Modifications to a commercially available linear mass spectrometer for mass-resolved microscopy with the pixel imaging mass spectrometry (PImMS) camera.

RATIONALE: Imaging mass spectrometry is a powerful analytical technique capable of accessing a large volume of spatially resolved, chemical data from two-dimensional samples. Probing the entire surface of a sample simultaneously requires a detector with high spatial and temporal resolutions, and the ability to observe events relating to different mass-to-charge ratios. METHODS: A commercially available time-of-flight mass spectrometer, designed for matrix-assisted laser desorption/ionization (MALDI) analysis, was combined with the novel pixel imaging mass spectrometry (PImMS) camera in order to perform multi-mass, microscope-mode imaging experiments. A number of minor modifications were made to the spectrometer hardware and ion optics so that spatial imaging was achieved for a number of small molecules. RESULTS: It was shown that a peak width of Δm50 % < 1 m/z unit across the range 200 ≤ m/z ≤ 800 can be obtained while also achieving an optimum spatial resolution of 25 µm. It was further shown that these data were obtained simultaneously for all analytes present without the need to scan the experimental parameters. CONCLUSIONS: This work demonstrates the capability of multi-mass, microscope-mode imaging to reduce the acquisition time of spatially distributed analytes such as multi-arrays or biological tissue sections. It also shows that such an instrument can be commissioned by effecting relatively minor modifications to a conventional commercial machine.

Geometry function of a linear brachytherapy source.

An equation is derived for the TG43 geometry function, G(r,theta), of a linear brachytherapy source in terms of its active length. This equation is validated by comparison to published values. It is then used to calculate values of the geometry function for the Model 200 (103)Pd seed, which is a segmented linear source.

Commissioning of a mobile electron accelerator for intraoperative radiotherapy.

Radiation performance characteristics of a dedicated intraoperative accelerator were determined to prepare the unit for clinical use. The linear accelerator uses standing wave X-band technology (wavelength approximately 3 centimeters) in order to minimize the mass of the accelerator. The injector design, smaller accelerator components, and low electron beam currents minimize radiation leakage. The unit may be used in a standard operating room without additional shielding. The mass of the accelerator gantry is 1250 Kg (weight approximately 2750 lbs) and the unit is transportable between operating rooms. Nominal electron energies are 4, 6, 9, and 12 MeV, and operate at selectable dose rates of 2.5 or 10 Gray per minute. D(max) depths in water for a 10 cm applicator are 0.7, 1.3, 1.7, and 2.0 for these energies, respectively. The depths of 80% dose are 1.2, 2.1, 3.1, and 3.9 cm, respectively. Absolute calibration using the American Association of Physicists in Medicine TG-51 protocol was performed for all electron energies using the 10 cm applicator. Applicator sizes ranged from 3 to 10 cm diameter for flat applicators, and 3 to 6 cm diameter for 30 degrees beveled applicators. Output factors were determined for all energies relative to the 10 cm flat applicator. Central axis depth dose profiles and isodose plots were determined for every applicator and energy combination. A quality assurance protocol, performed each day before patient treatment, was developed for output and energy constancy.

Shielding assessment of a mobile electron accelerator for intraoperative radiotherapy.

A new approach to intraoperative radiotherapy makes use of a mobile electron linear accelerator delivering therapeutic radiation doses in an operating room suite. This unconventional technology has raised questions concerning protection for personnel and the necessity of shielding the adjoining areas. In this study, the leakage and scatter radiation from the mobile electron accelerator is measured and characterized in a series of spherical projections. An analysis is performed to determine the need for shielding or, alternatively, patient-based load restrictions in the operating room. This investigation provides a resource to assess shielding and/or patient load restrictions for any facility performing intraoperative radiotherapy with a similar unit. The data presented indicates that the mobile electron accelerator may be operated in an area with little or no shielding under nominal patient load expectations.

Posttransplantation lymphoproliferative disorder initially seen as iris mass and uveitis.

Primary ocular posttransplantation lymphoproliferative disorder is rare. Epstein-Barr virus is implicated as the cause as a result of systemic immunosuppression after transplant surgery. We studied a patient who developed ocular posttransplantation lymphoproliferative disorder after orthotopic liver transplantation. Slitlamp and light microscopic photographs confirmed the diagnosis.

An assessment of intraocular pressure rise in patients with gas-filled eyes during simulated air flight.

PURPOSE: To investigate the safety of aircraft flight for patients with small volumes of residual postoperative intraocular gas. DESIGN: Nonrandomized comparative trial. PARTICIPANTS: Seventeen eyes (nine gas filled and eight control eyes) of nine patients and one eye of one control subject were tested. METHODS: Patients with postoperative intraocular gas and the control subject were tested in the controlled environment of a hypobaric chamber to simulate the cabin depressurization associated with a typical commercial aircraft flight. Before, during, and after a simulated flight, the intraocular pressure (IOP) in the gas-containing and contralateral eyes was tested using the Perkins (Edinburgh, UK) and Tono-Pen XL (Jacksonville, FL) tonometers. MAIN OUTCOME MEASURES: The absolute and percentage change in IOP with varied cabin pressurization. RESULTS: Of the nine patients with intraocular gas, seven had 10% to 15% gas volume and two had 20% gas volume. In the 10% to 15% gas volume group, the IOP rose by an average of 109% from baseline during ascent to an average cabin altitude of 7429 feet above sea level. The IOP dropped to an average of 30% above baseline IOP during the cruise phase and further decreased to an average of 38% below baseline IOP on return to baseline altitude. In the 20% gas volume group, the IOP rose by an average of 84% from baseline during ascent to an average cabin altitude of 3400 feet above sea level. The IOP dropped to an average of 42% below baseline IOP on return to baseline altitude. The IOP in the contralateral control eyes did not vary with altitude changes. No patient experienced pain or visual loss during the experiments. CONCLUSIONS: Our results demonstrate that IOP may rise significantly in gas-filled eyes during simulated air flight, supporting the current conservative recommendation against air travel for most patients with intraocular gas bubbles. Further testing is warranted to develop a more objective measure of intraocular gas volume estimation and to define better the tolerability of aircraft flight for patients with intraocular gas.

The role of drug treatment in children with strabismus and amblyopia.

Strabismus, or misalignment of the eyes, is a common ophthalmic problem in childhood, affecting 2 to 5% of the preschool population. Amblyopia is an important cause of visual morbidity frequently associated with strabismus, and both conditions should be treated simultaneously. Pharmacological means for treating strabismus and amblyopia can be divided into 3 categories: paralytic agents (botulinum toxin) used directly on the extraocular muscles to affect eye movements; autonomic agents (atropine, miotics) used topically to manipulate the refractive status of the eye and thereby affect alignment, focus and amblyopia; and centrally acting agents, including levodopa and citicoline, which affect the central visual system abnormalities in amblyopia. Botulinum toxin, the paralytic agent that causes the clinical symptoms of botulism poisoning, can be injected in minute quantities to achieve controlled paralysis of the extraocular muscles. Although the role of botulinum toxin is established in adults with paralytic strabismus, its usefulness in the treatment of comitant childhood strabismus (primary esotropia and exotropia) is not universally accepted. Botulinum injections tend to be more effective with smaller degrees of strabismus, in patients with good binocular fusion, and in managing overcorrections or undercorrections after traditional muscle surgery. Inadvertent ptosis and paralysis of adjacent muscles, unpredictable responses and technical constraints of the injections limit its use in children. Miotic therapy, by altering the refractive state of the treated eye, offers an alternative to optical correction with bifocals in treating esotropia due to excessive accommodative convergence. It is also effective in treating residual esotropia following surgery. The ease of use of glasses restricts the wide application of miotics in these common strabismus syndromes. Atropine, an anticholinergic agent, paralyses the ability of the eye to focus or accommodate. In amblyopia therapy, atropine is used to blur vision in the non-amblyopic eye and offers a useful alternative to traditional occlusion therapy with patching, especially in older children who are not compliant with patching. The neurotransmitter precursor levodopa and the related compound citicoline have been demonstrated to improve vision in amblyopic eyes. The therapeutic role of these centrally acting agents in the clinical management of amblyopia remains unproven.

Anterior segment ischemia after strabismus surgery with microvascular dissection.

Anterior segment ischemia is a rare but well-known complication of extraocular muscle surgery.(1) Several surgical techniques have been used to prevent this complication in high-risk patients. A number of studies have suggested that microvascular dissection and preservation of the anterior ciliary vessels during strabismus surgery may reduce the risk of ischemic complications. (2-4) We present a case in which anterior segment ischemia occurred despite the use of this vessel-sparing technique.

Preparing a cost analysis for the section of medical physics-guidelines and methods.

Radiation oncology is a highly complex medical specialty, involving many varied routine and special procedures. To assure cost-effectiveness and maintain support for the medical physics program, managers are obligated to analyze and defend all aspects of an institutional billing and cost-reporting program. Present standards of practice require that each patient's radiation treatments be customized to fit his/her particular condition. Since the use of personnel time and other resources is highly variable among patients, graduated levels of charges have been established to allow for more precise billing. Some radiation oncology special procedures have no specific code descriptors; so existing codes are modified or additional information attached in order to avoid payment denial. Recent publications have explored the manpower needs, salaries, and other resources required to perform radiation oncology "physics" procedures. This information is used to construct a model cost-based resource use profile for a radiation oncology center. This profile can be used to help the financial officer prepare a cost report for the institution. Both civil and criminal penalties for Medicare fraud and abuse (intentional or unintentional) are included in the False Claims Act and other statutes. Compliance guidelines require managers to train all personnel in correct billing procedures and to review continually billing performance.

The eye in childhood.

Normal visual development is rapid during the first six months of life and continues through the first decade. Young children are uniquely sensitive to conditions that interfere with vision and visual development. Amblyopia, or functionally defective development of the central visual system, may be caused by common vision problems such as strabismus, uncorrected refractive errors and deprivation secondary to occlusion. Prematurity is especially associated with eye pathology, including retinopathy of prematurity, amblyopia, strabismus and refractive errors. When detected early, amblyopia and many other childhood vision abnormalities are treatable, but the potential for correction and normal visual development is inversely related to age. Since many affected children are asymptomatic, early detection of abnormal visual function requires effective screening throughout early childhood. Special considerations apply to screening examinations of children born prematurely.

Retinoblastoma in transgenic mice: models of hereditary retinoblastoma.

Retinoblastoma, the most common intraocular malignancy ill childhood, has served as a paradigm for the study of genetic mechanisms of oncogenesis. The retinoblastoma susceptibility gene RB1 was the first tumor suppressor gene to be cloned, and genetic and molecular biologic studies of this tumor have greatly expanded the understanding of the mechanics of tumorigenesis. Human retinoblastoma has essentially no naturally occuring animal counterpart. The development of transgenic murine models of retinoblastoma have created an experimental tool for manipulation of a tumor gene system in vivo. These models have also enabled studies of new therapeutic modalities. This review outlines the development of the transgenic murine models of retinoblastoma, together with the genetic mechanisms of retinoblastoma origin. Current therapeutic innovations developed by means of the transgenic models are described.

Perianesthesia care of adult and pediatric strabismus surgery patients.

Strabismus procedures on children and adults are frequently performed in an outpatient setting. Perianesthesia care of patients having strabismus procedures may be optimized by recognizing the characteristics of strabismus patients, the frequently associated diagnoses that may affect perioperative care, and the specific surgical techniques used to treat strabismus. Complications including postoperative nausea, pain, prolonged PACU stay, and unplanned postoperative admissions can be minimized and treatment facilitated by preparing patients with preoperative instructions, careful choice of anesthetic agents and postoperative medications, and appropriate perioperative care. This report will provide a brief review of surgical strabismus, including current techniques, and present guidelines for perioperative care of pediatric and adult strabismus patients.

Retinoblastoma in an eye with congenital uveal coloboma.

Retinoblastoma and congenital ocular abnormalities rarely coexist. The appearance of an intraocular tumor in a child with preexisting leukokoria may make the diagnosis of retinoblastoma more challenging. This report describes a unique case of unilateral congenital uveal coloboma and ipsilateral retinoblastoma in a patient with no family history of either abnormality and normal cytogenetic analysis.

Pharmacotherapy of photorefractive keratectomy.

PURPOSE: To compare the pharmacotherapeutic practices of high-volume photorefractive keratectomy (PRK) surgeons with suggested practices gleaned from the current literature. SETTING: York Finch Eye Associates, Toronto, Canada. METHODS: Seventy-five ophthalmic surgeons believed by the authors to do a high-volume of PRKs were surveyed over the summer of 1994 about their pharmacotherapeutic practices. The results were compared with suggested practices extracted from a review of the current literature. RESULTS: Relatively consistent approaches to the management of post-PRK pain and prevention of acute post-PRK subepithelial infiltrative keratitis were reported. The administration of topical steroids after PRK was almost universally employed. Post-PRK analgesia was most commonly achieved with nonsteroidal anti-inflammatory drugs (NSAIDs) and a soft contact lens, but surgeons were not convinced of the benefits of long-term NSAID administration to control myopic regression and haze. There seemed to be no agreed-on solution to the infrequent problems of severe haze and regression and steroid-induced elevated intraocular pressure after PRK; however, many useful suggestions for the management of these problems were proposed. CONCLUSION: In general, high-volume PRK surgeons use topical steroids, NSAIDs, and a soft contact lens in the immediate postoperative period, although they are uncertain about the long-term effectiveness of NSAIDs in controlling regression and haze.

Glaucoma following childhood cataract surgery.

Glaucoma has been recognized as an infrequent but serious complication following surgery for congenital and acquired cataracts in childhood. Little is known concerning the influence of factors on the risk of glaucoma such as age at surgery, type of cataract, associated ocular abnormalities, and type of surgery. We reviewed records of 240 eyes of 155 patients on whom cataract surgery had been performed between January 1965 and July 1990 at Children's Hospital, Boston. After excluding those patients who had been followed up less than 5 years after surgery, and those who had had surgery after the age of 10 years, 125 eyes of 82 patients were included in the study group. We identified 14 eyes of 9 patients that had developed open-angle glaucoma 5.3 to 13.1 years following surgery (average 7.4 years). An additional 4 eyes of 3 patients developed angle closure glaucoma, which was diagnosed at 146, 177, 2911, and 2939 days following surgery. A fifth patient developed acute angle closure 1.7 years following primary cataract surgery and 53 days following secondary discission. All but one of the patients who developed glaucoma had cataract surgery at less than 1 year of age. Age at surgery for the entire study group averaged 1.9 years, and ranged from 25 days to 9.6 years. We conclude that patients having cataract surgery before 1 year of age are at the greatest risk of developing postoperative open-angle glaucoma. Additional increased relative risk was found in eyes with microcornea, congenital rubella syndrome, and poor pupillary dilation with 1% cyclopentolate (Cyclogyl). No significant difference was seen among the various surgical methods of cataract removal.