Maximum pixel spectrum: a new tool for detecting and recovering rare, unanticipated features from spectrum image data cubes.

A new software tool, the maximum pixel spectrum, detects rare events within a spectrum image data cube, such as that generated with electron-excited energy-dispersive X-ray spectrometry in a scanning electron microscope. The maximum pixel spectrum is a member of a class of 'derived spectra' that are constructed from the spectrum image data cube. Similar to a conventional spectrum, a derived spectrum is a linear array of intensity vs. channel index that corresponds to photon energy. A derived spectrum has the principal characteristics of a real spectrum so that X-ray peaks can be recognized. A common example of a derived spectrum is the summation spectrum, which is a linear array in which the summation of all pixels within each energy plane gives the intensity value for that channel. The summation spectrum is sensitive to the dominant features of the data cube. The maximum pixel spectrum is constructed by selecting the maximum pixel value within each X-ray energy plane, ignoring the remaining pixels. Peaks corresponding to highly localized trace constituents or foreign contaminants, even those that are confined to one pixel of the image, can be seen at a glance when the maximum pixel spectrum is compared with the summation spectrum.

Improving the quality of electron backscatter diffraction (EBSD) patterns from nanoparticles.

In this study, we investigated the relative contributions of atomic number (Z) and density (rho) to the degradation of the electron backscatter diffraction (EBSD) pattern quality for nanoparticles < 500 nm in diameter. This was accomplished by minimizing the diffuse scattering from the conventional thick mounting substrate through the design of a sample holder that can accommodate particles mounted on thin-film TEM substrates. With this design, the contributions of incoherently scattered electrons that result in the diffuse background are minimized. Qualitative and quantitative comparisons were made of the EBSD pattern quality obtained from Al(2)O(3) particles approximately 200 nm in diameter mounted on both thick- and thin-film C substrates. For the quantitative comparison we developed a 'quality' factor for EBSD patterns that is based on the ratio of two Hough transforms derived from a given EBSD pattern image. The calculated quality factor is directly proportional to the signal-to-noise ratio for the EBSD pattern. In addition to the comparison of the thick and thin mounting substrates, we also estimated the effects of Z and rho by comparing the EBSD pattern quality from the Al(2)O(3) particles mounted on thin-film substrates with the quality of patterns obtained from Fe-Co nanoparticles approximately 120 nm in diameter. The results indicate that the increased background generated in EBSD patterns by the electrons escaping through the bottom of the small particles is the dominant reason for the poor EBSD pattern quality from nanoparticles < 500 nm in size. This was supported by the fact that we were able to obtain usable EBSD patterns from Al(2)O(3) particles as small as 130 nm using the thin-film mounting method.

Visibility of objects in computer simulations of noisy micrographs.

Thresholds of visibility for objects in images with random pixel noise are predicted in terms of the signal-to-noise ratio. From trials with volunteers marking test images, we determined visibility thresholds of objects obscured by random pixel noise. The test images had objects with a variety of simple shapes and relatively little internal structure. Aside from the noise, the background of the test images was smooth and featureless. We extend the threshold signal-to-noise ratio measurements of Rose and others to a variety of object sizes and shapes. For objects with areas less than a disc subtending 2 degrees at the eye, visibility depends on the averaged difference in intensity from background, the noise level and the number of pixels in the object. Visibility does not seem to depend on object shape.

Long-term pain control by direct peripheral-nerve stimulation.

In 1970, we began implanting electrodes for prolonged stimulation of injured peripheral nerves to reduce chronic pain. Thirty-eight peripheral nerves in thirty-five patients have been stimulated with electrodes for a period ranging from four to nine years. Nineteen electrode systems were implanted in the upper extremity (eleven on the median nerve, six on the ulnar nerve, one on the median and ulnar nerves, and one on the median and radial nerves), with successful relief of pain in 52..6 per cent of the patients. Sixteen stimulators have been implanted on the sciatic nerve with a success rate for pain relief of 31 per cent. Failures in the lower extremity were found primarily in lesions of the posterior tibial nerve at the ankle. We speculate that the stress of weight-bearing and the anatomical position of the posterior tibial nerve may partially account for this rate of failure. Use of the electrode-implant systems required careful preoperative assessment by an experienced team, meticulous technique, and a mechanical system that tolerates stress. The location and characteristics of the lesion affect the response to electrical stimulation.

Microvascular management of ring avulsion injuries.

Microsurgical revascularization has proved to be a useful method in managing the ring avulsion injury where both neurovascular bundles are damaged with only partial skin avulsion. Representative cases are used to illustrate guidelines for a practical classification for helping to decide the optimal method of treatment of acute ring avulsion injuries in light of digital revascularization techniques. Nine ring fingers were successfully revascularized of 24 acute ring avulsion injuries reviewed. Sensibility recovery was good and a functional range of motion obtained. No patient who has had his ring finger revascularized has requested its amputation because of appearance, painful neuromas, stiffness, or cold intolerance. Complete amputations, especially proximal to the superficialis insertion, and complete degloving injuries of the ring finger are usually best managed by surgical amputation of the digit.

Digital sensibility following replantation.

The amputated digit serves as an excellent model for the examination of digital nerve repair. When amputation is complete, there is no question of cross-over or anomalous innervation. The sensibility of 35 replanted digits in 29 patients was evaluated. Sensory return was related most closely to restored digital vascularity, as measured by Allen test, pulse volume flow, and Doppler. Level of amputation, mechanism of injury, and age of patient also affected ultimate sensation. All patients experienced cold intolerance and some were considerably disabled because of it. The severity of cold intolerance with pain and requiring prolonged rewarming was directly proportional to digital vascularity. When one digital artery thrombosed, ipsilateral digital sensation was not diminished as long as flow through the contralateral vessel was adequate. Two-point discrimation in our series was not as good as that reported for digital nerve repair in the nonamputated digit. Establishing and maintaining adequate digital flow at the time of replantation is essential to obtain good digital sensibility and to avoid symptoms of cold intolerance.

Temperature monitoring in digital replantation.

Postoperative monitoring of replanted and revascularized digits with skin temperature probes was performed on the 20 patients admitted to the Duke University Medical Center Orthopaedic Replantation Service from April to July, 1977. Using multiple probes, temperatures were recorded for the replanted digit, a control digit on the same hand, and the dressing which represented the ambient temperature. In addition, the following simultaneous clinical inspections were performed on the digits: capillary refill, skin color, turgor, audibility of arterial Doppler tones, and amplitude of pulp pressure tracing. Temperatures of the replanted digits were in the range of 26.0 degrees to 35.0 degrees C. Control temperatures remained relatively stable, in the range of 33.0 degrees to 35.0 degrees C. From the authors' experience the patterns of temperature change which signaled changes in perfusion of the replanted digit and possible poor prognosis were (1) the temperature of the replanted digit dropping more than 2.5 degrees C while the control temperature stayed constant; (2) the temperature of the replanted digit dropping below 30.0 degrees C for longer than 1 hour; and (3) the control temperature dropping below 30.0 degrees C with no correctable cause found.

Management of bone in digital replantation: free vascularized and composite bone grafts.

Microvascular surgical techniques have been applied to the problem of digital amputation, persistent nonunion and complicated extremity injuries with segmental bone and soft tissue loss. In replantations, adequate bone shortening and fixation with intramedullary pins or rods is mandatory. Proper patient selection, preoperative management of the amputated parts, application of microsurgical disciplines, employment of an organized surgical sequence, and rigid postoperative monitoring has resulted in an 80% viability rate in 121 replantations. Recent advances in the management of skeletal injuries using microvascular techniques include free vascularized bone grafting and salvage of the preamputation limb using free composite grafts of skin, subcutaneous tissue and bone. These free composite grafts techniques are exacting and time consuming. Meticulous planning, preoperative rehearsal and careful coordination between the operating teams make the functional restoration of a severely injured limb possible.

Experimental evaluation of microsurgical techniques in small artery anastomoses.

A number of factors that influence the success of microvascular anastomosis have been studied, including adventitial stripping, choice of suture material and needles, suturing technique, and perfusion of the distal lumen. It is apparent that only minimal stripping of the adventitia is indicated in order to prevent increased necrosis of the vessel ends at the anastomosis site. The use of 10-0 monofilament nylon suture material with needles 75 microns or less in diameter achieves the best results in small vessel anastomoses. Optimal anastomosis of 1 mm. vessels requires interrupted full thickness sutures with minimal adventitial stripping and the use of the smallest number of sutures possible. We do not advocate routine perfusion of small arteries unless there are specific indications. An experienced team of microsurgeons utilizing these principles along with proper patient selection and a sound postoperative regimen should be able to achieve more than a 70 per cent success rate in replantation of completely amputated digits and hands.