Diagnostic ultrasound ( PDFDrive )

APPENDIX Ultrasound Artifacts: A Virtual Chapter
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FIG. A.41 Side or Grating Lobe. In this patient with a ureterovesical
junction stone there are echoes seen in the nondependent portion of
the bladder. These are due to grating lobe artifact, wherein off-axis
signal projects into the ield of view. 18 Note also the shadowing behind
the bladder stone. 18 (See Chapter 9, Fig. 9.43.)
FIG. A.42 Partial Volume Averaging. The bladder wall is indistinct
in region of this image. It is unclear if there are masses or if this is due
to grating lobe artifact or partial volume artifact or both. Moving the
patient or transducer to avoid bowel gas and putting the focal zone in
the region in question should aid in evaluation. For the area closer to
the patient’s anterior abdominal wall, a higher-frequency transducer
might be helpful. 18 (See Chapter 9, Fig. 9.57.)
Partial Volume Averaging
he ultrasound beam not only has a complex shape in the imaging
plane but also has a real proile in the third dimension, called
the “elevation plane” or “Z plane.” he ultrasound image appears
as a lat two-dimensional image, but the brightness of each pixel
is representative of the average sum of all the echoes received
within the thickness of the beam in the elevation plane. his
results in echoes being projected in structures that should be
anechoic.
Click here to see an explanatory video of partial volume
averaging (Video A.18).
FIG. A.43 Partial Volume Averaging. A radiofrequency ablation
zone present in the liver just outside the scanning plane is depicted
onto the lungs through both partial volume averaging and mirror image
artifacts.