Proton spectroscopic imaging (Dixon method) of the liver: clinical utility

Small hepatocellular carcinoma: assessment with T1-weighted spin-echo magnetic resonance imaging with and without fat suppression

OBJECTIVE

We examined the detectability of small hepatocellular carcinomas (HCCs) and the factors that affect hyperintensity of small HCC on T1-weighted images (T1W) by using T1-weighted fat-suppressed images (T1FS).

METHODS

Thirty-nine HCCs (29 patients) measuring 30 mm or less were enrolled. The mean size of HCCs was 21.0+/-4.9 mm. Spin-echo T1W, T2-weighted images (T2W), and T1FS were obtained using a 1.5 T system. We evaluated the detectability in each sequence by receiver-operating-characteristic (ROC) analysis and the tumor-to-hepatic parenchyma contrast-to-noise ratio (CNR), the variance in the detectability among all interpreters with each sequence, and the presence or absence of improvement in the detectability by interpreting T1FS in addition to conventional T1W plus T2W. The contents of fat, copper, and iron in histologically diagnosed HCCs showing hyperintensity on both T1W and T1FS were measured. For determination of heavy metals, we used a particle induced X-ray emission analytical instrument.

RESULTS

ROC analyses revealed that T1FS were superior to T1W and T2W in detecting small HCCs (0.900+/-0.017 for T1FS, 0.859+/-0.019 for T1W, and 0.745+/-0.030 for T2W). The detectability by interpreting T1FS in addition to conventional T1W plus T2W was improved (0.931+/-0.013 for the conventional images and 0.973+/-0.008 for the conventional images plus T1FS, P<0.001). The detected lesions on T1FS demonstrated favorable CNR values. The copper content in the cancer and the ratio of the copper content in the cancer to that in the non-cancerous tissue were 275.4+/-219.0 microg/g dry weight, 6.9+/-5.5 in HCCs showing hyperintensity on both T1W and T1FS. Both were significantly higher (P<0.05).

CONCLUSION

T1FS showed excellent sensitivity and specificity in detecting small HCCS irrespective of the experience of interpreters. The use of T1FS suggested the involvement of copper might be one of the factors in hyperintensity of HCCs on T1W.

Nondiffuse fatty change of the liver: discerning pseudotumor on MR images enhanced with ferumoxides-initial observations

PURPOSE

To clarify the findings of nondiffuse fatty change of the liver on ferumoxides-enhanced magnetic resonance (MR) images.

MATERIALS AND METHODS

Of 202 patients who underwent ferumoxides-enhanced MR imaging, eight who had nondiffuse fatty change of the liver at computed tomography (CT) were examined as study subjects. MR imaging findings before and 1 hour after ferumoxides administration were compared with CT findings.

RESULTS

Focal fatty areas of the liver showing low attenuation on CT images were depicted as areas of relatively high intensity on the ferumoxides-enhanced T1-weighted images in all patients. On enhanced T2-weighted images, focal fatty change showed relatively high intensity in three and isointensity in one of the four patients. Focal spared areas appearing as areas of relatively high attenuation on CT images were depicted as areas of relatively low intensity on the ferumoxides-enhanced T1- and T2-weighted images in all patients.

CONCLUSION

Although prior reports of hepatic MR imaging with ferumoxides indicated that there is accumulation of ferumoxides within focal fatty areas that are no longer seen after the administration of contrast medium, this study revealed that focal fatty change and focal spared areas of fatty liver may be pseudotumors because of the relatively high intensity of fatty areas of the liver. Radiologists can distinguish these conditions from hepatic tumors by using the opposed-phase gradient-echo sequence or the fat-saturation technique.

Fast magnetic resonance imaging of liver

Recent magnetic resonance (MR) units with a stronger gradient system have allowed various fast MR imaging techniques to develop. These fast scan techniques have easily realized breath-holding acquisition in the liver and the image quality has been greatly improved without sacrificing spatial resolution. The majority of the fast imaging techniques have been devoted to T2-weighted imaging to obtain useful T2-weighted images in the shortest possible time. Among the fast sequences, fast spin-echo (FSE) sequence is the most promising technique and allows high-quality T2-weighted images with reduced motion artifacts. However, FSE sequences using multiple refocused pulses may essentially realize only poor soft-tissue contrast due to magnetization transfer and T2-filtering effects, and therefore, echo-planar (EP) imaging is expected to provide high image contrast. In addition, single-shot EP imaging allows even diffusion-weighted (DW) and perfusion-weighted (PW) imaging in the liver due to its short scanning time. Recent development of fast gadolinium-enhanced 3D MR angiography has also impacted liver imaging. Combined with such gadolinium-enhanced 3D-MRA sequences and zerofilling image interpolation technique, biphasic gadolinium-enhanced 3D-MRA (whole-liver dynamic MR imaging in the arterial phase and MR portography in the portal phase) can be obtained.

Hepatic metastases

Developments in ultrasound, CT scan, and MR imaging have increased our ability to detect and characterize focal liver lesions. Advances in the medical and surgical treatment of secondary liver tumors have continued to challenge these advances in radiology. A successful outcome depends on knowledge of the size and location of the tumor burden, and accurate radiologic assessment is crucial to identify those subgroups who may benefit from surgery and to prevent unnecessary radical surgery in those likely to gain only a short-term benefit.

Comparison between in-phase and opposed-phase T1-weighted breath-hold FLASH sequences for hepatic imaging

PURPOSE

Our goal was to compare in-phase (IP) and opposed-phase (OP) sequences for GRE breath-hold hepatic imaging.

METHOD

Non-contrast-enhanced IP and OP GRE breath-hold images were obtained in 104 consecutive patients referred for abdominal MRI at 1.0 T. For both sequences, the TR, FA, matrix, FOV, slice thickness, interslice gap, and measurements were kept constant. Images were compared quantitatively [liver/spleen and liver/lesion signal difference/noise ratio, (SD/N)] and qualitatively (artifacts, lesion detection and conspicuity, and intrahepatic anatomy).

RESULTS

There was no statistically significant difference when comparing IP and OP sequences for liver/spleen and liver/lesion SD/N or for the qualitative parameters. In patients with fatty infiltration, the OP sequences yielded substantially lower values for liver/spleen and liver/lesion SD/N (0.9 and -1.2, respectively) than the IP sequences (20 and 17, respectively). Furthermore, in several cases with fatty infiltration, many more lesions were identified using IP images.

CONCLUSION

The use of IP and OP GRE sequences provides complementary diagnostic information. Focal liver lesions may be obscured in the setting of fatty infiltration if only OP sequences are employed. A complete assessment of the liver with MR should include both IP and OP imaging.

Enhanced tumor detection in the presence of fatty liver disease: cell-specific contrast agents

It is assumed that hepatobiliary, cell-specific contrast agents will be adversely affected by the presence of diffuse liver disease. The diagnostic efficacy for tumor detection in the presence of fatty liver disease was experimentally studied at contrast-enhanced magnetic resonance (MR) imaging with manganese-DPDP (N,N'-dipyridoxylethylenediamine-N,N'-diacetate 5,5'-bis[phosphate]) and gadobenate dimeglumine (Gd-BOPTA/dimeg) and compared with conventional and chemical shift imaging. Carcinosarcoma was implanted into the liver of rats, and fatty liver was induced with L-ethionine. Without contrast agents, the tumor-fatty liver contrast-to-noise ratio (C/N) was increased on T1-weighted and decreased on T2-weighted MR images relative to tumor-bearing control rats without fatty liver. Chemical shift imaging (phase-contrast method) increased the tumor-fatty liver C/N from 2.3 +/- 1.0 to 6.1 +/- 1.7 (P < .001). Mn-DPDP and Gd-BOPTA/dimeg increased the tumor-fatty liver C/N from -5.4 +/- 1.6 to -11.0 +/- 1.9 and -9.8 +/- 3.4, respectively (P < .001). The hepatobiliary, cell-specific contrast agents were equally effective in both fatty and non-fatty liver and outperformed both chemical shift and conventional MR imaging in detecting liver tumors.

Fat suppression techniques in MR imaging of mature ovarian teratomas: comparison with CT

OBJECTIVE

The aim of this study is to analyze the ability of MR fat suppression techniques to characterize fat components of ovarian mature cystic teratomas (MCT) shown by CT.

SUBJECTS AND METHODS

MR images of eight MCTs of the ovary were obtained using standard sequences followed by a SPIR (spectral presaturation with inversion recovery) sequence in six cases and by Dixon sequences in two cases. In all cases correlation with CT and pathologic findings was achieved.

RESULTS

MR fat suppression sequences showed to be as accurate as CT in detecting fat inside the cystic part of the teratomas (8/8).

CONCLUSION

MR fat suppression sequences should be performed when presence of fat is suspected on images of ovarian tumors produced by standard MR sequences.

Preoperative evaluation of patients for liver resection. Appropriate CT imaging

OBJECTIVE

The authors determined which combination of computed tomography scans is most helpful for preoperative assessment of patients with liver tumors.

SUMMARY BACKGROUND DATA

Multi-institutional studies have shown that the most important prognostic factors for selection of patients with metastatic colorectal cancer considered for liver resection are: Dukes' stage of primary tumor, the number of hepatic metastases if greater than 3, the presence of extrahepatic cancer, and the ability to resect tumors with an adequate margin (> 1 cm.) Therefore the ability to predict the presence of extrahepatic disease and the number and location of hepatic tumors are important in these patients.

METHODS

One hundred and nine consecutive patients with evidence of hepatic tumors were evaluated by computed tomography with arterial portography (CTAP) and abdominal computed tomography after a 4-hour delay (CT-D). Results of these studies and conventional computed tomography (CT-C) were compared with findings at operation.

RESULTS

CTAP proved to be the most sensitive test for assessing distribution of intrahepatic disease. CT-D was no more sensitive than CT-C for the detection of hepatic or extrahepatic disease.

CONCLUSIONS

CT-C in concert with CTAP provides the most reasonable CT evaluation of patients considered for operation for the treatment of hepatic tumors.

Diagnosis of fatty liver with MR imaging

The diagnosis of fatty liver with magnetic resonance (MR) imaging was evaluated in experimental rat models of simple fatty infiltration and fatty liver with hepatocellular injury. T1 and T2 were measured ex vivo and correlated with the histologic degree of fatty infiltration. Enhancement of fatty liver with four different cells-specific contrast agents was studied with ex vivo relaxometry and in vivo MR imaging. Quantitative analysis of conventional and chemical shift MR images was correlated with biochemically determined fat content of the liver. Diet-induced simple fatty infiltration of the liver caused a decrease in T1 of 15%, whereas the T1 of L-ethionine-induced fatty liver with hepatocellular injury increased by 12%. T2 showed a positive correlation with the degree of fatty infiltration in both models. Cell-specific hepatobiliary contrast agents showed the same liver uptake and relaxation enhancement in fatty livers as in normal livers. Conventional T1-weighted images and chemical shift images showed good correlation (r = .83 and .80, respectively) between signal intensity and the degree of fatty infiltration. However, only chemical shift imaging was reliable in the diagnosis of fatty liver.