A pruning method for the recursive least squared algorithm

The recursive least squared (RLS) algorithm is an effective online training method for neural networks. However, its conjunctions with weight decay and pruning have not been well studied. This paper elucidates how generalization ability can be improved by selecting an appropriate initial value of the error covariance matrix in the RLS algorithm. Moreover, how the pruning of neural networks can be benefited by using the final value of the error covariance matrix will also be investigated. Our study found that the RLS algorithm is implicitly a weight decay method, where the weight decay effect is controlled by the initial value of the error covariance matrix; and that the inverse of the error covariance matrix is approximately equal to the Hessian matrix of the network being trained. We propose that neural networks are first trained by the RLS algorithm and then some unimportant weights are removed based on the approximate Hessian matrix. Simulation results show that our approach is an effective training and pruning method for neural networks.

A local training and pruning approach for neural networks

The training of neural networks using the extended Kalman filter (EKF) algorithm is plagued by the drawback of high computational complexity and storage requirement that may become prohibitive even for networks of moderate size. In this paper, we present a local EKF training and pruning approach that can solve this problem. In particular, the by-products obtained along with the local EKF training can be utilized to measure the importance of the network weights. Comparing with the original global approach, the proposed local EKF training and pruning approach results in a much lower computational complexity and storage requirement. Hence, it is more practical in solving real world problems. The performance of the proposed algorithm is demonstrated on one medium- and one large-scale problems, namely, sunspot data prediction and handwritten digit recognition.

Evaluation of a new referral system for the management of dyspepsia in Hong Kong: role of open-access upper endoscopy

BACKGROUND

In the management of dyspepsia, upper endoscopy is an important component. In our locality, patients requiring upper endoscopy are conventionally referred to specialist clinics by family physicians. We have introduced the first open-access upper endoscopy service in Hong Kong, which has allowed family physicians to arrange endoscopy without prior specialist consultation. A study on the outcome of open-access upper endoscopy in contrast with the conventional referral system was conducted.

METHODS

For patients presenting with dyspepsia, family physicians in our region were given the option to arrange upper endoscopy directly with our Medical Endoscopy Unit in addition to the conventional referral to specialist clinics. The results were compared with those from the specialist clinic. A detailed prospective follow up was performed from June to September 1997 to evaluate the outcome and impact of open-access upper endoscopy.

RESULTS

From November 1996 to September 1999, 978 referrals for open-access upper endoscopy were received. The service significantly reduced the waiting time for the procedure by 16 weeks. Open-access upper endoscopy had similar detection rates for peptic ulcers and cancers compared with referrals from specialist clinics. Seventy-five percent of patients did not require further consultation with their family physicians within 2 months after endoscopy. It is a safe and effective procedure in establishing a definitive diagnosis. All family physicians were satisfied with the open-access upper endoscopy service.

CONCLUSIONS

This is the first Asian report on this service. Open-access upper endoscopy reduced waiting time from the patient perspective, decreased subsequent consultations with family physicians and reduced referral to specialist clinics as well as increased patient and doctor satisfaction. Both referral systems for endoscopy were similar in terms of the diagnostic yield.

(13)C-urea breath test without a test meal is highly accurate for the detection of Helicobacter pylori infection in Chinese

BACKGROUND

Conventional (13)C-urea breath testing ((13)C-UBT) includes a test meal to delay gastric emptying, which, theoretically, improves the accuracy of the test. Citric acid has been proposed as the best test meal. However, recent studies have suggested that a test meal may not be necessary.

AIM

To investigate a new (13)C-UBT protocol without a test meal in a Chinese population.

METHODS

Consecutive dyspeptic patients referred for upper endoscopy were recruited. (13)C-UBT was performed on two separate days with or without a test meal (2.4 Gm citric acid) and compared with the 'gold standard' (CLO test and histology).

RESULTS

Two hundred and two patients were tested. Using receiver operating characteristics (ROC) analysis, the optimal delta-value and optimal measurement interval for UBT were 5% and 30 min, respectively, both with or without a test meal. The sensitivity, specificity, positive predictive value, negative predictive value and accuracy of (13)C-UBT with citric acid (96.5%, 97.7%, 98.2%, 95.6%, 97.0%) were similar to (13)C-UBT without a test meal (94.7%, 97.7%, 98.2%, 93.5%, 96.0%).

CONCLUSION

This simplified (13)C-UBT protocol without a test meal produced highly accurate and reliable results in the Chinese population.

Enhanced accuracy of needle placement in horizontal stereotactic core biopsy by a plastic slot

Horizontal stereotactic core biopsy can be used in the investigation of clinically occult mammographic abnormalities especially when breast thickness is less than 3 cm. We designed a 6-mm plastic slot that can be inserted between the bushing and the biopsy gun to enhance the accuracy of needle placement within the lesion. With this device, the centre of the lesion can be targeted at the centre of the biopsy trough. We advocate the use of this piece of small, simple and inexpensive instrument in every case of horizontal stereotactic core biopsy.

p53 inactivating mutations in chinese breast carcinomas

While previous reports on breast cancers indicate that Caucasian women have a low frequency of p53 mutations, higher frequencies of mutations are reported in some Japanese populations. There are few reports regarding p53 mutations in Chinese breast carcinomas. Using a previously established sensitive p53 yeast functional assay, we screened 23 Chinese breast carcinomas for mutations. The p53 was mutated in 5/23 (21.7%) specimens. Two of these mutations were detected in exon 5 and one was detected in each of exons 6, 7 and 8. All of these mutations have previously been shown to be mutated in Caucasian and Japanese breast cancers, but two have not previously been observed in Chinese breast cancers and one has also not been observed in Japanese.

Expression of Endochitinase from Trichoderma harzianum in Transgenic Apple Increases Resistance to Apple Scab and Reduces Vigor

ABSTRACT The goal of this research was to improve scab resistance of apple by transformation with genes encoding chitinolytic enzymes from the bio-control organism Trichoderma harzianum. The endochitinase gene, as cDNA and genomic clones, was transferred into apple cv. Marshall McIntosh by Agrobacterium-transformation. A total of 15 lines were identified as transgenic by NPTII enzyme-linked immunosorbent assay and polymerase chain reaction and confirmed by Southern analysis. Substantial differences in endochitinase activity were detected among different lines by enzymatic assay and western analysis. Eight lines propagated as grafted and own-rooted plants were inoculated with Venturia inaequalis. Six of these transgenic lines expressing endochitinase were more resistant than nontransformed cv. Marshall McIntosh. Disease severity compared with cv. Marshall McIntosh was reduced by 0 to 99.7% (number of lesions), 0 to 90% (percentage of leaf area infected), and 1 to 56% (conidia recovered) in the transgenic lines tested. Endochitinase also had negative effects on the growth of both inoculated and uninoculated plants. There was a significant negative correlation between the level of endochitinase production and both the amount of disease and plant growth.

Algorithm for optimizing bipolar interconnection weights with applications in associative memories and multitarget classification

An algorithm for optimizing a bipolar interconnection weight matrix with the Hopfield network is proposed. The effectiveness of this algorithm is demonstrated by computer simulation and optical implementation. In the optical implementation of the neural network the interconnection weights are biased to yield a nonnegative weight matrix. Moreover, a threshold subchannel is added so that the system can realize, in real time, the bipolar weighted summation in a single channel. Preliminary experimental results obtained from the applications in associative memories and multitarget classification with rotation invariance are shown.

Negative captopril renography on patients with renin mediated hypertension due to page kidney and reninoma

Through a mechanism similar to renal artery stenosis, patients with reninoma and page kidney also suffered from renin mediated hypertension. Captopril renograms performed on our patients with the latter two conditions, however, did not yield diagnostic findings. Therefore, equivocal or negative captopril renography cannot serve to rule out conditions with elevated renin other than renal artery stenosis.

Simple approach to the creation of a strange nonchaotic attractor in any chaotic system

A simple approach to the creation of a strange nonchaotic attractor in any chaotic system is described. The main idea is to control the parameter of the system in such a manner that the system dynamics is expanding at some times, but converging at others. With this approach, a strange nonchaotic attractor can be found in a large region in the parameter space near the boundaries between chaotic and regular phases or within the chaotic region far from the regular one. The maximum nontrivial Lyapunov exponent of the system can pass through zero nonsmoothly and cannot be fitted by a linear function.

Large needle core biopsy--avoidance of biopsy table bombardment by the biopsy needle in stereotactic guided breast biopsy

Table bombardment by automated biopsy needle is an occasional technical problem during stereotactic core biopsy of the breast. It is most commonly encountered in small breasts and when lesions are close to the biopsy table. A reference chart is devised for stereotactic core biopsy using an add-on erect stereotactic biopsy table and automated spring-loaded biopsy gun. The chart serves as a reference for pre-biopsy assessment of the feasibility of core biopsy in the vertical approach due to the constraints of lesion depth and breast thickness. It allows easy and quick reference for the required needle length input for the stereotactic system to prevent table bombardment.

Effectiveness of non-mydriatic retinal photography and direct ophthalmoscopy in detecting diabetic retinopathy

This is a prospective study to compare the effectiveness of non-mydriatic photography with that of direct ophthalmoscopy in screening for diabetic retinopathy in 153 patients attending a hospital clinic in Hong Kong. Retinal photography under physiological mydriasis and direct ophthalmoscopy of patients with dilated pupils were compared with the ophthalmologists' examination results as a reference standard. The prevalence of diabetic retinopathy in this sample population was 15%. The sensitivity of detecting diabetic retinopathy by retinal photography was higher than that of direct ophthalmoscopy (64% versus 41%; 95% confidence interval of difference, 1.2%- 44.3%). Of five patients who had serious retinopathy, retinal photography failed to detect the disease in two; direct ophthalmoscopy failed to detect the disease in all five patients. Specificities of retinal photography and direct ophthalmoscopy were 90% (95% confidence interval, 84%-96%) and 93% (95% confidence interval, 88%-97%), respectively. We conclude that retinal photography is significantly more effective than direct ophthalmoscopy in detecting diabetic retinopathy. In addition, the non-mydriatic camera is easy to use and is the preferred method of screening.

Why are thalassaemia patients born when prenatal screening is available?

Thalassaemia major is a classic example of a disease that is preventable by prenatal diagnosis. Although the technology was introduced to Hong Kong more than a decade ago, new patients are continuously seen in the Hong Kong Administrative Region. This retrospective review concerns children who were diagnosed to have severe beta-thalassaemic syndromes at the Tuen Mun Hospital from 1990 to 1996. Seventeen children (including a pair of identical twins) with homozygous beta-thalassaemia and five children with double heterozygous beta-E thalassaemia were identified. All except three children were transfusion-dependent. Thirty-six parents were available for the thalassaemic study. Thirty-one of them had beta-thalassaemic traits and the other five were carriers of haemoglobin E. Two of the parents with beta-thalassaemic traits and all five haemoglobin E carriers had a mean corpuscular volume above the cut-off for screening in antenatal diagnosis (>75 fL). Of the 21 at-risk pregnancies, seven were managed by public hospitals, 11 by maternal and child health centres, and two by private practitioners. Thalassaemia had not been diagnosed prenatally because of the lack of maternal screening (n=9), lack of paternal screening (n=3), late antenatal visit (n=7), and parental refusal (n=1). Thus, many of our patients are not benefiting from the availability of prenatal screening.

Prevention of beta-thalassemia major by antenatal screening in Hong Kong

The thalassemias are common in Hong Kong. One of the severe forms, beta-thalassemia major, has been preventable locally by antenatal screening since 1983. Yet new patients are still being diagnosed. In this retrospective study, 34 children with severe beta-thalassemia syndromes were diagnosed in two major public hospitals between 1990 and 1996. They included one pair of identical twins and two pairs of siblings. Twenty-seven (79%) had homozygous beta-thalassemia and seven (21%) had beta E thalassemia. All but four (12%) were transfusion dependent. Fifty-five (89%) parents had been evaluated for their thalassemia status. Forty-eight had beta-thalassemia traits and seven were hemoglobin E carriers. The reasons for the birth of these children with severe beta-thalassemia syndromes were (1) late or no antenatal visit (n = 8, 24.2%), including three cross-border deliveries in which the pregnant mothers came from mainland China to Hong Kong for confinement, (2) lack of maternal screening (n = 13, 39.4%), (3) lack of paternal screening (n = 7, 21.2%), (4) parental refusal (n = 3, 9.1%), and (5) unknown (n = 2, 6.1%). These findings suggest that several factors undermine the effectiveness of antenatal screening for prevention of thalassemias. Many medical practitioners and the general public are still not aware of the screening procedures. The migration of population from mainland China to Hong Kong may result in the birth of many more children with beta-thalassemia major.

Intrathecal methotrexate overdose

We report two cases of intrathecal methotrexate overdose. A 3-y-old girl with acute lymphoblastic leukaemia and a 4-y-old boy with Burkitt's lymphoma were to receive an intrathecal injection of methotrexate after completion of intravenous methotrexate infusion. Instead of 12.5 mg, they both received a dose of 125 mg. Both children developed generalized convulsion 3 h after the overdose, but afterwards recovered completely. Intravenous folinic acid and dexamethasone rescue were employed, but no attempt was made to exchange the cerebrospinal fluid. In addition to the staff's failure to check the drug label carefully, the marked resemblance of the two dose preparations of methotrexate (50 mg/5 ml and 500 mg/5 ml) may have been contributory.

Case report: rupture and growth of adrenal myelolipoma in two patients

Two cases of pathologically confirmed adrenal myelolipoma are described in Chinese patients. The first patient presented with tumour rupture and perinephric haemorrhage. The second patient was operated on 18 months after the incidental discovery of the tumour, due to its large size and the interval growth.

Optical Omega network: a compact implementation technique

We propose a technique for the compact implementation of an optical Omega network. This technique utilizes the concept that both the perfect-shuffle interconnection and the switching stages can be realized by the same procedures, i.e., duplicate, shift, superimpose, and mask. As a result, a single set of optics is sufficient to realize the whole Omega network in a time-multiplexed recursive manner. Optical setups were designed and a proof-of-principle experiment was performed.

Space-variant optical logic operations based on operation-dependent encoding method

We propose performing space-variant optical logic operations in a space-invariant optical system by selectively assigning encoding states that are operation dependent. With this method, encoders using liquid-crystal cells and liquid-crystal light valves to perform space-variant encoding for all 16 Boolean functions are designed. Multiple-instruction-multiple-data processing can then be realized in optical logic systems.

Recording complex holograms on photoresist by using an ion-implantation method

Photoresists have traditionally been used as a holographic recording medium for phase holograms. We demonstrate the recording of a binary amplitude hologram on photoresist by using an ion-implantation method. This amplitude recording property is based on the fact that the optical transmittance of photoresist can be changed by a high-dose ion implantation. A novel complex-hologram recording method is proposed in which the phase is represented by photoresist thickness and the amplitude is encoded on its optical transmittance.

Changing patterns of infectious keratitis: overview of clinical and histopathologic features of keratitis due to acanthamoeba or atypical mycobacteria, and of infectious crystalline keratopathy

Acanthamoeba keratitis, infectious crystalline keratopathy and atypical mycobacterial keratitis have recently emerged as important types of infectious keratitis. These corneal infections have been associated with contact lens wear and with corneal surgical procedures such as radial keratotomy and penetrating keratoplasty, and the clinical setting of each of these infections is important in alerting the clinician to the possible diagnosis. There have been improvements in rapid diagnostic techniques for such infections in the last several years. Treatment has also improved, but remains a difficult problem, especially for Acanthamoeba. An overview of recent developments in the clinical and histopathologic methods for diagnosis and treatment options of these three corneal infections is provided.

Design of digital-optical processors by using both intensity and polarization-encoding schemes

Here we propose two encoding schemes that utilize both light intensity and polarization to code input data in digital-optical computing. This approach results in a more efficient information carrying and processing technique when compared with the traditional intensity-only or polarization-only encoding schemes. Optical logic units that are based on the proposed encoding schemes are designed. A recursive parallel adder and a carry look-ahead adder that use these logic units as building blocks are also described.

Intravitreal antibiotic therapy with vancomycin and aminoglycoside: examination of the retinal toxicity of repetitive injections after vitreous and lens surgery

The combination of vancomycin and an aminoglycoside antibiotic is frequently injected into aphakic/vitrectomized eyes for the treatment of endophthalmitis. At 2 weeks after lens and vitreous removal, rabbit eyes received an injection of a combination of 1 mg vancomycin and either 400 micrograms amikacin or 100 micrograms gentamicin. Furthermore, the effects of repeating the same combination a second and third time at intervals of 48 h were examined by light and transmission electron microscopy at 7 days to 4 months after the last injection. A single injection of either combination produced no toxicity. After 2 or 3 sets of injections of either combination, 13 of 16 eyes displayed retinal toxicity manifested by macrophages in the subretinal space, disorganization of the outer segments and retinal pigment epithelium, and discontinuities in Bruch's membrane. These results indicate that whereas a single injection of these combinations is not toxic to aphakic/vitrectomized eyes, repetitive injections may result in increasing toxicity.

Intraocular penetration of rifampin after oral administration

Rifampin, the most potent anti-staphylococcal drug known, was examined for its penetration into the aqueous and vitreous of rabbits after a single oral dose of 150 mg, 300 mg, or 600 mg. Maximum levels after the 150 mg dose were achieved at 4 h and were 4.2 micrograms/ml in the aqueous and 2.2 micrograms/ml in the vitreous. After the 300 mg dose, maximum levels were also achieved at 4 h, and were 5.0 micrograms/ml in the aqueous and 2.6 micrograms/ml in the vitreous. The 600 mg dose produced maximum levels at 6 h after administration, with 20.0 micrograms/ml in the aqueous and 15.2 micrograms/ml in the vitreous. These levels exceed the minimum inhibitory concentration for many microorganisms and suggest additional investigation into possible applications of systemic rifampin in the prophylaxis and treatment of bacterial endophthalmitis.

Intravitreal antibiotic therapy with vancomycin and aminoglycoside. An experimental study of combination and repetitive injections

We evaluated the retinal toxic reaction of combined intravitreal therapy with regimens of 1.0 mg of vancomycin hydrochloride and 400 micrograms of amikacin sulfate or 1.0 mg of vancomycin hydrochloride and 100 micrograms of gentamicin sulfate in the rabbit eye. The effects of reinjecting each combination a second or third time, separated by 48-hour intervals, were also examined by ophthalmoscopy and light and transmission electron microscopy. The initial administration of either regimen did not produce toxic reaction. After two injections, five of six eyes with vancomycin-gentamicin therapy and three of six eyes with vancomycin-amikacin therapy displayed focal areas of retinal toxic reaction on histologic study. After three injections, all eyes treated with either regimen showed histologic evidence of more advanced retinal toxic reaction primarily involving the outer retina and retinal pigment epithelium. The present study demonstrates the safety of an initial intravitreal injection of vancomycin and aminoglycoside but shows increasing retinal toxic reaction with repetitive combination therapy.

Ocular involvement associated with chronic Epstein-Barr virus disease

Ocular involvement with acute Epstein-Barr virus infection is usually limited to a transient follicular conjunctivitis, although other lesions have been reported. Chronic Epstein-Barr virus infection has recently gained attention, but ocular manifestations have not been emphasized. We describe three patients with chronic infection with prominent ocular involvement. Bilateral uveitis was noted in all patients, ranging from an anterior uveitis that was responsive to steroids to a severe panuveitis with vitritis, cataract, optic disc swelling, and macular edema. In one patient, topical acyclovir ointment resulted in a substantial decrease in the inflammatory reaction when added to systemic acyclovir therapy. Another patient displayed a keratitis that resolved with topical steroid therapy. Cataract and vitreous surgery were also beneficial in the management of these patients.