Modified Dixon Technique Research Articles

O5: THE CLIFF AND CONOR STUDIES NOVEL ASSESSMENT TOOLS IN COLORECTAL LIVER METASTASES (CLIFF STUDY - CHANGE IN LIVER FUNCTION AND FAT IN PRE-OPERATIVE CHEMOTHERAPY FOR COLORECTAL LIVER METASTASES, CONOR STUDY

Abstract Introduction Hepatic resection is the only potentially curative treatment for patients with colorectal liver metastases (CLM). Patient selection is key, but there is wide variation in practice. Pre-operative chemotherapy can improve oncological outcomes, however chemotherapy-associated liver injury (CALI) may hinder liver regenerative capacity. Standard pre-operative assessments fail to accurately capture factors such as CALI and future liver remnant (FLR) function. The CLiFF and CoNoR studies utilise two novel assessment techniques, aiming to improve patient outcomes. Method The CLiFF study prospectively assesses two primary outcomes in 35 patients undergoing pre-operative chemotherapy for CLM: 1) change in liver function (via LiMAx test: direct assessment of hepatic functional capacity), and 2) change in liver fat (via advanced MR imaging (in-house spectroscopy and modified Dixon technique, scaled up via Perspectum LiverMultiScan)). The CoNoR study assesses potential added benefit of these novel tools in CLM resectability decision-making via sequential workstreams: a systematic review and international hepatobiliary expert interviews inform the online survey, assessing added benefit via online MDT scenarios. Result Preliminary CLiFF analysis suggests that CALI changes in liver fat and function are unrelated. Liver fat analysis techniques are compared and correlated with digital histological analysis. The CoNoR systematic review identifies key factors influencing CLM resectability decision-making and informs the international expert interviews, scheduled to occur during a February 2020 international hepatobiliary conference. Conclusion These studies are the first to assess where these novel tools might be utilised to maximal patient benefit within the Hepatobiliary MDT, and the first systematic review in CLM resectability decision-making. Take-home message These two linked studies evaluate the use of two novel assessment tools in the treatment of colorectal liver metastases, with the potential to improve patient selection for curative resection and patient outcomes. PATEY PRIZE SESSION

Use of Quantitative Vertebral Bone Marrow Fat Fraction to Assess Disease Activity and Chronicity in Patients with Ankylosing Spondylitis

ObjectiveWe quantitatively measured the fat fraction (FF) in the vertebrae of patients with ankylosing spondylitis (AS) using magnetic resonance imaging (MRI) and investigated the role of FF as an indicator of both active inflammation and chronicity.Materials and MethodsA total of 52 patients with AS who underwent spinal MRI were retrospectively evaluated. The FF values of the anterosuperior and anteroinferior corners of the bone marrow in the L1-S1 spine were assessed using the modified Dixon technique. AS activity was measured using the Bath Ankylosing Spondylitis Disease Activity Index (BASDAI), Bath Ankylosing Spondylitis Functional Index (BASFI), AS Disease Activity Score (ASDAS), and serum inflammatory marker levels. AS disease chronicity was assessed by AS disease duration and the modified Stoke Ankylosing Spondylitis Spinal Score (mSASSS). Univariable and multivariable regression analyses were conducted to investigate the correlation between FF and other clinical characteristics.ResultsThe mean FF ± standard deviation of the total lumbar spine was 43.0% ± 11.3%. At univariable analysis, spinal FF showed significant negative correlation with BASDAI (β = −0.474, p = 0.002) and ASDAS with C-reactive protein (ASDAS-CRP; β = −0.478, p = 0.002) and a significant positive correlation with AS disease duration (β = 0.440, p = 0.001). After adjusting for patient age, sex, and total mSASSS score, spinal FF remained significantly negatively correlated with BASDAI (β = −0.543, p < 0.001), ASDAS-CRP (β = −0.568, p < 0.001), and ASDAS with erythrocyte sedimentation rate (β = −0.533, p = 0.001). Spinal FF was significantly lower in patients with very high disease activity (ASDAS-CRP > 3.5) than in those with only high disease activity (2.1 ≤ ASDAS-CRP ≤ 3.5) (p = 0.010).ConclusionSpinal FF may help assess both AS disease activity and chronicity.

Evaluation of disease chronicity by bone marrow fat fraction using sacroiliac joint magnetic resonance imaging in patients with spondyloarthritis: A retrospective study

This study investigated the use of fat fraction (FF) measurements in the sacroiliac (SI) joint to determine radiologic progression in patients with spondyloarthritis (SpA). A total of 138 patients who underwent pelvic magnetic resonance imaging (MRI) between September 2014 and March 2015 were retrospectively evaluated. The FF based upon fat deposition (%) using fat signaling on T1 and T2 weighted images in the sacroiliac joint was quantified using a 6-echo variant of the modified Dixon technique. We defined the normal bone marrow as normal FF, bone marrow edema as active inflammatory FF, and fat metaplasia as post-inflammatory FF. The mean FF of normal marrow was 52.0%±10.4% and 50.5%±10.1% in the left and right SI joints, respectively. The mean FF of post-inflammatory fat deposition was 81.9%±9.7% and 82.3%±9.6% in the left and right SI joints, respectively. The mean FF of active inflammatory fat deposition was 15.8%±5.9% and 13.5%±6.7% in the left and right SI joints, respectively. In multiple linear regression, post-inflammatory FF was found to be significantly associated with radiologic progression, such as symptom duration, SI joint grade, and modified Stoke Ankylosing Spondylitis Spine Score. Post-inflammatory FF indicates the chronicity of SpA. Evaluating FF using MRI in the SI joint will help to determine radiologic progression.

Using the modified Dixon technique to evaluate incidental adrenal lesions on 3 T MRI

ObjectivesTo use the mDIXON-Quant sequence to quantify the fat fraction of adrenal lesions discovered incidentally on CT studies. To analyze the relation between the signal loss between in-phase and out-of-phase T1-weighted sequences and the fat fraction in mDIXON-Quant. To compare the sensitivity and specificity of the two methods for characterizing adrenal lesions. Material and methodsThis prospective descriptive study included 31 patients with incidentally discovered adrenal lesions evaluated with 3T MRI using in-phase and out-of-phase T1-weighted sequences and mDIXON-Quant; the fat fraction of the adrenal lesions was measured by mDIXON-Quant and by calculating the percentage of signal loss between in-phase and out-of-phase T1-weighted sequences. ResultsThe percentage of signal loss was significantly higher in the group of patients with adenoma (61.3±20.4% vs. 5.1±5.8% in the group without adenoma, p<0.005). The mean fat fraction measured by mDIXON-Quant was also higher for the adenomas (26.9±10.8% vs. 3.4±3.0%, p<0.005). The area under the ROC curve was 0.99 (0.96–1.00) for the percentage of signal loss and 0.98 (0.94–1.00) for the fat fraction measured by mDIXON-Quant. The cutoffs obtained were 24.42% for the percentage of signal loss and 9.2% for the fat fraction measured by mDIXON-Quant. The two techniques had the same values for diagnostic accuracy: sensitivity 96% (79.6–99.9), specificity 100% (39.8–100.0), positive predictive value 100% (85.8–100.0), and negative predictive value 80% (28.4–99.5). ConclusionThe fat fraction measured by the modified Dixon technique can differentiate between adenomas and other adrenal lesions with the same sensitivity and specificity as the percentage of signal loss between in-phase and out-of-phase T1-weighted sequences.

Valoración mediante Dixon modificado de las lesiones suprarrenales incidentales en RM 3T

ObjectivesTo use the mDIXON-Quant sequence to quantify the fat fraction of adrenal lesions discovered incidentally on CT studies. To analyze the relation between the signal loss between in-phase and out-of-phase T1-weighted sequences and the fat fraction in mDIXON-Quant. To compare the sensitivity and specificity of the two methods for characterizing adrenal lesions. Material and methodsThis prospective descriptive study included 31 patients with incidentally discovered adrenal lesions evaluated with 3T MRI using in-phase and out-of-phase T1-weighted sequences and mDIXON-Quant; the fat fraction of the adrenal lesions was measured by mDIXON-Quant and by calculating the percentage of signal loss between in-phase and out-of-phase T1-weighted sequences. ResultsThe percentage of signal loss was significantly higher in the group of patients with adenoma (61.3% ± 20.4% vs. 5.1% ± 5.8% in the group without adenoma, p<0.005). The mean fat fraction measured by mDIXON-Quant was also higher for the adenomas (26.9% ±10.8% vs. 3.4% ± 3.0%, p<0.005).The area under the ROC curve was 0.99 (0.96 – 1.00) for the percentage of signal loss and 0.98 (0.94 – 1.00) for the fat fraction measured by mDIXON-Quant. The cutoffs obtained were 24.42% for the percentage of signal loss and 9.2% for the fat fraction measured by mDIXON-Quant. The two techniques had the same values for diagnostic accuracy: sensitivity 96% (79.6 – 99.9), specificity 100% (39.8 – 100.0), positive predictive value 100% (85.8 – 100.0), and negative predictive value 80% (28.4 – 99.5). ConclusionThe fat fraction measured by the modified Dixon technique can differentiate between adenomas and other adrenal lesions with the same sensitivity and specificity as the percentage of signal loss between in-phase and out-of-phase T1-weighted sequences.

Fracture of ankle: MRI using opposed-phase imaging obtained from turbo spinecho modified Dixon image shows improved sensitivity.

To evaluate if opposed-phase (OP) imaging obtained from the turbo spin echo (TSE) modified Dixon (mDixon) technique can increase the sensitivity of MRI for diagnosing ankle fractures. This study included 95 CT-confirmed ankle fractures with additional MRI of the ankle using a TSE modified Dixon (mDixon) technique. Two groups of images were analyzed independently: Group 1-imaging group without OP imaging; Group 2-imaging group with OP imaging. Readers assessed the images using a 4-point confidence score to detect fractures. During the first review session, the fracture site was blinded. For the second review session, the fracture site was provided. Sensitivity and positive-predictive value were calculated. In both sessions, the sensitivity for Group2 was significantly greater than that for Group 1 (Session 1: 76.3% vs 62.6%, p < 0.0001; Session 2: 80.5% vs 65.3%, p < 0.0001). The positive-predictive value of Group2 was significantly lower in both sessions 1 and 2 (Session 1: 85.8% vs 97.5%, p < 0.0001; Session 2: 90.5% vs 96.9%, p = 0.0068). Among the 28 false-negative fractures missed in Group 1 (Session 1), 12 (9 minimal displaced and 4 small diameter fractures) were identified in Group 2 (Session 1). While 8.9% showed lower movement, 33.6% showed upper movement in Group2 compared with Group 1. Possible causes of false-positive lesions were subcutaneous fat, bone marrow edema, and intraosseous vessel mimic fractures. OP imaging obtained using the modified Dixon technique provided better sensitivity and improved descriptions of fractures, especially for minimal displaced fractures and small diameter fractures. However, caution is required when diagnosing fractures with OP imaging because pseudofractures can appear as a result of adjacent bone marrow edema, vascular structures, or subcutaneous fat lobules. Advances in knowledge: In MRI, minimal displaced or small chip bone fracture maybe missed, OP imaging obtained using the mDixon technique provided better sensitivity and improved descriptions of fractures using the black boundary artifact.

Role of Whole-Body Magnetic Resonance Imaging in the Evaluation of Extrapulmonary Tuberculosis in Immunocompetent Patients

The aim of this study was to evaluate the role of whole-body magnetic resonance imaging (WB-MRI) in imaging of extrapulmonary tuberculosis. Eighteen patients with single-site extrapulmonary tuberculosis were evaluated with contrast-enhanced dedicated MRI of the clinically symptomatic site followed by WB-MRI using contrast-enhanced 3-dimensional (3D) modified DIXON technique (m-DIXON) and diffusion-weighted WB imaging with background body signal suppression (DWIBS) sequences. Studies were read by 2 experienced radiologists, and additional lesions seen on WB-MRI were separately charted. Of 18 patients, 14 were found to have asymptomatic involvement of other organs on WB-MRI. In 5 patients, the information was helpful in choosing an easily accessible site for biopsy/aspiration. Postcontrast 3D m-DIXON was better in picking up brain and lymph nodal lesions, whereas DWIBS was better in detecting vertebral lesions. Whole-body MRI may be used for assessing the asymptomatic involvement of other body organs in tuberculosis. The combination of postcontrast 3D m-DIXON and DWIBS is complementary and may provide a road map for biopsy of accessible lesions.

Quantitative evaluation of vertebral marrow adipose tissue in postmenopausal female using MRI chemical shift-based water–fat separation

To investigate the feasibility of assessing vertebral marrow adipose tissue using a magnetic resonance imaging (MRI) chemical shift-based water-fat separation technique at 3 T. A modified Dixon technique was performed to obtain the vertebral marrow fat fraction (FF) in a study of 58 postmenopausal females (age range 49.2-77.4 years), including 24 normal bone density, 19 osteopaenia, and 15 osteoporosis as documented with dual-energy X-ray absorptiometry. The reliability of FF measurements performed by two radiologists independently was evaluated with the intraclass correlation coefficient (ICC). Ten participants were scanned twice to assess the reproducibility of FF measurements. FF values were compared between each vertebral level and between groups. The mean coefficient of variation of FF measurements was 2.1%. According to the ICC, the measurements were reliable (ICC = 0.900 for normal bone density, ICC = 0.937 for osteopaenia and ICC = 0.909 for osteoporosis, p < 0.001 for all). There was an inverse association between mean FF at L1-L4 vertebrae and lumbar spine BMD (r = -0.459, p = 0.006), which remained significant even after controlling for confounders (age, height, and body weight). FF values at different vertebral levels were significantly correlated to each other (r = 0.703-0.921, p < 0.05 for all). There was a general trend toward increased marrow adiposity for more inferior vertebral bodies. Patients with osteopaenia and osteoporosis had a higher marrow fat content compared with normal bone mass after adjusting for confounders, although no significant differences in each vertebral level and average marrow fat content were found between the osteopaenia and osteoporosis groups. Chemical shift-based water-fat separation enables the quantitation of vertebral marrow adiposity with excellent reproducibility, which appears to be a useful method to provide complementary information to osteoporosis-related research fields.

Mapping of the Magnetic-Field Distribution in Cancellous Bone

aging sequence, with the 1807 refocusing pulse shifted relaThe incremental transverse relaxation time, T *2 , of protons tive to its appearance in the regular spin-echo imaging sein regions of human vertebral cancellous bone closely correquence, such that the time interval between the 907 and 1807 lates with trabecular structural arrangement (1) , comprespulses is (TE 0 t) /2 and that between the 1807 pulse and sive elastic modulus (2) , and fracture risk (3, 4) . The phethe gradient-echo is (TE / t) /2, where TE is the time of nomena are believed to arise from the magnetic-field perturoccurrence of the gradient echo. The refocusing times for bation due to differences in diamagnetic susceptibility of the spin echo and the gradient echo therefore differ by an mineralized bone and surrounding marrow constituents (5– amount t. In the presence of local magnetic-field perturba9) . In this paper, a modified Dixon technique (10) was tions, due to the presence of adjacent diamagnetic trabeculae, implemented on a 9.4 T NMR microimaging system to investhe resulting change in the Larmor frequency of the proton tigate the effects of the trabecular network on the proton causes a net phase shift relative to a regular spin-echo image. NMR signal, providing direct evidence for the T *2 behavior The phase shift Df(x , y) is given by observed clinically (3, 11) . The results indicate a volume susceptibility of the trabeculae of about 00.3 to 00.5 ppm Df(x , y) A g DBz(x , y) t, [1] (SI units) relative to water, and further that the local magnetic-field effect is only sensitive to trabeculae oriented perwhere DBz(x , y) represents the local magnetic-field perturbapendicular to the external field. Therefore, in most MRI tion, which can be computed from the phase image Df(x , y). systems widely used clinically, T *2 of the human vertebral The imaging experiments were performed on a Bruker body is sensitive only to the number density of horizontal AMX-400 9.4 T spectrometer equipped with microimaging trabeculae, the preferential loss of which is known to inaccessory. Spin-echo images were acquired using the pulse crease vertebral fracture incidence by causing buckling of sequence shown in Fig. 1 with tA 0 and 1 ms at a resolution load-bearing vertical trabeculae (12–14) . The findings in of 29 1 29 1 250 mm. The choice of t A 1 ms allows this work thus have clinical implications for the early detecmapping of local magnetic fields of{0.06 G without causing tion of loss of horizontal trabeculae, corroborating the ratioaliasing. TR was 2000 ms and TE was 20 ms with a 512 1 nale for using T *2 measurements as a clinical tool to diagnose 512 image matrix. Both real and imaginary parts of the mild to severe vertebral osteoporosis. Further investigation reconstructed data were stored. Magnitude images showing of the magnetic-field distribution within this heterogeneous the trabecular structure were generated from the t A 0 data. material also explains the voxel size dependence of T *2 reThe corresponding field maps were then obtained by taking ported previously (7, 15) . the phase difference of the images acquired at t A 0 and 1 Cancellous bone specimens from human lumbar vertebrae ms, and phase wrapping problems were reduced by em(L4–L5) were obtained at autopsy and kept frozen until ploying complex division instead of using phase differences used. Cylindrical cores parallel to the spinal axis were drilled (16) . All the image calculations were performed on Silicon to about 1 cm in volume and marrow was subsequently Graphics workstations using Matlab software. removed. Air bubbles were carefully removed following susFollowing the generation of the magnetic-field map for pension of the cleaned specimens in distilled water. the bone specimens, a simple model of a diamagnetic cylinA modified Dixon technique (10) (Fig. 1) was used to der was used to estimate the susceptibility of mineralized investigate microscopically the local magnetic-field distributrabeculae. Assuming an infinitely long diamagnetic cylinder tion within cancellous bone. It is basically a spin-echo imoriented along the y axis, perpendicular to an external magnetic field Bo along the z direction, the local field outside the cylinder is given by (17) * To whom correspondence should be addressed. † MRI/S Laboratory, Institute of Biomedical Sciences, Academia Sinica, Nankang, Taipei, Taiwan 11529, Republic of China. ‡ Department of Radiology, University of Pennsylvania Medical Center, DBz(x , z) A Dx 2 B0R 2 (z 2 0 x ) (x 2 / z ) 2 , [2] Philadelphia, Pennsylvania 19104.

Variable flip angle imaging and fat suppression in combined gradient and spin-echo (GREASE) techniques

Conventional “proton density” and “ T 2-weighted” spin-echo images are susceptible to motion induced artifact, which is exacerbated by lipid signals. Gradient moment nulling can reduce motion artifact but lengthens the minimum TE, degrading the “proton density” contrast. We designed a pulse sequence capable of optimizing proton density and T 2-weighted contrast while suppressing lipid signals and motion induced artifacts. Proton density weighting was obtained by rapid readout gradient reversal immediately after the excitation RF pulse, within a conventional spin-echo sequence. By analyzing the behavior of the macroscopic magnetization and optimizing excitation flip angle, we suppressed T 1 contribution to the image, thereby enhancing proton density and T 2-weighted contrast with a two- to four-fold reduction of repetition time. This permitted an increased number of averages to be used, reducing motion induced artifacts. Fat suppression in the presence of motion was investigated in two groups of 8 volunteers each by (i) modified Dixon technique, (ii) selective excitation, and (iii) hybrid of both. Elimination of fat signal by the first technique was relatively uniform across the field of view, but it did not fully suppress the ghosts originating from fat motion. Selective excitation, while sensitive to the main field inhomogeneity, largely eliminated the ghosts (0.21 ± 0.05 vs. 0.29 ± 0.06, p < 0.01). The hybrid of both techniques combined with bandwidth optimization, however, showed the best results (0.17 ± 0.04, p < 0.001). Variable flip-angle imaging allows optimization of image contrast which, along with averaging and effective fat suppression, significantly improves gradient- and spin-echo imaging, particularly in the presence of motion.