Brain MRI lesion volume measurement reproducibility is not dependent on the disease burden in patients with multiple sclerosis

We evaluated the potential effect of the lesion burden on the reproducibility of repeated lesion volume (LV) measurements from brain magnetic resonance imaging (MRI) scans of patients with multiple sclerosis (MS). Dual-echo, conventional spin echo brain MRI scans were obtained from 107 patients with MS. On proton density-weighted images, LV was assessed three times by the same raters, using a semi-automated, local thresholding technique for lesion segmentation. Mean LV (MLV) was 16.1 mL (range = 0.7–57.3 mL). The mean intra-observer coefficient of variation (COV) for the three measurement replicates was 2.6% (range = 0.2–7.2%). The intra-observer measurement variance (Var) increased with MLV and the fitted model was Var = 0.00187 MLV^1.84. This indicates that LV measurements can be considered as measures whose variances are proportional to the square of their mean values, i.e., these measures have constant COV. Using a semi-automated, local thresholding segmentation technique, the reproducibility of LV measurements from brain MRI scans of patients with MS is not significantly influenced by varying lesion burdens.     

低场MRI系统中线扫描扩散张量成像方法的研究

磁共振扩散张量成像(DTI)是在扩散加权成像(DWI)基础上发展起来的一种新型技术,可以无创伤显示脑白质纤维,诊断脑白质病变. 但是由于各种原因,DTI一般只在超导高场磁共振成像(MRI)仪器上进行,这就限制了这一重要诊断手段临床应用的广泛性. 本文在低场磁共振成像系统上应用线扫描实现了扩散张量成像,并测量了健康志愿者大脑内主要解剖结构的表观扩散系数(ADC)和各项异性分数(FA),得到的数据与高场仪器上的相关数据比较是吻合的. 因此临床上使用在低场强上得到的DTI图像评价脑白质是可行的,而且通常在临床上这也是足够的.     

用伪同色光谱图像检测色觉正常观察者的锥细胞光谱响应

为了能够快速、准确的检测色觉正常观察者的辨色差异，从而对其红、绿、蓝三通道的锥细胞光谱响应进行研究，设计并制作了由背景层（或和明度层）以及数字层组成的伪同色光谱图像，其中背景层和数字层具有不同的光谱反射曲线，经过照明光源以及人眼锥细胞光谱响应的共同作用，使色觉正常的观察者产生不同的颜色感知差异。实验首先基于不同光谱原色的输出设备，在不同的照明光源下，制作出能够放大观察者差异的近同色异谱色样对。要求用不同颜色匹配函数计算近同色异谱色样对的CIEDE2000色差值，有的色差在人眼辨色阈值之内，有的色差人眼可明显识别。通过优化计算，将放大观察者色觉差异的近同色异谱色样对应用于伪同色光谱图像的数字层和背景层，并利用Epson Stylus Pro7908喷墨打印机和OKI C9600激光打印机分别输出伪同色光谱图像的背景层和数字层。同时组织了72名色觉正常的观察者（包含55名18～25岁的年轻观察者和17名62～74岁的老年观察者）分别在D65和LED-5000K两种光源下，对伪同色光谱图像进行识读检验。识读结果表明，伪同色光谱图像可以较为准确的判定年轻和老年观察者的视网膜锥细胞光谱响应是否老化。同种照明光源下，年轻观察者可以识读出数字的伪同色光谱图像（②/④）老年观察者不能识读，老年观察者可以识读的伪同色光谱图像（①/③）大多年轻观察者不能识读，且55名年轻观察者中有4名观察者的目视结果与老年人相同。另外，年轻观察者的锥细胞光谱响应与CIE1964和CIE2006（age=25 y）颜色匹配函数较为一致，而老年观察者的锥细胞光谱响应与CIE1931和CIE2006（age=75 y）颜色匹配函数更为一致。对比颜色匹配函数的分布，发现老年观察者的锥细胞光谱响应向长波段偏移，同时由于屈光系统光学密度增加导致其锥细胞光谱响应有所降低。     

Improving background suppression in diffusion-weighted imaging of the abdomen and pelvis using STIR with single-axis diffusion encoding

Bowel contents and peripheral nerves often show high signal intensity at diffusion-weighted imaging (DWI) of the abdomen and pelvis, obscuring or mimicking pathology. This study introduced and compared short tau inversion recovery (STIR) with single-axis DWI to the usual combination of spectral fat suppression (SFS) with trace DWI in the suppression of bowel contents and peripheral nerves. Five volunteers underwent both STIR with single-axis DWI and SFS with trace DWI of the abdomen and pelvis. Images were evaluated by two observers with respect to the suppression of signal of bowel contents and peripheral nerves using four-point grading scales (4=poor suppression; 3=moderate suppression; 2=good suppression; 1=excellent suppression). Mean scores (±S.D.) regarding the suppression of bowel contents were 1.60±0.55 and 1.40±0.89 for STIR with single-axis DWI and 3.40±0.55 and 3.00±1.00 for SFS with trace DWI for observers 1 and 2, respectively. Mean scores regarding the suppression of peripheral nerves were 1.20±0.45 and 1.20±0.45 for STIR with single-axis DWI and 2.40±0.89 and 2.80±0.84 for SFS with trace DWI for observers 1 and 2, respectively. In conclusion, STIR with single-axis DWI is superior to SFS with trace DWI in the suppression of bowel signal and peripheral nerves.     

Quantitative MRI: Defining repeatability,reproducibility and accuracy for prostate cancer imaging biomarker development

IntroductionQuantitative MRI (qMRI) parameters have been increasingly used to develop predictive models to accurately monitor treatment response in prostate cancer after radiotherapy. To reliably detect changes in signal due to treatment response, predictive models require qMRI parameters with high repeatability and reproducibility. The purpose of this study was to measure qMRI parameter uncertainties in both commercial and in-house developed phantoms to guide the development of robust predictive models for monitoring treatment response.Materials and methodsADC, T1, and R2* values were acquired across three 3 T scanners with a prostate-specific qMRI protocol using the NIST/ISMRM system phantom, RSNA/NIST diffusion phantom, and an in-house phantom. A B1 field map was acquired to correct for flip angle inhomogeneity in T1 maps. All sequences were repeated in each scan to assess within-session repeatability. Weekly scans were acquired on one scanner for three months with the in-house phantom. Between-session repeatability was measured with test-retest scans 6-months apart on all scanners with all phantoms. Accuracy, defined as percentage deviation from reference value for ADC and T1, was evaluated using the system and diffusion phantoms. Repeatability and reproducibility coefficients of variation (%CV) were calculated for all qMRI parameters on all phantoms.ResultsOverall, repeatability CV of ADC was <2.40%, reproducibility CV was <3.98%, and accuracy ranged between −8.0% to 2.7% across all scanners. Applying B1 correction on T1 measurements significantly improved the repeatability and reproducibility (p<0.05) but increased error in accuracy (p<0.001). Repeatability and reproducibility of R2* was <4.5% and <7.3% respectively in the system phantom across all scanners.ConclusionRepeatability, reproducibility, and accuracy in qMRI parameters from a prostate-specific protocol was estimated using both commercial and in-house phantoms. Results from this work will be used to identify robust qMRI parameters for use in the development of predictive models to longitudinally monitor treatment response for prostate cancer in current and future clinical trials.     

Lesion load measurements in multiple sclerosis: the effect of incorporating magnetization transfer contrast in fast-FLAIR sequence

We compared the ability and reproducibility of a fast fluid-attenuated inversion recovery (fast-FLAIR) sequence with and without a magnetization transfer (MT) pulse for detecting and measuring multiple sclerosis (MS)-related abnormalities on magnetic resonance imaging (MRI) scans from 20 patients. The Contrast-to-Noise ratios between lesions and normal-appearing white matter, lesion numbers, lesion volumes and the variability of such measurements were similar for the two sequences. This suggests that the addition of MT to FLAIR sequences as currently implemented on standard MRI scanners does not improve the detection of MS lesions.     

High-field MRI and US evaluation of the pelvis in women with leiomyomas

Magnetic resonance imaging (MRI) and real-time transabdominal ultrasonography (US) were performed on 23 women with uterine leiomyomas. The uterus, ovaries, and cul de sac were evaluated. Accurate determination of uterine volume was possible in all cases by MRI, but was limited on US in uteri larger than 140 cc. Marked enlargement also prevented visualization of contour abnormalities in eight patients on US, but none on MRI. The endometrial stripe and junctional zone could not be adequately visualized in 21/23 US examinations, whereas they were identified in all 23 MRI (8 normal and 15 distorted). Individual leiomyomas were clearly depicted on 4 US and 19 MR scans, the smallest being 1.1 cm and 0.8 cm, respectively. Of the 31 fibroids present on MRI: 13 were intramural, 4 subserosal, and 14 submucosal. MRI successfully identified 44/46 ovaries as compared to 21/46 on US. Cul de sac fluid was noted in seven women by MRI alone. This data suggests that MRI is superior to US in examination of the entire pelvis in women with leiomyomas.     

A comparison of the sensitivity of MRI after double- and triple-dose Gd-DTPA for detecting enhancing lesions in multiple sclerosis

We compared the number and volume of enhancing lesions detected in patients with multiple sclerosis (MS) seen on post-contrast T(1)-weighted scans obtained after the injection of different gadolinium-DTPA (Gd) doses. Enhanced magnetic resonance imaging (MRI) scans were obtained from 16 patients with relapsing remitting or secondary progressive MS on two different occasions separated by an interval of approximately 24 h. On the first occasion, enhanced scans were obtained 15 min after the injection of a double dose of Gd (0.2 mmol/Kg), on the second 15 min after the injection of a triple dose (0.3 mmol/Kg) of Gd. Scans were assessed by consensus in a random order by two observers unaware of the dose of Gd used. We counted the same 30 enhancing lesions on both double dose and triple dose scans from 9 patients. The mean (SD) volumes of enhancing lesions were 1.7 (2.7) mL on double dose and 1.9 (3.4) mL on triple-dose scans. This difference was not statistically significant. This study demonstrated that double dose of Gd has a sensitivity for detecting MS activity similar to that of a triple dose, with the advantage of a significant cost saving.     

Lesion load quantification on fast-FLAIR, rapid acquisition relaxation-enhanced, and gradient spin echo brain MRI scans from multiple sclerosis patients.

Previous studies have addressed the issue of the usefullness of fast fluid-attenuated (fast-FLAIR), rapid acquisition relaxation-enhanced (RARE), and gradient spin echo (GRASE) sequences in small groups of patients with multiple sclerosis (MS). The aim of this study was to assess and compare the lesion volumes and the intra-rater reproducibility of such measurements using fast-FLAIR, dual echo RARE, and dual echo GRASE brain scans from a large sample of MS patients. Using a 1.5 Tesla scanner, fast-FLAIR, dual echo RARE, and dual echo GRASE scans (24 axial, 5-mm thick contiguous interleaved slices) of the brain were obtained from 50 MS patients. Total lesion loads (TLL) were assessed twice using a semi-automated local thresholding segmentation technique by the same rater from the scans obtained with the three techniques. Mean TLL were 20.3 mL for fast-FLAIR, 16.6 mL for RARE, and 17.6 mL for GRASE sequences. Mean TLL detected by the three techniques were significantly heterogeneous (p < 0.001); at post-hoc analysis, the mean lesion volume detected on fast-FLAIR images was significantly higher than that on both RARE and GRASE images (p < 0.001) and the mean TLL on GRASE scans was significantly higher than that on RARE scans (p = 0.001). The mean values of intra-observer coefficient of variation for TLL measurements were similar for the three techniques (2.69% for fast-FLAIR, 2.33% for RARE, and 2.65% for GRASE). Our results confirm that fast-FLAIR sequences detect higher lesion volumes than those detected by other magnetic resonance imaging (MRI) sequences with shorter acquisition times. However, the reproducibility of TLL measurements is comparable among fast-FLAIR, RARE, and GRASE. This suggests that when assessing MS disease burden with MRI, the choice of the pulse sequence to be used should be dictated by the clinical setting.     

Detection of multiple sclerosis lesions using EPI-FLAIR images

Fast fluid-attenuated inversion recovery (fast-FLAIR) sequences are very sensitive for detecting lesions of patients with multiple sclerosis (MS). Echo planar imaging allows to obtain FLAIR images (EPI-FLAIR) with significantly shorter scanning times. EPI-FLAIR images obtained with 10 measurements are as sensitive as fast-FLAIR for the detection of large MS lesions. Aim of this study was to compare the numbers of MS lesions seen on EPI-FLAIR images with fewer measurements (and, as a consequence, very short scanning times) with those seen on EPI-FLAIR images with 10 measurements. EPI-FLAIR scans with 2 (EPI-2), 4 (EPI-4), 6 (EPI-6), 8 (EPI-8) and 10 (EPI-10) measurements were obtained from 29 MS patients. Lesions seen using each of the five approaches were counted by agreement by two observers. EPI-10 images were used as the "gold standard" for pairwise comparisons. EPI-FLAIR scans with fewer measurements (EPI-2, -4, -6, -8) were all significantly less sensitive than EPI-10 for the detection of small, intermediate and large MS lesions. All the EPI-FLAIR scans, however, fulfilled MR diagnostic criteria for definite MS. When rapid MR scanning of uncooperative MS patients is needed, EPI-FLAIR images covering the entire brain in less than one minute may be considered.     

The Elgin marvel: using magnetic resonance imaging to look at a moldic fossil from the Permian of Elgin, Scotland, UK

The successful use of magnetic resonance imaging (MRI) of a moldic fossil dicynodont from the Permian aeolian Hopeman Sandstone Formation of Elgin, Scotland, UK, provides paleontologists with a nondestructive technique for examining fossils preserved in this fashion. For large moldic fossils, medical scanners such as the Phillips Gyroscan MRI, provide adequate resolution for gross morphologic determination. The 3-D rendered images using software such as Philips Easivision allows the fossil to be examined and dissected without causing any physical damage to the original material. From the scans it is also possible to produce 3-D stereolithographs for a more tactile manipulation of the renderings.     

Abdominal imaging studies: comparison of diagnostic accuracies resulting from ultrasound, computed tomography, and magnetic resonance imaging in the same individual

We retrospectively compared the diagnostic accuracy of abdominal ultrasound (US), computed tomography (CT), and magnetic resonance imaging (MRI) studies performed on the same individual to determine the relative performance of these modalities in the evaluation of disease processes, arising from different intra-abdominal organ systems. We retrospectively reviewed all procedure codes accrued by our abdominal imaging section during a 1-year period to determine how many patients underwent all three imaging procedures in our institution within a 2-week interval. These cases were then further evaluated to determine: (1) the primary organ system of disease involvement, (2) the final diagnosis, and (3) the imaging modality that provided the most accurate information upon which appropriate medical management was based. Imaging findings were determined by review of diagnostic reports, and medical management was determined by chart review. Two thousand six hundred-ninety five patients underwent ultrasound, 4,394 patients underwent CT, and 872 patients underwent MRI for the investigation of abdominal disease. Among these 5,126 patients, 26 underwent sequential US, CT, and MRI evaluation within a two-week interval. Appropriate clinical management was based on the US findings in 12/26 cases (46%; 95% CI: 27-67%), CT findings in 16/26 cases (62%; 95% CI: 41-80%), and MRI findings in 24 cases (92%; 95% CI: 75-99%). Significant differences in directing appropriate clinical management were found when comparing the relative diagnostic accuracies of MRI to US (p = 0.0003) and MRI to CT (p = 0.009). However, differences were not significant when comparing CT to US (p = 0.27). All final diagnoses in a given patient were accurately determined by US in 7/26 cases (27%), by CT in 10/26 cases (38%), and by MRI in 23/26 cases (88%). When analyzed according to individual diagnoses (61 total), US detected 33 of 61 (54%) abnormalities, CT detected 41 (67%) abnormalities, and MRI detected 51 (84%) abnormalities. US correctly characterized 32 (52%) abnormalities, CT correctly characterized 36 (59%) abnormalities, and MRI correctly characterized 49 (80%) abnormalities. Ultrasound, CT, and MR imaging correctly diagnosed the disease process in 3 of 12 (25%), 3 of 12 (25%), and 10 of 12 (83%) patients, respectively, with liver disease; 2 of 9 (22%), 6 of 9 (66%), and 9 of 9 (100%) patients, respectively, with pancreatic disease; 17 of 17 (100%), 8 of 17 (47%), and 10 of 17 (58%) patients, respectively, with gallbladder and biliary disease; 2 of 8 (25%), 5 of 8 (63%), and 5 of 8 (63%) patients, respectively, with renal disease; 0 of 3 (0%), 2 of 3 (66%), and 3 of 3 (100%) patients, respectively, with adrenal disease; and 8 of 12 (75%), 12 of 12 (100%), and 12 of 12 (100%) patients with free intraperitoneal fluid. Our results provide new information, regarding the relative benefits of ultrasound, CT, and MRI for the investigation of abdominal diseases at our institution. This initial data suggests that ultrasound provides the most accurate diagnoses in the investigation of gallbladder disease; MRI provides the most accurate diagnoses in the investigation of hepatic, adrenal, and pancreatic disease; and either CT or MRI may be the most appropriate first imaging study for the detection of renal disease.     

Reproducibility of magnetic resonance imaging measurements of spinal cord atrophy: the role of quality assurance.

A sensitive magnetic resonance imaging (MRI) method to measure spinal cord cross-sectional area with the potential to monitor disease progression has recently been developed. As changes in cord area due to disease are usually small, assessment of the reliability of the methodology is essential in serial studies of spinal cord atrophy. The aim of this study was to institute and evaluate a protocol of quality assurance to determine long-term reproducibility of serial studies. Serial MRI of the spinal cord was carried out in five healthy volunteer controls over 1 year. Cross-sectional spinal cord areas were measured in a total of 46 scans. The mean coefficient of variation of all subjects over one year was 1.35%. The intra-observer coefficient of variation for same scan analysis was 0.63%. This study has confirmed high reliability of our serial data over one year and the on-going quality assurance protocol enables continuing evaluation of the reproducibility of results in serial studies. Quality assurance is an essential and practical component of all serial MRI studies, without which the clinical implications of change cannot be reliably evaluated.     

Evaluation of dosimetry and image of very low-dose computed tomography attenuation correction for pediatric positron emission tomography/computed tomography: phantom study

In this study, phantom was used to evaluate attenuation correction computed tomography (CT) dose and image in case of pediatric positron emission tomography (PET)/CT scan. Three PET/CT scanners were used along with acryl phantom in the size for infant and ion-chamber dosimeter. The CT image acquisition conditions were changed from 10 to 20, 40, 80, 100 and 160 mA and from 80 to 100, 120 and 140 kVp, which aimed at evaluating penetrate dose and computed tomography dose index_volume (CTDI_vol) value. And NEMA PET Phantom? was used to obtain PET image under the same CT conditions in order to evaluate each attenuation-corrected PET image based on standard uptake value (SUV) value and signal-to-noise ratio (SNR). In general, the penetrate dose was reduced by around 92% under the minimum CT conditions (80 kVp and 10 mA) with the decrease in CTDI_vol value by around 88%, compared with the pediatric abdomen CT conditions (100 kVp and 100 mA). The PET image with its attenuation corrected according to each CT condition showed no change in SUV value and no influence on the SNR. In conclusion, if the minimum dose CT that is properly applied to body of pediatric patient is corrected for attenuation to ensure that the effective dose is reduced by around 90% or more compared with that for adult patient, this will be useful to reduce radiation exposure level.     

Magnetic resonance imaging as an adjunct to sonography in the evaluation of the female pelvis

Magnetic resonance imaging (MRI) of the pelvis is generally considered to be most beneficial in those cases where the pelvic sonogram is limited or equivocal. All cases that underwent both sonographic and MRI examinations at our institution for the evaluation of the female pelvis in the past two years were retrospectively reviewed. We reviewed the sonographic and MRI reports and the subsequent clinical management in the 41 cases that had both studies to assess whether MRI contributed to the clinical management decision. Both studies were interpreted independently based upon the known clinical and laboratory data available at the time. MRI was obtained in 21 cases because the sonogram was suboptimal or inconclusive. In the other 20 cases it was obtained for additional information, even though the sonogram was diagnostic. Of the 21 inconclusive sonographic studies, MRI established or clarified the diagnosis in all cases. Of the 20 studies where MRI was obtained for additional information, MRI added useful data that helped contribute to the clinical management of 11 patients. MRI is an important adjunct to pelvic sonography. It established, clarified, or added significant data in 78% of cases.     

A Comparative Study of CT and MRI for Evaluating Hepatic Malignant and Focal Nodules Based on ROC Curves

The clinical use of magnetic resonance imaging (MRI) and multiphase enhanced computed tomography (CT) with the contrast media (Gd-EOB-DTPA) for detecting hepatic malignant and focal nodules prior to operation was examined based on the receiver operating characteristic (ROC) curve. This study included 70 patients with malignant and focal liver nodules who underwent MRI and multiphase CT scans before operation. Both scans for each patient were conducted within 1 month. For MRI, the T ₂-weighted image (single shot fast spin echo) and two-dimensional (2-D) and 3-D T ₁-gradient magnetic signals were obtained for all patients before administering the contrast media. The 2-D and 3-D T ₁-gradient magnetic signals were obtained in the same location after delivering the contrast media. For the CT scans, images of artery phase, portal phase, and delayed phase were obtained at a thickness of 5 mm or less after administering contrast similar to MRI. An ROC curve was used (paired-samples T test, P < 0.05) to evaluate the images. When the analysis was based on the ROC curve, MRI showed high values (P < 0.05) for area under curve (AUC), sensitivity, and specificity in terms of detection rates of small lesions (less than 2 cm and more than 2 cm) compared to multidetector computed tomography (MDCT) (for ≤2 cm, MRI: 0.928, 70, 93%, CT: 0.775, 30, 90%; for ≥2 cm, MRI: 0.744, 80%, 84%; CT: 0.692, 40%, 84%). Gd-EOB-DTPA contrast media-enhanced MRI scanner for detecting malignant and focal liver nodules before operation showed the higher detection rate of lesion and classification of lesion as either benign or malignant than multiphase enhanced MDCT when the ROC curve was used for analysis. Based on these results, we believe that analysis based on the ROC curve will provide guidelines for evaluating malignant and focal hepatic lesions prior to operation.     

Quantitative quality assurance in a multicenter HARDI clinical trial at 3 T

A phantom-based quality assurance (QA) protocol was developed for a multicenter clinical trial including high angular resolution diffusion imaging (HARDI). A total of 27 3 T MR scanners from 2 major manufacturers, GE (Discovery and Signa scanners) and Siemens (Trio and Skyra scanners), were included in this trial. With this protocol, agar phantoms doped to mimic relaxation properties of brain tissue are scanned on a monthly basis, and quantitative procedures are used to detect spiking and to evaluate eddy current and Nyquist ghosting artifacts. In this study, simulations were used to determine alarm thresholds for minimal acceptable signal-to-noise ratio (SNR). Our results showed that spiking artifact was the most frequently observed type of artifact. Overall, Trio scanners exhibited less eddy current distortion than GE scanners, which in turn showed less distortion than Skyra scanners. This difference was mainly caused by the different sequences used on these scanners. The SNR for phantom scans was closely correlated with the SNR from volunteers. Nearly all of the phantom measurements with artifact-free images were above the alarm threshold, suggesting that the scanners are stable longitudinally. Software upgrades and hardware replacement sometimes affected SNR substantially but sometimes did not. In light of these results, it is important to monitor longitudinal SNR with phantom QA to help interpret potential effects on in vivo measurements. Our phantom QA procedure for HARDI scans was successful in tracking scanner performance and detecting unwanted artifacts.     

The short TI inversion recovery sequence--an approach to MR imaging of the abdomen

Initial clinical experience with magnetic resonance imaging (MRI) of the abdomen using short TI inversion-recovery (STIR) pulse sequences is described and compared with X-ray CT in a variety of abdominal disease. The extent of abnormality shown with MRI was greater than that with CT in 21 of 30 cases and equal in 9 cases. Lesion contrast was greater with MRI in 15 cases, equal in 14 and less in 1. The level of artefact was equal in 27 cases and greater with MRI in 3 cases. The STIR pulse sequence has significant advantages in producing high soft-tissue contrast, controlling respiratory artefact, avoiding confusion with intra-abdominal fat and identifying bowel loops.     

Magnetic resonance imaging of soft-tissue tumors: Comparison with computed tomography

Twenty-seven patients with soft-tissue tumors were examined with a Picker 0.15-tesla resistive magnet and by computed tomography (CT). In all but one patient, MRI was better than or equal to CT in defining the anatomic extent of the tumor. We could determine whether major vascular structures were engulfed by the tumor in 80% of the MRI examinations but only in 62% of the CT scans. MRI and CT were equally effective in determining the presence or absence of bony invasion. The MRI images of all the tumors showed increased signal intensity relative to normal muscle when spin-echo (SE) sulse sequences with long repeat times were used (SE: echo time [TE], 60 ms; repetition time [TR], 2,000 ms). When T1 weighted pulse sequences were used (SE: TE, 30 ms; TR, 500 ms or inversion recovery: inversion time, 500 ms; TE, 40 ms; TR, 2,000 ms) the malignant tumors showed decreased signal intensity compared to normal muscle. Only lipomas showed high signal intensity on both T1 and T2 weighted pulse sequences.     

Towards safe operation of an active retinal prosthesis during functional MRI and diffusion tensor imaging

ObjectiveTo determine if the Argus II retinal prosthesis can operate during functional MRI (fMRI) and diffusion tensor imaging (DTI) acquisitions and if currents induced in the prosthesis by imaging are at safe levels.Materials and methodsOne Argus II retinal prosthesis was modified to enable current measurements during imaging. Active electronics were modified to enable operation during scans. Induced current was measured during diagnostic scans, which were previously shown to be safe for implanted patients, and during fMRI and DTI scans. All measurements were performed using an ASTM phantom to ensure reproducible placement.ResultsThe prosthesis was able to maintain communication with the external RF coil during the fMRI and DTI scans except briefly during pre-scans. Current levels induced during fMRI and DTI scans were consistently below those measured during diagnostic scans.ConclusionsfMRI and DTI may be safely performed while the Argus II retinal prosthesis is operating.