**9. Limitations of TE**

sonic properties of the radio-frequency back propagated signals acquired by the Fibroscan [92]. It is called controlled attenuation parameter (CAP). This ultrasonic attenuation coeffi‐ cient is an estimate of the total ultrasonic attenuation (go-and-return path) at the central fre‐ quency of the regular or M Fibroscan® probe, i.e. at 3.5 MHz, and is expressed in dB.m−1. CAP is evaluated using the same radio-frequency data and the same region of interest, as the region used to assess the LSM. CAP is only appraised if the acquisition is ''valid''. There‐ fore, CAP is guided by vibration-controlled transient elastography (VCTE), which ensures that the operator automatically obtains an ultrasonic attenuation value of the liver [92, 93]. The device is used to assess, at the same time, LS (which is related to liver fibrosis) and CAP

Even though relatively few studies have been published on this topic [92, 93, 94,95] the pre‐ liminary results showed that CAP is a promising non-invasive tool to detect steatosis in

In the study conducted by Sasso et al, the CAP performance was appraised on 115 patients, taking the histological grade of steatosis as reference. CAP was significantly correlated to steatosis with an AUROC equal to 0.91 and 0.95 for the detection of more than 10% and 33%

A study performed recently on 615 HCV patients, who underwent both Fibroscan (®) and liver biopsy showed in multivariate analysis, that CAP was related to steatosis, independ‐ ently of fibrosis stage (which was related to LS. The AUROCs of the were 0.80, 0.86 and 0.88 respectively, for predicting a fatty overload of more than 11%, 33%, and 66%, respec‐ tively. CAP also exhibited a good ability to differentiate steatosis grades (Obuchowski

CAP is evaluated using the same radio-frequency data and the same region of interest, as the region used to assess the liver stiffness for fibrosis quantification. Preliminary studies performed in our department have found significantly different CAP values for different steatosis grades and AUROCs of 0.830 and 0.85 respectively, for the prediction of a hepatic

**8. The advantages of TE in liver steatosis, fibrosis and cirrhosis diagnosis**

Compared with other diagnosis indicators or predictive models based on lab tests, the eval‐

**•** It is easy to use; noninvasive; pain-free; does not require anesthesia or hospitalization and

uation of fibrosis using elastography has some important advantages [98,99]:

**•** It is quick, the time needed for the examination being very short;

(which is related to liver steatosis).

224 Liver Biopsy – Indications, Procedures, Results

CHC patients.

of steatosis, respectively.

measure = 0.92) [96].

fat content over 33% and 66%, respectively [97].

is therefore easily accepted by the patient;

**•** It is not influenced by concomitant conditions;

**•** It is operator independent;

Liver fibrosis can not be evaluated by TE in 5-8 % of the cases. Some of the possible causes for this are listed below [16]:


The failure of TE varies according to different authors from 2.4% to 9.4% [16, 21, 24, 36, 74, 64, 100]. In a study performed on 2114 patients [101], liver stiffness could not be determined in 4.5% of the cases and multivariate analysis showed that the only element associated with measurement failure is a body mass index over 28. Yet, with more experience, one may real‐ ize that a thick thoracic wall is more likely to be a limiting factor for a failed measurement than the growth of the body mass index in itself [102].

Technical solutions regarding the design of the probe were investigated lately, in order to overcome these limitations. Recently a new probe became available, that was specially de‐ signed for obese patients, with a central frequency of 2.5% MHz (compared with the 5MHz probe that is usually used), and that is able to determine liver stiffness on a distance of 35-75 mm from the skin (while the normal probe is able to do that on distance of 25 to 45 cm). With the help of this new transducer, it was possible to obtain valid measurements in 49% of the patients with a BMI ≥30 kg/m2, in which the usual probe failed to determine the LS [103].

As far as predicting steatosis in HCV patients is concerned, CAP has further validation in larger populations and by independent teams, since there are rather few studies published until now. Another important limitation is that CAP cannot be used with measurements tak‐ en from the XL probe, which is a novel probe designed to assess liver stiffness in overweight and obese patients [75,76]. Thus, CAP needs to be developed to work with the XL probe.

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#### **10. Conclusions**

The possibility of concomitant assessment of liver fibrosis (using liver stiffness measure‐ ment) and of steatosis (using CAP) makes Fibroscan a promising non-invasive tool for as‐ sessing and quantifying both fibrosis and steatosis, that may broaden the spectrum of noninvasive methods used for the investigation and follow-up of patients with chronic hepatitis C. But it is important that interpretation of the liver stiffness values be done by an experi‐ enced physician and always within the clinical and biochemical context of the patient.
