Eur Radiol (****) **: **** ****

HEPATO BILI ARY-PANCREAS

DOI 10.1007/s00330-006-0205-6

Se Hyung Kim

Comparison of fundamental sonography,

Jeong Min Lee

tissue-harmonic sonography, fundamental

Kwang Gi Kim

Jong Hyo Kim

compound sonography, and tissue-harmonic

Joon Koo Han

Jae Young Lee

compound sonography for focal hepatic lesions

Byung Ihn Choi

Abstract Image qualities of funda- Compound imaging was significantly

Received: 1 September 2005

mental, tissue-harmonic, fundamental superior to fundamental imaging re-

Revised: 17 January 2006

compound, and tissue-harmonic com- garding lesion conspicuity, margin

Accepted: 9 February 2006

Published online: 29 March 2006 pound sonography for evaluating sharpness, and overall quality

# Springer-Verlag 2006 focal hepatic lesions were compared. (P

Two radiologists, blinded to the type and internal artifacts within the cyst,

S. Kim . J. Lee . J. Kim . J. Han .

of techniques and to the final diag- harmonic ultrasonography (US) was

J. Lee . B. Choi

nosis, independently evaluated 384 significantly better than fundamental

Department of Radiology,

images of 96 hepatic lesions: heman- US (P 0.81 to represent statistical analyses of the images of the four different

almost perfect agreement and values of 0.61 0.80 and techniques according to lesion types are summarized in

0.41 0.60 to represent substantial or moderate agreement, Table 4.

respectively. Values 0.81 is considered almost perfect agreement, 0.61~0.80 substantial agreement, 0.41~0.60 moderate

agreement, and 0.05; Figs. 5 and 6). previous articles [1, 3, 9, 25, 26].

Table 3 Comparative statistical analysis of the images obtained using four techniques used to evaluate each parameter

Lesion conspicuity (n=96) HCUS = FCUS > HUS = FUS

Margin sharpness (n=96)a HCUS = FCUS = HUS = FUS, HCUS > HUS = FUS, FCUS > FUS

Posterior enhancement (n=28) HUS = HCUS > FUS = FCUS

Internal artifact within the cyst (n=28) HCUS > FCUS = HUS > FUS

Overall image quality (n=96) HCUS = FCUS > HUS = FUS

FUS fundamental ultrasonography, HUS tissue-harmonic ultrasonography, FCUS fundamental compound ultrasonography, HCUS tissue-

harmonic compound ultrasonography

Data were analyzed using the Friedman test with post hoc analysis. A>B: A is better than B with statistical significance (P HUS = FUS

Cystic lesion (n=28) HCUS = FCUS > HUS = FUS

Cirrhosis-related nodule (n=22) HCUS = FCUS > HUS = FUS

Metastasis (n=10) HCUS = FCUS = HUS = FUS

Margin sharpness Hemangiomas (n=35) HCUS = FCUS = HUS = FUS, HCUS > HUS = FUS, FCUS > FUS

Cystic lesion (n=28) HCUS = FCUS = HUS = FUS, HCUS > HUS = FUS, FCUS > FUS

Cirrhosis-related nodule (n=22) HCUS = FCUS = HUS = FUS, HCUS > HUS = FUS, FCUS > FUS

Metastasis (n=10) HCUS = FCUS = HUS = FUS

Overall image quality Hemangiomas (n=35) HCUS = FCUS > HUS = FUS

Cystic lesion (n=28) HCUS = FCUS > HUS = FUS

Cirrhosis-related nodule (n=22) HCUS = FCUS > HUS = FUS

Metastasis (n=10) HCUS = FCUS > HUS = FUS

FUS fundamental ultrasonography, HUS tissue-harmonic ultrasonography, FCUS fundamental compound ultrasonography, HCUS tissue-

harmonic compound ultrasonography

Data were analyzed using the Friedman test with post hoc analysis

In particular, spatial compound US greatly improves the glint, dropout, and refractive shadows [29]. US images also

delineation of these surfaces, thereby allowing superior exhibit spurious echoes that arise from side lobes, grating

delineation in the lesion margins [27, 28]. This improve- lobes, multipath reverberation, and other acoustic phenom-

ment is likely due in part to the fact that the images are ena, collectively known as clutter, and which cause

unwanted echo within the cyst and may hinder cyst solid

acquired from multiple angles. As an image is generated

from more angles of insonation, a greater likelihood exists lesion differentiation. In compound US, scanning from

that one of these angles will be perpendicular to specular various viewing angles produces various artifact patterns.

reflectors, generate a higher echo amplitude, and thereby Summation of the independent frames obtained at various

reduce the anisotropic effect. Curved surfaces thus appear scanning angles substantially reduces interference caused

more continuous, and tissue-plane definition is improved. by artifacts. In other words, because signals from true

In addition, US is subject to a number of inherent artifacts structures are summed, whereas random and artifactual

that can compromise image quality. The contributing echoes are not, the resulting image is a more realistic

factors to image degradation in US are clutter, speckling,

Fig. 1 A 50-year-old woman

with hepatic hemangioma.

Upper left: Fundamental US

shows a slightly high echoic

nodule in segment VII of the

liver. Upper right: On tissue-

harmonic US, lesion conspicuity

and overall image quality are

slightly improved from those of

the fundamental image. Lower

left: Fundamental compound US

image allows better depiction of

the lesion. Lower right: Tissue-

harmonic compound US image

provides the best lesion conspi-

cuity and overall image quality

with better delineation of the

lesion boundary. Regarding

margin sharpness, this image is

the best compared with the other

types of sonograms

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Fig. 2 A 50-year-old man with hepatocellular carcinoma and liver spicuity enables slightly better depiction than do the FUS and HUS

cirrhosis. Upper left: Fundamental US (FUS) image shows a high images. However, the artifact is similarly depicted as in the FUS

echoic mass (arrow) in segment VIII of the liver. Note the image. Lower right: Tissue-harmonic compound US image provides

reverberation artifact (arrowhead) arising from the anterior abdom- the best lesion conspicuity and improved overall image quality, with

inal wall. Upper right: Tissue-harmonic US (HUS) image reveals better delineation of the lesion boundary. Note the dramatic decrease

markedly eliminated artifacts seen in the anterior abdominal wall. in the number of artifacts arising from the anterior abdominal wall

Lower left: On fundamental compound US image, lesion con-

Fig. 3 A 58-year-old woman

with focal nodular hyperplasia.

Upper left: Sagittal fundamental

US (FUS) image reveals an

eccentrically located low echoic

mass in segment IV of the liver.

Upper right: Tissue-harmonic

US (HUS) image shows similar

image qualities to the FUS

image in all parameters. Lower

left: On the fundamental com-

pound US image, lesion con-

spicuity and overall image

quality allow slightly better

depiction than FUS and HUS.

Lower right: Tissue-harmonic

compound US image provides

the best lesion conspicuity and

improved overall image quality,

with better delineation of the

lesion boundary. The internal

echo texture is more clearly

differentiated on this image

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Fig. 4 A 62-year-old man with

liver metastases from renal cell

carcinoma. Upper left: Funda-

mental US shows two low

echoic nodules in segment VII

of the liver. We analyzed only

the larger one (arrows). Upper

right: On tissue-harmonic US,

lesion conspicuity and overall

image quality are slightly im-

proved from those of the fun-

damental image. Lower left:

Fundamental compound US

image allows better depiction of

the lesion. Lower right: Tissue-

harmonic compound US image

provides the best lesion conspi-

cuity and overall image quality,

with better delineation of the

lesion boundary. Regarding

margin sharpness, this image is

the best compared with the other

types of sonograms

representation of actual tissue compared with the image involves minimal noise and successfully eliminates some

obtained by FUS. image-degrading artifacts. In our current study, with

respect to all evaluated parameters, the radiologists

HUS uses information from harmonics generated by the

nonlinear wave propagation of sound as it passes through grading tended to be better in tissue-harmonic images

tissue [4, 5]. Shorter harmonic frequency pulses provide than in fundamental images, although in some categories or

better axial resolution, and the narrowed beam width parameters there were no significant differences in the

improves lateral resolution [5]. The harmonic signal is various US methods. This positive effect of HUS can

significantly improve a lesion s conspicuity, especially in

generated within tissue, with the distorted and scattered

energy being much weaker than the transmitted energy, hepatic cysts, and can reduce internal clutter in cystic

thus generating much weaker harmonics. As a result, HUS

Fig. 5 A 45-year-old man with

simple hepatic cyst. Upper left:

Transverse fundamental US

(FUS) image reveals a lobulat-

ing simple cyst (arrow) in seg-

ment VII of the liver. The image

quality is degraded by artifacts

(arrowhead). Upper right:

Tissue-harmonic US (HUS)

image shows suppression of

clutter or speckle within the

cyst, but artifacts still remain in

the left portion of the cyst.

Lower left: Fundamental com-

pound US image shows more

artifact suppression; however,

some residual artifacts are seen

in the posterior aspect (arrow).

This compounded image also

provides better lesion conspi-

cuity and sharpness of the mar-

gin than in the FUS and HUS

images. Lower right: Tissue-

harmonic compound US image

demonstrates the best image

quality in all parameters

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Fig. 6 A 62-year-old woman with hepatic cyst. Upper left: HUS images. However, posterior enhancement is decreased,

Transverse fundamental US (FUS) image shows a septated cyst in especially in the periphery (arrow). Note the diagram illustrating

segment VIII of the liver. Subtle posterior enhancement is noted the posterior enhancement behind the lesion on the compound US

behind the cyst. Note a diagram that illustrates posterior enhance- image at the lower right corner of the image. Lower right: Tissue-

ment behind the lesion at the lower right corner of the image. Upper harmonic compound US has the best-quality lesion conspicuity and

right: On tissue-harmonic US (HUS), posterior enhancement is margin sharpness. However, as in FCUS imaging, the margin of

markedly delineated with sharp borders. Lower left: Fundamental posterior enhancement (arrow) becomes vaguer than in the FUS or

compound US (FCUS) image demonstrates the fine internal HUS images

architecture of the septated cyst more distinctly than the FUS or

structures because side-lobe artifacts generally predomi- image quality, and simultaneously, the worse the motion

nate in fluid-filled structures. artifacts. Our instrument can operate in two compound

We observed that for posterior enhancement only, imaging modes, target and survey, depending on the

compound US tends to be inferior to fundamental imaging number of summated images. The survey mode allows

(Figs. 5 and 6). This result might be explained by a rapid scanning by producing three coplanar images in the

potential drawback of compound US, which is that acoustic compound acquisition sequence and minimizes the blur-

shadowing or enhancement in a compound scan may be ring. The target mode maximizes the image quality by

diminished compared with that of a fundamental scan [25, producing nine coplanar images, but it has a greater

27]. Acoustic shadowing or enhancement can be a useful likelihood of motion blurring. Therefore, the tradeoff

US artifact for lesion recognition and conspicuity. In between improving image quality and minimizing motion

compound acquisition of a lesion with central enhancement blurring can be optimized for different clinical applications

by frame averaging, the nonoverlapping portions of the [28]. Usually, in the case of scanning areas that are

enhancements are diminished, and the overlapping en- susceptible to motion artifacts (such as the upper abdomen

hancements immediately behind the lesion are concen- and vascular structures), the survey mode is preferred,

trated in a triangular region. Thus, posterior echoes are whereas the target mode is preferred in areas that are static

focused in the central portion but are inevitably muted in (such as the breast, musculoskeletal areas, and the thyroid).

the periphery (Fig. 6). Another limitation of compound US Therefore, we usually use the survey mode in which the

is the image blurring caused by motion. This blurring is frame rate is similar to fundamental imaging in routine liver

caused by the longer time required for averaging the frames US, for minimizing motion blurring caused by respiration

obtained from multiple pulses and for displaying the or a probe, and for preserving the frame rate.

summated image. The number of frames and steering Several limitations of our study should be mentioned.

angles vary depending on the transducer characteristics and First, because only one radiologist obtained all four sets of

the clinical application. In general, the more frames in the US images, bias could therefore have affected the image

compound acquisition sequence, the better the compound collection process. Although the reviewers were not

2452

involved in performing the US exam and were blinded to sis. This preference may account for such an atypical

image type while they graded the sonograms, absolute proportion of focal hepatic lesions in our study. Such a

blinding was difficult to attain because the fundamental, small number of metastases may also obscure a significant

tissue-harmonic, and compound images differed so im- difference among the four techniques in terms of lesion

mensely in quality.Second, because only two abdominal conspicuity and margin sharpness. Finally, the study was

radiologists interpreted the US images in this study, our not designed to compare the diagnostic performance of the

study results may simply reflect the subjective trends or radiologists with respect to lesion characterization via the

bias of the radiologists. We would require a larger group of four US techniques. Therefore, we did not analyze the data

radiologists in order to evaluate inter- and intraobserver in the separate categories of benign and malignant lesions.

variability and to confirm the generality of our findings. In conclusion, our study demonstrated that compound

Third, in our study there were fewer metastases than other US improves lesion conspicuity, margin sharpness, and

focal hepatic lesions. As a minimally invasive therapy, overall image quality in focal hepatic lesions. In cases of

radiofrequency ablation has become more popular than hepatic cysts, HUS appears to be better than fundamental

before. Therefore, our oncologists prefer to order CT or imaging for eliminating artifacts and delineating posterior

MRI studies rather than US as a follow-up imaging enhancement.

modality in patients suspected of having hepatic metasta-

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