Search PubMed⌕ Search

Biomedical subjects

D R Haynor

Publications and source records attributed to D R Haynor.

At least 37 records · Page 2Linked to original sources
PubMed1996

Automatic fetal head measurements from sonographic images.

RATIONALE AND OBJECTIVES: We designed an image processing technique to automatically measure the biparietal diameter (BPD) and head circumference (HC) from prenatal sonograms. We evaluated the performance of the algorithm by comparing the resulting measurements with those made by experienced sonographers. METHODS: Thirty-five digitized sonograms of the fetal head were obtained during routine imaging. The BPD and HC were automatically computed by detecting the inner and outer boundaries of the fetal skull using the computer vision technique known as the "active contour model." Six experienced sonographers also measured the BPD and HC on these images. RESULTS: The algorithm failed to locate the boundaries in two of the 35 cases. For the remaining cases, the mean absolute difference between the automated measurements and the average of the six observers was 1.4% for BPD and 2.9% for HC. The correlations were .999 for the BPD and .994 for the HC. The computer's measurements were no different from the six observers' measurements than the observers' measurements were from one another. CONCLUSION: The tested algorithm effectively and accurately measures BPD and HC automatically. We are currently in the process of integrating this algorithm into an ultrasound machine.

Algorithms↗
PubMed1996

Interreader reliability for a new classification of lumbar disk disease.

RATIONALE AND OBJECTIVES: The nomenclature that divides disk herniations into protrusions and extrusions may increase the specificity of magnetic resonance (MR) imaging for clinically important lesions. Our goal was to determine this terminology's interreader reliability. METHODS: Three readers who were unaware of patients' histories independently read MR images of 34 consecutive patients with back pain. Readers classified disks at the lowest three lumbar levels as normal, bulging, protruded, or extruded. Kappa and weighted kappa values were the primary measures of agreement. RESULTS: Weighted kappa values showed fair-to-moderate agreement. Kappas for the dichotomous decision of extrusion present or absent were more variable, ranging from 0 to .78. Major disagreements (greater than a single category) occurred with 6.2% of all comparisons and in 10 of 34 volunteers; five involved extrusions. CONCLUSION: Overall, readers achieved moderate agreement for this new nomenclature. However, agreement for the presence or absence of an extrusion was less reliable.

Adult↗
PubMed1996

Ulnar nerve entrapment at the elbow: correlation of magnetic resonance imaging, clinical, electrodiagnostic, and intraoperative findings.

The diagnosis of ulnar nerve entrapment at the elbow has relied primarily on clinical and electrodiagnostic findings. Recently, magnetic resonance imaging (MRI) has been used in the evaluation of peripheral nerve entrapment disorders to document signal and configuration changes in nerves. We performed a prospective study on a population of 31 elbows in 27 patients with ulnar nerve entrapment at the elbow. The study correlated MRI findings with clinical, electrodiagnostic, and operative findings. A control population consisting of 10 asymptomatic subjects also was studied by MRI. Electrodiagnostic evaluation confirmed ulnar neuropathy in 24 (77%) elbows of the 31, with localization to the elbow region in 21 (68%). MRI, using a short tau inversion recovery sequence, demonstrated increased signal of the ulnar nerve in 30 (97%) elbows of the 31 and enlargement of the ulnar nerve in 23 (74%). No MRI abnormalities were found in the control population. MRI signal increase of the ulnar nerve occurred an average of 27 mm proximal to the distal humerus and extended distally an average of 4 mm below the distal humerus. The mean total length of increased ulnar nerve signal was 34 mm. Ulnar nerve enlargement occurred an average of 19 mm proximal to the distal humerus and extended distally an average of 8 mm above the distal humerus. The mean total length of ulnar nerve enlargement was 12 mm. The 12 patients who underwent a surgical procedure for ulnar nerve entrapment were found to have ulnar nerve compression, with 9 (75%) having excellent and 3 (25%) having good postoperative results. In this study, MRI was both sensitive and specific in diagnosing ulnar nerve entrapment at the elbow as defined by clinical, electrodiagnostic, and operative findings.

Adult↗
PubMed1996

Magnetic resonance neurography for cervical radiculopathy: a preliminary report.

Magnetic resonance neurography was used to directly image cervical spinal nerves in patients with clinical and radiographic evidence of cervical radiculopathy. A magnetic resonance imaging phased-array coil system was used to obtain high-resolution coronal T1-weighted spin echo, coronal/axial T2-weighted fast spin echo with fat saturation, and coronal/axial fast short tau inversion recovery weighted images of the cervical spine and spinal nerves. Three patients with neck and upper extremity pain and one asymptomatic volunteer were studied. The T2-weighted and the fast short tau inversion recovery images demonstrated markedly increased signal in the proximal portion of the affected spinal nerves. In two patients, contrast-to-noise measurements of the affected spinal nerves showed a markedly increased intensity compared with that of the noninvolved spinal nerves. Our findings demonstrate that phased-array coils used in conjunction with magnetic resonance neurography sequences can detect signal abnormalities within compressed cervical spinal nerves in patients with corresponding radicular symptoms and findings. This technique may prove to be helpful in evaluating patients with multilevel disc and/or spondylotic disease of the cervical spine.

Adult↗
PubMed1996

An efficient tissue classifier for building patient-specific finite element models from X-ray CT images.

We developed an efficient semiautomatic tissue classifier for X-ray computed tomography (CT) images which can be used to build patient- or animal-specific finite element (FE) models for bioelectric studies. The classifier uses a gray scale histogram for each tissue type and three-dimensional (3-D) neighborhood information. A total of 537 CT images from four animals (pigs) were classified with an average accuracy of 96.5% compared to manual classification by a radiologist. The use of 3-D, as opposed to 2-D, information reduced the error rate by 78%. Models generated using minimal or full manual editing yielded substantially identical voltage profiles. For the purpose of calculating voltage gradients or current densities in specific tissues, such as the myocardium, the appropriate slices need to be fully edited, however. Our classifier offers an approach to building FE models from image information with a level of manual effort that can be adjusted to the need of the application.

Algorithms↗
PubMed1996

Scatter and attenuation correction for 111In based on energy spectrum fitting.

A combined scatter and attenuation correction that does not require a transmission scan is proposed for 111In imaging. Estimates of the unscattered intensity at both 171 and 245 keV are obtained by fitting the observed energy spectrum at each pixel or region of interest using the measured scatter-free spectrum and a simple model for scatter. The scatter model for the 171 keV peak accounts for scatter contributed by both the 171 and 245 keV emissions. After correcting for scatter, the attenuation is estimated from the observed ratio of photopeak intensities using the known difference in attenuation at the two emission energies and a model based on a point source in water. Accurate scatter correction is a prerequisite for the success of this method because scatter from the higher energy emission will otherwise contaminate the lower photopeak. This differential attenuation method (DAM) of estimating attenuation is demonstrated and calibrated using a series of point source measurements with a wedge-shaped attenuator. The observed absolute and differential attenuation are in good agreement with the narrow-beam linear attenuation coefficients for water. Estimates of precision suggest a depth resolution of 1.0-2.5 cm for realistic count densities over the clinically relevant depth range (0-25 cm). The accuracy of DAM in a more realistic attenuation environment is assessed using a hot sphere inside the anthropomorphic data spectrum torso phantom viewed from several angles (with differing attenuation). Finally, the potential of DAM for SPECT attenuation correction was investigated by computer simulation using the SIMSET Monte Carlo software. Preliminary results based on measured planar data and simulated SPECT data indicate that DAM can improve the quality and quantitative accuracy of 111In images. In one SPECT simulation study, the average error in tumor to soft-tissue ratios was reduced from 32% for uncorrected data to 8% for data corrected with DAM. However, the technique is susceptible to significant noise amplification and can cause substantial streak artifacts in low-count SPECT studies if sufficient smoothing of the depth estimates is not performed.

Biophysical Phenomena↗
PubMed1996

Intraoperative ultrasound for monitoring anterior cervical vertebrectomy. Technical note.

The authors describe the use of intraoperative ultrasonography with a small high-frequency (15 mHz) probe for evaluation of the extent of lateral bone removal during anterior cervical vertebrectomy. The relationship of the bone resection margins to the lateral aspect of the spinal cord was visualized. Postoperative computerized tomography scans revealed the extent of bone removal to be similar to that demonstrated by ultrasound. Intraoperative ultrasonography may be useful during anterior cervical surgery to assure adequate decompression of the spinal canal and spinal cord.

Cervical Vertebrae↗
PubMed1996

Energy-based scatter corrections for scintillation camera images of iodine-131.

UNLABELLED: The use of high-dose 131I antibody therapy requires accurate measurement of normal tissue uptake to optimize the therapeutic dose. One of the factors limiting the accuracy of such measurements is scatter and collimator septal penetration. This study evaluated two classes of energy-based scatter corrections for quantitative 131I imaging: window-based and spectrum-fitting. METHODS: The window-based approaches estimate scatter from data in two or three energy windows placed on either side of the 364-keV photopeak using empirical weighting factors. A set of images from spheres in an elliptical phantom were used to evaluate each of the window-based corrections. The spectrum-fitting technique estimates detected scatter at each pixel by fitting the observed energy spectrum with a function that models the photopeak and scatter, and which incorporates the response function of the camera. This technique was evaluated using a set of Rollo phantom images. RESULTS: All of the window-based methods performed significantly better than a single photopeak window (338-389 keV), but the weighting factors were found to depend on the object being imaged. For images contaminated with scatter, the spectrum-fitting method significantly improved quantitation over photopeak windowing. Little difference, however, between any of the methods was observed for images containing small amounts of scatter. CONCLUSION: Most clinical 131I imaging protocols will benefit from qualitative and quantitative improvements provided by the spectrum-fitting scatter correction. The technique offers the practical advantage that it does not require phantom-based calibrations. Finally, our results suggest that septal penetration and scatter in the collimator and other detector-head components are important sources of error in quantitative 131I images.

Gamma Cameras↗
PubMed1995

Quality control of cathode-ray tube monitors for medical imaging using a simple photometer.

As computer monitors are used more in medical imaging and the use of picture archiving and communication system workstations with multiple monitors is increasing, quality control protocols become necessary to track subtle variations in performance characteristics. Several tests based on previously published work were applied to 10 monitors of three different types over a period of 5 months. Each test is explained, and the results are shown. For example, without corrective adjustments, 2 monitors from the same workstation showed a small but steady decline in maximum luminance of 8.1% and 7.6% over the course of 11 weeks that was not perceptible. From this experience, we took the first step toward developing a practical and useful quality control protocol. The proposed protocol requires only a photometer and the ability to generate the Society of Motion Picture and Television Engineers (SMPTE) test pattern, and takes approximately 5 minutes per monitor per week to gather data.

Data Display↗
PubMed1995

Persistent feeding arteries to angiographically completely embolized arteriovenous malformation demonstrated by intraoperative color-flow Doppler testing: report of two cases.

Two cases of arteriovenous malformation (AVM) treated preoperatively by endovascular embolization that appeared to be completely occluded after embolization are presented. Seven and 12 days later, respectively, these patients underwent resection of their AVM. At the time of surgery, intraoperative color-flow Doppler studies revealed persistent feeding arteries to an active residual nidus of the AVM. The significance of this finding is presented in light of previous published literature.

Adult↗
PubMed1995

Computational studies of transthoracic and transvenous defibrillation in a detailed 3-D human thorax model.

A method for constructing and solving detailed patient-specific 3-D finite element models of the human thorax is presented for use in defibrillation studies. The method utilizes the patient's own X-ray CT scan and a simplified meshing scheme to quickly and efficiently generate a model typically composed of approximately 400,000 elements. A parameter sensitivity study on one human thorax model to examine the effects of variation in assigned tissue resistivity values, level of anatomical detail included in the model, and number of CT slices used to produce the model is presented. Of the seven tissue types examined, the average left ventricular (LV) myocardial voltage gradient was most sensitive to the values of myocardial and blood resistivity. Incorrectly simplifying the model, for example modeling the heart as a homogeneous structure by ignoring the blood in the chambers, caused the average LV myocardial voltage gradient to increase by 12%. The sensitivity of the model to variations in electrode size and position was also examined. Small changes (< 2.0 cm) in electrode position caused average LV myocardial voltage gradient values to increase by up to 12%. We conclude that patient-specific 3-D finite element modeling of human thoracic electric fields is feasible and may reduce the empiric approach to insertion of implantable defibrillators and improve transthoracic defibrillation techniques.

Computer Simulation↗
PubMed1995

Predicting cardiothoracic voltages during high energy shocks: methodology and comparison of experimental to finite element model data.

Finite element modeling has been used as a method to investigate the voltage distribution within the thorax during high energy shocks. However, there have been few quantitative methods developed to assess how well the calculations derived from the models correspond to measured voltages. In this paper, we present a methodology for recording thoracic voltages and the results of comparisons of these voltages to those predicted by finite element models. We constructed detailed 3-D subject-specific thorax models of six pigs based on their individual CT images. The models were correlated with the results of experiments conducted on the animals to measure the voltage distribution in the thorax at 52 locations during synchronized high energy shocks. One transthoracic and two transvenous electrode configurations were used in the study. The measured voltage values were compared to the model predictions resulting in a correlation coefficient of 0.927 +/- 0.036 (average +/- standard deviation) and a relative rms error of 22.13 +/- 5.99%. The model predictions of voltage gradient within the myocardium were also examined revealing differences in the percent of the myocardium above a threshold value for various electrode configurations and variability between individual animals. This variability reinforces the potential benefit of patient-specific modeling.

Animals↗
PubMed1995

Multiwindow scatter correction techniques in single-photon imaging.

We studied the performance of linear scatter correction methods for single-photon imaging with Tc-99m and Tl-201, using a numerical model of the Rollo phantom and measurements with a gamma camera modified to record position and energy information in list mode form. We compared the performance of these methods to per-image optimized linear methods and to locally adaptive linear methods, and developed estimates of the limits on accuracy of scatter correction imposed by the presence of Poisson noise. For both Tc-99m and Tl-201 imaging at a fixed depth, particularly at low count rates, the performance of dual-window methods, or of adaptive methods, is near the best possible for linear methods. Smoothing of the scatter estimate results in minor improvement for Tl-201. Substantial gaps between the performance of any of these linear methods and the limits imposed by Poisson noise remain and are due primarily to bias, with the gap for Tl-201 being larger than that for Tc-99m.

Algorithms↗
PubMed1995

Carpal tunnel syndrome: correlation of magnetic resonance imaging, clinical, electrodiagnostic, and intraoperative findings.

We undertook a prospective study of 43 wrists in 32 patients who had been clinically diagnosed as having carpal tunnel syndrome (study group) and 5 wrists in people who had no symptoms (control group), correlating the clinical, electrodiagnostic, intraoperative, and magnetic resonance imaging (MRI) findings. MRI of the carpal tunnel and thenar eminence was performed, using coronal and axial T1- and T2-weighted, proton density, and short tau inversion recovery sequences. Abnormalities of the median nerve, as revealed by MRI, were found in 43 of 43 (100%) wrists in the study group and in 0 of 5 (0%) wrists in the control group. Increased signal of the median nerve was seen in 41 of 43 (95%) wrists, increased signal of the flexor tendon sheath in 41 of 43 (95%), volar bowing of the flexor retinaculum in 39 of 43 (91%), increased distance between the flexor tendons in 37 of 43 (86%), and abnormal nerve configuration in 28 of 43 (65%). Increased short tau inversion recovery signal of the thenar muscles was found in 5 of 43 (12%) wrists, all of which had undergone severe denervation changes, as revealed by electromyography. Operative release was performed for 27 of 43 (63%) wrists, and follow-up was obtained for 42 of 43 (98%). A good or excellent postoperative outcome resulted for 20 of 27 (74%) patients, a fair outcome for 2 of 27 (7%), and a poor outcome for 4 of 27 (15%), and 1 of 27 (4%) patients was lost to follow-up. For patients undergoing carpal tunnel release whose MRI revealed an abnormal nerve configuration, the outcome was improved, with good or excellent results in 15 of 18 (83%) patients. No association with outcome was seen with median nerve or flexor tendon signal changes, increased interspace between the flexor tendons, or flexor retinaculum bowing. Our results indicate that MRI is a sensitive diagnostic modality that can demonstrate signal and configurational abnormalities of the median nerve in patients diagnosed with carpal tunnel syndrome. Increased signal of the thenar muscles, as revealed by MRI, using short tau inversion recovery sequences, occurs only in muscles that have undergone severe denervation changes, as revealed by electromyography.

Carpal Tunnel Syndrome↗
PubMed1995

Similarities in degenerative findings on magnetic resonance images of the lumbar spines of identical twins.

Although the etiology of most degenerative changes in the lumbar spine is unclear, genetic factors may play an important role. To investigate this link, we reviewed magnetic resonance images of the lumbar spines of identical twins to assess the degree of similarities in degenerative findings in the discs. Observers who were blinded to twinship evaluated sagittal T1-weighted and T2-weighted magnetic resonance images of the lumbar spines of forty male identical twins (twenty pairs) with respect to changes in the end plates, desiccation of the discs, bulging or herniated discs, and decrease in the height of the disc space. Similarities between co-twins were significantly greater than would be expected by chance. Whereas smoking status and age explained 0 to 15 per cent of the variability in the various degenerative findings in the discs, 26 to 72 per cent of the variability was explained with the addition of a variable representing co-twin status. These findings are compatible with a marked genetic influence and warrant further investigation.

Adult↗
PubMed1994

The clinical efficacy of magnetic resonance imaging in neuroimaging.

PURPOSE: To assess the clinical efficacy of magnetic resonance imaging (MRI) for neuroimaging and to provide guidelines for clinical practice. STUDY SELECTION: After a comprehensive literature search, studies of the diagnostic accuracy of MRI alone or compared with other tests and of any impact on therapeutic choices or patient outcomes were reviewed by independent readers, followed by discussion to reach consensus conclusions. DATA EXTRACTION: Of 3125 citations retrieved, 156 studies with original data could be rated according to methodologic criteria for study design. One article contributed grade A quality information about diagnostic accuracy, 28 were graded B or C, and 113 were graded D. One randomized trial and 2 comparison studies contributed grade B or C information about the impact on therapeutic choices. Only 2 studies surveyed health status before and after magnetic resonance scanning. RESULTS: For most abnormalities, the sensitivity of MRI is equal to or better than competing technologies. Magnetic resonance imaging shows greater contrast and detail than computed tomography (CT) but also shows more clinically silent abnormalities or incidental findings. A few studies found a modest impact on therapeutic choices but no impact on quality of life or disability. Costs for MRI are high. Computed tomography is sufficient for initial diagnosis of most mass lesions or intracranial hemorrhages requiring immediate intervention. Magnetic resonance imaging is more accurate in the temporal lobes, posterior fossa, brainstem, and spinal cord. For lumbar radiculopathy, MRI and plain spinal CT are as accurate as post-myelographic CT and are less invasive. The role of magnetic resonance angiography for carotid artery stenosis is being studied. CONCLUSIONS: Although suggestions for appropriate use of MRI in clinical practice can be made, the supporting evidence in published studies is weak. Firm guidelines for appropriate use of MRI should be based on further clinical research using more rigorous methods.

Angiography↗