Are signal intensity and homogeneity useful parameters for distinguishing between benign and malignant soft tissue masses on MR images?: Objective evaluation by means of texture analysis

Objectives

To objectively identify possible differences in the signal characteristics of benign and malignant soft tissue masses (STM) on magnetic resonance (MR) images by means of texture analysis and to determine the value of these differences for computer-assisted lesion classification.

Method

Fifty-eight patients with histologically proven STM (benign, n=30; malignant, n=28) were included. STM texture was analyzed on routine T1-weighted, T2-weighted and short tau inversion recovery (STIR) images obtained with heterogeneous acquisition protocols. Fisher coefficients (F) and the probability of classification error and average correlation coefficients (POE+ACC) were calculated to identify the most discriminative texture features for separation of benign and malignant STM. F>1 indicated adequate discriminative power of texture features. Based on the texture features, computer-assisted classification of the STM by means of k-nearest-neighbor (k-NN) and artificial neural network (ANN) classification was performed, and accuracy, sensitivity and specificity were calculated.

Results

Discriminative power was only adequate for two texture features, derived from the gray-level histogram of the STIR images (first and 10th gray-level percentiles). Accordingly, the best results of STM classification were achieved using texture information from STIR images, with an accuracy of 75.0% (sensitivity, 71.4%; specificity, 78.3%) for the k-NN classifier, and an accuracy of 90.5% (sensitivity, 91.1%; specificity, 90.0%) for the ANN classifier.

Conclusion

Texture analysis revealed only small differences in the signal characteristics of benign and malignant STM on routine MR images. Computer-assisted pattern recognition algorithms may aid in the characterization of STM, but more data is necessary to confirm their clinical value.     

Assessment of the internal craniocervical ligaments with a new magnetic resonance imaging sequence: three-dimensional turbo spin echo with variable flip-angle distribution (SPACE)

Purpose

Lesions close to the internal craniocervical ligaments are a common problem in patients with whiplash injuries. The aim of this study was to evaluate the morphology and visibility of these ligamentous structures with a new isotropic three-dimensional (3D) turbo-spin-echo (TSE) technique.

Materials and Methods

MR (MR) images of the cervical spine of 52 healthy subjects (27 women and 25 men; mean age=29 years; age range=18–40 years) were taken with a T2-weighted 3D TSE sequence with variable flip-angle distribution [SPACE (Sampling Perfection with Application optimized Contrasts using different flip-angle Evolution)] at 1.5 T (Magnetom Avanto, Siemens Erlangen, Germany). Two experienced musculoskeletal radiologists read the images independently on a 3D imaging and postprocessing workstation. The visibility and morphology of the alar ligaments were evaluated on a five-point scale, and inter-reader correlation was assessed with kappa statistics.

Results

Both alar ligaments were detected in all subjects. Twenty-eight (53.8%) of the alar ligaments could not be seen within one slice of the standard coronal imaging plane but could adequately be visualized in an oblique reconstruction adapted to the orientation of the ligaments on the axial slices. Inter-reader correlation for visibility on MR imaging (MRI) of the internal craniocervical ligaments was high (left+right side, kappa=0.95). Most (94%) alar ligaments presented symmetrically. In the axial plane, 60% were oriented neutral and 40% had a backward orientation. In the coronal plane, 67% were oriented caudocranially and 33% were oriented horizontally. The shape of the ligaments was parallel in half and was V-shaped in the other half. The alar ligaments had homogeneous low-signal intensity in 56% and heterogeneous low-signal intensity in 44%. The apical ligament of the dens was seen (excellent–good–moderate) in 61% (reader 1) and 52% (reader 2). The tectorial membranes and the transverse ligament of the atlas were shown (excellent–good) in all subjects.

Conclusions

MRI with acquisition of an isotropic SPACE technique allows high-resolution imaging of the craniocervical ligaments in all orientations. Reconstruction of the image data in the variable orientation of the alar ligaments allowed for excellent depiction within one slice such that partial volume artifacts that hamper image analysis can be eliminated.     

Detection of focal liver lesions in unenhanced and ferucarbotran-enhanced magnetic resonance imaging: a comparison of T2-weighted breath-hold and respiratory-triggered sequences

Purpose

To investigate the image quality and detection rate of focal liver lesions by comparing a T2-weighted breath-hold single-shot sequence and a T2-weighted high spatial resolution fast spin-echo sequence with respiratory triggering via unenhanced and superparamagnetic iron oxide (SPIO)-enhanced liver imaging.

Materials and Methods

The study was approved by the local ethical review board; informed consent was waived. Liver-lesion contrast was measured and a qualitative consensus evaluation of image quality and lesion detection was performed in 42 consecutive patients using a 1.5-T MR system.

Results

The liver-lesion contrast was significantly higher (P<.05) for the respiratory-triggered sequence compared to the breath-hold sequence regarding unenhanced and SPIO-enhanced imaging. The respiratory-triggered sequences revealed significantly higher image quality scores as well as higher numbers of detected liver lesions compared to the breath-hold sequence on unenhanced and SPIO-enhanced imaging. The SPIO contrast did not significantly improve the number of detected lesions on the respective sequences (P>.05).

Conclusion

We find that respiratory-triggered fast spin-echo sequences produce a higher image quality and a more precise liver-lesion detection rate thereby justifying the increased acquisition time necessary for this method.     

The use of T2*-weighted multi-echo GRE imaging as a novel method to diagnose hepatocellular carcinoma compared with gadolinium-enhanced MRI: a feasibility study

Background

The goal of the study was to assess a T2*-weighted MRI sequence for the ability to identify hepatocellular carcinoma (HCC).

Methods

Hepatic iron deposition, which is common in chronic liver disease (CLD), may increase the conspicuity of HCC on GRE imaging due to increased T2* signal decay in liver parenchyma. In this study, a breath-hold T2*-weighted MRI sequence was evaluated by a blinded observer for HCC and the results compared to a reference standard of gadolinium-enhanced MRI in these same patients. Forty-one patients (mean age 56.2 years; 17 females) were included in this approved, retrospective study.

Results

By the reference standard, 14 of 41 patients had a total of 25 HCCs. The sensitivity of the T2*-weighted MR sequence for identifying HCC, per lesion, was 60%, while the specificity was 100%. There was a significantly lower T2* value of liver parenchyma in patients with HCC identified by the T2*-weighted sequence than in those with HCCs which were not identified by the T2*-weighted sequence (27.8±2.2 vs. 21.9±2.1 ms; P=.02).

Conclusions

A T2*-weighted MRI sequence can identify HCC in patients with CLD. This technique may be beneficial for imaging of patients contraindicated for gadolinium.     

Conspicuity of bone metastases on fast Dixon-based multisequence whole-body MRI: Clinical utility per sequence

Purpose

The purpose of the study was to evaluate the conspicuity of bone metastases on each of the numerous sequences produced by fast Dixon-based multisequence whole-body (WB) magnetic resonance imaging (MRI) scanning in order to determine the most clinically useful sequences overall and per anatomic region.

Materials and Methods

Twenty-seven breast cancer patients with bone metastases were prospectively studied with fast Dixon-based WB MRI including head/neck, chest, abdominal, pelvic, thigh, calf/feet and either cervical, thoracic and lumbar or cervical/thoracic and thoracic/lumbar regions. Sequences included coronal T2, axial T1 without and with intravenous gadolinium (+ C), sagittal T1 spine + C, each associated fat-only (FO) and fat-saturated (FS) sequence, axial diffusion-weighted imaging (DWI) and short tau inversion recovery (STIR). Blinded reviewers evaluated lesion conspicuity, a surrogate of clinical utility, on a five-point scale per anatomic region. Sequences were compared using analysis of variance, differences were detected with Tukey's honestly significant difference test, and the four sequences with highest mean conspicuity were compared to the remainder overall and per anatomic region.

Results

Overall, a significant lesion conspicuity difference was found (P < .0001), and lesion conspicuity was significantly higher on FS T1 + C, FO T1 + C, T1 + C sagittal and FS T1 + C axial sequences (P < .0001). Per-region results were the same in the head/neck. Other sequences overlapped with these and included the following: chest/abdomen — FO T2, DWI; pelvis — DWI, FO T2; thigh — FS T2, FO T2, FO T1 + C; calf/feet — FS T2, DWI, FO T2, STIR.

Conclusion

Overall, bone lesions were most conspicuous on FS T1 + C sagittal, FO T1 + C sagittal, T1 + C sagittal and FS T1 + C axial fast Dixon WB MRI sequences.     

Hepatocellular lesions with increased iron uptake on superparamagnetic iron oxide-enhanced magnetic resonance imaging in cirrhosis or chronic hepatitis: comparison of four magnetic resonance sequences for lesion conspicuity

Purpose

The aim of this study was to determine the adequate MR sequence for the lesion conspicuity of hepatocellular lesions with increased iron uptake on superparamagnetic iron oxide (SPIO)-enhanced MRI.

Materials and Methods

SPIO-enhanced MRI was performed using a 1.5-T system. Among 25 patients with hypovascular hepatocellular nodules on contrast-enhanced dynamic CT (no early enhancement at arterial phase and hypoattenuation at equilibrium phase), 39 lesions with increased iron uptake on SPIO-enhanced MRI were evaluated. SPIO-enhanced MRI included (1) T1-weighted in-phase gradient recalled echo (GRE) images, (2) T2-weighted fast spin echo (FSE) images, (3) T2*-weighted GRE with moderate TE (7 ms) and (4) long TE (12 ms). The lesion-to-liver contrast-to-noise ratios of the hepatocellular nodule and the signal-to-noise ratio (SNR) of the hepatic parenchyma were calculated by one radiologist for a quantitative assessment. MR images were reviewed retrospectively by two independent radiologists to compare the subjective lesion conspicuity in each image set based on a four-point rating scale.

Result

The mean lesion-to-liver contrast-to-noise ratios with T2*-weighted GRE with moderate TE (7 ms) was highest (5.79±3.71) and was significantly higher than those with T1-weighted, in-phase images (3.79±3.23, P<.01), T2-weighted images (2.72±1.52, P<.001) and T2*-weighted GRE with long TE (12 ms) (3.93±2.69, P<.05). The subjective rating of lesion conspicuity was best on the T2*-weighted GRE with moderate TE (7 ms), followed by that on the T2*-weighted GRE with moderate TE (7 ms; P<.05).

Conclusion

T2*-weighted GRE sequence with moderate TE (7 ms) showed high lesion-to-liver contrast-to-noise ratios in hepatocellular lesions with increased iron uptake on SPIO-enhanced MRI, indicating better lesion conspicuity of hypointense hepatocellular nodules in cirrhosis or chronic hepatitis.     

Impact of diffusion-weighted MR imaging on the characterization of small hepatocellular carcinoma in the cirrhotic liver

Purpose

The purpose of this study was to determine whether or not adding diffusion-weighted magnetic resonance imaging (DWI) to conventional magnetic resonance (MR) imaging sequences improves the characterization of small hepatocellular carcinoma (HCC) (≤2 cm) in the setting of cirrhotic liver compared to conventional sequences alone.

Materials and Methods

A total of 62 cirrhotic liver patients with 82 nodules smaller than 2 cm in diameter were enrolled, and all lesions were pathologically confirmed. For the first reading session, which included precontrast T1- and T2-weighted images and T1 dynamic contrast-enhanced images, preindicated lesions by a study coordinator were characterized by two radiologists. They determined the confidence levels in consensus for the presence of small HCC into four grades. In another session, respiratory-triggered diffusion-weighted MR images (b factor=50, 400 and 800 s/mm²) were added to the previously reviewed images, and the same two radiologists again determined the confidence levels. The diagnostic performance of the combined DWI–conventional sequences set and the conventional sequences alone set was evaluated using receiver operating characteristic curves. Sensitivity and specificity values for characterizing small HCCs were also calculated.

Results

The area under the receiver operating characteristic curve for the second interpretation session (0.86) was significantly higher (P=.038) than that of the first session (0.76). The sensitivity was significantly increased from 75.7% to 87.8% by adding DWI to the conventional sequences (P=.015). No significant differences were observed for specificity values.

Conclusion

Adding DWI to conventional imaging modalities improves the diagnosis of small HCCs in the cirrhotic liver in terms of diagnostic performance and sensitivity by increasing reader confidence.     

Feasibility of fat-saturated T2-weighted magnetic resonance imaging with slice encoding for metal artifact correction (SEMAC) at 3T

Background and Purpose

Fluid-sensitive MR imaging in postoperative evaluation is important, however, metallic artifacts is inevitable. The purpose is to investigate the feasibility of fat-saturated slice encoding for metal artifact correction (SEMAC)-corrected T2-weighted magnetic resonance (MR) at 3T in patients with spinal prostheses.

Methods

Following institutional review board approval, 27 SEMAC-encoded spinal MRs between September 2012 and October 2013 in patients with spinal metallic prostheses were analyzed. The MR images were scanned on a 3T MR system including SEMAC-corrected and uncorrected fast spin echo (FSE) T2-weighted MR images with fat-saturation. Two musculoskeletal radiologists compared the image sets and qualitatively analyzed the images using a five-point scale in terms of artifact reduction around the prosthesis, visualization of the prosthesis and pedicle, and intervertebral neural foramina. Quantitative assessments were performed by calculating the ratio of signal intensity from the fixated vertebra and that from upper level vertebra. For statistical analyses, paired t-test was used.

Results

Fat-saturated SEMAC-corrected T2-weighted MR images enabled significantly improved metallic artifact reduction (P < 0.05). Quantitative evaluation of the signal intensity ratio of screw-fixated vertebra and upper level vertebra showed a significantly lower ratio on fat-saturated SEMAC images (P < 0.05), however, the high signal intensity of signal pile-up could be not completely corrected.

Conclusion

SEMAC correction in fat-suppressed T2-weighted MR images can overcome the signal loss of metallic artifacts and provide improved delineation of the pedicle screw and peri-prosthetic region. Signal pile-up, however, could not be corrected completely, therefore readers should be cautious in the evaluation of marrow around the prosthesis.     

Image quality and diagnostic performance of silicone-specific breast MRI

Purpose

To compare the image quality of three techniques and diagnostic performance in detecting implant rupture.

Materials and Methods

The study included 161 implants for the evaluation of image quality, composed of water-saturated short TI inversion recovery (herein called “water-sat STIR”), three-point Dixon techniques (herein called “Dixon”), and short TI inversion recovery fast spin-echo with iterative decomposition of silicone and water using least-squares approximation (herein called “STIR IDEAL”) and included 41 implants for the evaluation of diagnostic performance in detecting rupture, composed of water-sat STIR and STIR IDEAL.Six image quality categories were evaluated and three classifications were used: normal implant, possible rupture, and definite rupture.

Results

Statistically significant differences were noted for the image quality categories (p < 0.001). STIR IDEAL was superior or equal to water-sat STIR in all image quality categories except artifact effects and superior to Dixon in all categories. Water-sat STIR performed the poorest for water suppression uniformity.The sensitivity and specificity in detecting implant rupture of STIR-IDEAL were 81.8 % and 77.8 % and the difference between two techniques was not statistically significant.

Conclusion

STIR-IDEAL is a useful silicone-specific imaging technique demonstrating more robust water suppression and equivalent diagnostic accuracy for detecting implant rupture, than water-sat STIR, at the cost of longer scan time and an increase in minor motion artifacts.     

Usefulness of slice encoding for metal artifact correction (SEMAC) for reducing metallic artifacts in 3-T MRI

Purpose

The purpose of the study was to assess the usefulness of slice encoding for metal artifact correction (SEMAC) in 3.0-T magnetic resonance (MR) in minimizing metallic artifacts in patients with spinal prostheses.

Materials and Methods

Institutional review board approval and informed consent were obtained for this study. Twenty-seven spine MR scans were performed with metal artifact reduction SEMAC between May 2011 and July 2012 in patients with metallic devices. The MR scans were performed on a 3-T MR system (Achieva; Philips Healthcare, Best, the Netherlands) including SEMAC-corrected T2-weighted axial/sagittal images and two-dimensional fast spin echo (FSE) axial/sagittal images. The SEMAC-corrected images were compared to conventional T2-weighted FSE images. Two musculoskeletal radiologists qualitatively analyzed the images in terms of visualization of the pedicle, vertebral body, dural sac, intervertebral disc, intervertebral neural foramina, screws and metallic artifacts. The paired images were rated using a 5-point scale. P values less than .05 were considered to indicate statistically significant differences.

Results

The SEMAC-corrected MR images significantly reduced the metal-related artifacts. The T2-weighted images with SEMAC sequences enabled significantly improved periprosthetic visualizations of the pedicle, vertebral body, dural sac and neural foramina, with the exception of the intervertebral disc (P < .05). In addition, there was significant improvement in prosthesis visualization (P < .05).

Conclusion

MR images with SEMAC can reduce metal-related artifacts, providing improved delineation of the prosthesis and periprosthetic region. However, for the evaluation of the intervertebral disc, the SEMAC-corrected MR images showed no significant benefits.     

A next-generation,flow-diverting implant used to treat brain aneurysms: in vitro evaluation of magnetic field interactions,heating and artifacts at 3-T

Background and Purpose

Fine-mesh braided, stent-like structures (flow diverters) have been proposed for treatment of brain aneurysms. To date, the safety of performing magnetic resonance imaging (MRI) in patients with these implants is unknown. Therefore, the purpose of this study was to evaluate MRI issues at 3-T for a new flow-diverting implant used to treat brain aneurysms.

Methods

The Surpass NeuroEndoGraft (Surpass Medical, Ltd., Tel Aviv, Israel) underwent evaluation for magnetic field interactions, MRI-related heating and artifacts using standardized techniques. Magnetic field interactions were assessed for this implant with regard to translational attraction (i.e., using the deflection angle technique) and torque (qualitative assessment method). MRI-related heating was evaluated by placing the implant in a gelled-saline-filled, head/torso phantom and performing MRI using a transmit/receive radiofrequency body coil at a whole-body-averaged specific absorption rate of 2.9 W/kg for 15 min. Artifacts were characterized using T1-weighted, spin echo (SE) and gradient echo (GRE) pulse sequences.

Results

The Surpass NeuroEndoGraft exhibited minor magnetic field interactions (21° deflection angle and no torque), which were acceptable from a safety consideration. Heating was not substantial, with the highest temperature change being 2.3°C (background temperature rise without the implant was 1.5°C). Artifacts may create issues if the area of interest is in the same area or close to this implant.

Conclusions

The findings demonstrated that it would be acceptable for patients with this next-generation, flow-diverting implant to undergo MRI at 3-T or less.     

MR evaluation of breast lesions obtained by diffusion-weighted imaging with background body signal suppression (DWIBS) and correlations with histological findings

Objectives

Diffusion imaging represents a new imaging tool for the diagnosis of breast cancer. This study aims to investigate the role of diffusion-weighted MRI with background body signal suppression (DWIBS) for evaluating breast lesions.

Methods

90 patients were prospectively evaluated by MRI with STIR, TSE-T2, contrast enhanced THRIVE-T1 and DWIBS sequences. DWIBS were analyzed searching for the presence of breast lesions and calculating the ADC value. ADC values of ≤ 1.44 × 10^- 3 mm²/s were considered suspicious for malignancy. This analysis was then compared with the histological findings. Sensitivity, specificity, diagnostic accuracy (DA), positive predictive value (PPV) and negative (NPV) were calculated.

Results

In 53/90 (59%) patients, DWIBS indicated the presence of breast lesions, 16 (30%) with ADC values of  > 1.44 and 37 (70%) with ADC ≤ 1.44. The comparison with histology showed 25 malignant and 28 benign lesions. DWIBS sequences obtained sensitivity, specificity, DA, PPV and NPV values of 100, 82, 87, 68 and 100%, respectively.

Conclusion

DWIBS can be proposed in the MRI breast protocol representing an accurate diagnostic complement.     

Diffusion-weighted echo-planar imaging of the head and neck using 3-T MRI: Investigation into the usefulness of liquid perfluorocarbon pads and choice of optimal fat suppression method

Purpose

To investigate whether image quality can be improved using liquid perfluorocarbon pads (Sat Pad) and clarify the optimal fat-suppression method among chemical shift selective (CHESS), water excitation (WEX), and short TI inversion recovery (STIR) methods in diffusion-weighted imaging (DWI) of the head and neck using 3-T magnetic resonance imaging. Correlations between results of visual inspection and quantitative analysis were also examined.

Material and Methods

This study was approved by our Institutional Review Board and informed consent was waived. DWI was performed on 25 subjects with/without Sat Pad and using three fat-suppression methods (6 patterns). Image quality was evaluated visually (4-point scales and lesion-depiction capability) and by quantitative analysis (signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR)). Two-way repeated-measures analysis of variance (ANOVA) was used to detect significant differences in scores of visual evaluation, SNR, and CNR.

Results

Mean visual evaluation scores were significantly higher with Sat Pad using STIR than without Sat Pad for all fat-suppression methods (P < 0.05). DWI with Sat Pad using STIR tended to be useful for depicting lesions. DWI using STIR showed reduced W-SNR (W: whole area of depicted structure) and CNR (between semispinalis capitis muscle and subcutaneous fat) due to fewer artifacts and uniform fat suppression.

Conclusion

Combining Sat Pad with STIR provides good image quality for visual inspections. When numerous artifacts are present and fat suppression is insufficient, higher SNR and CNR do not always provide good diagnostic image quality.     

Ultrasmall superparamagnetic iron oxides enhanced MR imaging in rats with experimentally induced endometriosis

Purpose

The purpose of our study was to evaluate the feasibility of magnetic resonance imaging (MRI) using ultrasmall superparamagnetic iron oxides (USPIO) in the detection of experimentally induced endometriosis.

Materials and methods

Endometriosis was surgically induced in rats by transplanting an autologous fragment of uterine tissue onto the inner surface of the abdominal wall, the posterior surface of the uterine body and the arterial cascades of the small intestines adjacent to mesenteric blood vessels. Six weeks later, MRI using Gd-DTPA and USPIO was performed for the evaluation of the ectopic uterine tissue (EUT). A scoring system was developed for image interpretation (0=absence, 1=probably absence, 2=probably presence and 3=presence). We defined MR index (MRIx) as the sum of T1-weighted and enhanced T1-weighted and T2-weighted image scores, and USPIO MRIx (MRIx^+USPIO) as the MRIx score plus the score of USPIO-enhanced T2-weighted image.

Results

The MRIx^+USPIO was also higher in the successfully autotransplanted group than in the failed group (6.19±1.72 versus 3.94±1.20, P<.001). There was also a significant linear relationship between MRIx^+USPIO and pathologic status (R²=0.494, P<.001). Thirty-one (64.6%) of the 48 implanted uterine tissues were histologically confirmed on pathologic review. The area of MRIx and MRIx^+USPIO in the detection of EUT more than 3 mm in size was 0.739 and 0.913, respectively.

Conclusion

Our results suggest that USPIO-enhanced MRI could be a novel diagnostic tool for diagnosis in experimentally induced peritoneal endometriosis.     

Magnetic resonance differentiation between T2 and T1 gallbladder carcinoma: significance of subserosal enhancement on the delayed phase dynamic study

Purpose

The aim of this study is to investigate whether subserosal enhancement on the delayed-phase dynamic magnetic resonance (MR) study (SED) can differentiate T2 from T1 gallbladder carcinoma (GBC).

Methods

The institutional research board approved this retrospective study. Between 1997 and 2006, there were surgically proven 11 T1 and 21 T2 GBC in 30 patients, all of whom had undergone preoperative contrast enhanced dynamic MR study, either with a 2D sequence (n=17) or 3D sequences (n=15). All images were reviewed by two radiologists for the presence of SED, and receiver operating characteristic (ROC) curve analysis was performed. Sensitivity, specificity, positive and negative predictive values were calculated by consensus.

Results

The areas under the ROC curves of the two readers were 0.91 and 0.86, and the kappa value was 0.78. Of the 21 T2 GBC, 18 and 3 showed positive and negative SED, respectively. Of the 11 T1 GBC, 1 and 10 showed positive and negative SED, respectively. The sensitivity, specificity, positive and negative predictive values of SED for diagnosing T2 lesions were 86%, 88%, 91% and 77%, respectively.

Conclusions

In conclusion, SED may be a useful sign to differentiate T2 from T1 GBC, which would affect the preoperative surgical planning of the patients.     

Diffusion-weighted imaging versus superparamagnetic iron oxide (SPIO)-enhanced MRI: exclusive and combined values in the assessment of hepatic metastases

Purpose

The purpose was to validate diffusion-weighted imaging (DWI) in the assessment of hepatic metastases compared with superparamagnetic iron oxide (SPIO)-enhanced magnetic resonance imaging.

Materials and Methods

For 21 consecutive patients with 160 metastases from extrahepatic malignancy and 25 benign focal lesions, two radiologists evaluated four separate review sessions (I, SPIO-enhanced T2?-weighted images; II, precontrast DWI; III, SPIO-enhanced T2?-weighted images and precontrast DWI; IV, SPIO-enhanced T2?-weighted images plus precontrast and SPIO-enhanced DWI) and assigned confidence levels using a five-grade scale for each hepatic lesion.

Results

The A_z values after receiver operating characteristic curve analysis for Reader 1 and Reader 2 were 0.80 and 0.75 on session I, 0.91 and 0.91 on session II, 0.97 and 0.96 on session III and 0.96 and 0.96 on session IV, respectively. The A_z value of session II was significantly higher than that of session I (Reader 1, P=.004; Reader 2, P<.001), and that of session III was significantly higher than that of session I (P<.001 for each reader) or session II (Reader 1, P=.004; Reader 2, P=.003). Although there was no significant difference of A_z value between session III and session IV (Reader 1, P=.231; Reader 2, P=.878), the sensitivity improved for session IV compared with that for session III (Reader 1, P=.031; Reader 2, P=.039).

Conclusion

In the assessment of hepatic metastases, DWI can provide more accurate information than can SPIO-enhanced images. Diagnostic accuracy can be increased even more through the combination of both techniques.     

A new vascular coupling device: Assessment of MRI issues at 3-tesla

Objective

Vascular grafting frequently involves a time-consuming operation. A new vascular coupling device (VCD) made from metallic material was recently developed that may be advantageous because of the reduced operative time and decreased patient risks. Because of the metal, there are safety concerns related to MRI. Therefore, the purpose of this investigation was to use standardized testing techniques to evaluate MRI issues for this VCD in association with a 3-Tesla MR system.

Methods

The VCD (corlife oHG, Hannover, Germany) was evaluated for magnetic field interactions (translational attraction and torque), MRI-related heating, and artifacts at 3-Tesla. MRI-related heating was assessed with the VCD in a gelled-saline-filled phantom with MRI performed at a whole body averaged SAR of 2.9-W/kg for 15-min. Artifacts were assessed using T1-weighted, spin echo, and gradient echo pulse sequences.

Results

The VCD exhibited minor magnetic field interactions and minimal heating (maximum temperature elevation, 1.8 °C). Artifacts were relatively small in relation to the size and shape of this implant. The lumen of the VCD could not be visualized using the gradient echo pulse sequence.

Conclusions

The metallic VCD that underwent evaluation is MR conditional for a patient undergoing an MRI procedure at 3-Tesla or less.     

Magnetic resonance T1ρ imaging of osteoarthritis: a rabbit ACL transection model

Objective

The objective of this study was to develop quantitative T_1ρ-weighted magnetic resonance imaging methodology for the detection and characterization of cartilage degeneration in a rabbit anterior cruciate ligament (ACL) transection model.

Methods

The right knee ACLs of 18 adult female New Zealand white rabbits were transected. The left knee joint served as a sham control. The rabbits were euthanized at 3 (Group 1), 6 (Group 2) and 12 (Group 3) weeks postoperatively. High-resolution 3D fat-saturated spoiled gradient echo images and T_1ρ-weighted images were obtained in both the sagittal and axial planes at 3 T using a quadrature wrist coil. Following MR analysis, histological slides from the lateral femoral condyle cartilage were graded using the Mankin grading system.

Results

For all three groups, the average overall T_1ρ values were significantly higher in the ACL-transected knee compared to control knee, and the percentage differences in T_1ρ values between ACL-transected and control increased with the duration of time after transection. The average Mankin score for ACL-transected knees was higher than that for control for each time point, but this difference was statistically significant only for all groups combined.

Conclusions

This study demonstrates the feasibility of using T_1ρ-weighted imaging as a useful tool in the detection and quantification of cartilage damage in all knee compartments in an ACL-transected rabbit model of cartilage degeneration.     

Dual-source parallel radiofrequency transmission for magnetic resonance breast imaging at 3 T: Any added clinical value?

Purpose

To investigate the influence of dual-source parallel radiofrequency (RF) excitation on clinical breast MR images.

Methods

A 3 T MR system with both dual-source and conventional single-source RF excitations was used to examine 22 patients. Axial TSE-T₂WI with fat suppression, TSE-T₁WI without fat suppression, THRIVE (3D field echo) and DWI (SE-EPI) were obtained by using both excitation techniques. Image homogeneity, image contrast and lesion conspicuity were measured or independently scored by two radiologists and were compared by paired-sample t test or Wilcoxon test.

Results

Both excitations revealed 24 lesions. For SE sequences using dual-source mode, image homogeneity was improved (P = 0.00), scan time was reduced, and ghost artifacts on DWI were significantly reduced (P = 0.00). However, image contrast was not increased and lesion conspicuity had no significant difference between two modes, except DWI on which lesion conspicuity was significantly improved (P = 0.00), due to less ghost artifacts. For field-echo sequence, image homogeneity, acquisition time, image contrast and lesion conspicuity had no significant difference between the two modes.

Conclusions

Dual-source parallel RF transmission has some added value for improving breast image quality. However, its value is limited in terms of improving lesion detection and characterization.     

3D high-resolution contrast enhanced MRI of carotid atheroma — a technical update

Objective

Development of a fast 3D high-resolution magnetic resonance imaging (MRI) protocol for improved carotid artery plaque imaging.

Methods

Two patients with carotid atherosclerosis disease underwent 3D high-resolution MRI which included time-of-flight and T₁-weighted variable flip angle, fast-spin-echo (FSE) imaging, pre- and post-intravenous gadolinium-based contrast agent administration.

Results

Good quality images with intrinsic blood suppression were obtained pre- and post-contrast administration using a 3D FSE sequence. The plaque burden, lipid core volume, hemorrhage volume and fibrous cap thickness were well determined.

Conclusions

3D high-resolution MR imaging of carotid plaque using TOF and 3D FSE can achieve high isotropic resolution, large coverage, and excellent image quality within a short acquisition time.