Portal venous phase

Fig. 8.5 Haemangioma (see arrow). Dynamic CT (contrast-enhanced) portal venous phase (s. figs. 6.15 8.9 36.6, 36.7)...

Fig. 36.3 CT in the portal venous phase FNH with star-shaped scar...

On CT, an area of low attenuation with calcifications and disruption of the normal contour can be identified. On enhanced CT, the tumor will show a momentary enhancement that will be higher in the arterial phase compared with the portal venous phase. 

The appropriate examination technique is critical for sensitive detection and specific characterization of focal liver lesions. A biphasic examination of the liver with a late-arterial and a portal venous phase can be regarded as standard today. For specific indications, like the follow-up of hepatocellular carcinoma (HCC) after transarterial chemoembolization (TACE) or for the depiction of the arterial vessels prior to angiography, an early arterial phase scan, which can be post-processed into CT angiography, is helpful (Fig. 3.2). The value of delayed scans (e.g. 5 min after contrast agent injection) is controversial in the literature mainly centers with a focus on imaging in liver cirrhosis consider the use of late phase images as necessary, whereas other authors see no added value for it [21,45]. 

Fig. 3.2. Axial and coronal sections in the early arterial phase (left), late arterial phase middle) and portal venous phase (right) in a female patient suffering from hepatocellular carcinoma (HCC) under treatment with transarterial chemoembo-lization (TACE). In the early arterial phase only the liver arteries are properly enhanced the portal vein and also the liver parenchyma are not yet opacified. The two HCC nodules in segment 2/3 and segment 6 (marked by large arrows) are also both not properly demarcated. The early arterial phase, therefore, is not suitable for detection of hypervascular tumors it is rather a CT angiographic phase and can be omitted in most cases. The most important phase for detection of hypervascular tumors is the late-arterial phase (also called arterial-dominant phase or phase of portal venous inflow). In this phase there is already enhancement in the portal-vein (small arrow in the upper row) and in the liver parenchyma. The liver veins are not yet opacified in this phase (small arrow in the lower row). Most hypervascular tumors reach their highest attenuation in this phase. In the portal venous phase enhancement of the liver parenchyma is highest, the vascular enhancement in the portal venous system and in the hepatic vein is similar. Hypervascular tumors show decreased attenuation compared to the late-arterial phase depending on the degree of wash-out they can be still hyperdense (as in this case), isodense (see Fig. 3.4) or even hypodense...

Fig. 3.4a,b. MDCT in the late arterial (a) and portal venous phase (b) in a male patient suffering from a neuro-endocrine carcinoma with liver metastases (arrows). Note the strong wash-out of the metastases to nearly isointensity, so that even the larger lesions can retrospectively not be properly detected in the portal venous phase in contrast to the excellent conspicuity of the lesions in the arterial phase. This example strikingly demonstrates the importance of a correctly timed late arterial phase... 

Fig. 3.6a-C. MDCT in portal venous phase (a) and MRI with a Tl-w 3D gradient-echo sequence after gadolinium-injection (b) and a T2 -w gradient-echo sequence after injection of the SPIO contrast agent ferucarbotran (c) in a male patient suffering from a colorectal carcinoma in whom atypical resection of a liver metastasis in the right lobe of the liver had been performed previously. Note the postoperative bilioma (marked by the asterisk). In the MDCT examination no further liver lesions can be detected, whereas the gadolinium-enhanced MRI faintly shows a hypervascular lesion arrow). The SPlO-enhanced MRI scan clearly depicts a newly developed metastasis with a high contrast between lesion and adjacent liver parenchyma...

Fig.3.7a-d. MDCT in the arterial phase (a) and MRI with the hepato-biliary contrast agent Gd-EOB-DTPA in the arterial phase (b), portal venous phase (c) and liver-specific phase 20 min after injection (c) each examined with a Tl-w 3D GRE sequence with fat-saturation in a patient with a neuroendocrine tumor and liver metastases. The hypervascular metastases were not detected with MDCT. In the arterial phase after Gd-EOB-DTPA injection hyperintense lesions are demarcated. The hypervascular metastases show a wash-out to isointensity in the portal venous phase. With Gd-EOB-DTPA liver-specific phase imaging can be performed in addition to the early dynamic phase. Note the signal increase in the normal liver parenchyma in (d) caused by the physiological Gd-EOB-DTPA up-take whereas the suspected liver metastases are demarcated as areas spared from specific Gd-EOB-DTPA up-take... 

With 4-slice CT scanners, the entire abdomen can be scanned continuously with slices as thin as 2-3 mm. When scanning from top to bottom, the liver should be imaged during the portal venous phase and the... 

As with other scanners, the liver should be scanned during the portal venous phase, immediately followed by scanning of the pelvis. When a continuous scan from top to bottom is performed with a delay of 60 s, the pelvis tends to be scanned too early. Here, the examiner must decide whether the advantage of an uninterrupted scan with the option of creating continuous coronal reconstructions is more important than scanning of the pelvis during the optimal imaging window. 

Scanning on a 64-slice CT scanner requires only some minor adjustments of the scanning protocol. A continuous examination of the chest, abdomen, and pelvis may be beneficial in individual cases. When scanning from top to bottom, the scan delay for the chest should be between 50 and 55 s in order to scan the liver during the portal venous phase. However, with this delay, one will miss the phase of maximum enhancement of the pulmonary arteries. 

CT of the pelvis is predominantly performed for cancer staging, which means that the CT examination should include the upper abdomen. Scanning of the pelvis during a specific perfusion phase is less critical than for the liver, which should be scanned during the portal venous phase 50-70 s after intravenous contrast medium injection. If the scans are obtained too early, there is the risk of overlooking thromboses due to incomplete enhancement of the pelvic veins. 

The pancreatic phase of contrast enhancement optimizes our ability to detect pancreatic adenocarcinoma and differentiate it from normal pancreatic tissue. Studies have shown that because pancreatic ductal adenocarcinoma often has a marked desmoplastic response associated with it, it will be hypo-attenuating relative to the normal pancreas after contrast enhancement during the pancreatic phase (Lu et al. 1997). The degree of tumor conspi-cuity is enhanced during the pancreatic phase and decreases during the portal venous phase. This... 

Fig. 3.10. Dual phase MDCT of pancreatic cancer. Axial CT obtained during the pancreatic phase of enhancement (left) shows 2 cm hypo-vascular pancreatic adenocarcinoma (arrow). During the portal venous phase (right) the tumor is isoattenuating (arrow)...

The portal venous phase of contrast enhancement is performed approximately 80-90 s after the bolus of contrast enhancement using state of the art MDCT scanners. For the portal venous phase of contrast enhancement, scanning is initiated from the dome of the liver through the abdomen and pelvis. The portal venous phase of enhancement is criti-... 

The use of intravenous injection of iodinated contrast medium is reserved to cases where evaluation of the extracolonic findings is needed (i.e., staging of CRC patients under surveillance program), and it is performed with the acquisition of a contrast-enhanced supine scan during the portal venous phase (Laghi et al. 2003). 

Scott DJ, Guthrie JA, Arnold P etal. (2001) Dual phase helical CT versus portal venous phase CT for the detection of colorectal liver metastases correlation with intraoperative sonography, surgical and pathological findings 56 235-242... 

Fig. 41.2a-c. Portal venous phase CT in a patient with cho-langiocellular carcinoma (a). The corresponding FDG PET/ CT (b) demonstrates vital tumor tissue at the rim. Corresponding C-arm CT with the catheter in the right hepatic artery (c) displays that the tumor must be supplied not only from the right, but also from the left hepatic artery. Furthermore, the area of high contrast enhancement in C-arm CT corresponds well to the location of the FDG uptake... 

Fig 1.5. a CT scout image in a newborn demonstrating hepatomegaly, b CT arterial phase demonstrating multiple hypodense masses within the liver, c CT portal venous phase demonstrating multiple masses with nodular enhancement... 

Portal venous phase 60 s (or bolus tracking 40 s after aortic arrival) for stomach... 

Fig. 2.1. Diagram of multiphasic vascular enhancement of the liver. Around 20 s (representing the average delay time usually calculated on the basis of bolus test) following the beginning of contrast medium injection first breath-hold acquisition of two consecutive scans is obtained. At around 60 s the second breath-hold scan is acquired followed by the equilibrium phase. CM, contrast me-dimn EAP, early arterial phase LAP, late arterial phase PVP, portal venous phase EP, equilibrium phase...

Fig. 2.2. Time-density curves representing enhancement of aorta, portal vein and liver parenchyma during each scan. Please note clear separation of different vascular phases with early arterial phase demonstrating exclusive enhancement of arterial vessels with absolutely no venous contamination. EAP, early arterial phase LAP, late arterial phase PVT, portal venous phase P, equilibrium phase...

Fig. 2.5a-e. Hepatocellular carcinoma (arrow), a In the basal scan the lesion appears as a slightly hy-podense nodular area, b No nodule is detected on early arterial phase, c In late arterial phase a marked hyperdense nodule is observed, d On portal venous phase contrast enhancement is still persistent, e Complete wash-out is demonstrated on equilibrium phase, where the lesion is detected as hypodense nodule... 

In contrast, other authors demonstrated that the portal venous phase showed no significant differences in lesion detection compared with delayed phase imaging, or better still when combined, spiral CT of the arterial and the delayed phases revealed 91% of lesions, whereas a combination of the arterial and portal venous phases or the combination of all three phases revealed 92% of lesions therefore, the combination of the arterial and portal venous phases is equal to the combination of three phases for detection of hypervascular hepatocellular carcinomas, and the delayed phase becomes superfluous (Choi et al. 1997). However, in this series of patients only hypervascular hepatocellular carcinoma was included, whilst in clinical practice, there are also cases of hypovascular hepatocellular carcinoma. This concept has been confirmed by other authors, who stated that portal venous-phase images are inferior to late phase images for detecting HCC nodules in the same paper sensitivity of the unenhanced phase was also evaluated and it was demonstrated not to be necessary (Kim et al. 1999). 

Even with regard to the use of an unenhanced phase opinions are controversial with papers demonstrating no additionally detected lesions (hepatomas or metastases) compared with other phases and other experiences showing a 3% increase in the detection rate for hepatocellular carcinomas compared with arterial and portal venous phases (Miller et al. 1998 Oliver et al. 1996). 

Fig. 2.8a-d. Tjfpical haemangioma, a In the basal scan it appears as slightly hypodense area, b The lesion presents an initial peripheral enhancement during the arterial phase, c In the portal venous phase a globular centripetal enhancement is observed, d In the delayed phase the lesion shows an almost complete filling... 

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