Ultra-high field upper extremity peripheral nerve and non-contrast enhanced vascular imaging.

OBJECTIVE: The purpose of this study was to explore the efficacy of Ultra-high field [UHF] 7 Tesla [T] MRI as compared to 3T MRI in non-contrast enhanced [nCE] imaging of structural anatomy in the elbow, forearm, and hand [upper extremity]. MATERIALS AND METHOD: A wide range of sequences including T1 weighted [T1] volumetric interpolate breath-hold exam [VIBE], T2 weighted [T2] double-echo steady state [DESS], susceptibility weighted imaging [SWI], time-of-flight [TOF], diffusion tensor imaging [DTI], and diffusion spectrum imaging [DSI] were optimized and incorporated with a radiofrequency [RF] coil system composed of a transverse electromagnetic [TEM] transmit coil combined with an 8-channel receive-only array for 7T upper extremity [UE] imaging. In addition, Siemens optimized protocol/sequences were used on a 3T scanner and the resulting images from T1 VIBE and T2 DESS were compared to that obtained at 7T qualitatively and quantitatively [SWI was only qualitatively compared]. DSI studio was utilized to identify nerves based on analysis of diffusion weighted derived fractional anisotropy images. Images of forearm vasculature were extracted using a paint grow manual segmentation method based on MIPAV [Medical Image Processing, Analysis, and Visualization]. RESULTS: High resolution and high quality signal-to-noise ratio [SNR] and contrast-to-noise ratio [CNR]-images of the hand, forearm, and elbow were acquired with nearly homogeneous 7T excitation. Measured [performed on the T1 VIBE and T2 DESS sequences] SNR and CNR values were almost doubled at 7T vs. 3T. Cartilage, synovial fluid and tendon structures could be seen with higher clarity in the 7T T1 and T2 weighted images. SWI allowed high resolution and better quality imaging of large and medium sized arteries and veins, capillary networks and arteriovenous anastomoses at 7T when compared to 3T. 7T diffusion weighted sequence [not performed at 3T] demonstrates that the forearm nerves are clearly delineated by fiber tractography. The proper digital palmar arteries and superficial palmar arch could also be clearly visualized using TOF nCE 7T MRI. CONCLUSION: Ultra-high resolution neurovascular imaging in upper extremities is possible at 7T without use of renal toxic intravenous contrast. 7T MRI can provide superior peripheral nerve [based on fiber anisotropy and diffusion coefficient parameters derived from diffusion tensor/spectrum imaging] and vascular [nCE MRA and vessel segmentation] imaging.

Ultra-high-field RF coil development for evaluating upper extremity imaging applications.

The purpose of this study is to develop and evaluate a custom-designed 7  T MRI coil and explore its use for upper extremity applications. An RF system composed of a transverse electromagnetic transmit coil and an eight-channel receive-only array was developed for 7  T upper extremity applications. The RF system was characterized and evaluated using scattering parameters and B1+ mapping. Finite difference time domain simulations were performed to evaluate the B1+ field distribution and specific absorption rate for the forearm region of the upper extremity. High-resolution 7  T images were acquired and compared with those at 3 T. The simulation and experimental results show very good B1+ field homogeneity across the forearm. High-resolution images of musculotendinous, osseocartilaginous, and neurovascular structures in the upper extremity are presented with T1 volumetric interpolated breath-hold examination, T2 double-echo steady state, T2 * susceptibility weighted imaging (SWI), diffusion tensor imaging, and time-of-flight sequences. Comparison between 3  T and 7  T is shown. Intricate contextual anatomy can be delineated in synovial, fibrocartilaginous, interosseous, and intraosseous trabecular structures of the forearm, as well as palmar and digital vascular anatomy (including microvascular detail in SWI). Ultra-high-field 7  T imaging holds great potential in improving the sensitivity and specificity of upper extremity imaging, especially in wrist and hand pathology secondary to bone, ligament, nerve, vascular, and other soft or hard tissue etiology.

The role of imaging in patient selection, preoperative planning, and postoperative monitoring in human upper extremity allotransplantation.

Objective. To describe the role of imaging in vascular composite allotransplantation based on one institution's experience with upper extremity allotransplant patients. Methods. The institutional review board approved this review of HIPAA-compliant patient data without the need for individual consent. A retrospective review was performed of imaging from 2008 to 2011 on individuals undergoing upper extremity transplantation. This demonstrated that, of the 19 patients initially considered, 5 patients with a mean age of 37 underwent transplantation. Reports were correlated clinically to delineate which preoperative factors lead to patient selection versus disqualification and what concerns dictated postoperative imaging. Findings were subdivided into musculoskeletal and vascular imaging criterion. Results. Within the screening phase, musculoskeletal exclusion criterion included severe shoulder arthropathy, poor native bone integrity, and marked muscular atrophy. Vascular exclusion criterion included loss of sufficient arterial or venous supply and significant distortion of the native vascular architecture. Postoperative imaging was used to document healing and hardware integrity. Postsurgical angiography and ultrasound were used to monitor for endothelial proliferation or thrombosis as signs of rejection and vascular complication. Conclusion. Multimodality imaging is an integral component of vascular composite allotransplantation surgical planning and surveillance to maximize returning form and functionality while minimizing possible complications.

Vertebral fractures and trabecular microstructure in men with prostate cancer on androgen deprivation therapy.

Androgen deprivation therapy (ADT), a treatment for prostate cancer, is associated with bone loss and fractures. Dual-energy X-ray absorptiometry (DXA)-measured bone mineral density does not assess vertebral fractures (VF). High-resolution micro-magnetic resonance imaging (HR-MRI) assesses bone microarchitecture and provides structural information. To determine if VF identification increased the diagnosis of osteoporosis beyond DXA and if HR-MRI demonstrated skeletal deterioration in men with VF, we cross-sectionally studied 137 men aged ≥ 60 years with nonmetastatic prostate cancer on ADT for ≥ 6 months. Vertebral fracture assessment (VFA) by DXA was confirmed with X-rays. HR-MRI of the wrist included bone volume to total volume (BV/TV), surface density (trabecular plates), surface/curve ratio (plates/rods), and erosion index (higher depicts deterioration). VF were found in 37% of men; the majority were unknown. Seven percent of participants were classified as osteoporotic by hip or spine DXA. Thirty-seven percent of men without osteoporosis by DXA had VF identified, suggesting that 90% of patients with clinical osteoporosis would have been misclassified by DXA alone. By ANOVA comparison across VF grades, the BV/TV, surface density, and spine, hip, and wrist DXA were lower, and erosion index was higher in men with moderate-severe VF compared with lesser grades (all p < 0.05). By unadjusted ROC analysis, the addition of HR-MRI to DXA at the spine, hip, and femoral neck added substantially (AUC increased 0.831 to 0.902, p < 0.05) to prediction of moderate-severe vertebral fracture. HR-MRI indices were associated with spine, hip, and wrist DXA measures (p < 0.01). Longer duration of ADT was associated with lower BV/TV, surface density, and surface/curve ratio (p < 0.05). ADT for men with prostate cancer is associated with silent VF. DXA alone leads to misclassifications of osteoporosis, which can be avoided by VF assessment. HR-MRI provides a novel technique to assess deterioration of structural integrity in men with VF and adds micro-structural information.

Compare display schemes for lung nodule CT screening.

This study investigated the relative efficiencies of a stereographic display and two monoscopic display schemes for detecting lung nodules in chest computed tomography (CT). The ultimate goal was to determine whether stereoscopic display provides advantages for visualization and interpretation of three-dimensional (3D) medical image datasets. A retrospective study that compared lung nodule detection performances achieved using three different schemes for displaying 3D CT data was conducted. The display modes included slice-by-slice, orthogonal maximum intensity projection (MIP), and stereoscopic display. One hundred lung-cancer screening CT examinations containing 647 nodules were interpreted by eight radiologists, in each of the display modes. Reading times and displayed slab thickness versus time were recorded, as well as the probability, location, and size for each detected nodule. Nodule detection performance was analyzed using the receiver operating characteristic method. The stereo display mode provided higher detection performance with a shorter interpretation time, as compared to the other display modes tested in the study, although the difference was not statistically significant. The analysis also showed that there was no difference in the patterns of displayed slab thickness versus time between the stereo and MIP display modes. Most radiologists preferred reading the 3D data at a slab thickness that corresponded to five CT slices. Our results indicate that stereo display has the potential to improve radiologists' performance for detecting lung nodules in CT datasets. The experience gained in conducting the study also strongly suggests that further benefits can be achieved through providing readers with additional functionality.

Characterization of radiologists' search strategies for lung nodule detection: slice-based versus volumetric displays.

The goal of this study was to assess whether radiologists' search paths for lung nodule detection in chest computed tomography (CT) between different rendering and display schemes have reliable properties that can be exploited as an indicator of ergonomic efficiency for the purpose of comparing different display paradigms. Eight radiologists retrospectively viewed 30 lung cancer screening CT exams, containing a total of 91 nodules, in each of three display modes [i.e., slice-by-slice, orthogonal maximum intensity projection (MIP) and stereoscopic] for the purpose of detecting and classifying lung nodules. Radiologists' search patterns in the axial direction were recorded and analyzed along with the location, size, and shape for each detected feature, and the likelihood that the feature is an actual nodule. Nodule detection performance was analyzed by employing free-response receiver operating characteristic methods. Search paths were clearly different between slice-by-slice displays and volumetric displays but, aside from training and novelty effects, not between MIP and stereographic displays. Novelty and training effects were associated with the stereographic display mode, as evidenced by differences between the beginning and end of the study. The stereo display provided higher detection and classification performance with less interpretation time compared to other display modes tested in the study; however, the differences were not statistically significant. Our preliminary results indicate a potential role for the use of radiologists' search paths in evaluating the relative ergonomic efficiencies of different display paradigms, but systematic training and practice is necessary to eliminate training curve and novelty effects before search strategies can be meaningfully compared.

Head-mounted versus remote eye tracking of radiologists searching for breast cancer: a comparison.

PURPOSE: We compared performance and visual search parameters of radiologists detecting masses on mammograms by using both a head-mounted (HDMT) and a remote (REM) eye tracker. MATERIALS AND METHODS: Five experienced radiologists read twice a case set of 20 one-view (medial-lateral oblique) mammograms, of which 12 contained a malignant mass and eight were lesion-free. For each observer, one trial used an HDMT eye-tracking system and the other used an REM system. Trials were separated on average by 2 months. Time to hit the location of the mass, dwell, and number of fixations in the location of the mass were measured. The same parameters were measured on a per-trial basis to determine whether there were memory effects from the previous trial. RESULTS: Dwell times in the location of true-positive, false-positive, and false-negative results were significantly shorter (P < .05) using the HDMT (median, 0.395 seconds) than REM (median, 0.482 seconds) systems, but the number of fixations in the location of the response was smaller using the REM system (median, 4.33 versus 5.0 for the HDMT). The observed differences did not seem to be caused by a memory effect. In addition, the relative lack of head mobility using the REM system caused observers to report neck strain. CONCLUSION: Overall, radiologists' visual search behavior was very similar using both types of eye-tracking device. However, because the REM system did not contain a magnetic head tracker, radiologists were allowed very limited head movements when using it, which made them uncomfortable during the experiment.

Stereo CT image compositing methods for lung nodule detection and characterization.

RATIONALE AND OBJECTIVES: Stereographic display has been proposed as a possible method of improving performance in reading computed tomographic (CT) examinations acquired for lung cancer screening. Optimizing such displays is important given the large volume of image data that must be evaluated for each of these examinations. This study is designed to explore certain tradeoffs between rendering methods designed for the stereo display of CT images. MATERIALS AND METHODS: Stereo CT image compositing methods, including distance-weighted averaging, distance-weighted maximum intensity projection (MIP), and conventional MIP, were applied to lung CT images and compared for lung nodule detection and characterization. RESULTS: Using the Jonckheere test indicated a statistically significant (P < .01) increase in contrast among the three compositing methods. Wilcoxon-Mann-Whitney test showed significant differences in contrast between distance-weighted averaging and conventional MIP (P < .01) and between averaging and distance-weighted MIP (P < .05), but not between distance-weighted MIP and conventional MIP (P > .05). Conventional MIP compositing provided the highest image contrast, but produced ambiguities in local geometric detail and texture, whereas averaging resulted in the lowest contrast, but preserved geometric detail. Distance-weighted MIP partially recovered geometric information, which was lost in images composited by means of conventional MIP. CONCLUSION: Our results indicate that distance-weighted MIP may be a better choice for nodule detection in stereo lung CT images for its high local contrast and partial preservation of geometric information, whereas compositing by means of distance-weighted averaging is preferable for nodule characterization. The relative clinical value of these compositing methods needs to be evaluated further.

Effects of lesion conspicuity on visual search in mammogram reading.

RATIONALE AND OBJECTIVES: The goal of mammography screening is to detect breast cancer at early stages, but because of the complexity of the breast parenchyma and the variability of signs of the disease, many cancers go unreported when initially visible on the mammogram. We compared the visual search strategy used by experienced mammographers in a case set where they examined both the mammogram in which a malignant mass was discovered at screening mammography and the most recent prior mammogram. MATERIALS AND METHODS: Four experienced mammographers participated in this experiment. They read a case set of 20 two-view mammograms, of which 15 contained a malignant mass and 5 were lesion-free, in two trials. For each of the cancer cases, two versions were shown to the observers: the one in which the cancer was reported in the clinical practice, called the "current" mammograms, and the most recent prior. Each trial had a balanced mix of current and prior mammograms. In addition, the same set of lesion-free cases was shown to the observers in both trials. The eye movements of the observers were tracked, and visual search parameters such as time to hit the location of the malignant mass, dwell, and mean pupil size in the location of the cancer were collected. Statistical analyses were used to determine whether there were differences between the current and prior mammograms. RESULTS: A total of 66% of the malignant masses in the current mammograms and 57% in the priors attracted some amount of visual attention. From these, 71% yielded a report on the current mammograms, but only 40% on the priors. In the cases where the observer saw the malignant mass, they did so within 2 seconds of image display, regardless of whether the mammogram was current or prior. CONCLUSION: Most unreported malignant masses attracted some amount of visual attention, but it was in the processing of the information extracted in the location of the lesion that most errors occurred. In our experiment, approximately 70% of the total time used by the observers for visual scan of the cases was spent gathering information to corroborate the hypothesis already formed by the radiologist.

Prevalence effect in a laboratory environment.

PURPOSE: To measure observer performance at various levels of prevalence. MATERIALS AND METHODS: A multiobserver multiabnormality receiver operating characteristic (ROC) study to assess the effect of prevalence on observer performance was conducted. Fourteen observers, including eight faculty members, two fellows, and four residents, interpreted 1,632 posteroanterior chest images with five prevalence levels by using a nested study design. Performance comparisons were accomplished by using a multireader multicase approach to assess the effect of prevalence from 28% (69 of 249) to 2% (31 of 1,577) on diagnostic accuracy. The mean times required to review and report a case were analyzed and compared for different levels of prevalence and readers' experience. RESULTS: Area under the ROC curve demonstrated that, with the study experimental conditions, no significant effect could be measured as a function of prevalence (P >.05) for any abnormality, group of cases, or readers. There were no significant differences (P >.05) in the mean times required to review and report cases at different prevalence levels and with different groups of readers. CONCLUSION: The consistency in the results and the size of this study suggest that with laboratory conditions, if a prevalence effect exists, it is quite small in magnitude; hence, it will not likely alter conclusions derived from such studies.

Hip biomechanics: importance to functional imaging.

Although well recognized the hip joint is not well understood. In many respects knowledge of the hip is similar to that of the knee several decades ago. Increased understanding of the hip's structure and function will improve our ability to diagnose and treat pre-end-stage hip joint disease. This article describes relevant anatomy and mechanics and details the crucial role that imaging plays in current assessments of hip function.

Observer performance studies: detection of single versus multiple abnormalities of the chest.

OBJECTIVE: We used receiver operating characteristic (ROC) analysis to compare two methods of evaluating observer performance in detecting an abnormality on chest radiographs. In the first method, the abnormality in question, rib fracture, was one of five investigated, and it was the only one of interest in the second. MATERIALS AND METHODS: Eight experienced observers viewed 117 posteroanterior chest radiographs in two interpretation modes. Fifty-four of these images depicted rib fractures that had been rated as subtle for detection. The likelihood of the presence of a rib fracture was rated as one of five abnormalities in question in one mode and the sole abnormality of interest in the other mode. RESULTS: Six of the observers performed better during the single-abnormality mode, one performed equally well in both modes, and one performed better during the multiple-abnormality mode. The average area under the ROC curves (A(z)) was 0.73 +/- 0.07 for the multiple-abnormality mode and 0.80 +/- 0.04 for the single-abnormality mode. The results were significantly different (p < 0.05). CONCLUSION: Study methodology can significantly affect the results in ROC studies, particularly for abnormalities that may not be perceived as primary or important. The order in which abnormalities appear on a checklist report form may be important.