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Original Research |
1 Department of Diagnostic Radiography, Chonbuk National University Hospital and
Medical School, Jeonju, South Korea.
2 Department of Radiology and Institute of Radiation Medicine, Seoul National
University Hospital, 28, Yongon-dong, Chongno-gu, Seoul 110-744, South
Korea.
Received July 29, 2004;
accepted after revision January 11, 2005.
Address correspondence to J. M. Lee.
Abstract
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MATERIALS AND METHODS. Thirty-one patients with 53 hepatocellular carcinomas underwent gadobenate dimeglumine-enhanced dynamic MRI and multiphasic CT using 16-MDCT within a mean interval of 5 days (range, 3-9 days). The dynamic MRI examination was performed using 3D fat-saturated volumetric interpolated imaging and sensitivity encoding on a 1.5-T unit. Both dynamic MRI and multiphasic MDCT included dual arterial phase images. Three observers independently interpreted the CT and MR images in random order, separately, and without patient identifiers. The diagnostic accuracy of each technique was evaluated using the alternative-free response ROC method. The sensitivity and positive predictive values were also calculated.
RESULTS. The sensitivities of gadobenate dimeglumine-enhanced MRI for all observers were significantly higher than those of MDCT for all the lesions and for lesions 1.0 cm or smaller (p < 0.05); however, for lesions larger than 1.0 cm, the sensitivities of the two imaging techniques were similar. The mean area under the ROC curve (Az) of gadobenate dimeglumine-enhanced MRI (0.87 ± 0.03 [SD]) was higher than that of MDCT (0.83 ± 0.04), but no significant difference was found between them (p = 0.31). The number of false-positive findings on dynamic MRI was slightly higher than on MDCT, but no significant difference in the positive predictive value between the two imaging techniques was detected (observer 1, p = 0.06; observer 2, p = 0.13; observer 3, p = 1.00).
CONCLUSION. Gadobenate dimeglumine-enhanced MRI has a higher
sensitivity for small hepatocellular carcinomas (
1 cm) but a higher
false-positive rate due to nonspecific enhancement of benign lesions, such as
arterioportal shunt, leading to no significant difference of overall accuracy
when compared with MDCT.
Keywords: CT • hepatocellular carcinoma • liver disease • MR contrast agents • MRI
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Thanks to the advantages of a multirow detector array with a fast gantry rotation time, MDCT permits improved z-axis coverage speed over that attainable on conventional single-detector helical CT [9, 10]. For liver imaging examinations to evaluate hepatocellular carcinoma, these technical improvements translate into acquisition of dynamic images with double arterial phase images and high longitudinal resolution; this may allow increased detection of small hepatocellular carcinomas by reducing the chance of misregistration of the arterial phase scan [11].
The inherently slow scanning speed of MRI limits both in-plane and z-axis spatial resolution of dynamic images for the detection of focal liver lesions [3, 12]. However, with the recent introduction of 3D T1-weighted imaging and parallel acquisition techniques, the imaging acquisition time has been remarkably shortened and the z-axis spatial resolution has improved [13-16]. The combined use of both techniques allows acquisition of dynamic liver MR images with double arterial phases and thinner sections, thereby improving the detection of hypervascular hepatocellular carcinoma [17]. Moreover, the variety of MR contrast agents has greatly contributed to the accurate detection and characterization of focal liver lesions [18-23]. Because gadobenate dimeglumine (MultiHance, Bracco) is a novel gadolinium-based paramagnetic contrast agent with a twofold higher T1 relaxivity than conventional gadolinium chelates, it may be able to improve the detection rate of hypervascular liver neoplasms, such as hepatocellular carcinoma [24-26].
To our knowledge, there have been no comparative studies of gadobenate dimeglumine-enhanced 3D dynamic MRI using sensitivity encoding (SENSE) and 16-MDCT for the detection of hepatocellular carcinoma. The purpose of this study was to compare the diagnostic performance of gadobenate dimeglumine-enhanced 3D dynamic MRI with that of 16-MDCT for the detection of hepatocellular carcinoma using alternative-free response receiver operating characteristic (ROC) curve analysis with multiple observers.
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The remaining 31 patients (28 men, three women; age range, 36-66 years; mean age, 57 years) with hepatocellular carcinoma were included in this study. All except one of these patients had liver cirrhosis associated with viral hepatitis B, and one patient had alcoholic cirrhosis. In 26 of these 31 patients, liver cirrhosis was confirmed by histology. In the other five patients, the diagnosis of liver cirrhosis was made on the basis of a combination of clinical course, blood chemistry test results (aspartate aminotransferase, alanine aminotransferase, alkaline phosphatase, bilirubin, albumin, and globulin levels), and typical findings on CT and MRI. The severity of liver cirrhosis, based on the Child-Pugh classification [27], in 28 patients was class A and was class B in the remaining three patients.
Lesion Confirmation
A total of 53 tumors (size range, 0.6-6.6 cm; mean, 1.8 cm) in 31 patients
were included in this study. Of the 31 patients, 19 had solitary lesions,
seven had two lesions, and the remaining five patients had three to five
lesions each. The final diagnosis of hepatocellular carcinoma was proven by
surgical specimens in 16 patients and by core needle biopsy in 10 patients.
Core needle biopsy was performed in all suspected lesions of each patient by
one radiologist using sonographic guidance. In the remaining five patients
without histologic confirmation who underwent transarterial chemoembolization,
the diagnosis of hepatocellular carcinoma depended on a combination of
elevated serum 
-fetoprotein level (> 400 ng/mL), characteristic
angiographic findings, and iodized oil (Lipiodol, Guerbet) uptake on Lipiodol
CT [28] or on the typical CT
findings during hepatic arteriography and arterioportography.
For Lipiodol CT, hepatic angiography was performed by one interventional radiologist with 15 years of experience in transarterial chemoembolization using a digital angiography unit (Angiostar, Siemens Medical Solutions). Before the procedure, the interventional radiologist was made aware of the location and number of liver masses found on MRI or CT. An emulsion of 5-10 mL of iodized oil with anticancer drugs was injected through a catheter, the tip of which was placed superselectively into the segmental or subsegmental arteries feeding the tumor. On the CT examination performed 1 month after the procedure, nodular areas of retained Lipiodol were diagnosed as hepatocellular carcinoma.
Determination of the total number of hepatocellular carcinomas in 16 patients (19 lesions) who underwent hepatic surgery was based on pathologic analysis of the surgical specimens and intraoperative sonography. One hepatobiliary surgeon with 20 years of experience in liver surgery performed all the hepatic surgeries using intraoperative sonography. The average interval between surgery and the last imaging study was 10 days (range, 4-17 days). Before surgery, the location and number of liver masses on preoperative MRI or CT were carefully reviewed jointly by the surgeon and two radiologists who were not involved in image interpretation. After resection of a liver mass (segmentectomy, n = 10; enucleation, n = 9), the histopathologic results of the resected hepatic specimens were correlated with the preoperative imaging findings.
In 10 patients with 14 hepatocellular carcinomas who underwent imaging-guided core needle biopsy, the standard of reference for the presence of hepatocellular carcinoma was the combined results of biopsy and findings on follow-up contrast-enhanced MDCT or MRI at a minimum of 6 months. Of the 10 patients, seven patients with 10 hepatocellular carcinomas were treated by transarterial chemoembolization and the remaining three patients with four lesions underwent radiofrequency thermal ablation. In five patients with 20 hepatocellular carcinomas who underwent transcatheter arterial chemoembolization, the standard of reference for the presence of hepatocellular carcinoma was the combined results of iodized oil CT after transcatheter arterial chemoembolization, CT angiography findings, and follow-up contrast-enhanced MDCT or MRI findings.
Follow-up contrast-enhanced CT or MRI was performed for a minimum of 6 months (range, 6-12 months) on all patients. On follow-up contrast-enhanced MDCT or MRI, no new liver masses were found; therefore, we concluded that the total number of lesions in each patient coincided with the findings of all diagnostic procedures. For the 16 patients who underwent hepatic surgery, follow-up images ascertained the absence of tumor nodules in the remaining liver after resection.
MRI
All MRI examinations were performed on a 1.5-T superconducting scanner
(Magnetom Symphony, Siemens Medical Solutions) with the combination of a
phased-array body coil and spine array coil for signal reception. Baseline MR
images, including a respiratory-triggered T2-weighted turbo spin-echo sequence
and a breath-hold T1-weighted fast low-angle shot (FLASH) sequence, were
obtained.
Dynamic imaging, a volumetric interpolated breath-hold examination (VIBE) with a SENSE with a reduction factor of 2, was performed using the following parameters: TR/TE, 4.3/2.0; flip angle, 12°; bandwidth, 450 Hz/pixel; matrix, 256 (read) x 135 (phase) x 40-44 (partition); effective slice thickness, 3.5-4 mm; and field of view, 32-35 cm [13]. The SENSE with a reduction factor of 2 was applied in an in-plane phase-encoding direction of 3D dynamic imaging. SENSE allowed acquisition of folded images in each receiver channel by reduced k-space sampling and then unwrapped those images in the reconstruction process from a reference scan [29]. All images were obtained in the axial plane.
Dynamic imaging was performed before and after administration of gadobenate dimeglumine. The determination of the scan delay for image acquisition timing was achieved using a test-bolus technique in which 1 mL of gadobenate dimeglumine was injected with a saline flush and the vessel of interest (abdominal aorta) was scanned approximately once per second. Dynamic images, consisting of early arterial (mean, 25 sec), late arterial (mean, 35 sec), portal (70 sec), and equilibrium (180 sec) phases, were acquired after a bolus injection of 0.1 mmol/kg of gadobenate dimeglumine. The contrast material was injected into the antecubital vein using an automated injector (Spectris MR, Medrad Europe), and a 20-mL saline flush followed the contrast injections. Early and late arterial phase images were obtained consecutively for approximately 22 sec during a single breath-hold. However, the portal and equilibrium phase images were acquired during separate breath-holds of 10-11 sec each.
MDCT
CT examinations were performed with an MDCT scanner (Sensation 16, Siemens
Medical Solutions) with 16 detector rows. Images were acquired through the
liver in a craniocaudal direction with 1.5 x 16 beam collimation. Other
scanning parameters were as follows: 150 mAs, 120 kVp, 1.5-mm detector
collimation, table speed of 24 mm per rotation, reconstruction interval of 3.0
mm, and a 0.5-sec gantry rotation time. Before the examinations, patients were
instructed to hold their breath to avoid motion artifact.
Unenhanced MDCT was performed starting from the top of the liver in a cephalocaudal direction. After acquisition of unenhanced liver images, contrast medium with an iodine concentration of 370 mg I/mL (Ultravist 370, Schering) was administered using a power injector (Multilevel CT, Medrad). The contrast medium was injected at a rate of 3 mL/sec through an 18-gauge plastic IV catheter placed in an antecubital vein. The volume of contrast medium delivered varied depending on the body weight of each patient (2 mL/kg of body weight); therefore, the total volume of contrast medium administered was 110-150 mL (mean, 120 ± 10 [SD] mL). Determination of the scanning delay for arterial phase imaging was achieved using an automatic bolus-tracking technique. The single-level monitoring low-dose scanning (120 kVp, 20 mA) was initiated 10 sec after contrast injection. The contrast enhancement was automatically calculated in the ROI cursor placed over the vessel of interest (abdominal aorta), and the level of trigger threshold was set at an increase of 80 H. Five seconds after the trigger threshold was reached, early arterial phase scanning began automatically. Dynamic imaging consisted of four phases—that is, early and late arterial phases, portal phase, and equilibrium phase. The mean scanning time delays of the early and late arterial phases were 25 and 38 sec, respectively. The early and late arterial phases were acquired consecutively during each breath-hold. The portal venous phase and equilibrium phase were acquired 70 and 180 sec after administration of contrast medium, respectively. The acquisition time for each phase was 5-7 sec according to the scanning range.
Imaging Analysis
Three gastrointestinal radiologists who are experienced in interpreting
liver images in their daily clinical practice for at least 5 years reviewed
the images both independently and separately; they were unaware of the design
of the present study. These observers knew that the patients had liver
cirrhosis and were at risk for hepatocellular carcinoma, but they were unaware
of the presence and location of liver lesions and of the results of the other
imaging examinations. Two separate sets of images were analyzed—that is,
the 3D dynamic gadobenate dimeglumine-enhanced images (unenhanced T1-weighted
images and early arterial, late arterial, portal, and equilibrium phase
images) and the MDCT images (unenhanced, early arterial, late arterial,
portal, and equilibrium phases). To minimize any learning bias, we scheduled a
3-week interval between the two interpretation sessions, and the images were
randomly presented regardless of whether they were CT or MR images—that
is, without any order between CT and MRI. All images were reviewed on a 2,000
x 2,000 PACS workstation (Marotech) monitor.
The criteria for hepatocellular carcinoma on both contrast-enhanced MDCT and MRI were defined as a nodule showing enhancement foci during the early or late arterial phases (or both) and washout during the portal venous and equilibrium phases. In addition, the following lesions were regarded as hepatocellular carcinomas: hypoattenuated nodules in any phase of dynamic images with a mosaic pattern, pertitumoral capsule, or fatty metamorphosis and a nodule larger than 1 cm that was predominantly hypoattenuating during all dynamic phases [30-32].
Each observer recorded the presence and segmental location of the lesions, assigning each a confidence level on a 4-point scale: 1, probably not present; 2, possibly present; 3, probably present; and 4, definitely present. Before image interpretation, all observers were aware that the sensitivity calculations were based on only those lesions awarded a confidence rating of 3 or 4. To achieve an accurate correlation between the findings of the scored lesions and the findings of the gold standard, including intraoperative sonography, Lipiodol CT with hepatic angiography, CT angiography, and follow-up images, each observer recorded the individual image number and the segmental location and size of each lesion. For patients with multiple lesions in the same segment, the observers added information regarding the size and location of the lesion within each segment to avoid confusion in the data analysis. A study coordinator correlated the scored lesions by the observers and the standard of reference on the basis of the description regarding the size and location of the lesion.
Statistical Analysis
Based on the reviews of the three observers, alternative-free response ROC
curve analysis was performed on a tumor-by-tumor basis
[33]. For each imaging set, an
alternative-free response ROC curve was fitted to each observer's confidence
rating data using a maximum likelihood estimation program (ROCKIT 0.9B, C. E.
Metz) [34,
35]. The diagnostic accuracy
of each imaging set for each observer and the composite data were calculated
by measuring the area under the alternative-free response ROC curve (A index,
Az). The differences between imaging sets in terms of the mean
Az values were statistically analyzed using the two-tailed
Student's t test for paired data. The sensitivity and positive
predictive values for each image set were then calculated. The sensitivity of
each observer and of each set of images was determined by the number of
lesions assigned a confidence level of 3 or 4 from among the 53 hepatocellular
carcinomas. To provide a range of plausible differences in sensitivity, we
also calculated the 95% confidence intervals (CIs)
[36]. The sensitivity and
positive predictive values of both MR and CT images were compared using the
McNemar test. A two-tailed p value of less than 0.05 was considered
to indicate a significant difference.
To assess interobserver agreement for the evaluation of the two imaging techniques, we calculated the kappa statistic for multiple observers [37]. The agreement among blinded observers is reported in terms of kappa values: those greater than zero indicate a positive correlation; less than 0.20, positive but poor agreement; 0.21-0.40, fair agreement; 0.41-0.60, moderate agreement; 0.61-0.80, good agreement; and greater than 0.81, excellent agreement. The significance of the difference between the kappa values of the two imaging techniques was tested using the z test. The level for statistical significance was a p value of less than 0.05. The statistical analyses were calculated using SPSS 8.0 computer software (Statistical Package for the Social Sciences).
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The sensitivity and positive predictive values from each observer for each image set for the detection of hepatocellular carcinoma are summarized in Table 2. Overall, there was a trend toward increased sensitivity for gadobenate dimeglumine-enhanced MRI compared with MDCT, and the sensitivities of gadobenate dimeglumine-enhanced MRI in all observers were significantly higher than those of MDCT (Figs. 1A, 1B, 1C, 1D, 1E, and 1F) (observer 1, p = 0.016; observer 2, p = 0.004; observer 3, p = 0.008). Of the 53 hepatocellular carcinomas, gadobenate dimeglumine-enhanced MRI allowed detection of 50 lesions (sensitivity, 94.3%; 95% CI, 84.3-98.8%) by observers 2 and 3 and 49 lesions (sensitivity, 92.5%; 95% CI, 91.8-97.9%) by observer 1. MDCT allowed detection of 42 lesions (sensitivity, 79.2%; 95% CI, 65.9-89.1%) by observers 1 and 3 and 41 lesions (sensitivity, 77.4%; 95% CI, 63.8-87.7%) by observer 2. Most of the false-negative lesions except two on both MDCT and MRI were 1.0 cm or smaller, so sensitivities of gadobenate dimeglumine-enhanced MRI (82.4%, 95% CI, 56.6-96.0% for observers 1 and 2; 88.2%, 95% CI, 63.5-98.2% for observer 3) were significantly higher than those of MDCT (47.1%, 95% CI, 23.0-72.1% for observers 1 and 3; 41.2%, 95% CI, 18.5-67.0% for observer 2) for small hepatocellular carcinomas of 1.0 cm or less. However, for lesions larger than 1.0 cm, sensitivities of MDCT (94.4%; 95% CI, 81.3-99.2%) and MRI (97.2%; 95% CI, 85.4-99.5%) were similar for all observers.
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Among the 53 lesions, two (0.6 and 2.0 cm) were not detected by any of the observers on either gadobenate dimeglumine-enhanced MRI or MDCT. There were also five small lesions (0.6-1.2 cm in diameter) that were not detected on MDCT by any observer but were detected on gadobenate dimeglumine-enhanced MRI (Figs. 2A, 2B, 2C, and 2D). Of these lesions, three (0.6, 0.8, and 1.0 cm) were confirmed by surgery and the remaining two (1.0 and 1.2 cm) were confirmed by imaging-guided biopsy, hepatic angiography, and Lipiodol CT. On the contrary, no lesions were detected only on MDCT but not on MRI by all three observers. When we retrospectively analyzed five lesions missed on MDCT by all observers, four lesions were misinterpreted as pseudolesions because they had faint high and low attenuation with poor conspicuity on both the arterial and equilibrium phase images, respectively, whereas they were more conspicuous on MRI (Figs. 1A, 1B, 1C, 1D, 1E, and 1F). The remaining lesion appeared to exhibit only tiny areas of irregular low attenuation on MDCT images but clearly had high signal intensity on the gadobenate dimeglumine-enhanced arterial phase images (Figs. 2A, 2B, 2C, and 2D).
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For gadobenate dimeglumine-enhanced MRI and MDCT, the kappa values were 0.607-0.806 for the three observers. The mean kappa values for MDCT and MRI were 0.777 (95% CI, 0.680-0.875) and 0.693 (95% CI, 0.592-0.793), respectively, thus indicating good or excellent interobserver agreement regarding the presence of lesions (p < 0.0001) (Table 3). The difference between the two kappa values for each imaging technique was not significant (p = 0.24).
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Based on this background, we compared the diagnostic performance of gadobenate dimeglumine-enhanced 3D dynamic MRI with that of MDCT with 16 detector rows for detecting hepatocellular carcinoma in the same patients. In addition, we attempted to achieve robust imaging using a 16-MDCT scanner and a 1.5-T MRI unit equipped with the parallel acquisition technique. We also used equivalent imaging parameters in terms of temporal resolution and slice thickness—that is, a slice thickness of 3-4 mm—and four dynamic phases, including double arterial phases, which potentially could be the optimum parameter for dynamic liver imaging. Furthermore, to increase the sensitivity of MDCT to tumor enhancement, we used a highly concentrated iodine contrast agent (370 mg I/mL) for MDCT and gadobenate dimeglumine, which has a twofold T1 relaxivity over conventional gadolinium chelates, for liver MRI [25, 39]. A previous study by Furuta et al. [39] showed that a higher iodine concentration (370 mg I/mL) in the contrast medium improves contrast enhancement of the liver parenchyma on portal phase and late phase images, improves overall image quality, and helps to improve the diagnostic accuracy of multiphase dynamic MDCT for detecting liver diseases in patients with chronic liver disease. To our knowledge, our study is the first comparative study of dynamic MRI with SENSE and 16-MDCT using the most recently established technique for the detection of hepatocellular carcinoma.
On the basis of alternative-free response ROC analysis, this study revealed that all three observers achieved slightly higher diagnostic performance with gadobenate dimeglumine-enhanced MRI (mean Az, 0.87 ± 0.03) than with MDCT (mean Az, 0.83 ± 0.04), but the difference was not statistically significant (observer 1, p = 0.68; observer 2, p = 0.38; observer 3, p = 0.63). However, the sensitivities in detecting hepatocellular carcinoma for all three observers were significantly higher with gadobenate dimeglumine-enhanced 3D dynamic MRI than with MDCT (p < 0.05). This significant difference in overall detectability of hepatocellular carcinoma was attributed to the difference between the two image techniques for detecting small lesions of 1.0 cm or less; however, for lesions larger than 1.0 cm, the sensitivities of the two image techniques were similar. For all observers, five lesions in five patients were not detected with MDCT but were detected with gadobenate dimeglumine-enhanced MRI. Despite the higher sensitivity of gadobenate dimeglumine-enhanced MRI over MDCT, the insignificant difference in Az values between the two imaging techniques may be attributed to the higher false-positive rate of gadobenate dimeglumine-enhanced MRI compared with that of MDCT.
The higher sensitivity of gadobenate dimeglumine-enhanced MRI compared with that of MDCT in the present study may be explained by the following two factors. First, we believe that the almost twofold higher T1 relaxivity of gadobenate dimeglumine relative to a conventional gadolinium-based agent was the major contributing factor to the higher diagnostic capability of gadobenate dimeglumine-enhanced MRI over MDCT for detecting hepatocellular carcinoma [40]. This explanation may be possible in that the five lesions in our study detected only on MRI showed bright nodular enhancement on arterial phase gadobenate dimeglumine-enhanced MRI but not on MDCT, which showed faint enhancement or no enhancement on the arterial phase images. Because nearly the same techniques for the acquisition of arterial phase images and a similar slice thickness were used in both MDCT and MRI, the inappropriate timing of the arterial phase and partial volume averaging on MDCT may not be a correct explanation. Another possible reason for our study results may be the inherently excellent soft-tissue contrast of MRI together with the fat saturation used in the VIBE sequence [41]; that is, the inherently inferior soft-tissue contrast of CT, despite the higher in-plane resolution of CT (512 x 512) compared with MRI (256 x 135), might be the unsolved limitation in evaluating small liver lesions. In our study, we reviewed only dynamic VIBE images before and after administration of gadobenate dimeglumine.
In the present study, gadobenate dimeglumine-enhanced dynamic MRI had not only a higher sensitivity for the detection of hepatocellular carcinoma but also a higher false-positive diagnosis rate, perhaps related to arterioportal shunts. This may be explained by the fact that the combination of the higher enhancing capability of gadobenate dimeglumine and the VIBE sequence may maximize the sensitivity of detecting an enhancing hepatic lesion regardless of arterioportal shunt or true hypervascular liver lesion. Therefore, our data partially agree with the report of Ichikawa et al. [42], which explains that the increased enhancing effect of the faster injection of iodine contrast material on CT may improve the detection of hypervascular hepatocellular carcinoma and that of enhanced false-positive lesions. In addition, considering the possibility of the increased radiation exposure of patients with chronic liver disease who are at high risk for hepatocellular carcinoma but who should undergo periodic screening examination by liver imaging, the preferred choice of liver MRI over MDCT is logical. Because, in our study group, the mean body weight and height were 62.3 kg (range, 45-75 kg) and 170 cm (range, 153-182 cm), respectively, 150 mAs (300 mA, 0.5 sec of rotation time) was appropriate for high-quality MDCT. A higher millisecond-ampere setting may be necessary in North American populations who are expected to have a higher average body mass index.
Our study has some limitations. First, not all of the lesions were surgically confirmed, thereby potentially resulting in an overestimation of the actual sensitivity of both imaging techniques by minimizing the number of false-negative lesions. However, acquiring surgical confirmation of all hepatocellular carcinomas would have been difficult given that there are relatively few surgical candidates because of the lack of hepatic reserve resulting from coexisting advanced cirrhosis, widespread intrahepatic involvement, the concomitance of other diseases, and advanced patient age [43, 44]. Furthermore, considering that regenerating or dysplastic nodules cannot easily be differentiated from hepatocellular carcinoma on intra-operative sonography, hepatic resection using intraoperative sonography as a tool to localize the lesions may not be perfect for determining the presence of hepatocellular carcinoma. We assume that the most precise determination of the total number of lesions is possible only through liver transplantation and matched-pair analysis performed to verify that the lesions detected on MRI correspond to the lesions in the resected liver specimen.
A second criticism could be the high prevalence of patients with hepatitis B virus in our study group. Because many patients enrolled in our study had Child-Pugh class A cirrhosis, the results in our study may not be generalized to North American populations who usually have hepatocellular carcinoma in the setting of advanced liver cirrhosis. Indeed, several previous studies that estimated the sensitivity of preoperative CT or MRI for detecting hepatocellular carcinoma by comparing CT or MRI findings with the explanted livers showed that both techniques were insensitive for the detection of neoplasm in cirrhotic livers. Lastly, although double arterial phase scanning has the potential advantage of improving the detection of hypervascular hepatocellular carcinoma, it also poses the risk that neither phase is optimal for arterial phase imaging, as shown in a previous study [11]. However, in our study using an autonomic bolus-tracking technique, the mean time delay for late arterial phase imaging was 38 sec, which does not differ from the ideal timing for arterial phase imaging that has been reported in previous studies [45, 46].
In conclusion, multiphasic dynamic liver images with high temporal and spatial resolution made possible by recent technologic advances were obtained using both MDCT and MRI. For detecting small hepatocellular carcinomas of 1.0 cm or less, gadobenate dimeglumine-enhanced MRI using VIBE and SENSE showed greater sensitivity than did 16-MDCT with comparable imaging parameters, such as the acquisition of double arterial phases and thin sections. We believe that the combination of a newly developed 3D dynamic MRI sequence using SENSE and an MRI contrast agent with high T1 relaxivity could better highlight the inherent strong points of MRI over CT in this study. However, caution is required in the interpretation of gadobenate dimeglumine-enhanced MRI because of the greater possibility of detecting false-positive lesions relative to MDCT.
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