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Biomedical subjects

K J Lee

Publications and source records attributed to K J Lee.

At least 19 recordsLinked to original sources
PubMed2006

Stereotactic radiosurgery for brain arteriovenous malformations: quantitative MR assessment of nidal response at 1 year and angiographic factors predicting early obliteration.

INTRODUCTION: We investigated the role of magnetic resonance angiography (MRA) in the early follow-up of patients after stereotactic radiosurgery (STRS) for cerebral arteriovenous malformations (AVMs) and determined the influence of individual morphological factors of AVMs in early response to treatment. METHODS: A group of 40 patients (41 AVMs) consented to a dedicated 1.5-T MR protocol 12 months after receiving STRS for a brain AVM. In addition to standard spin echo sequences, 3-D contrast-enhanced sliding interleaved Ky MRA (CE-SLINKY) and dynamic time-resolved subtraction angiography (MR-DSA) were performed. Nidal volumes were calculated using CE-SLINKY data in patients with a persisting arteriovenous shunt. Planning angiographic data was investigated in all 40 patients. The following AVM factors were used in the statistical analysis to determine their role in nidus obliteration: (1) maximum linear dimension, (2) nidal volume, (3) AVM location (4) nidal morphology, (5) venous drainage, (6) "high-flow angiographic change", (7) prior embolization, and (8) dose reduction. RESULTS: Complete nidal obliteration was found in 9 patients, 26 showed greater than 50% nidal reduction and 6 had less than 50%. Two AVM factors, venous drainage and AVM location, were found to significantly correlate with rate of obliteration. CONCLUSION: We successfully demonstrated the use of MRA to quantitatively assess the response of AVMs to STRS. Two AVM factors, venous drainage and AVM location were found to correlate with rate of obliteration prior to the application of the Bonferroni correction, but if this more rigorous statistical test was applied then none of the factors was found to be significant.

Adolescent↗
PubMed2006

Combined simulated annealing and Shinnar-Le Roux pulse design of slice-multiplexed RF pulses for multi-slice imaging.

Slice-multiplexed RF pulses have recently been introduced for simultaneous multi-slice imaging. Their novel aspect is that each slice is given a different linear phase profile, and hence a different slice-rephasing requirement, by the pulse. During readout, extra slice gradients are applied such that when one slice is rephased, the others are dephased to prevent aliasing. In this paper, an improved method of designing slice-multiplexed RF pulses is presented: component pulses which are optimized with simulated annealing for a specific rephasing are combined using Shinnar-Le Roux methods. In this way, non-linearities at higher flip angles are taken into account and more slices can be excited. Bloch simulations show the phase and amplitude profile of component pulses are faithfully preserved in the multiplexed pulse. Three- and four-slice multiplex pulses are demonstrated in gradient- and spin-echo in-vivo imaging.

Algorithms↗
PubMed2005

Gabapentin reduces rectal mechanosensitivity and increases rectal compliance in patients with diarrhoea-predominant irritable bowel syndrome.

BACKGROUND: Gabapentin has been shown to reduce elements of central sensitization in human experimental hyperalgesia. It remains uninvestigated whether gabapentin has beneficial effects for irritable bowel syndrome associated with visceral hypersensitivity. AIMS: To evaluate the effects of gabapentin on sensory and motor function of the rectum in patients with diarrhoea-predominant irritable bowel syndrome. METHODS: Forty patients with diarrhoea-predominant irritable bowel syndrome completed this randomized, double-blind, placebo-controlled, parallel-grouped study. All patients received a barostat study and were subsequently randomized for 5-day treatment with gabapentin 300 mg/day and then 600 mg/day or placebo. On day 6, after subjects had their morning dose, the barostat experiment was repeated. RESULTS: The threshold pressures for bloating, discomfort and pain significantly increased after gabapentin, but not after placebo. Significant increase in the pressure and corresponding wall tension inducing discomfort or pain were observed in the gabapentin group, but not in the placebo group. Rectal compliance significantly increased after gabapentin, but not after placebo. The postprandial increase of rectal tone was not affected by gabapentin. CONCLUSION: Our results show that gabapentin reduces rectal sensory thresholds through attenuating rectal sensitivity to distension and enhancing rectal compliance in diarrhoea-predominant irritable bowel syndrome patients. The clinical efficacy of this drug in irritable bowel syndrome patients warrants investigation.

Adult↗
PubMed2005

Brain arteriovenous malformations: measurement of nidal volume using a combination of static and dynamic magnetic resonance angiography techniques.

Arteriovenous malformations of the brain are complex vascular lesions that are an important cause of death and long-term disability. Currently, catheter angiography (CA) is the reference standard procedure for the diagnosis and follow-up of treated arteriovenous malformations (AVMs). This is an invasive procedure with potential risks. Magnetic resonance angiography (MRA) is commonly used in neurovascular imaging as a non-invasive alternative. Various MRA techniques have been used in the diagnosis and follow-up of AVMs but these have suffered from lack of temporal or spatial resolution. In this 60-patient study we describe the combination of two techniques: dynamic magnetic resonance digital subtraction angiography with a high temporal resolution, and a non-dynamic contrast-enhanced time-of-flight sequence with a high spatial resolution technique, in the assessment of AVM. The results showed an excellent correlation between MRA and CA measurement of both maximum linear dimension and AVM nidus volume.

Adult↗
PubMed2005

Method of generalized projections algorithm for image-based reduction of artifacts in radial imaging.

This work describes the method of generalized projections (MGP) as an image-based, postprocessing method to correct for phase inconsistencies caused by echo misalignments in radial imaging. Computer simulations show that MGP can correct for echo shifts, constant phase, and amplitude errors, but the accuracy of the correction is limited, and this accuracy is reduced by the addition of more degrees of freedom. In phantom experiments, MGP performed better than magnitude filtered backprojection and anti-parallel projections correction.

Algorithms↗
PubMed2005

Simultaneous multislice imaging with slice-multiplexed RF pulses.

A method for simultaneous multislice imaging is presented that uses a multislice RF pulse that imparts a different linear phase profile to each slice. During readout, slices are unaliased by using extra slice-select gradient lobes, which rephase and dephase individual slices one at a time. Compared to other simultaneous slice methods, this method avoids distortion by slice-select gradients, and does not require extra views or additional hardware. However, because one echo per slice is required, the method requires a longer read period. This can cause non-ideal rephasing of the individual slices due to susceptibility gradients, which manifests itself as crosstalk between slices. There is also a concomitant increase in the minimum TR of the sequence. The method is demonstrated with phantom and in vivo images using gradient-echo and spin-echo versions.

Algorithms↗
PubMed2005

CT halo sign: the spectrum of pulmonary diseases.

The CT halo sign indicates ground glass attenuation surrounding a pulmonary nodule on CT. Although it was initially proposed as an early, specific finding of invasive pulmonary aspergillosis, it can be caused by many other pathological conditions such as infection, neoplastic and inflammatory diseases. The halo of ground glass attenuation pathologically represents pulmonary haemorrhage, tumour infiltration, or non-haemorrhagic inflammatory processes. Although non-specific, this sign is important because the clinical setting and associated radiological features may give a clue to the differential diagnosis. In this review, we demonstrate the spectrum of pulmonary diseases showing the "CT halo sign" on thin-section CT and discuss their radiological and clinical features.

Adult↗
PubMed2004

A method of generalized projections (MGP) ghost correction algorithm for interleaved EPI.

Investigations into the method of generalized projections (MGP) as a ghost correction method for interleaved EPI are described. The technique is image-based and does not require additional reference scans. The algorithm was found to be more effective if a priori knowledge was incorporated to reduce the degrees of freedom, by modeling the ghosting as arising from a small number of phase offsets. In simulations with phase variation between consecutive shots for n-interleaved echo planar imaging (EPI), ghost reduction was achieved for n = 2 only. With no phase variation between shots, ghost reduction was obtained with n up to 16. Incorporating a relaxation parameter was found to improve convergence. Dependence of convergence on the region of support was also investigated. A fully automatic version of the method was developed, using results from the simulations. When tested on in vivo 2-, 16-, and 32-interleaved spin-echo EPI data, the method achieved deghosting and image restoration close to that obtained by both reference scan and odd/even filter correction, although some residual artifacts remained.

Algorithms↗
PubMed2004

Effect of diets containing gossypol on blood parameters and spleen structure in tilapia, Oreochromis sp., reared in a recirculating system.

The high cost of fish meal in tilapia diets warrants the potential use of cottonseed meal (CSM) as an alternative source of high quality protein. The effects of varying levels of CSM (0, 25, 50, 75 and 100%) as fish meal protein replacement on growth, blood parameters, spleen characteristics, free and bound gossypol in blood plasma, haemoglobin and haematocrit were determined in tilapia. Gossypol (C(30)H(30)O(8)) is a polyphenolic substance found in cottonseed that has known toxic effects in fish. Tilapias (n = 219, average weight = 11.3 +/- 3.9 g) were randomly distributed into 15, 32-L glass aquaria, representing five dietary treatments and three replicates per treatment. Each aquarium containing 13-16 fish was supplied with thermoregulated, recirculating water (27 +/- 1 degrees C) at 1 L min(-1) flow rate and photoperiod was constant (12 h L/12 h D). Fish fed 25-50% CSM protein replacement showed similar body weights and total lengths as the controls at the completion of the 16-week trial. Fish fed 75 and 100% CSM protein replacement showed a significant decline in body weight and total length. Fish fed 25-100% CSM protein replacement had significantly lower haematocrit and haemoglobin (ANOVA/LSD, P < 0.05) compared with levels in controls. The decline was most prominent in groups fed diets with 50-100% CSM protein replacement. Total and free gossypol concentrations of blood plasma significantly increased with increasing levels of CSM replacement (P < 0.05). No gossypol was found in blood plasma of fish from the control group. The occurrence of immature and abnormal erythrocytes was significantly greater among fish fed 75 and 100% CSM diets compared with fish fed 0-50% CSM diets. Spleen-somatic index (spleen weight/body weight x 100) did not differ between control fish and fish fed 50-100% CSM diets. Spleen abnormalities, such as large depositions of haemosiderin and melanin pigments and proliferation of melano-macrophage centres, lymphocytic depletion of the white pulp areas (hypocellularity), and presence of vacuoles and necrotic areas were observed among fish fed 50-100% CSM protein diets. In general, the pathological effects of gossypol in tilapia (low haemoglobin and haematocrit levels, abundance of immature red blood cells or polychromatocytes, abnormal spleen morphology) were similar to the effects of vitamin E and/or vitamin C deficiencies observed in other studies.

Analysis of Variance↗
PubMed2003

Magnetic resonance imaging with stepped B(0) fields.

This paper introduces the concept of imaging with stepped magnetic fields within the main B(0) field. The resonance frequency within each step is separated from the next by an amount greater than the imaging bandwidth. Each step thus gives rise to a separate imaging region enabling simultaneous imaging over multiple slices without aliasing. The auxiliary magnetic field regions are produced by coil inserts. The principle is illustrated using simple coil designs which introduce up to two steps into the main B(0) field. Phantoms placed in each uniform region were successfully imaged simultaneously with no aliasing.

Calibration↗
PubMed2003

[Development of gerontological nursing curriculum model].

PURPOSE: This study was conducted to develop gerontological curriculum model which reflects the need of Korean society. METHOD: Three round Delphi survey method was applied to find consensus of gerontological nursing competencies (knowledge, attitudes and skills) for graduates of nursing schools from the panel of gerontological nursing practice experts. Important concepts in gerontological nursing were delineated from literature review and discussions of gerontological nursing educators. Based on these results the gerontological nursing curriculum model was developed and course structure outlined by the researchers as a group. RESULT: As the result of delphi survey, 32 items of knowledge, 29 items of attitude, and 21 items of skill were identified. The curriculum model constructed around a cube with three plane- functional capacity levels, settings, and nursing practice. Specific knowledge, attitudes and skills for gerontological theory and practicum course were suggested. Competency items were assigned to theory and/or practice. CONCLUSION: A curriculum model for gerontological nursing has been developed by a group of gerontological nursing educators. The curriculum model should be further tested and developed with detailed theory and practicum course outline and textbooks.

English Abstract↗
PubMed2002

Image-based EPI ghost correction using an algorithm based on projection onto convex sets (POCS).

This work describes the use of a method, based on the projection onto convex sets (POCS) algorithm, for reduction of the N/2 ghost in echo-planar imaging (EPI). In this method, ghosts outside the parent image are set to zero and a model k-space is obtained from the Fourier transform (FT) of the resulting image. The zeroth- and first-order phase corrections for each line of the original k-space are estimated by comparison with the corresponding line in the model k-space. To overcome problems of phase wrapping, the first-order phase corrections for the lines of the original k-space are estimated by registration with the corresponding lines in the model k-space. It is shown that applying these corrections will result in a reduction of the ghost, and that iterating the process will result in a convergence towards an image in which the ghost is minimized. The method is tested on spin-echo EPI data. The results show that the method is robust and remarkably effective, reducing the N/2 ghost to a level nearly comparable to that achieved with reference scans.

Algorithms↗
PubMed2002

Fast two-dimensional MR imaging by multiple acquisition with micro B(0) array (MAMBA).

A new method for acquiring MR data in two dimensions is described. This is achieved by combining coils into an array so as to produce a unique local magnetic field within each coil when placed within the B(0) field of a standard MRI scanner. In this way each known location of a coil is associated with a unique resonant frequency. Each coil now represents a location of a pixel in the plane, and after Fourier transformation of the signal the resulting frequency spectrum gives immediately the spin distribution in the plane of the array. In effect, the two-dimensional spatial distribution is frequency encoded without the use of switched gradients or phase encoding. As only static fields are used, this technique offers the potential of fast imaging. Furthermore, signals from different locations would also be inherently time-registered. Initial experiments to demonstrate the principle are described, using a square array of 5 by 5 coils. The currents in the coils were determined by using a genetic algorithm. Echoes from pellet phantoms placed in the array were acquired using standard spin-echo sequences with gradients switched off. The results are promising, with the spectra showing generally good resolution between peaks, enabling localisation in up to half the pixels. Technical difficulties are discussed and possible applications are outlined.

Algorithms↗
PubMed2001

Hepatoprotective effects of Platycodon grandiflorum on acetaminophen-induced liver damage in mice.

The protective effects of an aqueous extract from the roots of Platycodon grandiflorum A. DC (Campanulaceae), Changkil (CK), on acetaminophen (APAP)-induced hepatotoxicities and the possible protective mechanisms involved were investigated in mice. Pretreatment with CK prior to the administration of APAP significantly prevented the increase in serum alanine aminotransferase and aspartate aminotransferase activity and hepatic lipid peroxidation in a dose-dependent manner. APAP-induced hepatotoxicity was also essentially prevented as evidenced by liver histopathology. Hepatic glutathione levels and glutathione-S-transferase activities were not affected by treatment with CK alone, but pretreatment with CK protected the APAP-induced depletion of hepatic glutathione levels. The effects of CK on cytochrome P450 (P450) 1A2 and 2E1, the major isozymes involved in APAP bioactivation, were investigated. In microsomal incubations, CK effectively inhibited P450 lA2-dependent methoxyresorufin O-deethylase activities and the P450 2E1-dependent p-nitrophenol and aniline hydroxylase. The results suggest that the protective effects of CK against the APAP-induced hepatotoxicity may, at least in part, be due to its ability to block P450-mediated APAP bioactivation.

Acetaminophen↗
PubMed2001

Identification of structural domains affecting transactivation potential of Nm23.

The strong transactivation activity of the C-terminal half (amino acids 76-152) of Nm23 was reported previously. Here we examined a structural domain preventing or necessary to its transactivation activity. The C-terminal 1/4 (amino acids 109-152) was sufficient for transactivation, but the C-terminal half with a longer N-terminal extension (amino acids 58-152) caused the loss of the transactivation ability. Furthermore, coexpression of the N-terminal half with the C-terminus of Nm23-H1 blocked the transactivation activity of the C-terminal half, where direct interaction of both truncated proteins was demonstrated in vitro. Transactivation activities in the C-terminal halves of the known mutants (P96S, H118F, S120G, and S120A) exhibiting differential antimetastasis effects were also tested. Significant reduction of transactivation activity was observed only in H118F, indicating that NPD kinase active-site histidine is required. This suggests that transactivation potential of Nm23 is related to NDP kinase activity but not to metastasis suppressor activity.

Binding Sites↗
PubMed2001

The role of Tyr248 probed by mutant bovine carboxypeptidase A: insight into the catalytic mechanism of carboxypeptidase A.

We have investigated the function of Tyr248 using bovine wild-type CPA and its Y248F and Y248A mutants to find that the K(M) values were increased by 4.5-11-fold and the k(cat) values were reduced by 4.5-10.7-fold by the replacement of Tyr248 with Phe for the hydrolysis of hippuryl-L-Phe (HPA) and N-[3-(2-furyl)acryloyl]-Phe-Phe (FAPP), respectively. In the case of O-(trans-p-chlorocinnamoyl)-L-beta-phenyllactate (ClCPL), an ester substrate, the K(M) value was increased by 2.5-fold, and the k(cat) was reduced by 20-fold. The replacement of Tyr248 with Ala decreased the k(cat) values by about 18- and 237-fold for HPA and ClCPL, respectively, demonstrating that the aromatic ring of Tyr248 plays a critical role in the enzymic reaction. The increases of the K(M) values were only 6- and 5-fold for HPA and ClCPL, respectively. Thus, the present study indicates clearly that Tyr248 plays an important role not only in the binding of substrate but also in the enzymic hydrolysis. The kinetic results may be rationalized by the proposition that the phenolic hydroxyl of Tyr248 forms a hydrogen bond with the zinc-bound water molecule, causing further activation of the water molecule by reducing its pK(a) value. The pH dependency study of k(cat) values and the solvent isotope effects also support the proposition. A unified catalytic mechanism is proposed that can account for the different kinetic behavior observed in the CPA-catalyzed hydrolysis of peptide and ester substrates.

Amino Acid Sequence↗