Optimal Pulse Sequence for Ferumoxides-Enhanced MR Imaging Used in the Detection of Hepatocellular Carcinoma: A Comparative Study Using Seven Pulse Sequences

Objective

To identify the optimal pulse sequence for ferumoxides-enhanced magnetic resonance (MR) imaging in the detection of hepatocelluar carcinomas (HCCs).

Materials and Methods

Sixteen patients with 25 HCCs underwent MR imaging following intravenous infusion of ferumoxides. All MR studies were performed on a 1.5-T MR system, using a phased-array coil. Ferumoxides (Feridex IV) at a dose of 15 µmol/Kg was slowly infused intravenously, and axial images of seven sequences were obtained 30 minutes after the end of infusion. The MR protocol included fast spin-echo (FSE) with two echo times (TR3333 8571/TE18 and 90-117), singleshot FSE (SSFSE) with two echo times (TR∞/TE39 and 98), T2*-weighted gradient-recalled acquisition in the steady state (GRASS) (TR216/TE20), T2*-weighted fast multiplanar GRASS (FMPGR) (TR130/TE8.4-9.5), and T2*-weighted fast multiplanar spoiled GRASS (FMPSPGR) (TR130/TE8.4-9.5). Contrast-to-noise ratios (CNRs) of HCCs determined during the imaging sequences formed the basis of quantitative analysis, and images were qualitatively assessed in terms of lesion conspicuity and image artifacts. The diagnostic accuracy of all sequences was assessed using receiver operating characteristic (ROC) analysis.

Results

Quantitative analysis revealed that the CNRs of T2*-weighted FMPGR and T2*-weighted FMPSPGR were significantly higher than those of the other sequences, while qualitative analysis showed that image artifacts were prominent at T2*-weighted GRASS imaging. Lesion conspicuity was statistically significantly less clear at SSFSE imaging. In term of lesion detection, T2*-weighted FMPGR, T2*-weighted FMPSPGR, and proton density FSE imaging were statistically superior to the others.

Conclusion

T2*-weighted FMPGR, T2*-weighted FMPSPGR, and proton density FSE appear to be the optimal pulse sequences for ferumoxides-enhanced MR imaging in the detection of HCCs.     

GRASE (gradient- and spin-echo) MR imaging: a new fast clinical imaging technique

A novel technique of magnetic resonance (MR) imaging, which combines gradient-echo and spin-echo (GRASE) technique, accomplishes T2-weighted multisection imaging in drastically reduced imaging time, currently 24 times faster than spin-echo imaging. The GRASE technique maintains contrast mechanisms, high spatial resolution, and image quality of spin-echo imaging and is compatible with clinical whole-body MR systems without modification of gradient hardware. Image acquisition time is 18 seconds for 11 multisection body images (2,000/80 [repetition time msec/echo time msec]) and 36 seconds for 22 brain images (4,000/104). With a combination of multiple Hahn spin echoes and short gradient-echo trains, the GRASE technique overcomes several potential problems of echo-planar imaging, including large chemical shift, image distortions, and signal loss from field inhomogeneity. Advantages of GRASE over the RARE (rapid acquisition with relaxation enhancement) technique include faster acquisition times and lower deposition of radio-frequency power in the body. Breath holding during 18-second GRASE imaging of the upper abdomen eliminates respiratory-motion artifacts in T2-weighted images. A major improvement in T2-weighted abdominal imaging is suggested.     

Adrenocortical carcinoma: MR imaging appearance with current techniques

The purpose of the study was to define the magnetic resonance (MR) imaging appearance of adrenocortical carcinoma (ACC) with current MR techniques. Eight patients with ACC underwent high-field-strength MR imaging with the following sequences: axial T1-weighted gradient echo, fat-suppressed T1-weighted spin echo, fat-suppressed T2-weighted spin echo, and gadolinium-enhanced T1-weighted gradient echo and fat-suppressed T1-weighted spin echo. Postcontrast images were also acquired in the sagittal (six patients) and coronal (three patients) planes. Out-of-phase gradient-echo images were obtained in two patients. Lesion morphology, signal intensity features, and presence of metastatic disease were retrospectively evaluated. MR imaging features of ACC included internal hemorrhage (seven of eight patients), central necrosis (seven of eight), and peripheral enhancing nodules (seven of eight). Out-of-phase images in two of two patients demonstrated signal loss compared with in-phase images, which may be a common feature of these tumors. Liver metastases were present in four patients. Consistent MR features of ACC are Identified.     

Comparing the FAISE method with conventional dual-echo sequences.

The FAISE (fast-acquisition interleaved spin-echo) technique consists of a hybrid rapid-acquisition relaxation-enhanced (RARE) sequence combined with a specific phase-encode reordering method. Implemented on a 1.5-T unit, this multisection, high-resolution technique permits convenient contrast manipulation similar to that of spin-echo imaging, with selection of a pseudo-echo-time parameter and a TR interval. With a TR of 2 seconds, eight 256 x 256 images are obtained in 34 seconds with either T2 or proton-density weighting. A direct comparison between FAISE and spin echo for obtaining T2-weighted head images in healthy subjects indicates that FAISE and spin-echo images are qualitatively and quantitatively similar. Image artifacts are more pronounced on "proton-density" FAISE images than on the T2-weighted FAISE images. T1 contrast can be obtained with inversion recovery and short TR FAISE images. Preliminary temperature measurements in saline phantoms do not indicate excessive temperature increases with extended FAISE acquisitions. However, extensive studies of radio-frequency power deposition effects should be performed if the FAISE technique is to be fully exploited.     

Superparamagnetic Iron Oxide Hepatic MR Imaging: Efficacy and Safety Using Conventional and Fast Spin-Echo Pulse Sequences

The purpose of this study was to evaluate the technical efficacy and safety of iv ferumozldes (Feridex^a), a superparamagnetic iron oxide contrast agent for detection of hepatic lesions using conventional spin-echo and fast spin-echo MR images. Precontract and postcontrast MR studies were performed on 25 patients with suspected focal hepatic lesions. Conventional Tl-and T2-weighted MR images, as well as fast spin-echo and fat suppressed fast spin-echo MR images, were evaluated. Quantitative assessment of the contrast agent was performed obtaining region of interest measurements of the liver, spleen, and selected hepatic lesions. The pulse sequences were also evaluated subjectively for overall image quality and a subjective assessment of lesion detection. The use of a superparamagnetic iron oxide contrast agent led to a decrease in hepatic signal intensity on all pulse sequences. Lesion-to-liver contrast increased 41.1%, 36.5%, and 32.0% on the conventional T2, fast spin-echo, and fat suppressed fast spin echo pulse sequences, respectively. Lesion-to-liver contrast decreased on the T1-weighted postcontrast pulse sequence by 23.8%. Despite Improvement in lesion-to-liver contrast, radiologists subjectively preferred the precontract sequences because of overall better image quality. At a dose of 10 μmol/kg, fenunoxides favorably impacts lesion-to-liver contrast, and may be useful in hepatic imaging, more with conventional T2-weighted spin-echo pulse sequences than with T2-weighted fast spin-echo pulse sequences.     

Ultrasmall superparamagnetic iron-oxide-enhanced MR imaging of normal bone marrow in rodents: original research original research

RATIONALE AND OBJECTIVES: The objective is to compare three different ultrasmall superparamagnetic iron oxides (USPIOs) for magnetic resonance (MR) imaging of normal bone marrow in rodents. MATERIALS AND METHODS: Femoral bone marrow in 18 Sprague-Dawley rats was examined by using MR imaging before and up to 2 and 24 hours postinjection (PI) of 200 mumol of Fe/kg of SHU555C (n = 6), ferumoxtran-10 (n = 6), or ferumoxytol (n = 6), using T1-weighted (50 ms/1.7 ms/60 degrees = repetition time [TR]/echo time [TE]/flip angle) and T2*-weighted (100 ms/15 ms/38 degrees = TR/TE/flip angle) three-dimensional spoiled gradient recalled echo sequences. USPIO-induced bone marrow was evaluated qualitatively and quantified as signal-to-noise ratio (SNR) and change in signal intensity (DeltaSI) values. A mixed-effect model was fitted to the SNR and DeltaSI values, and differences among USPIOs were tested for significance by using F tests. RESULTS: At 2 hours PI, all three USPIOs showed marked positive signal enhancement on T1-weighted images and a corresponding marked signal loss on T2*-weighted images. At 24 hours PI, the T1 effect of all three USPIOs disappeared, whereas T2*-weighted images showed persistent signal loss on SHU555C and ferumoxytol-enhanced MR images, but not ferumoxtran-10-enhanced MR images. Corresponding SNR and DeltaSI values on T2*-weighted MR images at 24 hours PI were significantly different from baseline for SHU555C and ferumoxytol, but not ferumoxtran-10. CONCLUSION: All three USPIO contrast agents, ferumoxtran-10, ferumoxytol, and SHU555C, can be applied for MR imaging of bone marrow. Ferumoxtran-10 apparently reveals a different kinetic behavior in bone marrow than ferumoxytol and SHU555C.     

OMR, a positive bowel contrast agent for abdominal and pelvic MR imaging: safety and imaging characteristics.

To determine the safety and imaging characteristics of OMR--an effervescent solution of ferric ammonium citrate--as a bowel contrast agent, magnetic resonance (MR) imaging at 1.5 T was performed in 29 volunteers. T1- and T2-weighted images of the upper abdomen and pelvis were obtained before and after oral administration of OMR at doses of 100-400 mg of iron in 300-600 mL of water. Respiratory-ordered phase encoding and presaturation pulses were used routinely for artifact suppression. All dose levels of OMR provided marking of the bowel by increasing intraluminal signal intensity; however, the degree and percentage of small bowel opacification appeared more prominent at higher dose levels of iron. Semisolid or watery bowel movements were noted in 31% of subjects, but no clinically important laboratory abnormalities were seen. OMR improved delineation of the head of the pancreas on T1-weighted images in 72% of subjects but was less useful in defining the body and tail. OMR is a safe and effective bowel contrast agent for MR imaging. Because artifacts due to movement of hyperintense bowel may degrade the images, OMR may be most useful on short TR/TE or fast imaging pulse sequences or when combined with antiperistaltic agents.     

T2-weighted MR imaging of focal hepatic lesions: Comparison of various RARE and fat-suppressed spin-echo sequences

The authors prospectively compared four T2-weighted magnetic resonance (MR) sequences, including high-resolution 512 × 512 (matrix size) RARE (rapid acquisition with relaxation enhancement), 256 × 256 RARE, 128 × 256 breath-hold RARE, and 192 × 256 fat-suppressed spin-echo (T2FS) sequences, in the evaluation of 16 patients with focal hepatic masses. MR images were evaluated by quantitative lesion-liver signal difference-to-noise ratios (SDNRs) and subjective evaluation of image artifact and image quality. No significant differences were observed between RARE sequences in SDNR values. The T2FS sequence had a significantly higher SDNR than the 512 × 512 RARE sequence (24.6 ± 15.0 vs 14.5 ± 9.7) (P =.008). Image quality was rated highest for the 512 × 512 RARE and T2FS sequences (P =.006). The inherent advantage of high spatial resolution suggests that the 512 × 512 RARE sequence may be of value in detecting hepatic lesions.     

Invited. Ultrafast T2-weighted imaging of the abdomen and pelvis: Use of single shot fast spin-echo imaging

Single shot (SS) rapid acquisition with relaxation enhancement (RARE) and half Fourier SS-RARE (HFSS-RARE, HASTE, or SS-FSE) sequences allow ultrafast imaging acquisition and generate high imaging quality. Images can be acquired within a very short time, without artifacts from physiologic motion. They are widely applied in the abdominal MRI. Clinical application of the ultrafast SS-RARE imaging techniques provide not only improved temporal resolution but better spatial resolution, higher SNR, and higher tissue contrast. Imaging parameters must be optimized for different MR scanners to obtain diagnostic images.     

On-line monitoring of ultrasonic surgery with MR imaging

Ultrasonic surgery was performed in rabbits and dogs under the guidance of magnetic resonance (MR) imaging. Two different MR techniques were used to guide the ultrasound beam. T2-weighted images showed lesion formation within a few minutes after sonication. T1-weighted GRASS (gradient-recalled acquisition in the steady state) images were sensitive to temperature elevations, permitting monitoring of lesion creation with MR imaging. Short TR T1-weighted GRASS images were not as helpful in detecting temperature elevation because of a reduction in signal-to-noise ratio. T2-weighted fast spin-echo images were compared with conventional T2-weighted spin-echo images. The former produced high-quality images in a fraction of the imaging time. This study shows that it is possible to monitor and guide ultrasonic surgery with MR imaging.     

Multislice T1-weighted hybrid rare in CNS imaging: Assessment of magnetization transfer effects and artifacts

Using a T1-weighted hybrid rapid acquisition with relaxation enhancement (RARE) MR sequence that implements an echo-to-view mapping scheme termed “low-high profile order,” we evaluated signal intensity changes in different brain tissues as a function of number of slices, interslice gap, and echo train length (ETL). We also measured phase-encode and frequency-encode noise as well as blurring artifacts along the phase-encode direction as a function of ETL. Off-resonance magnetization transfer effects were demonstrated to be responsible for signal intensities changes in white matter and gray matter when using multislice techniques. These effects are amplified by increasing the number of slices and ETL. Due to the nature of the implemented echo-to-view mapping scheme, no on-resonance magnetization transfer effects were observed from the intraslice echo train. Selective background (white matter and gray matter) suppression in multislice T1-weighted hybrid RARE, secondary to off-resonance magnetization transfer effects, may provide better contrast resolution of enhancing central nervous system (CNS) lesions at much shorter scan time as compared to conventional spin-echo T1-weighted sequences. This improvement in contrast resolution as a function of ETL may be limited by worsening phase-encode noise and blurring artifacts.     

Characterization of focal hepatic lesions with ferumoxides-enhanced MR imaging: utility of T1-weighted spoiled gradient recalled echo images using different echo times

PURPOSE: To evaluate the different signal characteristics of focal hepatic lesions on ferumoxides-enhanced MR imaging, including T1-weighted spoiled gradient recalled echo (GRE) images using different echo times (TE) and T2- and T2*-weighted images. MATERIALS AND METHODS: Ferumoxides-enhanced MR imaging was performed using a 1.5-T system in 46 patients who were referred for evaluation of known or suspected hepatic malignancies. One hundred and seven lesions (42 hepatocellular carcinomas [HCC], 40 metastases, 13 cysts, eight hemangiomas, three focal nodular hyperplasias [FNHs], and one cholangiocarcinoma) were evaluated. Postcontrast MR imaging included 1) T2-weighted FSE; 2) T2*-weighted GRE; 3) T1-weighted spoiled GRE using moderate (TE = 4.2-4.4 msec) TE; and 4) minimum (TE = 1.8-2.1 msec) TE. Signal intensities of the focal lesions were rated by two radiologists in conference as follows: hypointense, isointense or invisible, hyperintense, and markedly hyperintense. Lesion-to-liver contrast-to-noise ratio (C/N) was measured by one radiologist for a quantitative assessment. RESULTS: On ferumoxides-enhanced FSE images, 92% of cysts were "markedly hyperintense" and most of the other lesions were "hyperintense", and the mean C/N of cysts was significantly higher than that of other focal lesions. T2*-weighted GRE images showed most lesions with similar hyperintensities and the mean C/N was not significantly different between any two types of lesion. T1-weighted GRE images using moderate TE showed all FNHsand hemangiomas, 29 (69%) HCCs and eight (20%) metastases as "hyperintense". On T1-weighted GRE images using minimum TE, however, all HCCs and metastasis except one were iso- or hypointense, while all of the FNHs and hemangiomas were hyperintense. Ring enhancement was highly suggestive of malignant lesions, and was more commonly seen on the minimum TE images than on the moderate TE images. CONCLUSION: Addition of T1-weighted GRE images using minimum and moderate TE is helpful for characterizing focal lesions in ferumoxides-enhanced MR imaging.     

Ampullary carcinoma: Demonstration by current MR techniques

The objective of this study was to demonstrate the appearance of ampullary carcinoma using current MR techniques, including fat suppression, gadolinium enhancement, and MR cholangiography. Nine patients with ampullary carcinoma were examined by MRI at 1.5 T. MR examinations included T1-weighted spoiled gradient echo, T1-weighted fat-suppressed, and immediate postgadolinium spoiled gradient echo images for all patients and MR cholangiography for three patients. The imaging features of ampullary carcinomas, including tumor size and morphology, signal intensity, and enhancement characteristics, were determined. Ampullary carcinomas shown on MR images ranged in size from 1.5 to 5.5 cm. Tumors were low in signal intensity on precontrast T1-weighted spoiled gradient echo and T1-weighted fat-suppressed images relative to normal pancreatic tissue and enhanced less than normal pancreas on immediate postgadolinium spoiled gradient echo images. Tumor conspicuity was greatest on immediate postgadolinium spoiled gradient echo images. MR cholangiography demonstrated high grade obstruction of the common bile duct and mild dilatation of the pancreatic duct at the level of the ampulla with abrupt termination of the ducts in two untreated patients and moderate dilatation of the common bile duct in one patient who had a biliary stent. Ampullary carcinomas can be demonstrated on MR images as small masses arising at the ampulla. Tumors are well defined on immediate postgadolinium spoiled gradient echo images.     

Fast spin-echo imaging of the knee: Factors influencing contrast

Conventional T2-weighted spin-echo magnetic resonance imaging of the knee requires a long TR. Fast spin-echo (FSE) imaging can improve acquisition efficiency severalfold by collecting multiple lines of k space for each TR. Compromises in resolution, section coverage, and contrast inevitably result. The authors examined the compromises encountered in FSE imaging of the knee and discuss the variations in image contrast and resolution due to choices of sequence parameters. For short TR/TE knee imaging, FSE does not appear to offer any advantages, since the increased collection efficiency for one section reduces the available number of sections, so that the total imaging time for a given number of sections remains constant relative to conventional spin-echo imaging. For T2-weighted images, considerable time can be saved and comparable quality images can be obtained. This saved time can be usefully spent on increasing both the resolution of the image and its signal-to-noise ratio, while still reducing total acquisition time by a factor of two. The preferred FSE T2-weighted images were acquired with a TR of 4,500 msec, TE of 120 msec, and eight echoes. The available number of sections is compromised, and the sequence remains sensitive to flow artifacts; however, the FSE sequence appears to be promising for knee imaging.     

MR imaging in retinoblastoma

We studied the appearance of retinoblastoma on unenhanced and gadolinium-enhanced images and the accuracy of tumour staging with MR imaging. The MR images were obtained in 18 children with retinoblastoma and compared with histopathological findings after enucleation. The MR imaging included T1-weighted and dual-echo T2-weighted images before, and T1-weighted images after, gadopentetate dimeglumine injection. The contrast between tumour and ipsilateral vitreous strongly increased (57%) after gadolinium on T1-weighted images (p=0.004). Tumour was strongly hypointense as compared with ipsilateral vitreous in all patients using heavily T2-weighted (TE=120 ms) images (p=0.001). The estimated T2 of tumour (mean 96+14 ms) did not correlate with histological grading or degree of calcification. Unenhanced T1-weighted MR images rightfully excluded extrascleral growth in 16 of 16 cases, but its presence was confirmed after enucleation in only one of 2 abnormal MR scans. Invasion of the optic nerve behind the cribriform plate was confirmed in 2 of 3 abnormal gadolinium-enhanced MR scans, but also in 1 of the 15 cases in which MR images were normal. The T2-weighted images were useful in assessing retinal detachment. We conclude that heavily T2-weighted images, unenhanced T1-weighted images and gadolinium-enhanced T1-weighted MR images are complementary in characterizing and staging retinoblastoma.     

Detection and quantification of breast tumor necrosis with MR imaging: value of the necrosis-avid contrast agent Gadophrin-3

RATIONALE AND OBJECTIVES: The authors evaluated the use of T1-weighted magnetic resonance (MR) imaging with Gadophrin-3 enhancement and of plain T2-weighted MR imaging to detect and quantify breast tumor necrosis. MATERIALS AND METHODS: Twenty EMT-6 tumors (mouse mammary sarcoma), implanted into the mammary fat pad of BALB/c-AnNCrl mice, underwent MR imaging with plain T2-weighted and T1-weighted fast field echo sequences before and 24 hours after injection of Gadophrin-3, a new necrosis-avid contrast agent. Tumor necrosis on MR images was quantified by means of a dedicated segmentation program and was correlated with histologic findings. RESULTS: In all tumors a central necrosis was revealed by histopathologic analysis, and central enhancement was seen with Gadophrin-3 on T1-weighted images. Small tumors (diameter, < 1 cm) showed an inhomogeneous central enhancement, whereas larger tumors (diameter, > 1 cm) enhanced mainly in the periphery of necrotic tissue. Plain T2-weighted images showed a hyperintense central area in only three of 20 cases with a large central necrosis. CONCLUSION: Gadophrin-3-enhanced T1-weighted images are superior to plain T2-weighted images for the detection of necrosis in a murine tumor xenograft model.     

T1-Weighted MR imaging of the brain using a fast inversion recovery pulse sequence

The purpose of this paper was to develop and evaluate a fast inversion recovery (FIR) technique for T1-weighted MR imaging of contrast-enhancing brain pathology. The FIR technique was developed, capable of imaging 24 sections in approximately 7 minutes using two echoes per repetition and an alternating echo phase encoding assignment. Resulting images were compared with conventional T1-weighted spin echo (T1SE) images in 18 consecutive patients. Compared with corresponding T1SE images, FIR images were quantitatively comparable or superior for lesion-to-background contrast and contrast-to-noise ratio (CNR). Gray-to-white matter and cerebrospinal fluid (CSF)-to-white matter contrast and CNR were statistically superior in FIR images. Qualitatively, the FIR technique provided comparable lesion detection, improved lesion conspicuity, and superior image contrast compared with T1SE images. Although FIR images had greater amounts of image artifacts, there was not a statistically increased amount of interpretation-interfering image artifact. FIR provides T1-weighted images that are superior to T1SE images for a number of image quality criteria.     

Malignant lesions of the liver identified on T1- but not T2-weighted MR images at 1.5 T

The authors reviewed their 21/2-year experience with a magnetic resonance (MR) imaging protocol for a 1.5-T MR imager that included T2-weighted fat-suppressed spin-echo, T1-weighted breath-hold gradient-echo, and serial dynamic gadolinium-enhanced T1-weighted gradient-echo imaging to identify histologic types of malignant liver lesions more apparent on T1- than on T2-weighted images. MR images of 212 consecutive patients with malignant liver lesions were reviewed. T2-weighted, T1-weighted, and dynamic contrast-enhanced T1-weighted images were examined separately in a blinded fashion. Seven patients demonstrated liver lesions (lymphoma [two patients] and carcinoid, hepatocellular carcinoma, colon adenocarcinoma, transitional cell carcinoma, and melanoma [one patient each]) on T1-weighted images that were inconspicuous on T2-weighted images. In all cases, the lesions were most conspicuous on T1-weighted images obtained immediately after administration of contrast agent. Histologic confirmation was present for all seven patients. The consistent feature among these lesions was that they were hypovascular, due either to a fibrous stroma or to dense monoclonal cellularity. These results suggest that in some patients with hypovascular primary neoplasms, the lesions may be identified only on T1-weighted images, and that immediate postcontrast T1-weighted images are of particular value in demonstrating lesions.     

Ultrafast MR imaging of the pelvis.

MR gradient systems with higher slew rates and gradient amplitude enable certain forms of imaging that are not practical with older gradient systems. These newer pulse sequences include single shot half-Fourier T2-weighted images and echo planar imaging. More important in MR imaging of the pelvis, these gradient systems benefit more conventional imaging methods such as gadolinium-enhanced 3D MR angiography, dynamic gradient echo contrast-enhanced images, and T2-weighted fast spin echo images, by shortening echo times. For most MR imaging of the pelvis, spatial resolution is paramount, and therefore sequences such as half-Fourier acquisition Turbo spin echo (HASTE) and 3D gadolinium-enhanced dynamic imaging play a less important role than in the upper abdomen. The potential of these techniques for diffusion or perfusion studies in the pelvis has not been explored.     

T2-weighted echo planar MR imaging of the abdomen: optimization of imaging parameters

Echo planar imaging (EPI) is an ultra-fast magnetic resonance (MR) imaging method that provides strong T2-weighted contrast, which is important for the detection and characterization of various abdominal abnormalities. However, EPI may be associated with significant artifacts. The prominence of these artifacts, as well as overall image quality, is dramatically impacted by selection of imaging parameters. The purpose of this study is to demonstrate the effects of controlled alterations in operator-defined imaging parameters on image quality in breath-hold abdominal T2-weighted EPI. An understanding of these effects facilitates optimizing parameter selection for acquisition of abdominal EPI images.