Automatic image-to-world registration based on x-ray projections in cone-beam CT-guided interventions.

Intraoperative imaging offers a means to account for morphological changes occurring during the procedure and resolve geometric uncertainties via integration with a surgical navigation system. Such integration requires registration of the image and world reference frames, conventionally a time consuming, error-prone manual process. This work presents a method of automatic image-to-world registration of intraoperative cone-beam computed tomography (CBCT) and an optical tracking system. Multimodality (MM) markers consisting of an infrared (IR) reflective sphere with a 2 mm tungsten sphere (BB) placed precisely at the center were designed to permit automatic detection in both the image and tracking (world) reference frames. Image localization is performed by intensity thresholding and pattern matching directly in 2D projections acquired in each CBCT scan, with 3D image coordinates computed using backprojection and accounting for C-arm geometric calibration. The IR tracking system localized MM markers in the world reference frame, and the image-to-world registration was computed by rigid point matching of image and tracker point sets. The accuracy and reproducibility of the automatic registration technique were compared to conventional (manual) registration using a variety of marker configurations suitable to neurosurgery (markers fixed to cranium) and head and neck surgery (markers suspended on a subcranial frame). The automatic technique exhibited subvoxel marker localization accuracy (< 0.8 mm) for all marker configurations. The fiducial registration error of the automatic technique was (0.35 +/-0.01) mm, compared to (0.64 +/- 0.07 mm) for the manual technique, indicating improved accuracy and reproducibility. The target registration error (TRE) averaged over all configurations was 1.14 mm for the automatic technique, compared to 1.29 mm for the manual in accuracy, although the difference was not statistically significant (p = 0.3). A statistically significant improvement in precision was observed-specifically, the standard deviation in TRE was 0.2 mm for the automatic technique versus 0.34 mm for the manual technique (p = 0.001). The projection-based automatic registration technique demonstrates accuracy and reproducibility equivalent or superior to the conventional manual technique for both neurosurgical and head and neck marker configurations. Use of this method with C-arm CBCT eliminates the burden of manual registration on surgical workflow by providing automatic registration of surgical tracking in 3D images within approximately 20 s of acquisition, with registration automatically updated with each CBCT scan. The automatic registration method is undergoing integration in ongoing clinical trials of intraoperative CBCT-guided head and neck surgery.

Influence of recording instrumentation on the stimulus artifact tail in the surface acquisition of somatosensory evoked potentials.

Surface recorded somatosensory evoked potentials (SEPs) are neural signals elicited by an external stimulus. In the case of electrically induced SEPs, the artifact generated by the stimulation process can severely distort the signal. The artifact is characterized by a large impulse followed by a slowly decaying tail. In some cases, the artifact tail often lasts well into the initiation of the SEP making the determination of absolute latency very difficult. While the literature often states that the recording instrumentation plays a part in the generation of this artifact tail, no firm evidence has ever been presented. In this work, comparisons are made between three instrumentation systems (BJT, JFET and CMOS) with differing input impedances in an attempt to quantify the effects on the artifact tail. The conclusions from this investigation show that there is no significant interaction between the input impedance of the recording instrumentation and the duration of the artifact tail. Each amplifier type produced results with no significant statistical differences. It was also found that while stimulation amplitude has a weak effect on the artifact tail, the greatest contribution to variation has an inter-subject origin. Consequently, it is concluded that the time constant of the artifact tail must originate from other sources that are subject dependent.

Thermal cautery as a treatment for conjunctival inclusion cyst after strabismus surgery.

Conjunctival cysts may be congenital or acquired. A common cause of acquired conjunctival inclusion cysts is the implantation of conjunctival epithelium after surgery or trauma. These cysts often form at the site of muscle reattachment after strabismus surgery. They may disappear spontaneously, but persistent cases often require surgical excision. We report a new technique using cauterization under slit-lamp visualization to treat conjunctival inclusion cysts that can form after strabismus surgery. This procedure is fast, effective, and well tolerated by patients.

Treatment of recurrent conjunctival papillomatosis with mitomycin C.

PURPOSE: To report an effective treatment for recurrent squamous papillomas of the conjunctiva with excision and application of mitomycin C. METHOD: Case report. RESULTS: A 5-year-old African-American girl with recurrent squamous papillomas of the right bulbar and palpebral conjunctiva was treated with multiple therapies, including excision, cryotherapy, and conjunctival injection of alpha-interferon; all therapies were followed by recurrence. After treatment with excision followed by intraoperative application of mitomycin C to the involved conjunctiva, the patient had no recurrence in a 30-month period. CONCLUSIONS: Excision with application of mitomycin C was successful in managing a case of squamous papillomatosis that was resistant to traditional therapy.

Unusual variant of familial aniridia.

A woman and her two children had apparent dominantly inherited ocular abnormalities including aniridia, ptosis, nystagmus, corneal pannus, persistent pupillary membrane, lenticular opacities, and foveal hypoplasia. A broad spectrum of iris abnormalities was observed: the daughter had aniridia with persistent pupillary membrane strands traversing the anterior lens capsule; the iris of the mother and son had a velvety surface with no detailed crypts, but did have some persistent pupillary membrane tags extending from the collarette. All three family members had moderately severe bilateral ptosis, pendular nystagmus, corneal pannus, and visual acuity of 20/200. Several systemic abnormalities also were noted, including obesity and mental retardation in the two children, and alopecia, cardiac abnormalities, and frequent spontaneous abortion in the mother. Family history indicated that the children's maternal grandmother also had similar ocular findings. We believe that this constellation of findings represents a rare, apparently dominant, variant of aniridia.

Anatomy and embryology of the eyelids: a review with special reference to the development of divided nevi.

In this review of the basic anatomy and embryology of the human eyelids, the sequence of eyelid differentiation is discussed. The development is important in exploring the formation of divided or "kissing" nevi of the lids. Since the lids are fused from the ninth week until the twentieth week of gestation, one may propose that the precursor elements of the nevus develop during that specific time. Because the epithelium only is fused, melanocytes derived from the neural crest must begin their differentiation in the region of the fused epithelium.

Persistent hyperplastic primary vitreous in an adult: case report with fluorescein angiographic findings.

The clinical features and fluorescein angiographic findings of an 18-year-old man with PHPV are reported. The case is unusual in that the eye survived into adulthood. The lens resorbed spontaneously, thereby permitting study of the retrolental mass by fluorescein angiography. Fluorescein leakage from the persistent vessels was very slow but present, thus indicating a probable disruption of the endothelial tight junctions of the tunica vasculosa lentis.

Persistent pupillary membrane associated with aniridia.

Familial aniridia is an autosomal dominant condition in which only a small iris remnant is present. A controversy exists as to whether the pathogenetic, embryologic origin of this condition is neuroectodermal or mesodermal. We examined a male infant with bilateral congenital aniridia associated with persistent pupillary membranes. This child had a prominent arcade of vessels extending onto the anterior lens surface for 360 degrees from small iris remnants in both eyes. The presence of a mesodermal pupillary membrane despite absence of the iris suggested a primary neuroectodermal defect as the pathogenetic factor in this case of aniridia.

Ultrastructure of the hyaloid vasculature in primates.

The histology and ultrastructure of the hyaloid vascular system was studied in 16 monkeys, ages 85 days in utero to 3 years old. The well-developed hyaloid artery is identifiable ultrastructurally as an arteriole consisting of a nonfenestrated intima, a multilayered smooth muscular media, a connective tissue adventitia, and a perivascular sheath. By the fourth week after birth, the vessel walls appear hyalinized and acellular; the lumen is occluded by a thrombus. The time of the complete disappearance of the hyaloid artery varied considerably in individual monkeys; remnants of the hyaloid artery were often present on the disc (Bergmeister's papilla) in adult life. The vasa hyaloidea propria and tunica vasculosa lentis are small branches of the hyaloid artery which fill the primary vitreous. Ultrastructurally, they are Type A-1-alpha capillaries having a nonfenestrated endothelium, incomplete pericyte layer, and basement membranes surrounding each. Fluorescein angiography of several newborn monkeys revealed nonleakage of dye from the hyaloid artery and its branches, thus correlating with the presence of endothelial tight functions.

DNA synthesis in pancreatic islet and acinar cells in rats with streptozotocin-induced diabetes.

The rates of DNA synthesis in islet and acinar cells were compared at different intervals following streptozotocin-induced diabetes. Streptozotocin, injected I.V. at a dosage of 65 mg/kg, consistently produced a diabetic-like state in young rats, ages 33 to 42 days. At two, four, and seven days after streptozotocin administration, no significant difference in DNA synthesis per mm2 of islet and acinar tissue was evident. However, four days after streptozotocin injection, a significant increase over control values was observed in the number of cells per islet incorporating tritiated thymidine. Following streptozotocin administration, beta cells generally appeared degranulated but not necrotic. Transformation of acinar cells or ductal elements to beta cells was not observed, suggesting that proliferating beta cells are the progeny of pre-existing beta cells. This study suggests that a brief, temporary period of compensatory proliferation of beta cells follows the initial insult of the diabetogenic agent streptozotocin in young rats.

Histopathology and ultrastructure of busulfan-induced cataract.

A 49-year-old man with chronic myelogenous leukemia developed dense posterior subcapsular cataracts and punctate cortical opacities after five years of busulfan (Myleran) therapy. We found that the histopathologic appearance of busulfan-induced cataracts is similar to other forms of human and experimental cataracts, regardless of cause. Ultrastructural examination revealed cortical liquefaction with formation of Morgagnian droplets, involving primarily the region from the equator to the posterior subcapsular space. In contrast to previous findings in rats, we observed posterior migration of equatorial nuclei and bladder cell formation. Also present were socalled crystalloid rays and abundant degenerate lens fiber membranes manifested as mutli-layered, irregularly folded configurations resembling myelin figures.