Focal liver lesion detection and characterization: Comparison of non-contrast enhanced and SPIO-enhanced diffusion-weighted single-shot spin echo echo planar and turbo spin echo T2-weighted imaging

PurposeTo compare lesion conspicuity and image quality between single-shot spin echo echo planar imaging (SS SE-EPI) before, immediately and 5 min after intravenous (IV) injection of superparamagnetic iron oxide (SPIO) for detecting and characterizing focal liver lesions (FLLs).Materials and methodsTwenty-five patients suspected for colorectal liver metastases were prospectively included. Lesion detection and characterization were compared between all SS SE-EPI and T2-weighted turbo spin echo (T2w TSE) sets (two-sided Fisher’s exact test). Image quality and lesion conspicuity were compared for SS SE-EPI sets using rank order statistic (RIDIT). Reference standard comprised of surgery, biopsy and/or follow-up.ResultsReference standard demonstrated 18 benign and 43 malignant FLLs. Best lesion detection (p < 0.05) was achieved with non-contrast-enhanced SS SE-EPI. Lesion characterization was best using all T2w TSE sequences. Best image quality and lesion conspicuity (p < 0.05) was achieved with non-contrast-enhanced SS SE-EPI.ConclusionNon-contrast-enhanced SS SE-EPI was best for lesion detection. SS SE-EPI sequences were not useful for lesion characterization (differentiation between benign and malignant lesions). Unenhanced SS SE-EPI did not allow differentiation especially as many benign FLLs were hyperintense on the highest b-value images. Combining unenhanced and SPIO-enhanced SS SE-EPI performed better but still was not clinically useful due to variable degree of uptake and vascular pooling of SPIO for (especially) benign FLLs. T2w TSE with SPIO-enhancement was needed for characterization.     

Focal liver lesions: characterization with quantitative analysis of T2 relaxation time in TSE sequence with double echo time

PURPOSE: To evaluate the accuracy of calculation of T2 relaxation time with simplified algorithm in characterization of liver focal lesions with Turbo Spin Echo (TSE) T2-weighted sequences with double echo time (TE). MATERIALS AND METHODS: We carried out a retrospective analysis of 113 hyperintense hepatic focal lesions in T2-weighted sequences (52 metastases, 51 hemangiomas and 10 cysts). We have employed a single TSE T2-weighted sequence with effective TE of 83 and 165 msec and turbo factor 9. Signal intensity (IS) of each lesion was measured on different TE. Using these values, we calculated T2 relaxation time by the following simplified algorithm: T2(ms)=(TE2-TE1)/ (lnIS1-lnIS2). T2 relaxation time has been correlated with the final diagnosis, obtained by percutaneous biopsy, surgical resection or three months follow-up. RESULTS: The mean T2 relaxation time for metastases was 108,7 msec (+/-30), for hemangiomas 166,5 msec (+/- 29) and for cysts 312,4 msec (+/-19). The difference between the mean T2 relaxation time for metastases and hemangiomas was statistically significant (p<0.0001). Most metastases were best characterized between the threshold value of 130 and 140 msec. The values of specificity and sensitivity of the diagnosis of malignant hepatic lesion was respective 0,86 and 0,88. All false positive diagnoses were hemangiomas of less than one centimeter. CONCLUSIONS: Introducing double echo time TSE sequences in the protocol of liver study concurs to obtain high diagnostic accuracy in the characterization of the hepatic lesions. The quantitative analysis of T2 represents a useful additional instrument to the morphologic analysis in discrimination between hepatic lesions and can be carried out by TSE sequences with elevated reliability reducing the imaging time compared with conventional sequences. The evaluation of hepatic lesions of less than one centimeter should always include analysis of dynamic gadolinium-contrast images.     

Focal liver lesion detection and characterization: comparison of non-contrast enhanced and SPIO-enhanced diffusion-weighted single-shot spin echo echo planar and turbo spin echo T2-weighted imaging

Purpose

To compare lesion conspicuity and image quality between single-shot spin echo echo planar imaging (SS SE-EPI) before, immediately and 5 min after intravenous (IV) injection of superparamagnetic iron oxide (SPIO) for detecting and characterizing focal liver lesions (FLLs).

Materials and methods

Twenty-five patients suspected for colorectal liver metastases were prospectively included. Lesion detection and characterization were compared between all SS SE-EPI and T2-weighted turbo spin echo (T2w TSE) sets (two-sided Fisher’s exact test). Image quality and lesion conspicuity were compared for SS SE-EPI sets using rank order statistic (RIDIT). Reference standard comprised of surgery, biopsy and/or follow-up.

Results

Reference standard demonstrated 18 benign and 43 malignant FLLs. Best lesion detection (p < 0.05) was achieved with non-contrast-enhanced SS SE-EPI. Lesion characterization was best using all T2w TSE sequences. Best image quality and lesion conspicuity (p < 0.05) was achieved with non-contrast-enhanced SS SE-EPI.

Conclusion

Non-contrast-enhanced SS SE-EPI was best for lesion detection. SS SE-EPI sequences were not useful for lesion characterization (differentiation between benign and malignant lesions). Unenhanced SS SE-EPI did not allow differentiation especially as many benign FLLs were hyperintense on the highest b-value images. Combining unenhanced and SPIO-enhanced SS SE-EPI performed better but still was not clinically useful due to variable degree of uptake and vascular pooling of SPIO for (especially) benign FLLs. T2w TSE with SPIO-enhancement was needed for characterization.     

Magnetic resonance imaging of the liver: true fast imaging with steady state free precession sequence facilitates rapid and reliable distinction between hepatic hemangiomas and liver malignancies

OBJECTIVE: To assess the capability of the true fast imaging with steady state free precession (true FISP) sequence in the distinction between hemangiomas and malignant liver lesions. METHODS: Sixty-eight patients with 45 hemangiomas and 51 liver malignancies were included in this study. A 1.5-T magnetic resonance system and a phased-array body coil were used. In addition to true FISP, breath-hold and fat-suppressed, T2-weighted, half-Fourier single-shot turbo spin echo (HASTE) and both unenhanced and gadolinium (Gd)-enhanced T1-weighted sequences were acquired. Two radiologists evaluated the magnetic resonance images independently in a blinded fashion. Interobserver variations with true FISP and HASTE were determined. Lesion contrast-to-noise ratios were calculated from true FISP images. RESULTS: With true FISP, readers 1 and 2 made a correct distinction between hemangiomas and liver malignancies in 43 of 45 (96%) cases and 40 of 45 (89%) cases, respectively. The kappa value was 0.65. With HASTE, the success rates were 40 of 45 cases (89%) and 36 of 45 cases (80%), respectively, and the kappa value was 0.33. With a Gd-enhanced T1-weighted sequence, the correct classifications were 35 of 45 cases (78%) and 37 of 45 cases (82%), respectively. All hemangiomas appeared as bright and well-demarcated lesions on true FISP images. Malignant liver foci were heterogeneous with unsharp margins and nearly isointense relative to liver. The specificities of true FISP in lesion differentiation were 100% and 98% for readers 1 and 2, respectively. The mean contrast to noise ratio value of hemangiomas was 21.2 (standard deviation [SD] = 9.2), and that of malignant lesions was 4.9 (SD = 3.9). This difference was highly significant (P < 0.0001). CONCLUSION: Noninvasive, rapid, and reliable differentiation between hemangiomas and malignant liver lesions is possible by using the true FISP sequence.     

Quantitative assessment of iron-oxide-enhanced magnetic resonance imaging of the liver: Vessel isointensity is a potential characteristic of liver hemangiomas on late T1-weighted images

PURPOSE: To test whether a new quantitative measure, the tumor-to-vessel ratio, obtained from late post-iron-oxide-enhanced T1-weighted images allows for differentiating hemangiomas from liver metastases or all malignant liver lesions. MATERIAL AND METHODS: Twenty-six patients (mean 57, range 33-79 years) were prospectively studied at 1.5T magnetic resonance imaging (MRI) with a T1-weighted 2D fast low-angle shot (FLASH) sequence (repetition time/echo time/flip angle; 200 ms/4.8 ms/90 degrees ) and a T2-weighted turbo spin-echo sequence (4072 ms/99 ms/180 degrees ). Imaging was carried out before and at intervals up to 18 min after IV injection of Ferucarbotran (Resovist, Schering, Germany). In 19 patients, one representative malignant lesion was analysed. Eleven hemangiomas were evaluated in 7 patients. Two readers performed a consensus reading with a signal intensity measurement in a lesion, normal liver and hepatic veins, from which ratios were computed. RESULTS: On T1-weighted iron-oxide-enhanced MRI of 30 lesions, tumor-to-vessel signal intensity ratios were distinct in hemangiomas (median 1.04, range 0.99-1.10) as opposed to either metastases (0.64, 0.33-0.77; P < 0.05) or all malignant lesions taken together (0.64, 0.33-0.98; P < 0.05), while the tumor-to-liver ratio was not. CONCLUSION: The tumor-to-vessel ratio may help to differentiate between hemangiomas and metastases. A ratio greater than 0.98 allowed differentiating hemangiomas from metastases with a wide safety margin.     

Evaluation of turbo spin echo sequences for MRI of focal liver lesions at 0.5 T

To determine whether turbo spin echo (TSE) sequences can replace conventional T2-weighted spin echo (SE) sequences in MRI of the liver, 40 patients with focal liver lesions were imaged at 0.5 T. A T2-weighted SE sequences (TR/TE 1800/90 ms, number of signals averaged [NEX]=2, scan time=7:16 min), a TSE sequence (TR/TE 1800/90 ms, NEX=4, number of echos per excitation=13, echo spacing=12.9 ms, scan time=4:16 min) and a T1-weighted SE sequence (TR/TE 350/15 ms, NEX=2, scan time=4:21 min) were obtained and image quality, lesion detectability and lesion differentiation were evaluated qualitatively by subjective assessment using scores and quantitatively by lesion-liver contrast-to-noise (CNR) and tumour/liver signal intensity (SI) ratios. The image quality of the TSE sequence was substantially better compared with the T2-weighted SE sequence due to a reduction in motion artefacts and better delineation of anatomical details. Of a total of 158 visible lesions the T1-weighted SE, TSE, and T2-weighted SE sequences showed 91%, 81% and 65% of the lesions, respectively. Thus the TSE sequence depicted 24% (P< 0.001) more lesions than the T2-weighted SE sequence. In all types of pathology the lesion-liver CNR of the TSE sequence was significantly (P< 0.001) higher compared to the CNR of the T2-weighted SE sequence (+ 55–65%), indicating superior lesion conspicuity. Lesion characterization was equally good on the two T2-weighted sequences with no difference in the tumour/liver SI ratio. Using a criterion of tumour/liver SI ratio equal to or higher than 2, haemangiomas larger than 1 cm in diameter could be differentiated from other lesions with a sensitivity and specificity of 95% and 96%, respectively. Our results indicate that the TSE sequence is suitable for replacing the conventional T2-weighted SE sequence in MRI of focal liver lesions.This paper was presented at ECR 1993 Correspondence to: B. Kreft     

Differentiation of hepatic hemangiomas from metastases by dynamic contrast-enhanced MR imaging

Twenty-nine patients with hepatic hemangiomas (n = 14) and hepatic metastases (n = 15) underwent magnetic resonance (MR) imaging prior to and after an intravenous bolus injection of Gd-diethylenetriamine pentaacetic acid (0.2 mmol/kg). Before contrast application, a T2-weighted spin echo sequence (SE 1,600/105) and a T1-weighted gradient echo sequence (GE 315/14/90 degrees pulse angle) were performed. Beginning with injection of the contrast agent, a dynamic study was conducted for 10 min using a moderately T1-weighted gradient echo sequence (GE 40/14/40 degrees) with an acquisition time of 10.2 s per image. Delayed (11 min) and late (60 min) postcontrast images were obtained using a T1-weighted sequence (GE 315/14/90 degrees). In the dynamic study (0-10 min) the hemangiomas were characterized by peripheral contrast enhancement and a subsequent hyperintense fill-in. The metastases showed very mixed patterns of enhancement after contrast administration, and their signal intensity remained low compared with that of the hepatic tissue. In the delayed postcontrast examination (11 min) the hemangiomas had a very high and homogeneous signal intensity and the metastases were characterized by an inhomogeneous, hypointense to isointense signal. The contrast between tumor and liver [signal-difference-to-noise ratio (SD/N)] was higher for all hemangiomas than it was for the metastases. In the T2-weighted precontrast examination, on the other hand, five hemangiomas and seven metastases showed an overlap in the SD/N. The late postcontrast images (60 min) did not yield any further diagnostic information. We conclude that the combination of a dynamic MR study with delayed postcontrast T1-weighted imaging is a useful method of diagnosing hepatic hemangiomas.     

Malignant hepatic tumors: Changes on MRI after hepatic arterial chemoembolization – preliminary findings

This study describes the MR appearances of malignant hypervascular liver lesions pre- and post-hepatic-arterial chemoembolization, with correlation to serial imaging and clinical responses. Eight patients with malignant hypervascular liver lesions underwent pretreatment and posttreatment MR examination on a 1.5-T MR imager. MR sequences included T1-weighted spoiled gradient echo (SGE), T2-weighted fat-suppressed spin echo or turbo spin echo, and dynamic gadolinium-enhanced SGE images. All patients underwent pretreatment, initial posttreatment, and subsequent posttreatment MR studies. The histology of primary tumors included various types of hepatocellular carcinoma (HCC) (four patients: fibrolamellar HCC [one patient], HCC [two patients], mixed HCC/cholangiocarcinoma [one patient]) and liver metastases (four patients: untyped islet cell tumor [two patients], gastrinoma [one patient], carcinoid [one patient]). Response to chemoembolization was determined by three assessments: MR response, serial imaging response, and clinical response. The appearance of MR response to chemoembolization was determined based on the correlation with clinical and serial imaging response. The MR response of lesions that showed good clinical response included: increase in signal intensity on T1-weighted images (three patients), decrease in signal intensity on T2-weighted images (three patients), and negligible or minimal enhancement on immediate postgadolinium images (four patients) after chemoembolization. The most marked change in lesion appearance was observed in lesions < 1 cm, which had intense homogeneous enhancement on pretreatment MR studies and negligible enhancement on initial posttreatment MR examinations. MR response of lesions that showed moderate clinical response demonstrated a variety of lesion appearances from substantial change to minimal change. MR response of lesions that showed poor clinical response demonstrated no change in lesion appearances compared with the pretreatment MR study. Our results demonstrated change in appearance of liver lesions between pre- and post-hepatic-arterial chemoembolization MR studies. MR response correlated with response determined by serial imaging studies and clinical findings.     

Time-to-echo optimization for spin echo magnetic resonance imaging of liver metastasis using superparamagnetic iron oxide particles.

Superparamagnetic iron oxide (SPIO) particles are used as a contrast agent in liver magnetic resonance imaging (MRI). SPIO particles exert their greatest influence on T2-weighted MR signal intensity. The time-to-echo (TE) value that provides optimal contrast has not been systematically studied over the range of clinically relevant field strengths. The purpose of this study was to quantitatively evaluate the TE dependence of the post-SPIO tumor to liver contrast-to-noise ratio (CNR). The hypothesis was that there is a TE that provides an optimal CNR. Subjects having probable metastatic hepatic lesions secondary to colorectal carcinoma were studied. Pre- and post-SPIO images were acquired at TE-effective (TE(eff)) equal to 46, 76, and 106 msec by using a turbo spin echo pulse sequence at 0.2 T and 1.5 T. The CNR for all lesions greater than 1 cm in diameter was determined in pre- and post-SPIO images. A paired statistical design was used to identify TE-related CNR dependencies. The primary findings were as follows. (1) CNR differences attributable to TE(eff) variation over the range of 46-106 msec were less than 34%. For 0.2 T, TE(eff) = 46 msec yielded a statistically significantly greater CNR than did TE(eff) = 76 or 106 msec. The same was true at the higher field strength, but differences were not significant. (2) Signal-to-noise measures suggested that SPIO reduced the lesion signal. (3) Post-SPIO CNR was significantly greater at 1.5 T than at 0.2 T. The observations indicate that over the field strength range of 0.2-1.5 T, CNR differences attributable to the TE(eff) variation, while being statistically significant in some cases, are small relative to those resulting from the SPIO administration.     

Characterization of focal liver lesions with half-Fourier acquisition single-shot turbo-spin-echo (HASTE) and inversion recovery (IR)-HASTE sequences

The half-Fourier acquisition single-shot turbo-spinecho (HASTE) sequence allows for heavily T2-weighted images, and the inversion recovery (IR)-HASTE sequence represents the T1 value of the tissue in a very short time. This study was undertaken to determine whether characterizing focal liver lesions can be made by combination with these very fast sequences. Seventy-four patients (33 cysts, 28 hemangiomas, and 33 malignant solid liver masses [15 metastatic tumors, 14 hepatocellular carcinomas, and 4 cholangiocarcinomasl]) underwent dynamic CT and breath-hold abdominal MRI using turbo-spin-echo (TSE), HASTE, and IR-HASTE sequences with variable TI values on a 1.5-T MR unit. The imaging time for each slice was 2 seconds for HASTE imaging and 2 to 4 seconds for IR-HASTE imaging. Lesion detection and qualitative characterization were evaluated. Quantitative analysis was performed by measuring the contrast-to-noise ratios (CNRs) as well as visual analysis. The inversion time (TI) nulling values were also statistically analyzed. All cystic lesions were detected on both TSE and HASTE imagings. For solid lesions, TSE failed to detect one small solid lesion and HASTE sequence failed to detect three lesions. With HASTE sequences, all cysts and hemangiomas were markedly hyperintense in comparison with malignant solid masses. CNRs of hemangiomas or cysts were significantly higher than those of malignant solid masses (P < .01), and there was no overlap. The TI nulling value was 1,100 ± 100 msec for hemangiomas, 1,900 ± 110 msec for cysts, and 740 ± 140 msec for malignant solid masses. There was no overlap between the TI nulling values of hemangiomas and cysts (P < .01). By combining the CNR from the HASTE sequence and the TI nulling value from the IR-HASTE sequence, complete discrimination among malignant solid masses, hemangiomas, and cysts of the liver could be made. Application of HASTE (representing T2 values) and IR-HASTE (representing T1 values) sequences provided a rapid and reliable imaging method for characterizing focal liver lesions without the use of contrast medium.     

Can a multiphasic contrast-enhanced three-dimensional fast spoiled gradient-recalled echo sequence be sufficient for liver MR imaging?

OBJECTIVE: The purpose of this study was to determine the accuracy of a multiphasic gadolinium-enhanced three-dimensional (3D) fast spoiled gradient-recalled echo sequence alone in the detection and characterization of focal liver lesions compared with a comprehensive liver evaluation using multiphasic gadolinium-enhanced 3D fast spoiled gradient-recalled echo, T1-weighted, and fat-suppressed fast spin-echo T2-weighted sequences. MATERIALS AND METHODS:A retrospective review of abdominal MR imaging examinations in 61 patients was performed. All MR examinations included unenhanced spin-echo T1-weighted, unenhanced fat-suppressed fast spin-echo T2-weighted, and multiphasic gadolinium-enhanced 3D fast spoiled gradient-recalled echo sequences obtained during successive breath-holds. The liver was evaluated for focal lesions first with the 3D spoiled gradient-recalled echo sequences and then, during a separate sitting, with the T1- and T2-weighted sequences. The usefulness of each sequence in the detection and characterization of lesions was recorded. The gold standard for lesion detection and characterization was all three imaging sequences reviewed together. RESULTS:A total of 114 focal liver lesions were identified, 54 of which were simple cysts. The 3D spoiled gradient-recalled echo sequence alone detected 92 (81%) of the 114 lesions, and the T1- and T2-weighted sequences detected 95 (83%) of the 114 lesions. Of the 60 lesions that were not simple cysts, the 3D spoiled gradient-recalled echo sequence alone detected 58 (97%), and T1- and T2-weighted sequences detected 51 (85%). In 24% of the patients with lesions, the T1- and T2-weighted sequences were found to be helpful for the characterization of lesions. CONCLUSION:A multiphasic contrast-enhanced 3D fast spoiled gradient-recalled echo sequence alone detects most of the clinically relevant focal liver lesions. Additional liver examination using both unenhanced T1- and T2-weighted sequences is helpful for lesion characterization but increases the detection rate only minimally.     

Detection and characterization of focal hepatic tumors: A comparison of T2‐weighted MR images before and after the administration of gadoxectic acid

Purpose

To evaluate if T2‐weighted images (T2WI) after administration of gadoxetic acid have diagnostic capability comparable to precontrast T2WI in the detection and characterization of focal liver lesions.

Materials and Methods

Eighty patients with 128 liver lesions (71 hepatocellular carcinomas, 35 metastases, and 22 hemangiomas) underwent gadoxetic acid‐enhanced T1WI and precontrast and postcontrast turbo spin echo‐short tau inversion recovery (TSE‐STIR) and respiratory triggered (RT)‐TSE. The sensitivity for malignancy with combining T2WIs and enhanced T1WIs was evaluated and percentage of signal intensity loss (PSIL) and lesion‐liver contrast to noise ratio (CNR) were calculated for T2WIs. Lesion characterization with T2WIs as solid and nonsolid was evaluated using kappa statistics.

Results

The PSIL was higher with TSE‐STIR than with RT‐TSE (P = 0.0001). The malignancy‐liver CNRs on postcontrast T2WIs were higher than on precontrast T2WIs (P = 0.0001). Sensitivity for malignancy by combining postcontrast T2WIs and T1WIs (93.0% [hepatocellular carcinoma, HCC]; 97.1% [metastases]) was comparable to sensitivity of combining precontrast T2WIs and postcontrast T1WIs (91.6% [HCC]; 88.6% [metastases]). Kappa values for T2WIs indicated excellent agreement (k = 0.935).

Conclusion

Gadoxetic acid‐enhanced T2WIs showed a comparable diagnostic capability to precontrast T2WIs for the detection and characterization of hepatic tumors. J. Magn. Reson. Imaging 2009;30:437–443. © 2009 Wiley‐Liss, Inc.     

Addition of gadolinium chelates to heavily T2-weighted MR imaging: limited role in differentiating hepatic hemangiomas from metastases

OBJECTIVE: The purpose of this study was to determine whether the addition of gadolinium-enhanced imaging to heavily T2-weighted MR imaging of the liver is valuable in differentiating hemangiomas from metastases. The T2 relaxation time was also included in our analysis. SUBJECTS AND METHODS: Fifty-one patients with 52 proven liver lesions (24 hemangiomas and 28 metastases) larger than 1 cm underwent MR imaging at 1.5 T with T2-weighted spin-echo (TR/TE, 3000/80, 160) and gadolinium chelate-enhanced dynamic T1-weighted gradient-recalled echo (80/2.6, 80) pulse sequences. Images were reviewed by observers who were unaware of the patients' clinical history; first, only T2-weighted images were reviewed and then T2-weighted plus dynamic images were reviewed together. The T2 relaxation times were calculated for each lesion. Diagnostic accuracy by each method was compared using receiver operating characteristic analysis. RESULTS: Mean T2 relaxation times were 76 +/- 26 msec for metastases and 133 +/- 25 msec for hemangiomas. The addition of dynamic scanning to the T2-weighted sequence made a statistically significant difference for only one observer (p = 0.03). However, it did not make a statistically significant contribution for either observer when compared with the T2 relaxation time. Although addition of the dynamic images resulted in correct diagnosis of six lesions, three lesions were misdiagnosed after having been correctly characterized on the T2-weighted images alone. CONCLUSION: When optimized T2-weighted images are obtained and the T2 relaxation time is calculated, routine use of gadolinium enhancement for differentiation of hemangiomas from metastases is unnecessary although dynamic scanning is valuable in selected cases.     

Dual contrast enhanced magnetic resonance imaging of the liver with superparamagnetic iron oxide followed by gadolinium for lesion detection and characterization

AIM: Iron oxide contrast agents are useful for lesion detection, and extracellular gadolinium chelates are advocated for lesion characterization. We undertook a study to determine if dual contrast enhanced liver imaging with sequential use of ferumoxides particles and gadolinium (Gd)-DTPA can be performed in the same imaging protocol. MATERIALS AND METHODS: Sixteen patients underwent dual contrast magnetic resonance imaging (MRI) of the liver for evaluation of known/suspected focal lesions which included, metastases (n = 5), hepatocellular carcinoma (HCC;n = 3), cholangiocharcinoma(n = 1) and focal nodular hyperplasia (FNH;n = 3). Pre- and post-iron oxide T1-weighted gradient recalled echo (GRE) and T2-weighted fast spin echo (FSE) sequences were obtained, followed by post-Gd-DTPA (0.1 mmol/kg) multi-phase dynamic T1-weighted out-of-phase GRE imaging. Images were analysed in a blinded fashion by three experts using a three-point scoring system for lesion conspicuity on pre- and post-iron oxide T1 images as well as for reader's confidence in characterizing liver lesions on post Gd-DTPA T1 images. RESULTS: No statistically significant difference in lesion conspicuity was observed on pre- and post-iron oxide T1-GRE images in this small study cohort. The presence of iron oxide did not appreciably diminish image quality of post-gadolinium sequences and did not prevent characterization of liver lesions. CONCLUSION: Our results suggest that characterization of focal liver lesion with Gd-enhanced liver MRI is still possible following iron oxide enhanced imaging.Kubaska, S.et al. (2001). Clinical Radiology, 56, 410-415 Copyright 2001 The Royal College of Radiology.     

Characterization of Focal Liver Lesions with Superparamagnetic Iron Oxide-Enhanced MR Imaging: Value of Distributional Phase T1-Weighted Imaging

Objective

To determine the potential value of distributional-phase T1-weighted ferumoxides-enhanced magnetic resonance (MR) imaging for tissue characterization of focal liver lesions.

Materials and Methods

Ferumoxides-enhanced MR imaging was performed using a 1.5-T system in 46 patients referred for evaluation of known or suspected hepatic malignancies. Seventy-three focal liver lesions (30 hepatocellular carcinomas [HCC], 12 metastases, 15 cysts, 13 hemangiomas, and three cholangiocarcinomas) were evaluated. MR imaging included T1-weighted double-echo gradient-echo (TR/TE: 150/4.2 and 2.1 msec), T2*-weighted gradient-echo (TR/TE: 180/12 msec), and T2-weighted turbo spin-echo MR imaging at 1.5 T before and after intravenous administration of ferumoxides (15 mmol/kg body weight). Postcontrast T1-weighted imaging was performed within eight minutes of infusion of the contrast medium (distributional phase). Both qualitative and quantitative analysis was performed.

Results

During the distributional phase after infusion of ferumoxides, unique enhancement patterns of focal liver lesions were observed for hemangiomas, metastases, and hepatocellular carcinomas. On T1-weighted GRE images obtained during the distributional phase, hemangiomas showed a typical positive enhancement pattern of increased signal; metastases showed ring enhancement; and hepatocellar carcinomas showed slight enhancement. Quantitatively, the signal-to-noise ratio of hemangiomas was much higher than that of other tumors (p < .05) and was similar to that of intrahepatic vessels. This finding permitted more effective differentiation between hemangiomas and other malignant tumors.

Conclusion

T1-weighted double-echo FLASH images obtained soon after the infusion of ferumoxides, show characteristic enhancement patterns and improved the differentiation of focal liver lesions.     

T2-weighted breath-hold MRI of the liver at 1.0 T: Comparison of turbo spin-echo and HASTE sequences with and without fat suppression

To compare the clinical usefulness of T2-weighted breath-hold sequences for imaging the liver, 33 patients with 97 focal hepatic lesions were studied with a 1.0-T scanner by using T2-weighted breath-hold turbo spin-echo (SE) sequences and T2-weighted breath-hold half-Fourier single-shot turbo SE (HASTE) sequences with and without fat suppression. Images were quantitatively analyzed for liver signal-to-noise ratio (SNR) and lesion-to-liver contrast-to-noise ratios (CNR). Qualitative analysis was performed for lesion conspicuity, motion artifacts, and anatomic sharpness of extrahepatic structures. Breath-hold turbo SE imaging with fat suppression showed the highest CNR for cystic lesions and the best lesion conspicuity for cystic and solid lesions among the four sequences. For solid lesions, there was no significant difference of lesion-to-liver CNR between them. HASTE sequence was superior to turbo SE sequences in terms of motion artifacts; however, the usefulness for evaluating focal hepatic lesions was limited compared with turbo SE sequence with fat suppression. Addition of fat suppression was not helpful for HASTE imaging because of decreased lesion conspicuity and extrahepatic details without the advantage of reducing motion artifacts. This study suggests that turbo SE sequence with fat suppression is most useful for breath-hold T2-weighted liver imaging at 1.0 T. Addition of imaging without fat suppression can be considered for evaluating extrahepatic structures. HASTE sequence may have a role for imaging uncooperative patients due to absence of motion artifacts.     

Hepatic hemangiomas vs metastases: MR differentiation at 1.5 T

We retrospectively studied the value of MR imaging at 1.5 T in distinguishing hepatic hemangiomas (n = 15) from metastases (n = 15) by using (1) lesion/liver signal-intensity ratios, (2) contrast/noise ratios, and (3) T2 relaxation time on long TR/TE spin-echo (SE) sequences. Lesion/liver margin sharpness, lesion shape, and overall lesion morphologic pattern were evaluated also. Univariate logistic regression analysis of the quantitative data showed that T2 was the only statistically significant (p less than .02) variable for distinguishing a hemangioma from a metastasis. A receiver-operator-characteristic plot of T2 produced an area of 0.80 (+/- 0.08). T2 values for these lesions still overlapped with those for metastases. Morphologically, hemangiomas were sharply marginated (80%), rounded or oval (93%), homogeneous, hyperintense lesions (73%), whereas metastases were poorly marginated (66%) and inhomogenous (67%) lesions. The marked, hyperintense appearance was present in 27% of metastases. Retrospective, multivariate logistic regression analysis of T2 and the presence of hyperintense morphology did not improve results based on T2 alone. Morphologic criteria are helpful in differentiation, as some metastases have a prolonged T2 and are not homogenous, hyperintense lesions. In cases where T2 or morphology are equivocal, other diagnostic tests may help confirm the MR findings. We currently use a T2 of greater than 88 msec and the presence of hyperintense morphology to diagnose hemangiomas. Despite both quantitative and qualitative analysis, data for these hemangiomas and metastases still overlap.     

Differentiation of hepatic metastases from hepatic hemangiomas and cysts by using MR imaging

T1-weighted and T2-weighted pulse sequences were employed for MR imaging of hepatic metastatic tumors (98 patients), hemangiomas (24 patients), and cysts (seven patients); a 0.6-T superconducting magnet was used. In a retrospective study, signal intensity and morphology were used to establish criteria for differentiating metastases from hemangiomas and cysts. The signal intensity of the lesion alone failed to be an etiologic discriminator because over 96% of all masses had a signal intensity less than that of liver on T1-weighted sequences, and at least 90% had a signal intensity greater than that of liver on T2-weighted sequences. Morphologic features depicted on T2-weighted images were more specific than those depicted on T1-weighted images in differential diagnosis. Amorphous, target, and halo signs and a change in morphology were present only in metastatic disease, with a frequency of 45%, 27%, 13%, and 12%, respectively. Two other morphologic patterns--doughnut and lightbulb signs--were found to have overlapping causes. Overall, at least one of the specific signs was observed in 92% of patients with metastatic disease. These data suggest that T2-weighted pulse sequences are essential for discriminating between hepatic metastases and hepatic hemangiomas and cysts. MR imaging is a promising technique for distinguishing these lesions.     

Distinguishing hepatic metastases from hemangiomas: qualitative and quantitative diagnostic performance through dual echo respiratory-triggered fast spin echo magnetic resonance imaging

OBJECTIVE: To determine the relative value of qualitative (reader opinion) and quantitative (values derived from dual echo T2 fast spin echo [FSE]) measures in distinguishing hepatic metastases from hemangiomas. METHODS: Forty-nine patients with hemangiomas and 23 with metastases were studied with dual echo respiratory-triggered FSE and dynamic 2-dimensional spoiled gradient echo (GRE) imaging. Lesion T2 was estimated from signal intensity ratios on the first and second echoes. Two experienced radiologists independently evaluated groups of images based on 5 separate qualitative measures: first echo FSE, second echo FSE, first and second echo FSE, dynamic GRE, and all images together. RESULTS: The mean calculated T2s were 226 +/- 74 milliseconds for hemangiomas and 105 +/- 22 milliseconds for metastases (P < 0.001). A T2 cutoff of 130 milliseconds distinguished metastases from hemangiomas with a sensitivity of 94%, specificity of 91%, and accuracy of nearly 94%. There was no significant difference between the best quantitative measure and the best qualitative measure for either reader. CONCLUSION: Liver lesion T2 relaxation times calculated from dual echo FSE images provide information useful in discriminating metastases from hemangiomas, as does reader opinion.     

MRI of the lung: value of different turbo spin-echo, single-shot turbo spin-echo, and 3D gradient-echo pulse sequences for the detection of pulmonary metastases

PURPOSE: To compare the value of different MRI sequences of the lung for the detection of pulmonary metastases. MATERIALS AND METHODS: A total of 28 patients with 225 pulmonary metastases confirmed at multidetector-row computed tomography (MDCT) underwent MRI of the lung, including breathhold T2-weighted single-shot turbo spin-echo (half-Fourier single-shot turbo spin-echo [HASTE] and inversion recovery [IR]-HASTE) and conventional turbo spin-echo (TSE and short-tau inversion recovery [STIR]) sequences, a respiratory- and pulse-triggered black-blood STIR sequence (triggered STIR), and breathhold pre- and postcontrast volumetric interpolated 3D gradient-echo (VIBE) sequences. MR images were reviewed by three independent observers and results were correlated with MDCT, which served as standard of reference. Lesion-to-lung contrast-to-noise ratios (CNRs) and image artifacts were also assessed. RESULTS: CNRs were highest on TSE images (P < 0.001). Mean sensitivities for lesion detection with triggered STIR, TSE, and STIR were 72.0%, 69.0%, and 63.4%, respectively. With HASTE, IR-HASTE, and pre- and postcontrast VIBE, significantly lower sensitivities were obtained (P < 0.05), although artifacts due to physiological motion were less distinct with these sequences compared to TSE and STIR (P < 0.05). CONCLUSION: Conventional TSE sequences are more sensitive in depicting pulmonary metastases than single-shot TSE or 3D gradient-echo sequences. Respiratory and pulse triggering can improve lesion detection, but increases acquisition time substantially.