• Journal of Biomedical Engineering Research
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• v.17 no.1
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• pp.93-98
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• 1996

The purpose of this paper is to propose a new localized imaging method of reduced imaging time luting a locally-linear gradient. Since most fast MR(Magnetic Resonance) imaging methods need the whole $\kappa$-space(Spatial frequency space) data corresponding to the whole imaging area, there are limitstions in reducing the minimum imaging time. The imaging method proposed in this paper uses a specially-made gradient coil generating a local ramp-shape field and uniform field outside of the imaging areal Conventional imaging sequences can be used without any RF/gradient pulse sequence modifiestions except the change in the number of encoding steps and the field of view.

• Bulletin of the Korean Chemical Society
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• v.19 no.12
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• pp.1326-1333
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• 1998

The study of coupled relaxation for methyl spin system in 2,6-dichlorotoluene was performed on the basis of the magnetization mode formalism. Using five initial perturbing pulse sequences, eight experimntal data sets were obtained, which were fitted with theoretical expressions with nine spectral density parameters. The same experiment was carried out at both 50.3 MHz and 125.6 MHz in carbon frequency. The measured spectral densities at both fields are similar in the exception of that related with carbon random field term. Furthermore, from the dipolar spectral density, the physical values may be extracted depending on the model of molecular reorientation. For example, it was assumed that the molecular framework undergoes asymmetric diffusive rotational process and methyl group reorients by either diffusive rotation about its symmetry axis or jump among internal rotational potential minima.

• Investigative Magnetic Resonance Imaging
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• v.12 no.2
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• pp.178-187
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• 2008

Purpose : To evaluate and compare the diagnostic accuracy of MRI and ultrasound(US) for estimation of invasion depth of gastric carcinoma by correlation with histopathologic findings in vitro and to find out the best MR pulse sequence for detection and accurate delineation of tumor. Materials and Methods : Resected specimen of total or subtotal gastrectomy from 53 patients with gastric carcinoma were done of imaging studies of MRI and US. And US was examined by using high frequency linear transducer for tumor invasion depth by a radiologist. In each case, both imaging findings of MRI and US were evaluated independently for tumor detection and invasion depth by consensus of two radiologists and were compared the diagnostic accuracy between two imaging modalities according to the histopathologic findings. MR imaging with five MR pulse sequences, spin echo T1 and in- and out-of phase gradient echo T1 weighted images, FSE and SSFSE T2 weighted images, were performed. Five MR pulse sequences were evaluated and compared on the point of detection and accurate distinction of tumor from surrounding normal tissue. Results : In EGC, diagnostic accuracy of US(77%) was superior than that of MRI(59%) but no statistically significant difference was noted between two imaging modalities(p=0.096). In AGC, both imaging modalities of MRI and US showed relatively high diagnostic accuracy as 97% and 84% respectively. Diagnostic accuracy of MRI was statistically better than that of US at the significant level(p<0.001). The best MR pulse sequence among five in each specimen was FSE T2WI(75.5%, 40/53) in both EGC and AGC. In AGC, FSE T2WI showed excellent imaging quality by showing very high ratio (93.5%, 29/31) of accurate delineation of tumor. Conclusion : MRI and US show relatively high diagnostic accuracy in the evaluation of tumor invasion depth of resected specimen in AGC. The most excellent pulse sequence of MRI for the evaluation of tumor invasion depth is FSE T2WI on the point of detection and accurate delineation of tumor in both EGC and AGC.

• Progress in Medical Physics
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• v.5 no.1
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• pp.55-66
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• 1994

After proving home-made imaging pulse sequences including tailored RF pulse by phantom, susceptibility-contrast-enhanced MR venograms of cat brain were obtained using tailored RF gradient-echo(TRGE) method. Sagittal MR imaging of the cat brain obtained by TRGE technique shows several veins, for example, dorsal sagittal sinus, straight sinus, vein of corpus callosum and internal cerebral vein, etc., compared with cats anatomical figure. Tailored RF waveform was generated by PASCAL language in ASPECT 3000 computer(Switzland, Bruker). Rectangular-shaped slice profile with bi-linear ramp function as phase distribution in the slice, at which maximum value was 2$\pi$, was fourier transformed to make tailored RF pulse. Experimental MR imaging parameters were TR/TE=205/10 msec, slice thickness TH=7mm, maxtrix size=256$\times$256, in-plane resolution=0.62$\times$0.31mm$^2$, and field of view(FOV)=8cm for both conventional gradient-echo(GE) imaging and TRGE imaging techniques.

• Journal of Electrical Engineering and Technology
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• v.6 no.4
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• pp.543-550
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• 2011

Conductive SiC-$ZrB_2$ composites were produced by subjecting a 40:60 (vol%) mixture of zirconium diboride (ZrB2) powder and ${\beta}$-silicon carbide (SiC) matrix to spark plasma sintering (SPS). Sintering was carried out for 5 min in an argon atmosphere at a uniaxial pressure and temperature of 50 MPa and $1500^{\circ}C$, respectively. The composite sintered at a heating speed of $25^{\circ}C$/min and an on/off pulse sequence of 12:2 was denoted as SZ12L. Composites SZ12H, SZ48H, and SZ10H were obtained by sintering at a heating speed of $100^{\circ}C$/min and at on/off pulse sequences of 12:2, 48:8, and 10:9, respectively. The physical, electrical, and mechanical properties of the SiC-$ZrB_2$ composites were examined and thermal image analysis of the composites was performed. The apparent porosities of SZ12L, SZ12H, SZ48H, and SZ10H were 13.35%, 0.60%, 12.28%, and 9.75%, respectively. At room temperature, SZ12L had the lowest flexural strength (286.90 MPa), whereas SZ12H had the highest flexural strength (1011.34 MPa). Between room temperature and $500^{\circ}C$, the SiC-$ZrB_2$ composites had a positive temperature coefficient of resistance (PTCR) and linear V-I characteristics. SZ12H had the lowest PTCR and highest electrical resistivity among all the composites. The optimum SPS conditions for the production of energy-friendly SiC-$ZrB_2$ composites are as follows: 1) an argon atmosphere, 2) a constant pressure of 50 MPa throughout the sintering process, 3) an on/off pulse sequence of 12:2 (pulse duration: 2.78 ms), and 4) a final sintering temperature of $1500^{\circ}C$ at a speed of $100^{\circ}C$/min and sintering for 5 min at $1500^{\circ}C$.

• Investigative Magnetic Resonance Imaging
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• v.4 no.1
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• pp.7-13
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• 2000

Purpose : To assess the distortion of MRI with the Leksell stereotactic radiosurgery system in variable pulse sequence and imaging plane through phantom study, to find most adequate imaging plane and pulse sequence for stereotactic radiosurgery system. Materials and methods : We made the phantoms for MRI and get images in variable conditions and analyzed the image distortion using image analysis program, and statistically using paired student t-test. Results : The transeverse plane images had acceptable error ranges bless than 1.5mm) in all pulse sequence in both the analysis of fiducial marker in stereotactic G-frame and the phantom study. The coronal plane images had unacceptable large errors (more than 1.7mm) in the analysis of fiducial marker in the stereotactic G-frame, but had corrected small errors (less than 1.5mm) in the phantom study. Conclusion : We find from the phantom study that the present MR machines are adequate for stereotactic surgery system in frequently used pulse sequences, and imaging planes.

• Investigative Magnetic Resonance Imaging
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• v.18 no.4
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• pp.290-302
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• 2014

Purpose : Susceptibility-weighted magnetic resonance (MR) sequence is three-dimensional (3D), spoiled gradient-echo pulse sequences that provide a high sensitivity for the detection of blood degradation products, calcifications, and iron deposits. This pictorial review is aimed at illustrating and discussing its main clinical applications. Materials and Methods: SWI is based on high-resolution, 3D, fully velocity-compensated gradient-echo sequences using both magnitude and phase images. To enhance the visibility of the venous structures, the magnitude images are multiplied with a phase mask generated from the filtered phase data, which are displayed at best after post-processing of the 3D dataset with the minimal intensity projection algorithm. A total of 200 patients underwent MR examinations that included SWI on a 3 tesla MR imager were enrolled. Results: SWI is very useful in detecting multiple brain disorders. Among the 200 patients, 80 showed developmental venous anomaly, 22 showed cavernous malformation, 12 showed calcifications in various conditions, 21 showed cerebrovascular accident with susceptibility vessel sign or microbleeds, 52 showed brain tumors, 2 showed diffuse axonal injury, 3 showed arteriovenous malformation, 5 showed dural arteriovenous fistula, 1 showed moyamoya disease, and 2 showed Parkinson's disease. Conclusion: SWI is useful in detecting occult low flow vascular lesions, calcification and microbleed and characterising diverse brain disorders.

• Journal of Biomedical Engineering Research
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• v.16 no.2
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• pp.209-216
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• 1995

Recently, a new tailored RF gradient echo (TRFGE) sequence was reported. This technique not only enhances the magnetic susceptibility effect but also allows us to measure local changes in brain oxygenation. In this study, a phantom and cat brain experiments were performed on a 4.7 Tesla BIQSPEC (BRUKER) instrument with a 26 cm gradient system. We have demonstrated that the signal intensity (SI) of the TRFGE sequence varies according to the concentration of susceptibility contrast agent. Three capillary tubes with different concentrations of Gd-DTPA (0.01, 0.05, 0.1 mMOI/l) were placed at the middle of a cylindrical water phantom. Using both TRFGE and conventional gradient echo (CGE) sequences, phantom images of the slices which contain all three tubes were obtained. For the animal experiment, cats were anesthetized and ventilated using halotane (0.5%) and a $N_2O/ O_2$ mixture (2:1), and blood pressure and heart rate were monitored and kept normal. For the observation of tue first pass of Gd- DTPA, imaging was started at t = 0. At t = 8 ~ 12s, 0.2 mMol/Kg Gd-DTPA was manually injected in the femoral vein. The imaging parameters were TRITE = 25/10 msec, flip angle = $30^{\circ}$, FOV = 10cm, image matrix size = $128{\times}128$ with 64 phase encodings and the image data acquisition window was 10 msec. SI-time curves were then obtained from a series of 30 images which were collected at 2 sec intervals using both CGE and TRFGE pulse sequences before, during, and following the contrast injection.

• Journal of Korean Neurosurgical Society
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• v.30 no.9
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• pp.1120-1126
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• 2001

Objective : The development of magnetic resonance neurography(MRN) has made it possible to produce highresolution images of peripheral nerves themselves, as well as associated intraneural and extraneural lesions. We evaluated the clinical application and utility of high-resolution MRN techniques for the diagnosis and treatment of a variety of peripheral nerve disorder(PND)s. Material and Method : MRN images were obtained using T1-weighted spin echo, T2-weighted fast spin echo with fat suppression, and short tau inversion recovery(STIR) fast spin-echo pulse sequences. Fifteen patients were studied, three with brachial plexus tumors, five with chronic entrapment syndromes, and seven with traumatic peripheral lesions. Ten patients underwent surgery. Results : In MRN with STIR sequences of axial and coronal imagings, signals of the peripheral nerves with various lesions were detected as fairly bright signals and were discerned from signals of the uninvolved nerves. Increased signal with proximal swelling and distal flattening of the median nerve were seen in all patients of carpal tunnel syndrome. Among the eight patients with brachial plexus injury or tumors, T2-weighted MRN showed increased signal intensity in involved roots in five, enhanced mass lesions in three, and traumatic pseudomeningocele in three. Other associated MRI findings were adjacent bony signal change, neuroma, root adhesion and denervated muscle atophy with signal change. Conclusion : MRN with high-resolution imaging can be useful in the preoperative evaluation and surgical planning in patients with peripheral nerve lesions.

• Korean Journal of Radiology
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• v.1 no.1
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• pp.43-50
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• 2000

Objective: To evaluate the usefulness of MR imaging for diseases of the small intestine, emphasizing a comparison with CT. Materials and Methods: Thirty-four patients who underwent both CT and MR imaging using FLASH 2D and HASTE sequences were analyzed. All patients had various small bowel diseases with variable association of peritoneal lesions. We compared the detectabilities of CT and MR imaging using different MR pulse sequences. The capability for analyzing the characteristics of small intestinal disease was also compared. Results: MR imaging was nearly equal to CT for detecting intraluminal or peritoneal masses, lesions in the bowel and mesentery, and small bowel obstruction, but was definitely inferior for detecting omental lesions. The most successful MR imaging sequence was HASTE for demonstrating bowel wall thickening, coronal FLASH 2D for mesenteric lesions, and axial FLASH 2D for omental lesions. MR imaging yielded greater information than CT in six of 12 inflammatory bowel diseases, while it was equal to CT in six of seven neoplasms and inferior in five of seven mesenteric ischemia. In determining the primary causes of 15 intestinal obstructions, MR imaging was correct in 11 (73%) and CT in nine (60%) patients. Conclusion: MR imaging can serve as an alternative diagnostic tool for patients with suspected inflammatory bowel disease, small intestinal neoplasm or obstruction.