**2.1 Ultrasonography**

US is a rapid and non-invasive method for screening patients with suspected liver metastases but, although it is highly efficient in distinguishing patients with diffuse hepatic metastases that involve all the liver, it is more operator dependent than other imaging methods, fails to show parts of the liver in certain patients and its sensitivity (50-70%) and specificity are surpassed by other imaging studies.

The detection of hepatic metastases is substantially improved by contrast-enhanced US (CEUS) compared to conventional B-mode sonography, increasing the sensitivity per lesion from 71% to 87% (Oldenburg & Albrecht 2008). US contrast agents consist of microbubbles of gas that flood the blood pool after intravenous injection and are confined to the vascular compartment. These agents are safe, well tolerated and have very few contraindications. Metastases behave characteristically in three phases: arterial, portal venous and delayed (El Khodary et al. 2011). CEUS sensitivity and specificity in staging liver metastases (80–95% and 84–98%, respectively) approach those of CT and MRI. In addition, CEUS is useful to improve the detection rate of metastases smaller than 1 cm or of those lesions that are isoechoic with respect to adjacent liver parenchyma, thus improving the performance of sonography in around 13.7% of the cases (Chami et al. 2008).

In general, if an examination of the liver by US is insufficient, then examination by CEUS will also be insufficient. CEUS has limited ability to observe certain parts of the liver, especially in obese patients and/or in cases of steatosis and it is not possible to simultaneously examine multiple lesions in the arterial and early portal phases. Hypervascular metastases and haemangiomas on one hand and metastases and small cysts on the other can be difficult to differentiate (Larsen 2010).

Intraoperative diagnosis is based on IOUS and on diagnostic laparoscopy. IOUS has higher sensitivity than transabdominal US, MDCT and MRI, and allows identification of metastases 0.5 cm in size and defining the relationship between lesion, vessels and biliary structures. With a sensitivity of 98% and a specificity of 95%, IOUS is generally considered the gold standard for detecting liver lesions and is regarded as a routine investigation, modifying the planned surgical intervention in 18-30% of the patients. In addition, Doppler and spectral Doppler facilitate the technique of surgical resection. Laparoscopy, which is not routinely used in the pre-operative evaluation of the advanced disease, allows an assessment of the peritoneal and pelvic spread of the primitive cancer and, with the combined use of laparoscopic ultrasound (LIOUS), enables detection of small metastases, varying the initial surgical plan in 20–30% of the cases (Guglielmi et al. 2005). Contrast enhanced IOUS (CE-IOUS) shows some benefit over pre-operative imaging and IOUS since it seems to improve the ability to characterize already detected lesions and facilitate the detection of new metastatic lesions (Fioole et al. 2008; Leen et al. 2006; Nakano et al. 2008; Torzilli et al. 2005).

### **2.2 Computed Tomography**

MDCT has a sensitivity of 70–85% and a specificity of 90%, especially for lesions bigger than 1.5–2 cm. Sensitivity is lower for small subglissonian metastases, even though multi-slice CT allows identification of hepatic lesions of 0.5 cm in size (Guglielmi et al. 2005). Fast data acquisition and breath-hold scanning allows imaging of the liver twice. This bi-phasic contrast-enhanced scan during the arterial-dominant phase and the portal-venous perfusion phase after bolus-like contrast administration, prior to the equilibrium phase, is accepted as standard for the optimised display of the complex vascularization of the liver and potential hepatic lesions. Slice thicknesses of 2 or 4 mm are the most effective for detection of focal liver lesions, with an identical detection rate of 96% for both. 3-D data sets can be produced improving multiplanar imaging, which allows evaluation of subcapsular lesions, demonstration of vascular anatomy and better characterisation of the lesions. Together with improvements in bolus-tracking, MDCT scanning during the various vascular contrast and equilibrium phases allows performing CT-angiography of the liver and mesenteric vessels, which can be important in patients undergoing hepatic resection or transarterial chemo or radio-embolisation. MDCT portal venogram is useful in evaluation of the portal system. Additionally, quantitative perfusion studies can also be done. Thus, MDCT can be used for evaluating the liver lesion, liver parenchyma and hepatic vessels in the same sitting.

Metastases behave characteristically in three phases: arterial, portal venous and delayed (El Khodary et al. 2011). CEUS sensitivity and specificity in staging liver metastases (80–95% and 84–98%, respectively) approach those of CT and MRI. In addition, CEUS is useful to improve the detection rate of metastases smaller than 1 cm or of those lesions that are isoechoic with respect to adjacent liver parenchyma, thus improving the performance of

In general, if an examination of the liver by US is insufficient, then examination by CEUS will also be insufficient. CEUS has limited ability to observe certain parts of the liver, especially in obese patients and/or in cases of steatosis and it is not possible to simultaneously examine multiple lesions in the arterial and early portal phases. Hypervascular metastases and haemangiomas on one hand and metastases and small cysts

Intraoperative diagnosis is based on IOUS and on diagnostic laparoscopy. IOUS has higher sensitivity than transabdominal US, MDCT and MRI, and allows identification of metastases 0.5 cm in size and defining the relationship between lesion, vessels and biliary structures. With a sensitivity of 98% and a specificity of 95%, IOUS is generally considered the gold standard for detecting liver lesions and is regarded as a routine investigation, modifying the planned surgical intervention in 18-30% of the patients. In addition, Doppler and spectral Doppler facilitate the technique of surgical resection. Laparoscopy, which is not routinely used in the pre-operative evaluation of the advanced disease, allows an assessment of the peritoneal and pelvic spread of the primitive cancer and, with the combined use of laparoscopic ultrasound (LIOUS), enables detection of small metastases, varying the initial surgical plan in 20–30% of the cases (Guglielmi et al. 2005). Contrast enhanced IOUS (CE-IOUS) shows some benefit over pre-operative imaging and IOUS since it seems to improve the ability to characterize already detected lesions and facilitate the detection of new metastatic lesions (Fioole et al. 2008; Leen et al. 2006; Nakano et al. 2008; Torzilli et al. 2005).

MDCT has a sensitivity of 70–85% and a specificity of 90%, especially for lesions bigger than 1.5–2 cm. Sensitivity is lower for small subglissonian metastases, even though multi-slice CT allows identification of hepatic lesions of 0.5 cm in size (Guglielmi et al. 2005). Fast data acquisition and breath-hold scanning allows imaging of the liver twice. This bi-phasic contrast-enhanced scan during the arterial-dominant phase and the portal-venous perfusion phase after bolus-like contrast administration, prior to the equilibrium phase, is accepted as standard for the optimised display of the complex vascularization of the liver and potential hepatic lesions. Slice thicknesses of 2 or 4 mm are the most effective for detection of focal liver lesions, with an identical detection rate of 96% for both. 3-D data sets can be produced improving multiplanar imaging, which allows evaluation of subcapsular lesions, demonstration of vascular anatomy and better characterisation of the lesions. Together with improvements in bolus-tracking, MDCT scanning during the various vascular contrast and equilibrium phases allows performing CT-angiography of the liver and mesenteric vessels, which can be important in patients undergoing hepatic resection or transarterial chemo or radio-embolisation. MDCT portal venogram is useful in evaluation of the portal system. Additionally, quantitative perfusion studies can also be done. Thus, MDCT can be used for

evaluating the liver lesion, liver parenchyma and hepatic vessels in the same sitting.

sonography in around 13.7% of the cases (Chami et al. 2008).

on the other can be difficult to differentiate (Larsen 2010).

**2.2 Computed Tomography** 

It is important to take account of the time elapsed between the radiological study and the operation. One recent study showed that the utility of MDCT as a pre-operative tool to evaluate CRC liver metastases is inversely proportional to the time interval between imaging and surgery, which may explain conflicting reports of the accuracy of MDCT in the literature (Yang et al. 2010).

Hepatic volumetry, necessary to evaluate the feasibility of major hepatectomies, especially in the case of atypical resections, is provided by MDCT software able to highlight different liver segments and to create vascular maps for arterial and portal afferences, and for hepatic vein drainage. The volume of each single segment can be calculated and a simulation of surgical resection can be performed. Information can be displayed using coloured maps or three-dimensional movies (Laghi et al. 2005).
