each of the transducers but are shown only for the unfocused transducer (a).

View larger version (100K): [in a new window]   Figure 9.  Sample abdominal US image obtained with a manual, static B-mode imager. Also shown are several transducer positions and beam lines that contributed to the image acquisition.

View larger version (31K): [in a new window]   Figure 10.  Diagram shows the method of electronic beam scanning for a linear-array transducer.

View larger version (85K): [in a new window]   Figure 11a.  Photographs show ultrasound transducers with curvilinear (a), linear (b), and vector (c) arrays along with sample image FOVs.

View larger version (47K): [in a new window]   Figure 11b.  Photographs show ultrasound transducers with curvilinear (a), linear (b), and vector (c) arrays along with sample image FOVs.

View larger version (81K): [in a new window]   Figure 11c.  Photographs show ultrasound transducers with curvilinear (a), linear (b), and vector (c) arrays along with sample image FOVs.

View larger version (25K): [in a new window]   Figure 12.  Diagram shows the geometry of the US image plane and the three spatial resolution directions.

View larger version (11K): [in a new window]   Figure 13.  Diagram shows the progressive distortion of ultrasound waves that occurs as the waves propagate through tissue. A is the original (undistorted) wave, and B-D are the wave shapes that result from propagation through greater tissue path lengths. Wave D, which corresponds to the greatest path length, shows the greatest amount of distortion and contains the strongest harmonic signal.

View larger version (94K): [in a new window]   Figure 14a.  Fundamental (a) and harmonic (b) US images of a renal cyst show the benefits of harmonic imaging. The cyst in the harmonic image (b) appears much more anechoic and exhibits sharper, better-delineated margins. (Courtesy of Siemens Medical Solutions, Mountain View, Calif.)

View larger version (94K): [in a new window]   Figure 14b.  Fundamental (a) and harmonic (b) US images of a renal cyst show the benefits of harmonic imaging. The cyst in the harmonic image (b) appears much more anechoic and exhibits sharper, better-delineated margins. (Courtesy of Siemens Medical Solutions, Mountain View, Calif.)

View larger version (20K): [in a new window]   Figure 15a.  (a) Diagram shows the set of ultrasound beam lines used for conventional B-mode imaging. (b, c) Diagrams show two additional sets of beam lines that are used for spatial compound imaging. Data from up to nine such sets of beam lines are acquired and averaged together to form each compound image.

View larger version (28K): [in a new window]   Figure 15b.  (a) Diagram shows the set of ultrasound beam lines used for conventional B-mode imaging. (b, c) Diagrams show two additional sets of beam lines that are used for spatial compound imaging. Data from up to nine such sets of beam lines are acquired and averaged together to form each compound image.

View larger version (28K): [in a new window]   Figure 15c.  (a) Diagram shows the set of ultrasound beam lines used for conventional B-mode imaging. (b, c) Diagrams show two additional sets of beam lines that are used for spatial compound imaging. Data from up to nine such sets of beam lines are acquired and averaged together to form each compound image.

View larger version (169K): [in a new window]   Figure 16a.  Conventional B-mode (a) and spatial compound (b) US images of a breast mass show the benefits of spatial compound imaging. The mass in the compound image (b) is rendered in much greater spatial detail, as are all the tissues in the FOV. In addition, image graininess due to speckle is markedly decreased in the compound image (b). (Courtesy of Philips Ultrasound, Bothell, Wash.)

View larger version (141K): [in a new window]   Figure 16b.  Conventional B-mode (a) and spatial compound (b) US images of a breast mass show the benefits of spatial compound imaging. The mass in the compound image (b) is rendered in much greater spatial detail, as are all the tissues in the FOV. In addition, image graininess due to speckle is markedly decreased in the compound image (b). (Courtesy of Philips Ultrasound, Bothell, Wash.)

View larger version (95K): [in a new window]   Figure 17.  Extended FOV color flow image of the carotid artery shows the data acquisition process. The initial position of the transducer is at the right edge of the large FOV image, and the transducer is moved slowly to the left. The green and blue boxes indicate individual images acquired during this motion, with the solid box representing the last image that contributed to the composite large FOV image. (Courtesy of Siemens Medical Solutions.)

View larger version (14K): [in a new window]   Figure 18a.  Diagrams show a typical B-mode pulse (a), a chirp coded pulse (b), and a digitally coded pulse (c).

View larger version (34K): [in a new window]   Figure 18b.  Diagrams show a typical B-mode pulse (a), a chirp coded pulse (b), and a digitally coded pulse (c).

View larger version (34K): [in a new window]   Figure 18c.  Diagrams show a typical B-mode pulse (a), a chirp coded pulse (b), and a digitally coded pulse (c).

View larger version (99K): [in a new window]   Figure 19a.  Conventional B-mode (a) and coded pulse (b) US images of the liver show the benefits of coded pulse imaging. The spatial resolution of the coded pulse image (b) is very comparable with that of the 13-MHz conventional image (a). However, the useful imaging depth is about 7.5 cm for the coded pulse image (b) compared with only about 2.8 cm for the conventional image (a). (Courtesy of Siemens Medical Solutions.)

View larger version (115K): [in a new window]   Figure 19b.  Conventional B-mode (a) and coded pulse (b) US images of the liver show the benefits of coded pulse imaging. The spatial resolution of the coded pulse image (b) is very comparable with that of the 13-MHz conventional image (a). However, the useful imaging depth is about 7.5 cm for the coded pulse image (b) compared with only about 2.8 cm for the conventional image (a). (Courtesy of Siemens Medical Solutions.)

View larger version (160K): [in a new window]   Figure 20a.  US images of a phantom show much improved demonstration of small anechoic spheres in the image obtained with electronic focusing in the section thickness direction (b) than in the conventional B-mode image (a). (Courtesy of GE Medical Systems, Waukesha, Wis.)

View larger version (153K): [in a new window]   Figure 20b.  US images of a phantom show much improved demonstration of small anechoic spheres in the image obtained with electronic focusing in the section thickness direction (b) than in the conventional B-mode image (a). (Courtesy of GE Medical Systems, Waukesha, Wis.)

View larger version (131K): [in a new window]   Figure 21a.  Photographs show commercially available small US scanners from two vendors. (a) The upper scanners are 13.3 in (33.8 cm) tall and weigh 5.7 lb (2.6 kg), whereas the lower scanners weigh about 3 lb (1.4 kg). (b) The dedicated electronics module attached to the transducer cable weighs 10 oz (0.3 kg) and is 7.6 in (19.3 cm) long. (Fig 21a courtesy of SonoSite, Bothell, Wash; Fig 21b courtesy of Terason, Burlington, Mass.)

View larger version (92K): [in a new window]   Figure 21b.  Photographs show commercially available small US scanners from two vendors. (a) The upper scanners are 13.3 in (33.8 cm) tall and weigh 5.7 lb (2.6 kg), whereas the lower scanners weigh about 3 lb (1.4 kg). (b) The dedicated electronics module attached to the transducer cable weighs 10 oz (0.3 kg) and is 7.6 in (19.3 cm) long. (Fig 21a courtesy of SonoSite, Bothell, Wash; Fig 21b courtesy of Terason, Burlington, Mass.)