Liver metastases: detection with MR imaging at 0.5 and 1.5 T

LI-RADS technical requirements for CT, MRI, and contrast-enhanced ultrasound

Accurate detection and characterization of liver observations to enable HCC diagnosis and staging using LI-RADS requires a technically adequate imaging exam. To help achieve this objective, LI-RADS has proposed technical requirements for CT, MR, and contrast-enhanced ultrasound of liver. This article reviews the technical requirements for liver imaging, including the description of minimum acceptable technical standards, such as the scanner hardware requirements, recommended dynamic imaging phases, and common technical challenges of liver imaging.

High resolution T2 weighted liver MR imaging using functional residual capacity breath-hold with a 1.0-Tesla scanner

PURPOSE

During acquisition of rapid high resolution (HR) T2 weighted (T2W) liver magnetic resonance (MR) images using a 1.0-Tesla (T) scanner, the liver is segmented into odd and even sections that are acquired at two different times using the multi-breath-hold (MBH) strategy. Misalignment between the two breath-hold (B-H) images may result in the occurrence of a blind area and a decrease in diagnostic accuracy. Here, a functional residual capacity (FRC) B-H method was developed to overcome this problem.

MATERIAL AND METHODS

Twenty-five volunteers were enrolled. The sagittal images were reconstructed from whole liver transverse images. When the B-H phases are different, misalignment may occur in the craniocaudal and anterior-posterior (AP) directions. In this study, misalignments of the abdominal wall were measured in the AP direction. The misalignment was compared between four B-H phases, maximum inspiration (MI), maximum expiration (ME), voluntary expiration (VE) and FRC using one-way repeated measures ANOVA. Differences between groups were compared using the t-test for multi-group comparisons. In addition, qualitative analysis of misalignment was performed between VE and FRC in 52 clinical patients and the chi(2) test was performed.

RESULTS

The misalignment widths of FRC, ME, MI and VE B-Hs were 2.7+/-3.8, 6.4+/-7.4, 9.1+/-8.4 and 6.0+/-6.7 mm, respectively. Misalignment of the liver position using FRC was significantly smaller than for the other B-H methods (p<0.05). Significant differences between the VE B-H and FRC B-H were also observed in the qualitative analysis (p<0.05).

CONCLUSION

The liver positions obtained when using FRC B-H were significantly more reproducible than when using the other B-H methods. The FRC B-H method resulted in a reduction in the blind area and an extension of the diagnostic area to the whole liver.

Does T2-weighted MR imaging improve preoperative detection of malignant hepatic tumors? Observer performance study in 49 surgically proven cases

The purpose of our study was to determine whether or not the addition of T2-weighted fast spin-echo (SE) imaging to gadolinium-enhanced spoiled gradient-recalled-echo (GRE) imaging improves the observer performance in the preoperative detection of malignant hepatic tumors. Gadolinium-enhanced GRE and fat-suppressed T2-weighted fast SE images obtained in 49 patients with 82 surgically confirmed malignant hepatic tumors (40 hepatocellular carcinomas and 42 metastases) were retrospectively reviewed by three independent off-site observers. In the random review of images, gadolinium-enhanced GRE images were reviewed first; thereafter, T2-weighted fast SE images were added for combined review. Observer performance was evaluated with the McNemar's test and receiver operating characteristic curve analysis. For gadolinium-enhanced GRE images alone vs. combined images, sensitivities for detection were 78% vs. 79% for hepatocellular carcinomas (P>.05), 67% vs. 71% for metastases (P<.05) and 72% vs. 75% for tumors overall (P<.05), respectively. The Az values were 0.892 vs. 0.889 in hepatocellular carcinomas (P>.05), 0.797 vs. 0.828 in metastases (P<.05) and 0.839 vs. 0.846 in tumors overall (P>.05), respectively. Our results showed that the addition of T2-weighted fast SE imaging to gadolinium-enhanced GRE imaging improved the observer performance in the detection of metastases.

Feasibility of Application of Sensitivity Encoding to the Breath-Hold T2-Weighted Turbo Spin-Echo Sequence for Evaluation of Focal Hepatic Tumors

OBJECTIVE

The purpose of this study is to assess the feasibility of the application of sensitivity encoding (SENSE) to the T2-weighted breath-hold turbo spin-echo (BHTSE) sequence for evaluating focal hepatic lesions.

MATERIALS AND METHODS

Thirty consecutive patients with 43 focal liver lesions underwent BHTSE, BHTSE using SENSE with the conventional parameters, and BHTSE using SENSE with increased matrix and reduced echo-train length (ETL). There were 23 hepatocellular carcinomas in 21 patients, 10 hemangiomas in six, and 10 metastases in three. The images were compared quantitatively by measuring the signal-to-noise ratio (SNR) of the liver and the lesion and the lesion-liver contrast-to-noise ratio (CNR) and qualitatively by evaluating image quality, lesion conspicuity, artifact, and lesion detectability.

RESULTS

The SNR of lesions and the lesion-liver CNR were highest on BHTSE using SENSE with increased matrix and reduced ETL, which were significantly higher than conventional BHTSE (p <0.05). In qualitative analysis, the image quality and conspicuity of malignant lesions with BHTSE using SENSE with increased matrix and reduced ETL were better than with BHTSE and BHTSE using SENSE with the conventional parameter (p <0.05). The image artifacts were lower with two BHTSEs using SENSE than with BHTSE (p <0.05). Lesion conspicuity of malignancy on BHTSE using SENSE with the conventional parameter was superior to those on BHTSE (p <0.05). Although there was no significant difference in the lesion detectability among the three images, two malignant lesions were clearly depicted on BHTSE using SENSE with increased matrix and reduced ETL.

CONCLUSION

The application of SENSE to BHTSE can provide high-quality liver imaging with decreased acquisition time compared with conventional BHTSE.

MR imaging of the pancreas: a practical approach

This article reviews the current practical MRI techniques in assessment of the pancreas. With the comprehensive "one-stop-shopping" approach, the great majority of pancreatic diseases can be detected and characterized by the use of a combination of T1, T2-weighted, MRCP, and fat-suppressed T1-weighted dynamic post-gadolinium SGE sequences. This approach may provide the clinician with information regarding the site, nature, and staging of pancreatic tumor in a single setting. In many institutions worldwide, however, including our own, CT remains the main imaging method for the assessment of acute pancreatic diseases, due largely to its wide availability. MR imaging is reserved for the indications listed above, most importantly, the detection of small and non-organ-deforming pancreatic ductal adenocarcinoma, islet cell tumors, choledocholithiasis and pancreatic duct calculi, cholangiocarcinomas, and in cases of pancreatic head enlargement with no mass discernable on CT.

O valor da ressonância magnética na detecção de nódulos hepáticos utilizando-se diversas técnicas ponderadas em T2: existe consenso?

Desde o início da década de 80 a ressonância magnética vem sendo utilizada para o estudo do abdome e principalmente na detecção de nódulos hepáticos. As imagens ponderadas em T2 são as que trouxeram maior benefício quando comparadas à tomografia computadorizada com contraste. Inúmeras técnicas e seqüências de ressonância magnética ponderadas em T2 surgiram desde então, na tentativa de aumentar a eficácia diagnóstica, com menores tempos de exame. Neste sentido, foram publicados inúmeros trabalhos demonstrando a utilidade de seqüências rápidas e ultra-rápidas, com e sem supressão de gordura, em apnéia, com sincronizador respiratório e com bobinas de sinergia, entre outros avanços tecnológicos. No entanto, não há um consenso sobre qual a técnica mais apropriada e sensível para a detecção de lesões hepáticas focais. Neste artigo fazemos uma revisão bibliográfica e análise crítica das diversas técnicas de imagens ponderadas em T2, no que diz respeito às suas sensibilidades na detecção de nódulos hepáticos.

T2-weighted MR imaging for focal hepatic lesion detection: supplementary value of breath-hold imaging with half-Fourier single-shot fast spin-echo and multishot spin-echo echoplanar sequences

The purpose of our study was to evaluate the supplementary value of breath-hold fat-suppressed T2-weighted magnetic resonance (MR) imaging with half-Fourier single-shot fast spin-echo (SE) or multishot SE echoplanar (EP) sequences combined with respiratory-triggered fat-suppressed fast SE T2-weighted MR imaging for detection and characterization of focal hepatic lesions. MR images in 42 patients with 82 solid, malignant and 77 nonsolid, benign lesions were analyzed. Image review was conducted on a segment-by-segment basis; in all, 333 liver segments were reviewed separately for solid and nonsolid lesions by three independent radiologists. For solid lesions, observer performance with receiver-operating-characteristic (ROC) analysis in one radiologist and specificity in another significantly improved after adding single-shot fast SE images. For nonsolid lesions, observer performance with ROC analysis in one radiologist and specificity in another significantly improved after adding single-shot fast SE images. Combining breath-hold half-Fourier single-shot fast SE imaging with respiratory-triggered fast SE imaging may be recommended for improved detection and characterization of focal hepatic lesions. J. Magn. Reson. Imaging 2000;12:444-452.

A prospective assessment of breath-hold fast spin echo and inversion recovery fast spin echo techniques for detection and characterization of focal hepatic lesions

The purpose of this study was to prospectively assess two breath-hold T(2)-weighted fast spin-echo sequences and two breath-hold inversion recovery fast spin-echo sequences to determine their relative ability to detect and characterize focal hepatic lesions. Fourteen patients with a total of nineteen proven focal hepatic lesions were imaged with two breath-hold T(2)-weighted (T2W) fast spin echo sequences (HASTE TE = 66 and HASTE TE = 120), two breath-hold inversion recovery fast spin echo sequences (IRFSE TE = 64 and IRFSE TE = 95), and a nonbreath-hold T(2)-weighted fast-spin echo sequence (FSE TE = 96-120). Contrast-to-noise ratios (CNRs) were measured for all proven lesions on all sequences. Both IRFSE sequences and the HASTE sequence with TE = 66 showed an improvement in lesion-liver and liver-spleen CNRs compared to the nonbreath-hold T2W sequence. The mean difference in CNR between benign and malignant lesions was largest for the HASTE TE = 120 sequence. These preliminary results suggest that a breath-hold IRFSE sequence (TE = 64 or 95) has an equal ability to detect focal hepatic lesions as a nonbreath-hold T2W FSE sequence (TE = 96-120). The HASTE TE = 120 showed the greatest ability to discriminate between benign and malignant lesions.

Single breath-hold T2-weighted MR imaging of the liver: value of single-shot fast spin-echo and multishot spin-echo echoplanar imaging

OBJECTIVE

The objective of our study was to evaluate the efficacy of single breath-hold T2-weighted MR imaging for detection of focal hepatic lesions.

MATERIALS AND METHODS

T2-weighted MR images were retrospectively reviewed from 51 patients with 85 solid and 59 nonsolid lesions using the following four sequences: conventional spin-echo, respiratory-triggered fast spin-echo, single-shot fast spin-echo, and multishot spin-echo echoplanar imaging. Images were reviewed on a hepatic segment-by-segment basis; T2-weighted images of a total of 408 hepatic segments were reviewed separately and independently for solid and nonsolid lesions by four radiologists. Quantitative, qualitative, and receiver operating characteristic analyses were performed.

RESULTS

For solid lesions, no significant differences were seen among the lesion-to-liver contrast-to-noise ratios with the four sequences. In terms of solid lesion detection, no significant difference was seen between the diagnostic accuracy of multishot spin-echo echoplanar (Az = 0.90) and respiratory-triggered fast spin-echo (Az = 0.91) imaging, which showed the best performance of the four sequences. For nonsolid lesion detection, respiratory-triggered fast spin-echo and single-shot fast spin-echo imaging were judged the best (Az = 0.94).

CONCLUSION

Breath-hold single-shot fast spin-echo and multishot spin-echo echoplanar sequences can be substituted for conventional spin-echo and respiratory-triggered fast spin-echo T2-weighted sequences.

MR imaging of the liver: techniques and clinical applications

With a recent advance of fast MR imaging techniques including fast gradient-echo (GRE), fast spin-echo (FSE), single shot FSE (SSFSE) and echo-planar imaging (EPI), and availability of a phased-array torso coil, there can be many possible pulse sequences for liver MR imaging. In clinical practice, optimization of pulse sequences is important for improving diagnostic performance of liver diseases. In this article, we review the current status of liver MR imaging, focusing on the description of standard pulse sequences, and the utility of fast scanning technique and contrast-enhancement studies.

Effect of field strength on MR images: comparison of the same subject at 0.5, 1.0, and 1.5 T

To assess the effect of field strength on magnetic resonance (MR) images, the same healthy subject was imaged at three field strengths: 0.5, 1.0, and 1.5 T. Imaging was performed with three similarly equipped MR imagers of the same generation and from the same manufacturer. The same imaging sequences were used with identical parameters and without repetition time correction for field strength. Imaging was performed in four anatomic locations: the brain, lumbar spine, knee, and abdomen. Quantitative image analysis involved calculation of signal-to-noise ratio, contrast-to-noise ratio, and relative contrast; qualitative image analysis was performed by four readers blinded to field strength. The results of all of the examinations were considered to be of diagnostic value. In general, signal-to-noise ratio and contrast-to-noise ratio were lowest at 0.5 T and highest at 1.5 T; relative contrast was not related to field strength. At qualitative analysis, images obtained at 1.0 and 1.5 T were superior to images obtained at 0.5 T; qualitative differences were less important in locations where there is motion or high magnetic susceptibility differences between tissues (e.g., the spine and abdomen). However, excellent image quality was obtained with all three field strengths.

Fat-suppressed T2-weighted MR imaging of hepatocellular carcinoma and metastases: comparison of conventional spin-echo, fast spin-echo, and echoplanar pulse sequences

The purpose of our study was to compare the diagnostic accuracy of fat-suppressed T2-weighted magnetic resonance (MR) images obtained with conventional spin-echo (SE), respiratory-triggered fast SE, and breath-hold multishot SE echoplanar (EP) sequences for the detection of hepatocellular carcinoma and metastases. Images obtained with the three sequences in 17 patients (15 with cirrhosis) with 31 hepatocellular carcinomas and 14 patients with 45 metastases were retrospectively analyzed. Image review was conducted on a segment-by-segment basis; in all, 248 liver segments were reviewed separately and independently for detection of solid, malignant lesions. Diagnostic accuracy was evaluated with receiver-operating-characteristic (ROC) curve analysis. Diagnostic accuracy for hepatocellular carcinoma as determined by ROC curve analysis was better by a statistically significant amount for conventional SE (Az = 0.95) images when compared with respiratory-triggered fast SE (Az = 0.83, P < 0.05) and breath-hold multishot SE EP (Az = 0.80, P < 0.05) images. Conventional SE MR sequences should not be replaced with respiratory-triggered fast SE or breath-hold multishot SE EP sequences for T2-weighted MR imaging of patients with hepatocellular carcinoma in cirrhosis, unless sufficient contrast-enhanced dynamic MR imaging is subsequently performed.

Differentiation of hepatic cavernous hemangioma from metastases by rare sequence MR imaging

In this study, in order to differentiate cavernous hemangioma and hepatic metastases, rapid acquisition relaxation enhanced (RARE) sequence was used. First, in vivo measurements of T1, T2 relaxation times and proton density were obtained using T1, T2 calculation protocol (TOMIKON S50, 0.5T) and multipoint techniques. These measurements were made from regions of interest placed over the liver, spleen (because of similarity of relaxation time values between hepatic metastases and spleen) and cavernous hemangioma (HCH). Based on these intrinsic parameters, T2 curves signal intensity of three different tissues were constructed. At TE = 500 ms, the signal intensity of the liver and spleen has been near zero whereas in HCH, the signal intensity remained. As RARE sequence is very similar to spin echo (SE), by replacing effective TE(ETE) = 500 ms in the RARE equation, two dimensional contrast-to-noise ratio (CNR) contour plots were constructed demonstrating signal intensity contrast between liver-spleen, liver-Hemangioma for two different scan times (3 min, 7.5 s) and pulse timing. Then, optimal RARE factor and inter echo times were obtained in order to have maximum CNR between liver-Hemangioma and minimum CNR between liver-spleen. These optimal parameters were performed on ten normal and five persons with known HCH. Images showed that in both scan times (3 min, 7.5 s); the liver and spleen were suppressed whereas the HCH was enhanced. The image quality in the scan time of 3 min was better than the scan time of 7.5 s. Moreover, in this study, two different sequences were compared: i) Multi-slice single echo (MSSE) for T1 weighted image ii) RARE (ETE = 80 ms) for T2-weighted image. This comparison was done to show maximum CNR between liver-spleen (metastases) and to choose a better sequence for detecting metastases. CNR in the RARE sequence was more than in the MSSE sequence.

Focal hepatic lesion detection: comparison of four fat-suppressed T2-weighted MR imaging pulse sequences

PURPOSE

To evaluate fat-suppressed T2-weighted magnetic resonance (MR) imaging with conventional spin-echo (SE), breath-hold fast SE, respiratory-triggered fast SE, and breath-hold multishot SE echo-planar sequences for the detection of focal hepatic lesions.

MATERIALS AND METHODS

Fat-suppressed T2-weighted MR images obtained with the four sequences in 55 patients with 81 solid and 129 nonsolid lesions were retrospectively analyzed. Image review was conducted on a segment-by-segment basis; a total of 440 liver segments were reviewed separately for solid and nonsolid lesions by three independent radiologists. Diagnostic accuracy was evaluated with receiver operating characteristic analysis.

RESULTS

The mean lesion-to-liver contrast-to-noise ratio was highest on the multishot SE echo-planar images of both solid and nonsolid lesions. Fat-suppressed respiratory-triggered fast SE images had significantly better (P < .05) or comparative detectability of both solid and nonsolid lesions compared with the other types of images. Image quality was best on the respiratory-triggered fast SE images.

CONCLUSION

Fat-suppressed respiratory-triggered fast SE imaging should replace fat-suppressed conventional SE imaging as a standard T2-weighted imaging examination in the detection of focal hepatic lesions.

A retrospective analysis of the accuracy of T2-weighted images and dynamic gadolinium-enhanced sequences in the detection and characterization of focal hepatic lesions

The aim of this study was to determine the relative ability of T2-weighted and dynamic gadolinium-enhanced T1-weighted gradient-echo sequences to detect and characterize focal hepatic lesions. We retrospectively studied 37 patients with proven focal hepatic lesions using the following sequences: a T1-weighted spin-echo sequence (T1), a T2-weighted sequence (T2), and a series of breath-hold dynamic gadolinium-enhanced T1-weighted gradient-echo sequences (Gd). Two observers were asked to determine retrospectively the number and type of focal hepatic lesions present using images from three combinations of sequences (T1+T2, T1+Gd, T1+T2+Gd). Proof of the number and diagnosis of focal lesions in each patient was established using a consensus read. Both readers detected more focal lesions when both the T2-weighted sequences and the gadolinium-enhanced sequences were available than on either sequence alone, although this improvement reached statistical significance (P<0.05) only for one of the readers. There was no significant difference (P<0.05) in the ability to characterize lesions between any of the sets of sequences. The combination of dynamic gadolinium-enhanced images and T2-weighted images was shown to assess focal hepatic lesions better than either of these sequences alone.

Detection of hepatocellular carcinoma: comparison of T2-weighted breath-hold fast spin-echo sequences and high-resolution dynamic MR imaging with a phased-array body coil

The purpose of our study was to compare T2-weighted breath-hold fast spin-echo sequence (BHFSE) and high-resolution dynamic MR imaging (HR-DMRI) in the detection of hepatocellular carcinoma (HCC). Short and long T2-weighted BHFSE sequences and biphasic HR-DMRI including arterial-dominant and delayed phase images with a phased-array body coil were performed in 30 consecutive patients with 37 HCCs. The lesion-to-liver contrast-to-noise ratio (CNR) was quantitatively measured. The lesion conspicuity and delineation was qualitatively rated according to a four-point scale. The lesion-to-liver CNR was highest with the arterial-dominant phase HR-DMRI and was significantly higher than those obtained with both short and long T2-weighted BHFSE and those obtained with unenhanced and delayed HR-DMRI. The CNR obtained with short T2-weighted BHFSE was significantly higher than those obtained with long T2-weighted BHFSE and with unenhanced and delayed HR-DMRI. The sensitivity for the sequences was 78.4% (29/37) for short T2-weighted BHFSE, 67.6% (25/37) for long T2-weighted BHFSE, 37.8% (14/37) for unenhanced HR-DMRI, 97.3% (36/37) for arterial-dominant phase HR-DMRI, and 43.2% (16/37) for delayed HR-DMRI. The sensitivity of serial dynamic MR imaging combined with unenhanced, arterial-dominant phase imaging and delayed phase imaging was 100% (37/37). The score in the qualitative analysis of the lesion conspicuity and delineation was highest for the arterial-dominant phase HR-DMRI and was significantly higher than that for the short T2-weighted BHFSE. The score for the short T2-weighted BHFSE was significantly higher than that for the long T2-weighted BHFSE and that for the unenhanced HR-DMRI. Arterial-dominant phase HR-DMRI is superior to the T2-weighted BHFSE technique, and also HR-DMRI combined with unenhanced, arterial-dominant and delayed phases is the most sensitive technique in the detection of HCC.

Prospective comparison of fast SE and GRASE sequences and echo planar imaging with conventional SE sequences in the detection of focal liver lesions at 1.0 T

PURPOSE

Our goal was to investigate the value of T2-weighted fast SE (FSE) sequences, FSE sequences with shortened echo spacing (UFSE), combined gradient and spin echo sequences (GRASE), and segmented T1-weighted echo planar imaging (EPI) in comparison with conventional SE sequences in the detection of focal liver lesions.

METHOD

Thirty-five patients with malignant focal liver lesions underwent MRI at 1.0 T.

RESULTS

All fast T2-weighted imaging techniques (FSE, UFSE, GRASE) showed fewer artifacts and overall better image quality than the conventional SE sequence. Quantitative analysis demonstrated that UFSE imaging had the highest tumor/liver contrast/noise ratio (C/N) (13.9 +/- 5.5) followed by FSE (12.7 +/- 4.5), T2 SE (10.9 +/- 4.2), and GRASE (10.0 +/- 4.8) sequences. The differences in C/N between the UFSE and T2 SE sequences was statistically significant (p < 0.05). C/N was significantly higher (p < 0.01) for the T1 SE (-7.4 +/- 3.8) than for the EPI sequence (-0.5 +/- 5.6).

CONCLUSION

FSE sequences with shortened echo spacing are valuable for liver imaging at 1.0 T. In comparison with the T2 SE sequence, they yielded better image quality and comparable tumor/liver C/N.

Motion artifact in T2-weighted fast spin-echo images of the liver: effect on image contrast and reduction of artifact using respiratory triggering in normal volunteers

The purpose of our study was to evaluate the effect of respiratory motion on the image contrast of T2-weighted fast spin-echo (FSE) images of the liver as well as the reduction of motion artifact using respiratory triggering of the data acquisition. We imaged the livers of 10 healthy volunteers using a fast spin-echo T2-weighted sequence. Images were obtained both without and with patient triggering. Triggered images were acquired in a segmented fashion during multiple sequential breath-holds using an echo train of 8 or 16, both with and without flow compensation (gradient moment nulling). Ratios of signal difference to noise (SD/N) of the liver and gallbladder as well as the liver and spleen were compared for all sequences. All of the triggered images showed statistically significant improvement of SD/N for the liver and gallbladder as well as for the liver and spleen when compared with the nontriggered images. Triggered images obtained with an echo train length of 8 and, with flow compensation, showed the highest SD/N ratios. In one volunteer whose liver contained multiple small cysts, the triggered images showed improved visualization of individual cysts and identified a larger number of cysts. Respiratory motion causes a significant loss of contrast on T2-weighted fast spin-echo images of the liver. This can be reduced by using a segmented data acquisition triggered by the respiratory cycle obtained during sequential breath-holds.

Breath-hold MR imaging of focal liver lesions: comparison of fast and ultrasound techniques

The performance of breath-hold MR imaging using two T2-weighted hybrid sequences (TSE, TGSE), two T2-weighted single-shot sequences (HASTE, EPI-SE), and one T1-weighted gradient-echo sequence (FLASH) was compared with a standard conventional T2-weighted SE sequence in 20 patients with focal liver lesions. Liver signal-to-noise ratio was highest for the FLASH sequence (54.3 +/- 8.3) and the HASTE (41.1 +/- 12.5) sequence, whereas the highest spleen-liver contrast-to-noise ratio was obtained by the TSE sequence (38.9 +/- 20.7). Lesion-liver CNR was highest with the TSE sequence (63.9 +/- 21.4). With both TSE and HASTE significantly (p < 0.01) more lesions were detected as compared with SE and EPI-SE sequences. Our results indicate that breath-hold TSE and HASTE sequences will eventually replace conventional T2-weighted SE techniques, due to their insensitivity to motion artifacts, superior lesion detectability and inherently short acquisition times.

Liver MR imaging: comparison of respiratory triggered fast spin echo with T2-weighted spin-echo and inversion recovery

BACKGROUND

The purpose of this study was to compare a fast spin-echo sequence combined with a respiratory triggering device (R. trig. FSE) with conventional T2-weighted spin-echo (CSE) and inversion recovery (STIR) sequences for the detection of focal hepatic lesions.

METHODS

We performed a prospective study of 33 consecutive patients with known or suspected hepatic tumors. All patients underwent R. trig. FSE, CSE, and STIR imaging at 1.5 T. Acquisition times were 10.7 min for the CSE sequence and ranged from 12 to 15 min for STIR and from 5 to 7 min for R. trig FSE. For each sequence, liver-spleen contrast-to-noise ratio (CNR) and liver-lesion CNR were determined quantitatively. Image artifact and sharpness were graded by using a four-point scale on each sequence by two independent readers. Both readers also independently identified hepatic lesions (up to a maximum of eight per patient). For patients with focal lesions, the total number of lesions detected (on each sequence) and the minimum size of detected lesions were also determined by each reader.

RESULTS

No significant difference was detected between R. trig. FSE and CSE or STIR in either liver-spleen CNR or liver-lesion CNR. R. trig. FSE images were equivalent to CSE and superior to STIR in sharpness (p < 0.01) and presence of artifact (p < 0.01). R. trig. FSE detected a higher number of lesions (reader 1: n = 92, reader 2: n = 86) than CSE (reader 1: n = 70, reader 2: n = 69) and a significantly higher number than STIR (reader 1: n = 71, reader 2: n = 76). Lesion structure was significantly better defined with R. trig. FSE than with STIR (p < 0.01) and CSE (p < 0.05).

CONCLUSIONS

Compared with CSE and STIR, R. trig. FSE produces hepatic images of comparable resolution and detects an increased number of focal hepatic lesions in a shorter period of time.

Hepatic MR imaging: comparison of RARE derived sequences with conventional sequences for detection and characterization of focal liver lesions

BACKGROUND

We compared two T2-weighted turbo spin echo (TSE) sequences with a T2-weighted conventional SE (CSE) sequence to determine whether sequences derived from rapid acquisition with relaxation enhancement such as TSE could replace CSE for the detection and subsequent characterization of focal liver lesions.

METHODS

A total of 55 consecutive patients with 107 liver lesions underwent magnetic resonance imaging examinations at 1.5 Tesla, with a constant imaging protocol. TSE pulse sequences were acquired with eight echo trains (repetition time [TR], 4718 ms; echo time [TE], 90 ms; acquisition time [TA], 4.03 min; and a symmetric k-space ordering scheme) and 11 echo trains (TR, 4200 ms; TE, 140 ms; TA, 4.40 min; and an asymmetric k-space ordering scheme) and compared with CSE (TR, 2300 ms; TE, 45/90 ms; TA, 9.53 min). Images were analyzed qualitatively by scoring image quality and artifacts and counting focal liver lesions by independent reading with consensus obtained for discrepancies. Quantitative analysis was performed by measuring signal-to-noise (S/N), contrast-to-noise (C/N), and tumor-liver signal intensity (T/L) ratios.

RESULTS

T2-weighted TSE sequences provided better subjective image quality and reduced artifacts as compared with the T2-weighted CSE sequence. CSE and TSE sequences exhibited no statistically significant differences in liver S/N, lesion-liver C/N (CSE TE, 90 ms: 18.6 +/- 14.0; TSE TE, 90 ms: 16.5 +/- 12.9) and the detectability of focal liver lesions. Heavily T2-weighted TSE with a TE of 140 ms allowed correct characterization of focal liver lesions based on a T/L ratio of 3.0 in 84% of patients.

CONCLUSIONS

T2-weighted TSE sequences are as suited as CSE for the detection (TE, 90 ms), and appear to be superior for the characterization (TE, 140 ms), of focal hepatic lesions. Whether a single sequence, such as a double-echo TSE or a single-echo TSE sequence with a TE between 110 and 120 ms, might perform both functions as well or better than CSE is unknown. However, because of time savings, TSE eventually may be preferred over CSE.

MR of focal liver lesions: comparison of breath-hold and non-breath-hold hybrid RARE and conventional spin-echo T2-weighted pulse sequences

To compare liver lesion detection rates, tissue signal and noise data, and qualitative parameters for breath-hold (BH) and non-breath-hold (NBH) hybrid rapid acquisition with relaxation enhancement (RARE) and conventional spin-echo (CSE) T2-weighted (CSE-T2) MR sequences, 20 patients were imaged using all three sequences. Lesion detection rates were 73.5% for the CSE-T2 sequence and 81.1% and 88.6% for the BH-RARE and NBH-RARE sequences, respectively (P = .027). Mean lesion-to-liver signal-difference-to-noise ratio for the NBH-RARE sequence was 14.0 +/- 11.5, significantly greater than 9.8 +/- 7.8 obtained for the BH-RARE sequence (P = .050) and 9.0 +/- 6.2 obtained for the CSE-T2 sequence (P = .015). The NBH-RARE sequence demonstrated fewer artifacts and greater overall image quality compared to the CSE-T2 sequence. The NBH-RARE sequence is a useful alternative to the liver signal-difference-to-noise ratio and lesion detection rate and better overall image quality.

MR imaging of focal liver lesions: comparison between turbo spin-echo and conventional spin-echo pulse sequences

The aim of this study was to compare conventional spin-echo (CSE) T2-weighted (T2W) images with turbo spin-echo (TSE) T2W pulse sequences in their ability to detect focal liver lesions. Seventy-eight consecutive patients with focal liver lesions were entered into this study. All patients were imaged using the gradient-echo (GE) sequence with the breath-hold technique for T1-weighted (T1W) images, and CSE and TSE sequences for T2W images. Qualitative evaluation included lesion detection (number of lesions detected) and conspicuity (extent of visualization of lesional borders); quantitative evaluation included the signal-to-noise (S/N) ratio and the contrast-to-noise (C/N) ratio. TSE showed the best performance in terms of lesion detection; however, the difference between TSE and CSE was significant only in the case of benign cysts (p < 0.01). Conspicuity was higher with TSE and CSE, and lower with GE. The S/N and C/N ratios of the two T2W sequences were also comparable, and better than those of GE. However, the combined use of GE and TSE resulted in improved lesion detection. The results show that, because the acquisition time is greatly reduced with TSE sequences, these should be considered as first-line approach to magnetic resonance imaging of the liver for the study of focal lesions.

Cross-sectional imaging of the liver

The liver can be affected by a number of conditions that can involve the liver focally or diffusely. CT and MRI are reliable techniques for demonstrating these abnormalities, and both imaging tools play an important role in the clinical evaluation of the patients. However, each technique provides different information, and the most appropriate cross-sectional technique used should be tailored in each instance to the individual patient situation.

Quantitative MR imaging data in the evaluation of hepatic metastases during systemic chemotherapy

To identify changes induced by chemotherapy in hepatic metastases, 34 patients with metastases underwent magnetic resonance (MR) imaging before the start of systemic chemotherapy and monthly thereafter. The number, size, and morphologic patterns of the lesions and changes in quantitative parameters (signal-to-noise ratio [S/N]], contrast-to-noise ratio, and signal intensity ratio) were evaluated and correlated with response to treatment and prognosis. After treatment, seven patients showed a partial response, 18 had stable disease, and nine had progressive disease. No relevant changes in the patterns of the lesions were observed. Quantitative data showed that patients with a good prognosis had an increase in S/N on T1-weighted images and a relative decrease on T2-weighted images; patients with a poor prognosis showed a decrease in S/N on T1-weighted images and an increase on T2-weighted images. The differences between patient groups were significant for both T1- and T2-weighted images. This study demonstrates the value of MR imaging in follow-up of liver metastases and suggests the usefulness of quantitative MR imaging data.

New imaging modalities for follow-up of colorectal carcinoma

Recurrent disease after curative resection occurred in 37-44% of patients. The common sites of recurrent disease are at the anastomotic site, in the liver, in the lymph nodes, and in the peritoneal linings. Computed tomography (CT), barium enema, and endoscopy detected local recurrent disease in 61-88% of the patients, whereas magnetic resonance imaging (MRI) detected 80-88% of the cases reported in some Phase 1 studies. CT and MRI are equally effective in the detection of hepatic metastases when lesions are larger than 2 cm, with detectability rate of 95-100%. They are fair (50-60% detectability rate) when tumors are between 1 and 2 cm and poor (less than 40%) when tumors are smaller than 1 cm. For recurrent nodal metastases and peritoneal deposits, CT is the modality of choice.

Liver lesion detection: comparison between excitation-spoiling fat suppression and regular spin-echo at 1.5T

The role of excitation-spoiling fat suppression (fatsat) imaging in the detection of liver lesions was assessed comparing short TR/TE and lont TR/TE spin-echo (SE) sequences with and without excitation-spoiling fat suppression in 25 patients at 1.5T. The study included patients with liver metastases (n = 21), primary liver cancer (n = 3), and hepatic adenoma (n = 1). Liver lesion detection and lesion-liver signal-to-noise ratios (SNR) were determined for the various imaging sequences in a prospective fashion. Liver lesion-liver SNR were highest for long TR/TE (2000-2500/70-80) fatsat images (12.7 +/- 4.8) compared to long TR/TE regular SE (2000-2500/70-80) images (8.8 +/- 5.6) [(p = ns) (not significant)], short TR/TE (200-400/15-20) fatsat images (-6.2 +/- 4.8) (p = 0.05), and short TR/TE regular SE images (-4.9 +/- 3.2) (p < 0.01). Lesion detection was greatest for long TR/TE fatsat (86) followed by long TR/TE regular SE (78) (p = 0.05), short TR/TE fatsat (65) (p < 0.01), and short TR/TE regular SE (60) (p < 0.01). The results of this study suggest that excitation-spoiling fat suppression may improve liver lesion detection and conspicuity.

Magnetic resonance imaging of the liver: current clinical applications

Magnetic resonance imaging provides excellent anatomic depiction of the liver and important information about focal and diffuse diseases that affect this organ. In this report, the current clinical applications of magnetic resonance imaging of the liver in patients with known or suspected hepatic metastatic lesions, hepatocellular carcinoma, cavernous hemangiomas, focal fatty infiltration, focal nodular hyperplasia, hepatic adenoma, regenerative nodules in hepatic cirrhosis, or iron overload are reviewed, and the limitations of the technique are discussed.

Breath-hold T2-weighted sequences of the liver: a comparison of four techniques at 1.0 and 1.5 T

T2-weighted images are considered the most sensitive for lesion detection at high field; however, long imaging time is problematic. Accordingly, the authors compared four breath-hold T2 or T2* weighted sequences comprising T2*-weighted FLASH, T2*-weighted PSIF, T2-weighted rapid spin echo (RASE), and T2-weighted Turbo-FLASH (Turbo) in 20 different healthy volunteers, 10 at 1.0 T and 10 at 1.5 T with reference to regular T2-weighted spin echo. Images were evaluated quantitatively by liver signal to noise (S/N) and spleen-liver signal difference to noise (SD/N) ratios and qualitatively for presence of artifacts and image quality. Data were evaluated for 1.0 T and 1.5 T separately and combined. In the combined evaluation, T2*-FLASH had good S/N (23.1 + 5.1) but low SD/N (2.9 + 1.7) and suffered from susceptibility artifacts. T2* PSIF had good S/N (28.1 + 10.0) and moderate SD/N (6.0 + 2.4), but occasionally had heterogeneous signal intensity. Flow signal void was an attractive feature. T2 RASE had very low S/N (4.4 + 1.9) and low SD/N (2.3 + 1.1) and suffered from flow artifacts. T2-Turbo had good S/N (24.6 + 8.6) and SD/N (8.9 + 2.5). Flow signal void was present, but small matrix size decreased image quality. The results of our study suggest that T2*-PSIF and T2-Turbo have good S/N and SD/N and fair image quality which may be clinically useful for breath-hold T2-weighted sequences of the liver.

Hepatic metastases: CT versus MR imaging at 1.5T

A prospective multi-institutional study was performed to compare the sensitivity of computed tomography (CT) and high-field magnetic resonance (MR) imaging (1.5T) in the detection of hepatic metastases. T1-weighted and 72-weighted spin-echo (SE) MR images were compared with noncontrast, dynamic, and delayed CT. Sixty-nine oncology patients were studied. Noncontrast CT showed an overall sensitivity of 57%, dynamic CT 71%, delayed CT 72%, T1-weighted SE MR 47%, and T2-weighted SE MR 78%. Although there was no statistically significant (p less than 0.05) difference among dynamic CT, delayed CT, and T2-weighted SE MR, these three methods were significantly more sensitive (p less than 0.005) than noncontrast CT or T1-weighted SE MR. T2-weighted SE MR was significantly more sensitive (p less than 0.006) than CT or T1-weighted SE MR in the detection of small (less than 1 cm) lesions. CT was more sensitive in the detection of extrahepatic disease. These data confirm the superiority of T2-weighted SE over T1-weighted SE pulse sequences at 1.5T.

Dextran magnetite as a liver contrast agent

The superparamagnetic particle dextran magnetite was studied as a liver tumor contrast agent for magnetic resonance imaging (MRI). The effects of dextran magnetite on the longitudinal (T1) and transverse (T2) relaxation times in liver, spleen, and an implanted rat liver tumor were measured at 0.47 T (IBM/Bruker PC-20 relaxometer) over the dose range of 23 to 69 mumol Fe/kg. Dextran magnetite substantially reduced the T2 of the liver and spleen, but not of the tumor, thereby providing a basis for improved tumor imaging. The T1 of the tumor was not affected following injection of dextran magnetite in the dose range studied, while the spleen T1 was reduced substantially more than the T1 of the liver. Histological studies using the iron reaction for Prussian blue clearly showed dextran magnetite in the liver and spleen, but not in the tumor. While dextran magnetite was sequestered in macrophages in both liver and spleen, the distribution in the liver was more diffuse (70 microns average particle separation) than that in the spleen (25 microns separation). The lack of a T1 effect in the liver is consistent with the fact that a majority of the water in the tissue cannot diffuse to the relaxational centers on the time scale of the liver's intrinsic T1 (280 ms). In the spleen, however, the dextran magnetite is more densely packed in the red pulp allowing a significant fraction of the water to be relaxed by a T1 mechanism. Spin-echo images of the implanted tumor (mammary adenocarcinoma. R3230AC) in the livers of Fischer 344 rats were obtained at 0.50 T (Siemens Magnetom). The tumor-to-liver contrast was improved for both T1 and T2-weighted spin-echo images after intravenous injection of the dextran magnetite contrast agent. The contrast determined from these images agreed with that predicted by the measured T1 and the T2 (Hahn spin-echo) values. In addition, gradient-echo T2-weighted images with good contrast were obtained in a much shorter imaging time than was needed for T2-weighted spin-echo images. These results demonstrate that the MRI contrast enhancement observed with dextran magnetite is based on its selective uptake and distribution in the macrophages in the liver and spleen and that this agent has substantial potential as a superparamagnetic MR contrast agent.

Liver tumor imaging

Liver tumor imaging is the paradigm of the dilemma of diagnostic decision-making in the current era of abundant high technology. In part, this is a reflection of the multiplicity of imaging techniques now in wide use worldwide. These include ultrasound (US), radionuclide scintigraphy (RNS), computed tomography (CT), magnetic resonance imaging (MRI), and techniques especially designed for staging the extent of known liver cancer, such as computed tomography during arterial portography (CTAP) and intraoperative ultrasound (IOUS). Most authorities concede that CT scanning is the single test most closely fitting the designation "gold standard" for liver tumor imaging, although MRI, a less mature technique, is already preferred by some. Local factors profoundly influence the selection and sequence of imaging studies, including available equipment, radiologic skills, institutional interests, and especially the specific clinical circumstances of the patient. Thus, diagnostic algorithms or decision trees for sequential imaging workup of liver tumor suspects tend to be somewhat institution specific.

Magnetization prepared rapid gradient-echo (MP-RAGE) MR imaging of the liver: comparison with spin-echo imaging

We have implemented an MR technique that employs a rapid gradient echo sequence, preceded by magnetization preparation pulses to provide T1- and T2-weighted tissue contrast. With this technique, which can be identified as a member of a new family of pulse sequences, generically named Magnetization Prepared RApid Gradient Echo (MP-RAGE), very short repetition times are used, allowing acquisition times of less than one second and images virtually free of motion-induced artifacts during quiet respiration. Fifteen patients with known liver lesions (metastases, hemangiomas, and cysts) were examined using T1- and T2-weighted 2-dimensional MP-RAGE sequences, and the images were compared with conventional T1- and multi-echo T2-weighted spin-echo (SE) sequences. Signal difference-to-noise ratios (SD/Ns) of the lesions were calculated for all pulse sequences using corresponding axial images and were normalized for voxel volume. The mean normalized SD/Ns of the MP-RAGE sequences were generally comparable to those for the SE sequences. In addition, there were no noticeable respiratory artifacts on the MP-RAGE images whereas these were clearly present on the T2-weighted SE images and to a lesser degree on the T1-weighted SE images. It is concluded that the MP-RAGE technique could become an important method for evaluating the liver for focal disease.

MRI of liver tumors using gadolinium-DOTA: prospective study comparing spin-echo long TR-te sequence and CT

Thirty-nine patients with liver tumors were examined using MRI at 0.5 T before and after intravenous bolus injection of either 0.1 mmol/kg (n = 18) or 0.2 mmol/kg (n = 21) of Gadolinium-Dota, using spin-echo T1-and T2-weighted sequences before injections and spin-echo or gradient-echo sequences after injection. When contrast-to-noise (C/N) data were normalized relative to time, optimal mean C/N was observed after gadolinium injection. However, subjective study and case-by-case C/N measurement showed better contrast for SE 2000/60 and CT with injection in 62% and 42% of cases, respectively.

Liver imaging at 1.5 tesla: pulse sequence optimization based on improved measurement of tissue relaxation times

In order to predict the most sensitive MR imaging sequence for detecting liver metastases at 1.5 T, in vivo measurements of T1 and T2 relaxation times and proton density were obtained using multipoint techniques. Based on these measurements, two-dimensional contrast contour plots were constructed demonstrating signal intensity contrast between hepatic lesions and surrounding liver parenchyma for different pulse sequences and pulse timing parameters. The data predict that inversion recovery spin echo (IRSE) imaging should yield the greatest contrast between liver metastases and liver parenchyma at 1.5 T, followed by short tau inversion recovery (STIR) and spin-echo (SE) pulse sequences. T2-weighted SE images provided greater liver/lesion contrast than T1-weighted SE pulse sequences. Calculated T1, T2, and proton density values of the spleen were similar to those of hepatic metastatic lesions, indicating that the signal intensity of the spleen may be used as an internal standard to predict the signal intensity of hepatic metastases on T1- and T2-weighted images at 1.5 T.