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Comparison of Tissue Harmonic Imaging with Conventional US in Abdominal Disease¹

¹ From the Department of Diagnostic Radiology, Mayo Clinic and Mayo Foundation, 200 First St SW, Rochester, MN 55905. Recipient of a Magna cum Laude award and an Excellence in Design award at the 1998 RSNA scientific assembly. Received June 29, 1999; revision requested July 26; final revision received February 16, 2000; accepted March 10. Supported in part by an institutional grant from the Mayo Research Fund. Address correspondence to B.G.

View larger version (17K): [in a new window]   Figure 1.   Time sequence illustrates the generation of harmonic frequencies. Time step 1 contains a wave of single frequency. As the wave travels into the tissue (time step 2), it becomes distorted. Additional frequency components are created that are integer multiples of the initial frequency. These components are called "harmonic frequencies." As the wave continues to travel, it becomes highly distorted (time step 3) and very rich in harmonic frequencies. Note that the harmonic frequencies are created and accumulate as the wave travels through the tissue. Although many harmonic frequencies are produced with nonlinear wave propagation, the amplitudes of the higher harmonics are extremely small. Therefore, current technology uses only the second harmonic (2f), which is twice the nominal transmitted frequency.

View larger version (48K): [in a new window]   Figure 2.   Schematic depicts the relative intensities and frequency changes of harmonic ultrasound beams and fundamental transmitted waves with increasing depth in tissues.

View larger version (9K): [in a new window]   Figure 3.   Frequency spectrum of the transmitted and received waves. The fundamental wave (f) is generated at the transducer surface and attenuates linearly as it is transmitted through the body. The harmonic wave (2f) is generated as the fundamental wave travels through the body. The harmonic wave increases exponentially in intensity before attenuating within the deeper tissues. Harmonic imaging uses only the harmonic frequency in the echo signal received by filtering out the transmitted frequency spectrum in the signal.

View larger version (128K): [in a new window]   Figure 4a.   Gallbladder polyp. Small polyp on the anterior surface of the gallbladder is seen on the harmonic image (a) with marked reduction of noise in the gallbladder lumen compared with that on the conventional US image (b).

View larger version (129K): [in a new window]   Figure 4b.   Gallbladder polyp. Small polyp on the anterior surface of the gallbladder is seen on the harmonic image (a) with marked reduction of noise in the gallbladder lumen compared with that on the conventional US image (b).

View larger version (121K): [in a new window]   Figure 5a.   Renal cyst. (a) Because of marked clearing of noise, the harmonic image demonstrates septation and a mural nodule within the cyst. (b) Conventional US image shows artifact from noise.

View larger version (112K): [in a new window]   Figure 5b.   Renal cyst. (a) Because of marked clearing of noise, the harmonic image demonstrates septation and a mural nodule within the cyst. (b) Conventional US image shows artifact from noise.

View larger version (114K): [in a new window]   Figure 6a.   Cholelithiasis. Multiple small gallstones in the dependent portion of the gallbladder are depicted more clearly on the harmonic image (a) than on the conventional US image (b).

View larger version (102K): [in a new window]   Figure 6b.   Cholelithiasis. Multiple small gallstones in the dependent portion of the gallbladder are depicted more clearly on the harmonic image (a) than on the conventional US image (b).

View larger version (104K): [in a new window]   Figure 7a.   Hemangioma. Small hyperechoic mass in the dome of the liver is depicted on the harmonic image (a) but not on the conventional US image (b).

View larger version (106K): [in a new window]   Figure 7b.   Hemangioma. Small hyperechoic mass in the dome of the liver is depicted on the harmonic image (a) but not on the conventional US image (b).

View larger version (147K): [in a new window]   Figure 8a.   Diffuse fatty infiltration in the liver. Harmonic (a) and conventional (b) US images of a fatty liver show better penetration of the ultrasound beam in b.

View larger version (155K): [in a new window]   Figure 8b.   Diffuse fatty infiltration in the liver. Harmonic (a) and conventional (b) US images of a fatty liver show better penetration of the ultrasound beam in b.

View larger version (126K): [in a new window]   Figure 9a.   Renal carcinoma in an obese patient. Exophytic solid mass in the lower pole of the left kidney is seen on the harmonic image (a) but not on the conventional US image (b), which demonstrates the benefits of harmonic imaging in obese patients.

View larger version (139K): [in a new window]   Figure 9b.   Renal carcinoma in an obese patient. Exophytic solid mass in the lower pole of the left kidney is seen on the harmonic image (a) but not on the conventional US image (b), which demonstrates the benefits of harmonic imaging in obese patients.

View larger version (105K): [in a new window]   Figure 10a.   Hepatic metastases. In the liver, multiple isoechoic masses with peripheral hypoechoic halos are depicted more clearly on the harmonic image (a) than on the conventional image (b). The clarity in a improved diagnostic confidence.

View larger version (112K): [in a new window]   Figure 10b.   Hepatic metastases. In the liver, multiple isoechoic masses with peripheral hypoechoic halos are depicted more clearly on the harmonic image (a) than on the conventional image (b). The clarity in a improved diagnostic confidence.

View larger version (117K): [in a new window]   Figure 11a.   Choledocholithiasis with liver metastases. Both the harmonic (a) and conventional (b) US images show a dilated common duct and multiple liver metastases. The obstructing stone in the common duct was detected on only a, and diagnostic confidence was improved.

View larger version (119K): [in a new window]   Figure 11b.   Choledocholithiasis with liver metastases. Both the harmonic (a) and conventional (b) US images show a dilated common duct and multiple liver metastases. The obstructing stone in the common duct was detected on only a, and diagnostic confidence was improved.

View larger version (101K): [in a new window]   Figure 12a.   Right renal mass in an obese patient. Solid mass in the lower pole of the right kidney is seen equally well on the harmonic (a) and conventional (b) US images. Clinical management was not altered because a did not contribute information in addition to that in b.

View larger version (101K): [in a new window]   Figure 12b.   Right renal mass in an obese patient. Solid mass in the lower pole of the right kidney is seen equally well on the harmonic (a) and conventional (b) US images. Clinical management was not altered because a did not contribute information in addition to that in b.

View larger version (99K): [in a new window]   Figure 13a.   Liver abscess. The harmonic (a) and conventional (b) US images depicted the partially cystic abscess equally well. No additional information was contributed in b that altered the diagnosis.

View larger version (98K): [in a new window]   Figure 13b.   Liver abscess. The harmonic (a) and conventional (b) US images depicted the partially cystic abscess equally well. No additional information was contributed in b that altered the diagnosis.