Osteoporosis identification among previously undiagnosed individuals with vertebral fractures.

Because osteoporosis is under-recognized in patients with vertebral fractures, we evaluated characteristics associated with osteoporosis identification. Most patients with vertebral fractures did not receive evaluation or treatment for osteoporosis. Black, younger, and male participants were particularly unlikely to have had recognized osteoporosis, which could increase their risk of negative outcomes. INTRODUCTION: Vertebral fractures may be identified on imaging but fail to prompt evaluation for osteoporosis. Our objective was to evaluate characteristics associated with clinical osteoporosis recognition in patients who had vertebral fractures detected on their thoracolumbar spine imaging reports. METHODS: We prospectively identified individuals who received imaging of the lower spine at primary care clinics in 4 large healthcare systems who were eligible for osteoporosis screening and lacked indications of osteoporosis diagnoses or treatments in the prior year. We evaluated characteristics of participants with identified vertebral fractures that were associated with recognition of osteoporosis (diagnosis code in the health record; receipt of bone mineral density scans; and/or prescriptions for anti-osteoporotic medications). We used mixed models to estimate adjusted odds ratios (ORs) and 95% confidence intervals (95% CIs). RESULTS: A total of 114,005 participants (47% female; mean age 65 (interquartile range: 57-72) years) were evaluated. Of the 8579 (7%) participants with vertebral fractures identified, 3784 (44%) had recognition of osteoporosis within the subsequent year. In adjusted regressions, Black participants (OR (95% CI): 0.74 (0.57, 0.97)), younger participants (age 50-60: 0.48 (0.42, 0.54); age 61-64: 0.70 (0.60, 0.81)), and males (0.39 (0.35, 0.43)) were less likely to have recognized osteoporosis compared to white participants, adults aged 65 + years, or females. CONCLUSION: Individuals with identified vertebral fractures commonly did not have recognition of osteoporosis within a year, particularly those who were younger, Black, or male. Providers and healthcare systems should consider efforts to improve evaluation of osteoporosis in patients with vertebral fractures.

Ambient temperature and solar insolation are associated with decreased prevalence of SSRI-treated psychiatric disorders.

Serotonergic function is known to fluctuate in association with light and temperature. Serotonin-related behaviors and disorders similarly vary with climatic exposure, but the associations are complex. This complexity may reflect the importance of dose and timing of exposure, as well as acclimation. This cross-sectional study tests how average climate exposures (ambient temperature and solar insolation) vary with the prevalence of a group of SSRI-treated disorders. For comparison, we similarly studied a group of disorders not treated by SSRIs (i.e substance use disorders). Psychiatric prevalence data were obtained from the Collaborative Psychiatric Epidemiology Surveys (CPES). Average yearly solar insolation was obtained from NASA's NLDAS-2 Forcing Dataset Information. Average yearly temperature was obtained from NOAA's US Climate Normals. Logistic regression models were generated to assess the relationship between these two climatic factors and the prevalence of SSRI-treated and substance use disorders. Age, gender, race, income, and education were included in the models to control for possible confounding. Temperature and insolation were significantly associated with the SSRI-responsive group. For an average 1 GJ/m2/year increase, OR was 0.90 (95% CI 0.85-0.96, p = 0.001), and for an average 10 °F increase, OR was 0.93 (95% CI 0.88-0.97, p = 0.001). This relationship was not seen with substance use disorders (insolation OR: 0.97, p = 0.682; temperature OR: 0.96, p = 0.481). These results warrant further investigation, but they support the hypothesis that chronic exposure to increased temperature and light positively impact serotonin function, and are associated with reduced prevalence of some psychiatric disorders. They also support further investigation of light and hyperthermia treatments.

Multiplexing strategies for monolithic crystal PET detector modules.

To reduce the number of output channels and associated cost in PET detectors, strategies to multiplex the signal channels have been investigated by several researchers. This work aims to find an optimal multiplexing strategy for detector modules consisting of a monolithic LYSO scintillator coupled to a 64-channel PMT. We apply simulated multiplexing strategies to measured data from two continuous miniature crystal element (cMiCE) detector modules. The strategies tested include standard methods such as row column summation and its variants, as well as new data-driven methods involving the principal components of measured data and variants of those components. The detector positioning resolution and bias are measured for each multiplexing strategy and the results are compared. The mean FWHM over the entire detector was 1.23 mm for no multiplexing (64 channels). Using 16 principal component channels yielded a mean FWHM resolution of 1.21 mm, while traditional row/column summation (16 channels) yielded 1.28 mm. Using 8 principal component output channels resulted in a resolution of 1.30 mm. Using the principal components of the calibration data to guide the multiplexing scheme appears to be a viable method for reducing the number of output data channels. Further study is needed to determine if the depth-of-interaction resolution can be preserved with this multiplexing scheme.

Automatic localization and identification of vertebrae in arbitrary field-of-view CT scans.

This paper presents a new method for automatic localization and identification of vertebrae in arbitrary field-of-view CT scans. No assumptions are made about which section of the spine is visible or to which extent. Thus, our approach is more general than previous work while being computationally efficient. Our algorithm is based on regression forests and probabilistic graphical models. The discriminative, regression part aims at roughly detecting the visible part of the spine. Accurate localization and identification of individual vertebrae is achieved through a generative model capturing spinal shape and appearance. The system is evaluated quantitatively on 200 CT scans, the largest dataset reported for this purpose. We obtain an overall median localization error of less than 6mm, with an identification rate of 81%.

MR nerve imaging in a prospective cohort of patients with suspected carpal tunnel syndrome.

OBJECTIVES: To evaluate the reliability and diagnostic accuracy of high-resolution MRI of the median nerve in a prospectively assembled cohort of subjects with clinically suspected carpal tunnel syndrome (CTS). METHODS: The authors prospectively identified 120 subjects with clinically suspected CTS from five Seattle-area clinics. All subjects completed a hand-pain diagram and underwent a standardized nerve conduction study (NCS). The reference standard for determining CTS status was a classic or probable hand pain diagram and NCS with a difference >0.3 ms between the 8-cm median and ulnar peak latencies. Readers graded multiple imaging parameters of the MRI on four-point scales. The authors also performed quantitative measurements of both the median nerve and carpal tunnel cross-sectional areas. NCS and MRI were interpreted without knowledge of the other study or the hand pain diagram. RESULTS: Intrareader reliability was substantial to near perfect (kappa = 0.76 to 0.88). Interreader agreement was lower but still substantial (kappa = 0.60 to 0.67). Sensitivity of MRI was greatest for the overall impression of the images (96%) followed by increased median nerve signal (91%); however, specificities were low (33 to 38%). The length of abnormal signal on T2-weighted images was significantly correlated with nerve conduction latency, and median nerve area was larger at the distal radioulnar joint (15.8 vs 11.8 mm(2)) in patients with CTS. A logistic regression model combining these two MR variables had a receiver operating characteristic area under the curve of 0.85. CONCLUSIONS: The reliability of MRI is high but the diagnostic accuracy is only moderate compared with a research-definition reference standard.

A fast calibration method for 3-D tracking of ultrasound images using a spatial localizer.

We have developed a fast calibration method for computing the position and orientation of 2-D ultrasound (US) images in 3-D space where a position sensor is mounted on the US probe. This calibration is required in the fields of 3-D ultrasound and registration of ultrasound with other imaging modalities. Most of the existing calibration methods require a complex and tedious experimental procedure. Our method is simple and it is based on a custom-built phantom. Thirty N-fiducials (markers in the shape of the letter "N") embedded in the phantom provide the basis for our calibration procedure. We calibrated a 3.5-MHz sector phased-array probe with a magnetic position sensor, and we studied the accuracy and precision of our method. A typical calibration procedure requires approximately 2 min. We conclude that we can achieve accurate and precise calibration using a single US image, provided that a large number (approximately ten) of N-fiducials are captured within the US image, enabling a representative sampling of the imaging plane.

The Longitudinal Assessment of Imaging and Disability of the Back (LAIDBack) Study: baseline data.

STUDY DESIGN: Prospective cohort study of randomly selected Veterans Affairs (VA) outpatients. OBJECTIVE: To determine the prevalence of magnetic resonance imaging (MRI) findings in the lumbar spine among persons without current low back pain or sciatica and to examine which findings are related to age or previous back symptoms. SUMMARY OF BACKGROUND INFORMATION: Previous studies of patients without low back pain have not explored the possible association of various MRI findings to past symptoms. METHODS: We randomly selected an age-stratified sample of subjects without low back pain in the past 4 months from clinics at a VA hospital. We collected information on demographics, comorbidity, functional status, and quality of life. MR images were obtained using a standardized protocol through each of the five lumbar disc levels. RESULTS: Of 148 subjects, 69 (46%) had never experienced low back pain. There were 123 subjects (83%) with moderate to severe desiccation of one or more discs, 95 (64%) with one or more bulging discs, and 83 (56%) with loss of disc height. Forty-eight subjects (32%) had at least one disc protrusion and 9 (6%) had one or more disc extrusions. CONCLUSION: Many MR imaging findings have a high prevalence in subjects without low back pain. These findings are therefore of limited diagnostic use. The less common findings of moderate or severe central stenosis, root compression, and extrusions are likely to be diagnostically and clinically relevant.

Validating clustering for gene expression data.

MOTIVATION: Many clustering algorithms have been proposed for the analysis of gene expression data, but little guidance is available to help choose among them. We provide a systematic framework for assessing the results of clustering algorithms. Clustering algorithms attempt to partition the genes into groups exhibiting similar patterns of variation in expression level. Our methodology is to apply a clustering algorithm to the data from all but one experimental condition. The remaining condition is used to assess the predictive power of the resulting clusters-meaningful clusters should exhibit less variation in the remaining condition than clusters formed by chance. RESULTS: We successfully applied our methodology to compare six clustering algorithms on four gene expression data sets. We found our quantitative measures of cluster quality to be positively correlated with external standards of cluster quality.

Image acquisition: ultrasound, computed tomography, and magnetic resonance imaging.

As the transition toward total digital image acquisition continues, radiology is transcending the current standard of two-dimensional (2-D) cross-sectional anatomic imaging to more complex models. Among these are three-dimensional (3-D) anatomic images, constructed either from a synthesis of traditional 2-D data sets, or directly from volumetrically acquired data. However, current trends are moving beyond mere anatomic imaging to include physiological data once mainly obtained via nuclear medicine. Recent magnetic resonance pulse sequences, in addition to Doppler and harmonic ultrasound methods, are providing insight into blood flow, oxygenation, and metabolite concentrations non-invasively. Through image registration techniques, these data (even from differing modalities) are being assembled into 2-D and 3-D "fusion" images that promise to revolutionize diagnosis. Furthermore, with improvements in miniaturization, reliability, speed, built-in intelligence, and ease of use, these new developments are finding their way into use by nonspecialists. For instance, a new hand-held ultrasound unit will likely become a common tool among emergency medical teams, military medical teams, and in NASA's manned space program. Portable computed tomography (CT) scanners are already being used in the operating room. The increasing sophistication of imaging instruments will bring about a complementary increase in ease of use for both scanning and data interpretation, bringing diagnostic imaging and therapeutic capabilities closer to the patient, rather than the converse.

An investigation of the importance of myocardial anisotropy in finite-element modeling of the heart: methodology and application to the estimation of defibrillation efficacy.

Finite-element (FE) modeling has been widely used in studies of bioelectric phenomena of tissues, including ventricular defibrillation. Most FE models, whether built from anatomical atlases or subject-specific tomographic images, treat the myocardium as an isotropic tissue. However, myocardium has been experimentally shown to have significant anisotropy in its resistivities, although myocardial fiber directions are difficult to measure on a subject-specific basis. In this paper, we: 1). propose a method to incorporate a widely known myocardial fiber direction model to a specific individual and 2). assess the effects of myocardial anisotropy on myocardial voltage gradients computed for a study of implantable defibrillators. The thoracic FE model was built from CT images of a young pig, and the myocardial fiber structures were incorporated via elastic mapping. Our results demonstrate a good mapping of geometry between the source and target hearts with an average root-mean-square error of less than 2.3 mm and a mapped fiber pattern similar to those known to exist in vivo. With the mapped fiber information, we showed that the estimated minimal myocardial voltage gradient over 80% of the myocardium differs by less than 10% between using an isotropic and anisotropic myocardial models. Thus, myocardial anisotropy is expected to have only a small effect on estimates of defibrillation threshold obtained from computed voltage gradients. On the other hand, anisotropy may be essential if defibrillation efficacy is analyzed by transmembrane voltage of the myocardial cells.

A finite-element study of the effects of electrode position on the measured impedance change in impedance cardiography.

Traditional impedance cardiography (ICG) technique uses band electrodes both for delivering current to and measuring impedance change in the thorax. The use of spot electrodes increases the ease of electrode placement and comfort level for patients. Research has shown that changes in thoracic impedance can have multiple causes. In this study, we used finite element modeling to investigate the sources of impedance change for both band-electrode and spot-electrode ICG, and focused on how differences in electrode location affect the contribution of different sources to changes in impedance. The ultimate purpose is to identify the optimal electrode type and placement for the sensing of stroke volume (SV). Our models were built on sets of end-diastolic and end-systolic magnetic resonance images of a healthy human subject. The results showed that the effect of ventricular contraction is opposite to that of the other changes in systole: the expansion of major vessels, decrease in blood resistivity due to increased blood flow velocity, and decrease in lung resistivity due to increased blood perfusion. Ventricular contraction, the only factor that tends to increase systolic impedance, has a larger effect than any of the other factors. When spot electrodes are placed on the anterior chest wall near the heart, ventricular contraction is so dominant that the measured impedance increases from end-diastole to end-systole, and the change represents 82% of the contribution from ventricular contraction. When using the common band-electrode configuration, the change in measured impedance is a more balanced combination of the four effects, and ventricular contraction is overcome by the other three factors so that the impedance decreases. These results suggest that the belief that ICG can be used to directly measure SV based on the change in the whole thoracic impedance may be invalid, and that spot electrodes may be more useful for understanding local physiological events such as ventricular volume change. These findings are supported by previously reported experimental observations.

Ghost imaging for targeting breast masses with MR imaging: a phantom study.

RATIONALE AND OBJECTIVES: The purpose of this study was to test the accuracy of ghost magnetic resonance (MR) imaging for guiding core biopsies of simulated breast masses in a tissue phantom. MATERIALS AND METHODS: A tissue MR phantom implanted with 20 grapes as targets was placed into an interventional breast MR coil. The locations of the centers of the targets were determined, recorded, and saved as ghost images. A nonmagnetic phantom needle was constructed to avoid imprecision secondary to magnetic field inhomogeneity and was used to determine the three-dimensional location of the needle tip in the center of each grape on the ghost image. Once the positions were determined, the true needle was placed and biopsy specimens were taken. The needle was inspected for the presence of pulp after each pass. Each grape was inspected to determine the location of the needle track in relation to the center of the grape. The duration of the procedure was recorded. RESULTS: All grapes were hit by the biopsy needle, as demonstrated either by pulp within the needle or by a needle track within the grape. Seventeen of the 20 grapes (85%) were hit centrally. Three were sampled eccentrically, up to 5-6 mm from the center. Each biopsy took approximately 1 hour. CONCLUSION: These results suggest that ghost imaging may be ideal for needle guidance in core biopsy or preoperative localization, as it extends the period of visibility after a bolus injection of contrast material. Additionally, using a phantom needle for localization appears to overcome imprecision due to magnetic field inhomogeneity of the needle.

Edge-guided boundary delineation in prostate ultrasound images.

Accurate detection of prostate boundaries is required in many diagnostic and treatment procedures for prostate disease. In this paper, a new paradigm for guided edge delineation is described, which involves presenting automatically detected prostate edges as a visual guide to the observer, followed by manual editing. This approach enables robust delineation of the prostate boundaries, making it suitable for routine clinical use. The edge-detection algorithm is comprised of three stages. An algorithm called sticks is used to enhance contrast and at the same time reduce speckle in the transrectal ultrasound prostate image. The resulting image is further smoothed using an anisotropic diffusion filter. In the third stage, some basic prior knowledge of the prostate, such as shape and echo pattern, is used to detect the most probable edges describing the prostate. Finally, patient-specific anatomic information is integrated during manual linking of the detected edges. The algorithm was tested on 125 images from 16 patients. The performance of the algorithm was statistically evaluated by employing five expert observers. Based on this study, we found that consistency in prostate delineation increases when automatically detected edges are used as visual guide during outlining, while the accuracy of the detected edges was found to be at least as good as those of the human observers. The use of edge guidance for boundary delineation can also be extended to other applications in medical imaging where poor contrast in the images and the complexity in the anatomy limit the clinical usability of fully automatic edge-detection techniques.

Differential attenuation method for simultaneous estimation of activity and attenuation in multiemission single photon emission computed tomography.

A penalized weighted least squares reconstruction algorithm is described that simultaneously estimates activity and attenuation distributions from emission sinogram data alone. This estimation technique is based on differential attenuation information and is applicable to any single photon emission computed tomography imaging isotope with emissions at two or more distinct energies, after accurate compensation for Compton scatter. A rotation-based forward projector is used to efficiently model photon attenuation at multiple emission energies, as well as distance-dependent spatial resolution. The algorithm was tested using simulated scatter-free 201T1 projection data from a single-slice numerical cardiac phantom with and without cold myocardial defects. Poisson noise was added to the projection data to mimic clinically realistic count densities. The activity estimates resulting from the proposed method had fewer artifacts and were substantially more accurate than images reconstructed with filtered backprojection without compensation for attenuation. Several techniques were employed to reduce the time required for the iterative routine to converge and to reduce the sensitivity of the solution to noise in the projection data. These included: (1) a preconditioning image variable transformation; (2) a coarse-to-fine grid initialization schedule; and (3) a convex hull image mask determined directly from the data. The combined effect of these techniques substantially reduced the compute time required for the reconstruction.

Analysis of defibrillation efficacy from myocardial voltage gradients with finite element modeling.

Increasing defibrillation efficacy by lowering the defibrillation threshold (DFT) is an important goal in positioning implantable cardioverter-defibrillator electrodes. Clinically, the DFT is difficult to estimate noninvasively. It has been suggested that the DFT relates to the myocardial voltage gradient distribution, but this relation has not been quantitatively demonstrated. We analyzed the relation between the experimentally measured DFT's and the simulated myocardial voltage gradients provided by finite element modeling. We performed a series of experiments in 11 pigs to measure the DFT's, and created and solved three-dimensional subject-specific finite element models to assess the correlation between the computed myocardial voltage gradient histograms and the DFT's. Our data show a statistically significant correlation between the DFT and the left ventricular voltage gradient distribution, with the septal region being more significant (correlation coefficient of 0.74) than other myocardial regions. The correlation between the DFT and the right ventricular and the atrial voltage gradient, on the other hand, is not significant.

MR contrast media in neuroimaging: a critical review of the literature.

BACKGROUND AND PURPOSE: MR contrast media are commonly used but do not have evidence-based guidelines for their application. This investigation seeks to define specific methodological problems in the MR contrast media literature and to suggest guidelines for an improved study design. METHODS: To evaluate the reported clinical efficacy of MR contrast media in neuroimaging, we performed a critical review of the literature. From 728 clinical studies retrieved via MEDLINE, we identified 108 articles that evaluated contrast media efficacy for a minimum of 20 patients per study. The articles were randomly assigned to four readers (a fifth reader reviewed all of the articles) who were blinded to article titles, authors, institutions, and journals of publication. The readers applied objective, well-established methodological criteria to assign each article a rating of A, B, C, or D. RESULTS: One hundred one of 108 articles received a D rating, six received a C rating, and one received a B rating. In general, the Methods sections of the evaluated articles did not contain details that would allow the reader to calculate reliable measures of diagnostic accuracy, such as sensitivity and specificity. Specifically, a common problem was failure to establish and uniformly apply an acceptable standard of reference. In addition, images were not always interpreted independently from the reference standard. Radiologists and clinicians need to determine the applicability of any published study to their own practices. Unfortunately, the studies we reviewed commonly lacked clear descriptions of patient demographics, the spectrum of symptomatology, and the procedure for assembling the study cohort. Finally, small sample sizes with inadequate controls were presented in almost all of the articles. CONCLUSION: Although MR contrast media are widely used and play an essential role in lesion detection and confidence of interpretation, no rigorous studies exist to establish valid sensitivity and specificity estimates for their application. On the basis of this review, we herein describe basic methods to document improvements in technology. Such studies are essential to devise measures of diagnostic accuracy, which can form the basis for further studies that will assess diagnostic and therapeutic impact and, ultimately, patient outcomes.

Interactive 3-D registration of ultrasound and magnetic resonance images based on a magnetic position sensor.

The use of stereotactic systems has been one of the main approaches for image-based guidance of the surgical tool within the brain. The main limitation of stereotactic systems is that they are based on preoperative images that might become outdated and invalid during the course of surgery. Ultrasound (US) is considered the most practical and cost-effective intraoperative imaging modality, but US images inherently have a low signal-to-noise ratio. Integrating intraoperative US with stereotactic systems has recently been attempted. In this paper, we present a new system for interactively registering two-dimensional US and three-dimensional magnetic resonance (MR) images. This registration is based on tracking the US probe with a dc magnetic position sensor. We have performed an extensive analysis of the errors of our system by using a custom-built phantom. The registration error between the MR and the position sensor space was found to have a mean value of 1.78 mm and a standard deviation of 0.18 mm. The registration error between US and MR space was dependent on the distance of the target point from the US probe face. For a 3.5-MHz phased one-dimensional array transducer and a depth of 6 cm, the mean value of the registration error was 2.00 mm and the standard deviation was 0.75 mm. The registered MR images were reconstructed using either zeroth-order or first-order interpolation. The ease of use and the interactive nature of our system (approximately 6.5 frames/s for 344 x 310 images and first-order interpolation on a Pentium II 450 MHz) demonstrates its potential to be used in the operating room.

Geometric effects on resistivity measurements with four-electrode probes in isotropic and anisotropic tissues.

We studied via computer simulation the effects of electrode diameter, electrode length, interelectrode spacing, and tissue size on the accuracy of measured tissue resistivities and anisotropy ratios obtained with the widely used four-electrode technique. Such measurements commonly assume an ideal situation in which the four electrodes are infinitesimally small and the tissue is semi-infinite. Our study shows that these geometric factors can significantly affect measured resistivities, particularly for anisotropic tissues. The measured anisotropy ratio is decreased by either 1) increasing the electrode diameter or length relative to the interelectrode spacing of the probe or 2) decreasing tissue size. We have provided an equation for estimating errors in the measured anisotropy ratio from the parameters of electrode and tissue geometries. The simulation findings are supported by our in vitro experimental results.

Rapid MR imaging versus plain radiography in patients with low back pain: initial results of a randomized study.

PURPOSE: To demonstrate the feasibility of a randomized trial to compare rapid magnetic resonance (MR) imaging with plain radiography as the initial imaging study in patients with low back pain, to test measures of the decision-making process and patient outcomes, and to offer a model for using randomized clinical trials to evaluate diagnostic tests. MATERIALS AND METHODS: The authors randomly selected 62 patients with low back pain to undergo either rapid MR imaging or plain radiography. The authors measured functional status, satisfaction, and general health status at baseline and at 3 months. The modified Roland scale was the primary outcome measure. In addition, the authors examined diagnostic and therapeutic decision making and resources used by each group. RESULTS: There were no statistically significant differences between the two patient groups with respect to outcome (Roland score: MR imaging = 12.5, radiography = 12.1). MR imaging provided more useful information to clinicians and resulted in greater patient reassurance. CONCLUSION: Randomly selecting patients to undergo imaging examinations and measuring outcomes is feasible; however, a larger, multicenter study is necessary to determine whether rapid MR imaging is a cost-effective replacement for plain radiography in patients with low back pain.