Problem of track offset in optical disk systems.

In an optical disk drive, it is well known that a tilt of the disk causes an offset in the tracking-error signal (TES). One effect of disk tilt is the introduction of a dc component to the TES, which can be largely corrected by operation of the tracking system at the midpoint between the maximum and the minimum values of the open-loop TES. However, this method of correcting for the dc shift in the TES does not correct for the effect of coma in the focused spot, which leads to track offset. The track offset of a system is defined as the distance between the peak irradiance in the focused spot and the center of the groove when the tracking system is operating at the midpoint between the maximum and the minimum values of the open-loop TES in the presence of disk tilt. Calculations are performed that show the dependence of track offset on various system parameters, including track pitch, wavelength, and numerical aperture and rim intensity of the objective lens, and on the regions of the beam used to generate the TES. The track offsets for several beam-segmentation schemes are calculated for a digital versatile disk that uses push-pull and differential phase tracking. It is shown that for differential phase tracking the value of track offset depends on the mark length.

Recurrent tarsal tunnel syndrome and the radial forearm free flap.

Tarsal tunnel syndrome results from posterior tibial nerve entrapment beneath the flexor retinaculum and the deep fascia. The syndrome consists of pain, paresthesias, and vasomotor changes. Surgical correction via release of the flexor retinaculum is the treatment of choice. There is however, a 10% to 20% failure rate, with little in the literature addressing treatment options in this subset of individuals. Two patients with recurrent tarsal tunnel syndrome were treated with re-release of the retinaculum, followed by nerve coverage with a radial forearm free flap. At 15 and 27 months, both patients were pain-free, ambulatory, and able to return to work.

Forefoot pain in the athlete.

Forefoot pain in the athlete is common. Generally, the symptoms are a result of overuse. The initial treatment strategy is to modify both exercise and shoewear. Specific diagnoses of the problem is key to proper treatment. Usually, the history and physical examination are sufficient, but noninvasive as well as invasive diagnostic testing may be needed.

The use of magnetic resonance imaging in the diagnosis of stress fractures of the foot and ankle: four case reports.

Stress fractures result when bone is subjected to repeated loading which causes fatigue, cracking of the bone, and, eventually, a complete fracture. Stress fractures of the foot and ankle are common injuries affecting a broad range of the population, from the young to the elderly, the fitness enthusiast to the chronically debilitated. The diagnosis of stress fracture is not always obvious because radiographs are often negative, especially on initial presentation. In this report, we present four cases in which, after appropriate initial studies proved inconclusive, magnetic resonance imaging (MRI) was used to establish the diagnosis of stress fracture. We propose that MRI is a useful diagnostic modality in a select group of patients with suspected stress fractures of the foot and ankle.

Ligament strain and ankle joint opening during ankle distraction.

To determine the efficacy of ankle distraction and to investigate possible complications of the procedure, the strain on four ankle ligaments and the tibiotalar joint opening resulting from distraction force and various foot positions were studied. We mounted strain gauges on the deltoid, calcaneofibular, tibiofibular, and anterior talofibular ligaments of six fresh human cadaver ankles. An Acufex ankle distractor was used to apply forces of 45, 90, 135, and 180 N at 20 degrees dorsiflexion, neutral, and 10 degrees plantar flexion. The ankle distractor proved to be effective in opening the joint space for better visualization, but complications of pin bending, excessive ligament strain, and bony destruction did occur within the clinically recommended range. Based on the observed results, the safest method of distraction was to use forces < 135 N in the neutral position.

Basilar crescentic osteotomy. A three-dimensional computer simulation.

A three-dimensional computer simulation of the basilar crescentic osteotomy has been presented. The bunion deformity consists of hallux valgus, an increased first and second intermetatarsal angle, pronation of the great toe, and elevation of the first metatarsal head. Every foot is different and some may have more or less of each of the above noted components. Because the deformity is multiplanar, at least two roentgenograms are needed to evaluate the deformity. The weight-bearing, anterior-posterior roentgenogram is the principle radiograph used in preoperative planning. The use of a weight-bearing, sesamoid roentgenogram is recommended to quantify the anterior-posterior deflection and rotation of the first metatarsal head. A computer model (based on a cylinder) of the first metatarsal has been formulated. The osteotomy then was performed in a variety of scenarios in order to simulate the surgical correction. A great deal of flexibility is afforded by this osteotomy. The surgeon needs to be aware of the coupled motions that occur. That is, closure of the intermetatarsal angle may also cause head rotation, depression, or elevation. If the osteotomy is performed in an oblique multiplanar direction, then it is possible for the metatarsal head to elevate, pronate, and significantly shorten as the intermetatarsal angle is closed. If this scenario should occur, a poor surgical outcome will result. Excision of the medial eminence is recommended after the osteotomy has been completed and secured with stable fixation because of these rotational changes. The basilar crescentic osteotomy is an excellent method for correction of a marked metatarsus primus varus. It is important to pay close attention to a variety of anatomic considerations. The osteotomy must not be made in the diaphysis because of potential nonunion. There should be little dissection of the periosteum because of possible delayed union. As in any bunion surgery, it is essential to perform an adequate, distal, soft-tissue repair. Three dimensional preoperative planning is essential in obtaining correction of all components of a bunion. Specific guidelines, based on a three-dimensional computer model, are now available. An interactive computer program also is available to aid the surgeon in preoperative planning. We hope there will be better understanding of this technically difficult but highly versatile osteotomy.

The sprained ankle: current therapy.

The sprained ankle is one of the most common musculoskeletal injuries. Three treatments for severe acute sprain are advocated: immobilization, protected mobilization, and primary surgical repair. These injuries are cared for by different medical and paramedical specialties, each with varying skills and interests. In order to define the current preferred treatment, a survey was randomly distributed to 500 physicians. These data indicate that the treatment is generally conservative: cast immobilization was the preferred treatment for the moderate and severe sprain. These data also demonstrated that basic care (e.g., ice and elevation) and rehabilitation were often neglected. Significant differences were noted between the specialties of orthopaedic surgery, family practice, and emergency medicine.

A multidimensional slit-scan flow system.

A new slit-scan type flow system is described which provides three (X, Y, and Z) orthogonal one-dimensional projections of cell fluorescence. A photomultiplier tube and two semiconductor array detectors are used to obtain the three slit-scan contours from cells traversing a single fluorescence excitation beam. A high speed, dedicated preprocessor analyzes the three contours in parallel, extracting certain features useful for rejecting cells from which an accurate measurement of nuclear fluorescence cannot be obtain. Contour data is buffered and transferred to a PDP-11/40 computer where nuclear fluorescence is measured and cells are classified. It is anticipated that this new instrument will provide a significant reduction in false alarm rate when applied to prescreening of gynecologic cytology specimens.

Imaging in flow.

Imaging in flow has been valuable in investigating discrepancies in flow cell measurements due to cell orientation and flow dynamics. This paper discusses optical consideration in flow imaging, slit and full field imaging systems and various cell motion arresting techniques from the standpoint of image plane exposure and suitable detector choices. It concludes with an explanation of the slit-imaging techniques employed in a multidimensional slit-scan flow system and slit-scan correlation system.

False alarms in a slit-scan flow system: causes and occurrence rates. Implications and potential solutions.

A slit-scan technique was developed as a basis for an automated prescreening system for gynecologic cytology. A flow system based on this technique was fabricated and tested and results indicated that false alarms (misclassification of objects or events from normal specimens as abnormal) are the greatest remaining obstacle to development of an automated prescreening instrument. A dual view correlation system was fabricated to provide exact image-contour correlation in flow and permit precise determination of causes and occurrence rates of false alarms. This paper presents data from correlation analyses of 23 normal cytologic specimens. Major causes of false alarms and their implications to automated prescreening are discussed. A technique that would eliminate the majority of false alarms in flow is presented.

Imaging systems for correlation of false alarms in flow.

False alarms, arising from a variety of sources, are the greatest remaining obstacle to development of an automated prescreening system for gynecologic cytology. This paper describes two correlation systems under development at the University of Rochester and discusses their utilization in the study of false alarms in slit-scan cytofluorometry. Both systems permit imaging of objects in flow and correlation between images and corresponding slit-scan contours. Correlation systems will permit a detailed study of false alarm causes and aid in the search for new features to assist in their recognition.

Experimental findings on gynecologic cell orientation and dynamics for three flow nozzle geometries.

Gynecologic cell orientation and dynamics in sheath flow for three flow nozzle geometries are studied and compared. Cell orientations are classified into four categories based upon visual inspection of dark field laser stroboscopic photographs of cells in flow. Results are discussed in the context of slit-scan cytofluorometry.

Laser stroboscopic photography. Technique for cell orientation studies in flow.

Squamous cells in fluid flow are photographed using a laser stroboscopic technique. The technique provides either dark field or phase contrast multiple images of a cell on a single frame of film at resolutions permitted by the thickness of the cell stream. Cell orientation, velocity and acceleration are obtained from these photographs for evaluation of flow system performance.