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PubMedDate not supplied

Vascular tree object segmentation by deskeletonization of valley courses.

In this paper, we propose a valley-course-based image segmentation technique for tree-like object delineation, as an alternative to the traditional centerline-based methods. This technique consists of valley-course extraction, skeleton pruning and deskeletonization. Valley courses, constructed from valley points that are obtained by star-pattern scanning over an image, offer a natural manner of identifying tree skeletons. Unattached segments are removed using morphological operations. A structured tree is then constructed from the skeletons by using a tree pruning/spanning algorithm. A fleshy tree-like object is obtained by a deskeletonization procedure, which consists of extracting tree boundary in vicinity of the skeletons in the original image. The tree boundary is determined by identifying paired edge points at a valley point. A derivative-free edge identification approach is proposed, which defines an edge point at a side-slope by a relative intensity drop with respect to the local background. An empirical formula using a logarithmic function of local intensity contrast offers desirable characteristics of adaptability and stability. The adaptability of edge points to the local background is attributed to the compression behavior of logarithmic function. Furthermore, stability to noise is resulted because derivative operations are not used. The segmentation technique was validated using coronary angiographic images.

Algorithms↗
PubMed2000

Analysis of the compression mechanics of pharmaceutical agglomerates of different porosity and composition using the Adams and Kawakita equations.

PURPOSE: To analyze the mechanics of some pharmaceutical agglomerates during uniaxial confined compression by using compression parameters derived from the Heckel, Kawakita and Adams equations, and to study the influence of these compression parameters on the tablet-forming ability of agglomerates. METHODS: Force and displacement data sampled during in-die compression of agglomerates was used to calculate compression parameters according to the Heckel (sigmay), Kawakita (1/b and a), and Adams (tau0') equations. Mechanical strength of single agglomerates as well as the air permeability and tensile strength of tablets prepared from them were also determined. RESULTS: Sigmay- from the Heckel equation did not differ between agglomerates of different porosity. Both 1/b and tau0' varied with agglomerate porosity and composition. These two compression parameters were linearly related to each other. No general correlation was found between 1/b and tau0' and the strength of single agglomerates. The two parameters were related to the intergranular pore structure and tensile strength of tablets formed from the agglomerates. CONCLUSIONS: 1/b and tau0' may be interpreted as measures of the agglomerate shear strength during uniaxial confined compression, and as such they may be used as indicators of the tabletting performance of the agglomerates.

Algorithms↗
PubMed2005

Reconstruction of optical properties of phantom and breast lesion in vivo from paraxial scanning data.

We report on the reconstruction of absorption and reduced scattering coefficients of breast tissue in vivo of a patient with mastopathic disease. Distributions of times of flight of photons through the compressed breast were recorded by paraxial scanning. From data measured at four different source-detector offsets optical properties were reconstructed within the linear Rytov approximation by a fast inverse Fourier space method. Low-pass filtering in Fourier space was employed to remove excessive noise from high spatial frequency components and to reduce the computational efforts by a factor of 3, typically. The mammograms displaying reconstructed absorption and reduced scattering coefficients were compared with projection mammograms either obtained by time-window analysis of experimental data or based on average absorption and reduced scattering coefficients which were derived from measured temporal point spread functions within a simple homogeneous model. All inhomogeneities which were visible in the projection mammograms and which could be associated with specific breast tissue compartments could be correlated with inhomogeneities in the reconstructed absorption coefficient. In particular, the mastopathic disease was detected in the reconstructed absorption mammogram. In order to assess reliability of optical properties reconstructed from data obtained by paraxial scanning, corresponding phantom experiments and reconstructions of phantom optical properties were carried out. Because of the limited angular range sampled by the in vivo and phantom measurements, considerable blurring of the absorption coefficient occurs along the compression direction, compromising longitudinal resolution.

Algorithms↗
PubMed1999

ECG data compression using cut and align beats approach and 2-D transforms.

A new electrocardiogram (ECG) data compression method is presented which employs a two dimensional (2-D) transform. This 2-D transform method utilizes the fact that ECG signals generally show two types of redundancies--between adjacent heartbeats and between adjacent samples. A heartbeat data sequence is cut and beat-aligned to form a 2-D data array. Any 2-D compression method can then be applied. Transform coding using the 2-D discrete cosine transform (DCT) [2-D DCT] is employed here as an example. Using selections from the MIT-BIH arrhythmia and Medtronic databases, results are presented that illustrate substantial improvement in compression ratio over one-dimensional methods for comparable percent root-mean-square difference (PRD).

Algorithms↗
PubMed2002

Multiscale contrast enhancement for radiographies: Laplacian Pyramid versus fast wavelet transform.

Contrast enhancement of radiographies based on a multiscale decomposition of the images recently has proven to be a far more versatile and efficient method than regular unsharp-masking techniques, while containing these as a subset. In this paper, we compare the performance of two multiscale-methods, namely the Laplacian Pyramid and the fast wavelet transform (FWT). We find that enhancement based on the FWT suffers from one serious drawback-the introduction of visible artifacts when large structures are enhanced strongly. By contrast, the Laplacian Pyramid allows a smooth enhancement of large structures, such that visible artifacts can be avoided. Only for the enhancement of very small details, for denoising applications or compression of images, the FWT may have some advantages over the Laplacian Pyramid.

Algorithms↗
PubMed2001

Comparative evaluation of tableting compression behaviors by methods of internal and external lubricant addition: inhibition of enzymatic activity of trypsin preparation by using external lubricant addition during the tableting compression process.

This study evaluated tableting compression by using internal and external lubricant addition. The effect of lubricant addition on the enzymatic activity of trypsin, which was used as a model drug during the tableting compression process, was also investigated. The powder mixture (2% crystalline trypsin, 58% crystalline lactose, and 40% microcrystalline cellulose) was kneaded with 5% hydroxypropyl cellulose aqueous solution and then granulated using an extruding granulator equipped with a 0.5-mm mesh screen at 20 rpm. After drying, the sample granules were passed through a 10-mesh screen (1680 microm). A 200-mg sample was compressed by using 8-mm punches and dies at 49, 98, 196, or 388 MPa (Mega Pascal) at a speed of 25 mm/min. The external lubricant compression was performed using granules without lubricant in the punches and dies. The granules were already dry coated by the lubricant. In contrast, the internal lubricant compression was performed using sample granules (without dry coating) containing 0.5% lubricant. At 98 MPa, for example, the compression level using the external lubricant addition method was about 13% higher than that for internal addition. The significantly higher compressing energy was also observed at other MPas. By comparison, the friction energy for the external addition method calculated based on upper and lower compression forces was only slightly larger. The hardness of tablets prepared using the internal addition method was 34% to 48% lower than that for the external addition method. The total pore volume of the tablet prepared using the external addition method was significantly higher. The maximum ejection pressure using the no-addition method (ie, the tablet was prepared using neither dry-coated granules nor added lubricant) was significantly higher than that of other addition methods. The order was as follows: no addition, external addition, and then internal addition. The ejection energy (EE) for internal addition was the lowest; for no addition, EE was the highest. In the dissolution test, the tablets obtained using external addition immediately disintegrated and showed faster drug release than those prepared using internal addition. This result occurred because the water penetration rate of the tablet using the external addition was much higher. The trypsin activity in tablets prepared using the external addition method was significantly higher than that produced using the internal addition method at the same pressure. All these results suggest that the external addition method might produce a fast-dissolution tablet. Because the drug will be compressed using low pressure only, an unstable bulk drug may be tableted without losing potency.

Algorithms↗
PubMedDate not supplied

Wavelet based compression of medical ultrasound images using vector quantization.

In this paper, an efficient technique for compression of medical ultrasound (US) images is proposed. The technique is based on wavelet transform of the original image combined with vector quantization (VQ) of high-energy subbands using the LBG algorithm. First, we analyse the statistical behaviour of wavelet coefficients in US images across various subbands and scales. The analysis show that most of the image energy is concentrated in one of the detail subband, either in the vertical detail subband (most of the time) or in the horizontal subband. The other two subbands at each decomposition level contribute negligibly to the total image energy. Then, by exploiting this statistical analysis, a low-complexity image coder is designed, which applies VQ only to the highest energy subband while discarding the other detail subbands at each level of decomposition. The coder is tested on a series of abdominal and uterus greyscale US images. The experimental results indicate that the proposed method clearly outperforms the JPEG2000 (Joint Photographers Expert Group) encoder both qualitatively and quantitatively. For example, without using any entropy coder, the proposed method yields a peak signal to noise ratio gain of 0.2 dB to 1.2 dB over JPEG2000 on medical US images.

Algorithms↗
PubMed1992

Differential diagnosis and surgical treatment of pathologic spine fractures.

The prognosis for survival has improved dramatically for cancer patients over the past three decades. Advances in systemic therapy have prolonged survival even in those who cannot be cured. The importance of managing spinal column disease and protecting the spinal cord has subsequently been amplified. Almost any patient presenting with detectable neurologic function and enough physical reserve to withstand an operation will benefit from a spinal stabilization, pain relief, and neural decompression; there are few exceptions. Advances in surgical technique and biomaterials have not only improved survival and functional outcome, they have diminished many of the postoperative complications that plagued earlier treatment techniques. Methods of preventing or correcting iatrogenic deformity have improved outcome. Newer fixation techniques promise to eliminate many of the causes of hardware and fixation failure previously seen. Improved medical management, antibiotics, and preoperative planning, along with techniques of preoperative embolization and early postoperative mobilization have made surgical management much less risky. Vertebrectomy, considered a last alternative in the past, is now coming to be seen as the conservative approach to tumor management in many situations. Appropriate surgical treatment can have a dramatic impact on function and outcome in patients with tumors of the spinal column, and should never be dismissed as an option without serious consideration. Advances in fixation systems, local and systemic therapy, and in our understanding of the biology of cancer promise even greater improvements for the future.

Adult↗
PubMed2005

Diffusion tensor imaging of the human optic nerve using a non-CPMG fast spin echo sequence.

PURPOSE: To investigate the diffusion tensor properties of the human optic nerve in vivo using a non-Carr-Purcell-Meiboom-Gill (CPMG) fast spin echo (FSE) sequence. MATERIALS AND METHODS: This non-CPMG FSE sequence, which is based on a quadratic phase modulation of the refocusing pulses, allows diffusion measures to be acquired with full signal and without artifacts from geometric distortions due to magnetic field inhomogeneities, which are among the main problems encountered in the orbital area. RESULTS: Good-quality images were obtained at a resolution of 0.94 x 0.94 x 3 mm. The mean diffusivity (MD) and fractional anisotropy (FA) were respectively 1.1 +/- 0.2 x 10(-3) mm(2)/second and 0.49 +/- 0.06, reflecting the optic nerve anisotropy. CONCLUSION: This non-CPMG-FSE sequence provides reliable diffusion-weighted images of the human optic nerve. This approach could potentially improve the diagnosis and management of optic nerve diseases or compression, such as optic neuritis, orbit tumors, and muscle hypertrophy.

Algorithms↗
PubMed1997

Compression of nucleotide databases for fast searching.

MOTIVATION: International sequencing efforts are creating huge nucleotide databases, which are used in searching applications to locate sequences homologous to a query sequence. In such applications, it is desirable that databases are stored compactly, that sequences can be accessed independently of the order in which they were stored, and that data can be rapidly retrieved from secondary storage, since disk costs are often the bottleneck in searching. RESULTS: We present a purpose-built direct coding scheme for fast retrieval and compression of genomic nucleotide data. The scheme is lossless, readily integrated with sequence search tools, and does not require a model. Direct coding gives good compression and allows faster retrieval than with either uncompressed data or data compressed by other methods, thus yielding significant improvements in search times for high-speed homology search tools.

Algorithms↗
PubMed1993

Multichannel ECG data compression by multirate signal processing and transform domain coding techniques.

In this paper, a multilead ECG data compression method is presented. First, a linear transform is applied to the standard ECG lead signals which are highly correlated with each other. In this way a set of uncorrelated transform domain signals is obtained. Then, resulting transform domain signals are compressed using various coding methods, including multirate signal processing and transform domain coding techniques.

Algorithms↗
PubMed1996

Segmentation of digital signals based on estimated compression ratio.

We have studied the problem of approximating a digital signal with a suitable continuous broken line. We use the approximative broken line for further analysis of the signal as detection of peaks, waves, and other structural features. We can also save considerable amount of storage space with an approximation that does not lose too much significant information about the original signal. Our work is based on examining different distance metrics and different segmentation methods with respect to the remaining residual error in the resulting approximation. The aim of the work has been to develop a method that can perform segmentation with an acceptable amount of residual error without a need to define a large set of parameters that control the segmentation process. Our contribution is to examine the effect of the estimated compression ratio of the resulting approximation and finding an estimate of this compression ratio. We first define a target in the form of a compression ratio of the resulting approximation and then by applying our method, try to find a suitable threshold parameter to achieve this target. We have tested our method with electrocardiogram (ECG) signals and the compression ratio of the approximation has been found to be a suitable target to control the segmentation process.

Algorithms↗
PubMed2006

Group delay of acoustic emissions in the ear.

It is commonly accepted that the cochlea emits sound by a backward traveling wave along the cochlear partition. This belief is mainly based on an observation that the group delay of the otoacoustic emission measured in the ear canal is twice as long as the forward delay. In this study, the otoacoustic emission was measured in the gerbil under anesthesia not only in the ear canal but also at the stapes, eliminating measurement errors arising from unknown external- and middle-ear delays. The emission group delay measured at the stapes was compared with the group delay of basilar membrane vibration at the putative emission-generation site, the forward delay. The results show that the total intracochlear delay of the emission is equal to or smaller than the forward delay. For emissions with an f2/f1 ratio <1.2, the data indicate that the reverse propagation of the emission from its generation site to the stapes is much faster than a forward traveling wave to the f2 location. In addition, that the round-trip delays are smaller than the forward delay implies a basal shift of the emission generation site, likely explained by the basal shift of primary-tone response peaks with increasing intensity. However, for emissions with an f1 << f2, the data cannot distinguish backward traveling waves from compression waves because of a very small f1 delay at the f2 site.

Algorithms↗
PubMed2003

Management of acute cerebellar infarction: one institution's experience.

OBJECTIVE: The management of cerebellar infarctions is controversial. The aim of this study was to determine which patients require surgical treatment and which surgical procedure should be performed when a patient with a cerebellar infarction exhibits progressive neurological deterioration. METHODS: A total of 44 patients (24 male and 20 female patients; average age, 56 yr) were treated at our institution for cerebellar infarctions in the past 8 years. Twenty-five patients received conservative treatment; two patients who were deeply comatose received no treatment. The remaining 17 patients underwent emergency surgery. Of those 17 patients, 8 underwent external ventricular drainage alone, 5 underwent external ventricular drainage as the first treatment plus secondary suboccipital craniectomy, and 4 underwent suboccipital craniectomy, with removal of necrotic tissue, as the first treatment. RESULTS: Of the 25 conservatively treated patients, 20 experienced good outcomes, 4 experienced moderate outcomes, and 1 died as a result of pulmonary embolism. Of the 17 surgically treated patients, 10 experienced good functional recoveries (7 treated with external ventricular drainage only and 3 treated with drainage followed by suboccipital craniectomy) and 3 survived with mild neurological deficits (one patient underwent ventriculostomy, one suboccipital craniectomy plus external ventricular drainage, and one suboccipital craniectomy only). The overall mortality rate was 13.6% (6 of 44 patients). CONCLUSION: For patients with worsening levels of consciousness and radiologically evident ventricular enlargement, we recommend external ventricular drainage. We reserve surgical resection of necrotic tissue for patients whose clinical status worsens despite ventriculostomy, those for whom worsening is accompanied by signs of brainstem compression, and those with tight posterior fossae.

Adolescent↗
PubMed2001

Airway stenting.

Various airway pathologies may result in central airway obstruction. For patients who have benign and malignant disease, definitive surgical correction by tracheobronchial resection and reconstruction is preferred. Numerous patients, however, have unresectable airway lesions owing to the extent of disease or to medical or surgical contraindications. These patients can be palliated by several endoscopic strategies, including dilatation, core out of tumor, laser resection, endobronchial brachytherapy, or photodynamic therapy. Airway stenting with silicone or expandable metal stents provides reliable and durable palliation in 80% to 95% of properly selected patients. The major advantages of silicone stents are the ease of customization, repositioning, and removal, with the major drawbacks being stent migration or stent obstruction. Expandable metal stents have the advantage of ease of insertion, conformation to the airway, low inner-to-outer diameter ratio, and stent stability. These advantages, however, are offset by (1) the development of tumor ingrowth or of granulation at the end of the stent or through the interstices of the stent and (2) the difficulty or impossibility of stent repositioning or removal once it has been seated completely within the airway. Management of the patient who has central airway obstruction requires a thorough knowledge and consideration of the surgical and endoscopic management options and, usually, a multidisciplinary approach, with experienced thoracic surgical consultation to evaluate the potential for definitive surgical correction. The interventional bronchoscopist must consider the spectrum of endoscopic therapeutics fully. Most patients benefit from combining strategies in a flexible algorithm directed at optimizing patient outcomes. The benefits and risks of airway stenting must be considered in comparison with the other options for airway palliation. In refractory strictures, rapidly recurrent tumor, or extrinsic compression, endobronchial stenting likely will be necessary to achieve durable palliation of airway obstruction. The short- and long-term implications of airway stenting, including the complications of silicone versus expandable metal stents, should be considered thoroughly, while the physician bases treatment or procedure decisions on individual patient anatomy and expected natural history.

Airway Obstruction↗
PubMed2000

[Wavelet transform and its application in spectral analysis].

Recently, a new mathematical technique known as wavelet transform(WT) has become the focus of many science areas. In analytical chemistry, wavelet transform has been mainly utilized for signal smoothing, de-noising and compression. In this paper, the wavelet transform theory is introduced and its applications in spectral analysis are reviewed.

Algorithms↗
PubMed2001

Radial bending breaking resistance derived by densitometric evaluation predicts femoral neck fracture.

Bone mineral density (BMD) measurement by hip dual-energy X-ray absorptiometry (DXA) is considered the best predictor of osteoporotic fracture risk. BMD takes into account only in part the bone cross-sectional area that is an important determinant of both bone compression strength and of bending breaking resistance. From DXA measurements of proximal radius (Osteoplan, NIM, Verona, Italy) we obtained the projected outer diameter (D) and the mean diameter of the medulla (d), by an algorithm based on the assumption of a constant cortical volumetric density of 1050 g/cm3. The algorithm was validated by the good correlation found (r = 0.8) between calculated d and that actually measured by peripheral quantitative tomography (pQCT; XCT 960, Stratec, Unitrem, Italy) at the same radial site. The D and d values were used to calculate a bending breaking resistance index (BBRI) that is a component of the cross-sectional moment of inertia. The BBRI measured in 5460 women aged 35-89 years, was stable up to the age of 65-70 years and rapidly declined thereafter by 0.7% per year. This profile appears to be due to the fact that the increase in medullary area is compensated in terms of mechanical resistance by enlargement of cross-sectional area. In 68 women with either previous femoral neck (n = 41) or pertrochanteric fracture (n = 27) DXA measurements at proximal and ultradistal radius, lumbar spine and femoral neck were obtained together with the evaluation of proximal radius BBRI. The diagnostic accuracy of BBRI was somewhat comparable to that of spine and femoral neck BMD and significantly superior to that of ultradistal and proximal radius BMD, from which it was derived. Despite the obvious limitation of the cross-sectional nature of this study, our results indicate that a simple re-elaboration of the data obtained by peripheral radial densitometry may achieve diagnostic accuracy for hip fracture risk assessment only marginally lower than that of the direct measure of the BMD of the femoral neck. They also give additional support to the view that bone geometry, particularly for compact skeletal segments, is a determinant of its strength at least as important as bone density.

Absorptiometry, Photon↗