Youngjin Lee

The Effects of Total Variation (TV) Technique for Noise Reduction in Radio-Magnetic X-ray Image: Quantitative Study

In order to reduce the amount of noise component in X-ray imaging system, various reduction techniques were frequently used in the field of diagnostic imaging. Although the previous techniques –such as median, Wiener filters and Anscombe noise reduction technique – were able to reduce the noise, the edge information was still damaged. In order to cope with this problem, total variation (TV) noise reduction technique has been developed and researched. The purpose of this study was to evaluate and compare the image quality using normalized noise power spectrum (NNPS) and contrast-to-noise ratio (CNR) through simulations and experiments with respect to the above-mentioned noise reduction techniques. As a result, not only lowest NNPS value but also highest CNR values were acquired using a TV noise reduction technique. In conclusion, the results demonstrated that TV noise reduction technique is proved as the most practical method to ensure accurate denoising in X-ray imaging system.

Risk factors for urinary retention following minor thoracic surgery

OBJECTIVES Our goals were (i) to identify the incidence and risk factors of postoperative urinary retention in minor thoracic surgery patients and (ii) to develop a scoring system to predict postoperative urinary retention in these patients. METHODS Two hundred and ninety-two consecutive patients who underwent thoracic surgery without a pre- or intraoperative indwelling urinary catheter under general anaesthesia were used to identify the risk factors of postoperative urinary retention (post-void residual urine >200 ml) and to develop the scoring system predicting the incidence of this complication. We investigated past history, type of operation, operation time, amount of administered intravenous fluids, medications used perioperatively as well as demographic data. RESULTS The incidence rate of postoperative urinary retention was 11.6% (34/292). Independent risk factors and their scores were the following: age above 40 years (P < 0.001; two points); male (P = 0.002; one point); diabetes mellitus (P = 0.002; one point) and lung resection (P < 0.001; two points). The cut-off value for a model predicting postoperative urinary retention was five points (C-index = 0.88; 95% confidence interval: 0.83-0.94), with 73% sensitivity and 90% specificity. CONCLUSIONS In minor thoracic surgery patients, special attention should be paid to detect postoperative urinary retention in those with the following characteristics: age over 40 years, male gender, history of diabetes mellitus and candidates for lung resection. The use of the developed scoring system may help in identifying those high-risk patients who need more aggressive management to prevent bladder overdistension and associated urinary complications.

Fate of Newly Detected Lesions During Postoperative Surveillance for Non-Small Cell Lung Cancer

BACKGROUND Chest computed tomography (CT) is the mainstay of postoperative surveillance for non-small cell lung cancer (NSCLC). However, there is no clear consensus about the optimal management of newly detected lesions on follow-up CT. Our goals were (1) to determine the eventual outcome of newly detected lesions on follow-up CT in patients with previously resected NSCLC and (2) to determine the characteristics of the detected lesions that suggest recurrence. METHODS In this retrospective study, we investigated 116 patients with NSCLC who underwent operations between February 2004 and December 2011 and had newly detected lesions on postoperative surveillance CT at least once during the follow-up period (median, 29 months). We investigated lesion size, growth, laterality, multiplicity, and recurrence patterns, as well as demographic data. RESULTS One hundred fifty-seven new lesions were detected during the follow-up period. Of the 157 lesions, 139 were intrathoracic (lung, 83; lymph node, 34; pleura, 14; others, 8) and 18 were extrathoracic. Further investigation or follow-up confirmed that 78 lesions (49.7% [78 of 157]) were recurrences. Extrathoracic lesions showed a higher correlation with recurrence compared with intrathoracic ones (83.3% versus 45.3%; p = 0.002). Regarding lung lesions, solid nodules (p = 0.003; hazard ratio, 13.190) and lesions in patients with stage III disease (p = 0.043; hazard ratio, 6.464), were much more likely to reflect recurrence. CONCLUSIONS In patients with newly detected lesions on follow-up chest CT after resection of NSCLC, special attention should be paid to lesions with the following characteristics: extrathoracic lesions, solid lung nodules, and lung lesions in patients with stage III disease. It is necessary to investigate these lesions more aggressively because they suggest the presence of recurrent disease.

Comparison Study of Image Performance with Contrast Agent Contents for Brain Magnetic Resonance Imaging

The purpose of study was to evaluate SNR and CNR with different contrast agent contents (1.0 mmol/mL gadobutrol and 0.5 mmol/mL gadoterate meglumine) for spin echo (SE) and 3-dimension contrast-enhanced fast field echo (3D CE-FFE) pulse sequences. In this study, we compared the SNR and the CNR between 0.5 mmol/mL gadoterate meglumine and 1.0 mmol/mL gadobutrol according to the concentration of contrast agent in brain MRI. When we compared between SE and 3D CE-FFE pulse sequences, the higher SNR and CNR using 3D CE-FFE pulse sequence can be acquire regardless of contrast agent contents. Also, a statistically significant difference was found for SNR and CNR between all protocols. In conclusion, our results demonstrated that the SNR and CNR have not risen proportionately with contrast agent contents. We hope that these results presented in this paper will contribute to decide contrast agent contents for brain MRI.

A Numerical Study of Different Types of Collimators for a High-Resolution Preclinical CdTe Pixelated Semiconductor SPECT System

In single-photon-emission computed tomography (SPECT) with a pixelated semiconductor detector (PSD), not only pinhole collimators but also parallel-hole collimators are often used in preclinical nuclear-medicine imaging systems. The purpose of this study was to evaluate and compare pinhole and parallel-hole collimators in a PSD. For that purpose, we paired a PID 350 (Ajat Oy Ltd., Finland) CdTe PSD with each of the four collimators most frequently used in preclinical nuclear medicine: (1) a pinhole collimator, and (2) low-energy high-resolution (LEHR), (3) low-energy general-purpose (LEGP), and (4) low-energy high-sensitivity (LEHS) parallel-hole collimators. The sensitivity and spatial resolution of each collimator was evaluated using a point source and a hot-rod phantom. The highest sensitivity was achieved using LEHS, followed by LEGP, LEHR, and pinhole. Also, at a source-to-collimator distance of 2 cm, the spatial resolution was 1.63, 2.05, 2.79, and 3.45 mm using pinhole, LEHR, LEGP, and LEHS, respectively. The reconstructed hot-rod phantom images showed that the pinhole collimator and the LEHR parallel-hole collimator give a fine spatial resolution for preclinical SPECT with PSD. In conclusion, we successfully compared different types of collimators for a preclinical pixelated semiconductor SPECT system.

Evaluation of Electrokinetic Flow Mobility Using Isotacho-Electrophoresis Techniques

In the present study, we separated the marker particles from the suspending particle mixture solution using isotacho- electrophoresis technique, a novel quantitative ionic particle separation method, in the microchannel. A multiple stacking zone of the suspending particle was visualized with variations in electric field strength, pH value and concentration of the ionic solution. In particular, the electrophoretic mobility of ionic particle (fluorescein) was estimated based on the electrophoretic velocity value measured by the particle image velocimetry. As a result, isotacho-electrophoresis zones were clearly visualized as going downstream in the electric field. The particle migration velocity increased proportional to the applied voltage increase; it was also affected by the pH value variations in the ionic solution.