PubMed Health⌕ Search

Biomedical subjects

J Heikkonen

Publications and source records attributed to J Heikkonen.

At least 19 recordsLinked to original sources
PubMed2001

Multiphase method for automatic alignment of transmission electron microscope images using markers.

In order to successfully perform the 3D reconstruction in electron tomography, transmission electron microscope images must be accurately aligned or registered. So far, the problem is solved by either manually showing the corresponding fiducial markers from the set of images or automatically using simple correlation between the images on several rotations and scales. The present solutions, however, share the problem of being inefficient and/or inaccurate. We therefore propose a method in which the registration is automated using conventional colloidal gold particles as reference markers between images. We approach the problem from the computer vision viewpoint; hence, the alignment problem is divided into several subproblems: (1) finding initial matches from successive images, (2) estimating the epipolar geometry between consecutive images, (3) finding and localizing the gold particles with subpixel accuracy in each image, (4) predicting the probable matching gold particles using the epipolar constraint and its uncertainty, (5) matching and tracking the gold beads through the tilt series, and (6) optimizing the transformation parameters for the whole image set. The results show not only the reliability of the suggested method but also a high level of accuracy in alignment, since practically all the visible gold markers can be used.

Automation↗
PubMed2001

Automatic alignment of transmission electron microscope tilt series without fiducial markers.

Accurate image alignment is needed for computing three-dimensional reconstructions from transmission electron microscope tilt series. So far, the best results have been obtained by using colloidal gold beads as fiducial markers. If their use has not been possible for some reason, the only option has been the automatic cross-correlation-based registration methods. However, the latter methods are inaccurate and, as we will show, inappropriate for the whole problem. Conversely, we propose a novel method that uses the actual 3D motion model but works without any fiducial markers in the images. The method is based on matching and tracking some interest points of the intensity surface by first solving the underlying geometrical constraint of consecutive images in the tilt series. The results show that our method is near the gold marker alignment in the level of accuracy and hence opens the way for new opportunities in the analysis of electron tomography reconstructions, especially when markers cannot be used.

Animals↗
PubMed2001

Sebaceous carcinoma of the eyelid associated with retinoblastoma.

OBJECTIVE: To analyze the association between retinoblastoma (Rb) and sebaceous carcinoma (SC) of the eyelid to improve surveillance of survivors of RB: DESIGN: Case report and systematic literature review. METHODS: Ten patients who had SC develop after Rb were identified by systematic literature review, and a child who died with lymph node, lung, and liver metastases 7 years after irradiation for Rb is described. The data were analyzed by univariate statistics, including cumulative frequency distribution plots and Kaplan-Meier analysis. RESULTS: Of 11 children with SC of the eyelid who all had hereditary RB, 9 (82%; 95% confidence interval, 48-98) received a median of 46 Gy (range, 21-89) of radiotherapy at a median age of 16 months (range, 0.5-15 years) and had SC develop within the field of radiation. Their median age at diagnosis of SC was 14 years (range, 8-30 years), median diagnostic delay 12 months (range, 6 months-3 years), and median interval from irradiation 11 years (range, 5-26 years); 7 of them (78%; 95% confidence interval, 40-97) were diagnosed between 5 and 15 years after radiotherapy. SC also developed at the age of 32 and 54 years in two nonirradiated Rb patients. Five patients had regional lymph node metastases after a median time of 12 months (range, 1 month-24 years). The 5-year cumulative probability of survival was 87%. CONCLUSIONS: SC of the eyelid may occur in patients with hereditary Rb regardless of primary treatment, especially within the field 5 to 15 years after radiotherapy.

Adenocarcinoma, Sebaceous↗
PubMed2000

Linear classification of low-resolution EEG patterns produced by imagined hand movements.

Electroencephalograph (EEG)-based brain-computer interfaces (BCI's) require on-line detection of mental states from spontaneous EEG signals. In this framework, surface Laplacian (SL) transformation of EEG signals has proved to improve the recognition scores of imagined motor activity. The results we obtained in the first year of an European project named adaptive brain interfaces (ABI) suggest that: 1) the detection of mental imagined activity can be obtained by using the signal space projection (SSP) method as a classifier and 2) a particular type of electrodes can be used in such a BCI device, reconciling the benefits of SL waveforms and the need for the use of few electrodes. Recognition of mental activity was attempted on both raw and SL-transformed EEG data from five healthy people performing two mental tasks, namely imagined right and left hand movements.

Adult↗
PubMed1999

Visual function after strontium-90 plaque irradiation in patients with age-related subfoveal choroidal neovascularization.

PURPOSE: To report 2-year visual and angiographic results in eyes treated with strontium plaque irradiation for subfoveal choroidal neovascular membranes (CNVM) in age-related macular degeneration. METHODS: Twenty eyes with recent subfoveal CNVM were treated with local irradiation. The impact of the treatment on visual function was evaluated by visual acuity, contrast sensitivity and reading speed testing. RESULTS: At 12 months visual acuity had improved or remained the same in 9/ 20 eyes (45%). At 24 months visual acuity was stable in 5/18 eyes (28%). Eyes with signs of CNVM regression (13/18, 72%) lost a mean of 3.3 lines, but eyes with recurrent CNVM lost a mean of 5.1 lines of vision. The mean contrast sensitivity was better in the irradiated eyes than in the fellow eyes with late age-related macular degeneration at 24 months. Six of 17 irradiated eyes (35%) could read at least some words at 24 months. CONCLUSIONS: Visual function decreases in patients treated with strontium irradiation, but less in eyes showing regression of the CNVM than in eyes with further growth of the CNVM.

Aged↗
PubMed1998

Strontium plaque irradiation of subfoveal neovascular membranes in age-related macular degeneration.

PURPOSE: To determine the effect of focal strontium-90 plaque radiotherapy on subfoveal choroidal neovascularization in patients with age-related macular degeneration. METHODS: Twenty patients with age-related macular degeneration, presenting with a recent subfoveal neovascular membrane, were treated with local episcleral radiotherapy using a strontium-90 applicator. The applicator was applied to the sclera under the macular region and held there tightly for 54 min to obtain a dose of 15 Gy at a depth of 1.75 mm. The main parameters evaluated at follow-up after 3, 6 and 12 months were visual acuity and changes in fluorescein angiography. Twelve untreated patients with the same criteria were followed as controls. RESULTS: Early effects of radiation could be seen at 3 months, but became more obvious after follow-up for 6 and 12 months. At 6 months, regression of the choroidal neovascularization was detected in 14/19 patients (74%) as a decrease in the size of the lesion or as diminished leakage in late-phase fluorescein angiography. Likewise, in 14/19 patients (74%) at 12 months the neovascular membrane was partially or totally occluded. In all patients showing regression of the choroidal neovascular membrane, the neurosensory detachment had also dried. Visual acuity was unchanged (within 1 line) or improved in 11/20 (55%) and 9/20 (45%) treated patients after 6 and 12 months, respectively. In the controls, the choroidal neovascularization had increased in size in 9/12 patients (75%) at the last follow-up (mean 12.0 months). Visual acuity was unchanged in 3/12 patients (25%). CONCLUSION: Local low-energy beta irradiation with a strontium-90 applicator can induce regression of choroidal neovascularization. The effect of irradiation is seen as a decrease in the size of the choroidal neovascular membrane and disappearance of the neurosensory detachment and exudates.

Aged↗
PubMed1996

Interstitial radiotherapy of 25 parasellar/clival meningiomas and 19 meningiomas in the elderly. Analysis of short-term tolerance and responses.

I-125 seeds were permanently implanted into 25 parasellar-clival meningiomas (median age of patients, 56 y) and 19 globoid meningiomas in the elderly (median age of patients, 77 y) using stereotactic technique and 3-D dose planning. Total dose at the tumour margin was increased during the series from 100 Gy to 150 Gy. The procedure caused no mortality and no serious bleeding, but injury to the III cranial nerve due to puncture occurred in one (4%) of the 25 parasellar-clival meningiomas. In two (4.5%) of the 44 cases the postoperative CT scan showed a misplaced seed, located at the tumour surface. Nonenhancing hypodense rings developed around the seeds ('hot spots') with a median diameter of 10.5 mm at 12 months corresponding to a median initial activity of 8.7 mCi. In general, meningiomas responded by slow reduction in volume. The parasellar-clival meningiomas were followed-up for a median of 19 months (6-32), and so far 4 tumours have shrunk moderately, 13 slightly, and 5 not at all. Pre-operative III, V or VI cranial nerve signs were present in 17 patients and subsided in 8 of them. On the other hand, facial numbness developed or increased in 9 of the 25 patients, indicating that the V nerve is rather sensitive to this type of irradiation. In the 19 meningiomas of the elderly, the median follow-up time was 14 months (5-26). The median relative tumour volume was 46% at 12 months. Accounting for tumour-related deaths only, the actuarial survival rate was 78% at 12 months and 62% at 24 months. In general, brain oedema persisted despite reduction in tumour volume. Stereotactic implantation of I-125 seeds into intracranial meningiomas is relatively safe. Interstitial radiotherapy represents a potential tool in the control of medium-sized intracranial meningiomas with minimal brain oedema, but its long-term impact and untoward effects remain to be followed-up.

Adult↗
PubMed1996

Radiation related complications after ruthenium plaque radiotherapy of uveal melanoma.

AIMS/BACKGROUND: To analyse radiation related complications and secondary enucleation after irradiation of malignant uveal melanoma with ruthenium-106 plaques. METHODS: A series of 100 consecutive eyes irradiated in 1981-91 was analysed using the life table method and the Cox proportional hazards model. The median apical and scleral tumour dose was 100 Gy (range 15-200 Gy) and 1000 Gy (range 200-1200 Gy), respectively. The median follow up time was 2.8 and 2.0 years (range 1 month to 10 years) for anterior and posterior segment complications, respectively. RESULTS: The 3 and 5 year probabilities of being without radiation cataract were 73% and 63%, without neovascular glaucoma 91% and 81%, without vitreous haemorrhage 83% and 74%, without radiation maculopathy 85% and 70%, and without radiation optic neuropathy 90% and 88%, respectively. The risk of radiation cataract was highest with large tumour size (T1 + T2 v T3, p = 0.0027; height < or = 5 v > 5 mm, p = 0.029; largest basal diameter (LBD) < or = 15 v > 15 mm, p < 0.0001) and location of anterior tumour margin anterior v posterior to the equator (p = 0.0003); the risk of neovascular glaucoma with large size (T1 + T2 v T3, p = 0.039; LBD < or = 15 mm v 15 mm, p = 0.021); and the risk of maculopathy and optic neuropathy with proximity of the posterior tumour margin to the fovea and the optic disc (< or = 1.5 v > 1.5 mm; p = 0.030 and p = 0.0004, respectively). In Cox's multivariate analysis the strongest risk indicator for radiation cataract (RR 1.5, 95% CI 1.4-1.6) and vitreous haemorrhage (RR 1.6, 95% CI 1.4-1.8) was the height of the tumour; for neovascular glaucoma the TNM class (RR 6.2, 95% CI 2.7-13.8); for radiation maculopathy location of posterior tumour margin within 2 mm from the fovea (RR 3.4, 95% CI 2.0-6.0); and for radiation optic neuropathy location of tumour margin within 1 DD of the optic disc (RR 6.1, 95% CI 3.0-12.4). The 3 and 5 year probabilities of avoiding enucleation were 92% and 85%, respectively. Ten eyes were enucleated--six because of recurrent tumour growth, three because of treatment complications, and one because of mistakenly suspected extraocular growth. CONCLUSION: The results suggest that the frequency of radiation related complications after ruthenium brachytherapy of uveal melanoma is acceptable, in particular as regard irradiation of small and medium sized tumours for which ruthenium therapy generally is recommended.

Adult↗
PubMed1993

Survival of patients and metastatic and local recurrent tumor growth in malignant melanoma of the uvea after ruthenium plaque radiotherapy.

A series of 100 consecutive patients treated by ruthenium plaque radiotherapy for uveal malignant melanoma from 1981 to 1991 was studied to evaluate local recurrences, metastases, and melanoma-specific mortality. Follow up ranged from 1.0 to 10.1 years (mean, 3.3; median, 3.0 years). Local relapse was observed in 19 patients from 0.1 to 2.7 years (median, 0.7 years) after therapy. Six of these eyes were enucleated. The 5-year probability of local tumor control was 59%. Seven patients with local relapse developed metastasis 0 to 4.3 years (median, 1.4 years) later. Altogether, 18 patients developed metastases 0.9 to 4.6 years (median, 2.0 years) after the irradiation, and 15 of them died of melanoma 5 days to 3.3 years (median, 0.5 years) after detection of metastases. The 5-year probability of metastasis not developing was 61%. The overall 5-year survival was 78%, excluding causes other than malignant melanoma. Large tumor size and anterior tumor location, with or without ciliary body involvement, predicted poor prognosis both in terms of local growth, metastases, and melanoma-specific mortality. Local recurrent tumor growth was associated with a significant increase in metastasis but a nonsignificant increase in melanoma-specific mortality.

Aged↗
PubMed1992

Radiotherapy of malignant melanoma of the uvea with I-125 seeds.

Nineteen patients with malignant uveal melanomas were treated with I-125 applicators. There were 10 males and 9 females with a median age of 61 years (range 42-76). The tumour was located in the choroid in 12 eyes and in the choroid and ciliary body in 7 eyes. The size of the tumours was 7-18 mm in maximal basal diameter (median 12), 5-16 mm in minimal basal diameter (median 10), and 5.5-15 mm in thickness (median 8.5). The volume of the tumours was 123-1890 mm3 (median 540). All tumours were classified as large (T3). For the irradiation, a computer program, which calculates three-dimensional dose distribution of I-125 seeds in gold plaques, was developed. By modifying the seed positions, activity and the orientation, patients can be treated individually. Iodine-125 emits low energy photons, ideal for intraocular tumour therapy and tissue. Extra-ocular tissue located behind the applicator can be completely shielded by a 0.5 mm gold layer. The dose at the apex of the tumour ranged from 30 to 120 Gy (median 93). The treatment time ranged from 44 to 600 h (median 235). Preliminary results are good. After a median follow-up of 6 months, the tumour growth has been arrested in all eyes and in 10 eyes the tumour has decreased in size.

Adult↗
PubMed1990

Farmers' occupational health program in Finland, 1979-1988: from research to practice.

The Kuopio Regional Institute of Occupational Health, in collaboration with the Social Insurance Institution and the National Board of Health, conducted and evaluated a national model for the farmers' occupational health services. In January 1985 the National Board of Health instructed the Finnish municipal health centers to start the provision of farmers' occupational health services based on the recommendation given by the research group. The service was evaluated by experiments carried out during 1982, 1985, and 1986. The main problem in function of the services was that the health hazards (exposures) were difficult to observe and evaluate. The system of how the occupational health nurse evaluates the working conditions should be further developed. The efficiency of the services was studied by postal inquiries in 1982 and 1986. Farmers' knowledge about the appropriate means of reducing hazardous exposures had increased significantly due to the occupational health services. At the local level, the main problem in providing services for occupational farmers is that health centers do not have the resources to offer services for all farmers at the same time. Altogether by the end of 1986, about 30% of all active farmers in Finland (45,000 farmers) were willing to have occupational health services, which is voluntary for self-employed farmers.

Accidents, Occupational↗
PubMed1988

Regional blood flow in human tumours measured with argon, krypton and xenon.

Blood perfusion in 19 superficial tumour metastases was measured by injecting three tracers, 41Ar, 85Krm and 135Xe or 133Xe, simultaneously into the tissue. The blood flow rate was calculated from the constants of the biexponential functions fitted to the measured counts. The mean blood flow in the 19 tumours studied was 18 ml/(100 g min) (SD +/- 10). Alternatively, the relative partition coefficients of argon, krypton and xenon were calculated from the equations obtained using compartmental analysis. The mean values for the ratios of the partition coefficients of these nuclides were found to be between 0.82 and 1.07.

Argon↗
PubMed1987

Partition coefficient ratios and tumour perfusion studied with 85mKr and 133Xe.

The relative partition coefficients of krypton and xenon, and the regional blood flow in 27 superficial malignant tumour nodules in 22 patients with diagnosed tumours were measured using the 85mKr- and 133Xe-clearance method. In order to minimize the effect of biological variables on the measurements the radionuclides were injected simultaneously into the tumour. The distribution of the radiotracers was assumed to be in equilibrium at the beginning of the experiment. The blood perfusion was calculated by fitting a two-exponential function to the measuring points. The mean value of the perfusion rate calculated from the xenon results was 13 +/- 10 ml/(100 g.min) [range 3 to 38 ml/(100 g.min)] and from the krypton results 19 +/- 11 ml/(100 g.min) [range 5 to 45 ml/(100 g.min)]. These values were obtained, if the partition coefficients are equal to one. The equations obtained by using compartmental analysis were used for the calculation of the relative partition coefficient of krypton and xenon. The partition coefficient of krypton was found to be slightly smaller than that of xenon, which may be due to its smaller molecular weight.

Humans↗
PubMed1987

A computer program for I-125 seed implant.

A computer program, written in FORTRAN, for I-125 permanent interstitial implants has been developed. After implantation, isocentric radiographs are taken using radiotherapy simulator (Siemens) in order to obtain two X-ray images of seeds on the same film. Honeywell DPS8 computer and Hewlett-Packard 7221A plotter are used for the dose calculation. The program calculates the dose distribution at the plane desired using 100 X 100 matrix.

Brachytherapy↗