Search PubMed⌕ Search

Biomedical subjects

G T Chua

Publications and source records attributed to G T Chua.

At least 19 recordsLinked to original sources
PubMed2001

Correction of helical CT attenuation values with wide beam collimation: in vitro test with urinary calculi.

RATIONALE AND OBJECTIVES: Urinary calculi are now commonly detected with helical computed tomography (CT), and it has been proposed that stone composition can be determined from CT attenuation values. However, typical scans are made with a beam collimation of 5 mm or more, resulting in volume averaging and reduction in accuracy of attenuation measurement. The authors tested a model for correction of errors in attenuation values, even at section widths larger than the width of the object. MATERIALS AND METHODS: Human urinary stones were scanned with helical CT at different beam collimation widths. A computer model was used to predict the effect of beam width and stone size on accuracy of measured attenuation. RESULTS: At 3-mm collimation, the model corrected the attenuation readings with an underestimation of 12% +/- 1 (compared with values at 1-mm collimation; 127 stones; diameters of 1.7-11.3 mm). With attenuation measured at 10-mm collimation, the model underestimated the true value by 34% +/- 3 (103 stones), with a significant negative correlation with stone diameter on magnitude of error (diameters of 3.0-11.3 mm). Correlation of data from patient scans with subsequent in vitro scanning of the same stones confirmed the validity of the model, but corrected in vivo scans consistently yielded lower values for the stones than in vitro. CONCLUSION: Volume averaging effects on attenuation in helical CT are predictable in vitro for urinary calculi--and presumably for other roughly spherical structures--as long as section width does not excessively exceed the diameter of the structure.

Computer Simulation↗
PubMed2001

Effect of radiographic contrast material exposure on spiral CT attenuation of renal calculi.

RATIONALE AND OBJECTIVES: The authors performed this study to determine whether exposure of renal calculi to radiographic contrast material has an effect on the attenuation values at computed tomography (CT) performed with varying collimation widths. MATERIALS AND METHODS: Renal calculi (23 stones of various composition) were scanned with 1-, 3-, and 10-mm collimation. Stones were then exposed to a solution of radiographic contrast material for 5 minutes, washed with water, and rescanned 36 hours later. The reproducibility of the CT attenuation measurements on different days was evaluated by obtaining measurements in a subset of 16 renal stones on 4 different days. RESULTS: There was no statistically significant change in attenuation after contrast material exposure at narrow collimation. At wider collimation, statistically significant increases were noted in both attenuation and standard deviation. A small amount of variability between readings was noted on different days, with a minimal increase in attenuation each day. Correlation between readings remained very high. CONCLUSION: Exposure of stones to a radiographic contrast material had a statistically significant effect on CT attenuation values only at wide collimation. This may be related to technical factors including volume averaging. Absence of an effect at narrow collimation suggests that the attenuation values of renal stones do not significantly change after exposure to contrast material.

Contrast Media↗
PubMed2000

Calcium stone fragility is predicted by helical CT attenuation values.

BACKGROUND AND PURPOSE: Helical CT has become the preferred method for imaging urinary calculi, and so it would be useful if data from helical CT could also be used to predict the number of shockwaves (SWs) needed to break a given stone. METHODS AND MATERIALS: We measured the number of SWs required to comminute calcium stones in vitro. RESULTS: The SW requirement correlated with stone size (volume, weight, diameter) and with helical CT attenuation values when the scans were performed at 3-mm collimation. When CT scans were performed at 1-mm collimation, the number of SWs needed for comminution did not correlate with helical CT attenuation values. This result indicates that the correlation with 3-mm scans was attributable to volume-averaging effects, in which smaller stones yield smaller attenuation values. That is, attenuation values from helical CT at larger beam collimation widths contain information about stone size that can be exploited to predict the fragility of calcium stones. We observed that for calcium stones, the number of SWs to comminution was generally less than half the stone CT attenuation value in Hounsfield units. This "half-attenuation rule" predicted the number of SWs needed to complete fragmentation for 95% of calcium stones (24/24 calcium oxalate monohydrate, 13/13 hydroxyapatite, 8/10 brushite stones). CONCLUSION: This in vitro study suggests that it may be possible to predict effective SW dose using helical CT prior to lithotripsy.

Humans↗
PubMed2000

Helical CT of urinary calculi: effect of stone composition, stone size, and scan collimation.

OBJECTIVE: Helical CT has become the preferred methodology for identifying urinary calculi. However, the ability to predict stone composition, which influences patient treatment, depends on the accurate measurement of the radiographic attenuation of stones. We studied the effects of stone composition, stone size, and scan collimation width on the measurement of attenuation in vitro. MATERIALS AND METHODS: One hundred twenty-seven human urinary calculi of known composition and size were scanned at 120 kVp, 240 mA, and a 1:1 pitch at different collimations. A model, based on the physics of helical CT, was used to predict the effect of scan collimation width and stone size on measured attenuation. RESULTS: At a 1-mm collimation, stone groups could be differentiated by attenuation: the attenuation of uric acid was less than that of cystine or struvite, which overlapped; these were less than the attenuation of calcium oxalate monohydrate, which was in turn lower than that of brushite and hydroxyapatite, which overlapped and showed the highest values. At a wider collimation, attenuation was lower and the ability to differentiate stone composition was lost. Attenuation also decreased with smaller stones. At a 10-mm collimation, some uric acid stones (<approximately 6 mm) and other stones (< approximately 4 mm) had very low attenuation, so low that they could remain undetected on helical CT. The model predicted well the degree that attenuation was affected by stone size and collimation width. CONCLUSION: Stone composition and stone size, relative to CT collimation, independently influenced CT attenuation. The effect of stone size and collimation generally conformed to the model's predictions. We determined that small stones with low attenuation can be overlooked on helical CT.

Humans↗
PubMed1996

Reliability and role of plain film radiography and CT in the diagnosis of small-bowel obstruction.

OBJECTIVE: We compare the reliability and define the role of plain film radiography and CT in the assessment of various severities of small-bowel obstruction. MATERIALS AND METHODS: A blinded retrospective analysis was done on 78 patients who underwent plain abdominal radiography, CT, and enteroclysis to assess for suspected small-bowel obstruction. The findings at enteroclysis and the clinical outcomes were used as standards of reference. RESULTS: The sensitivity of plain film radiography for revealing small-bowel obstruction was 69% (44/64), and its specificity was 57% (8/14). Overall accuracy of plain film radiography was 67% (52/78). The sensitivity and specificity of CT were 64% (41/64) and 79% (11/ 14), respectively. Overall accuracy of CT was 67% (52/78). When obstructions were classified as low- and high-grade partial obstruction, plain film radiography and CT had sensitivities of 86% (24/28) and 82% (23/28), respectively, for high-grade obstruction and 56% (20/36) and 50% (18/36), respectively, for low-grade obstruction. CT revealed the cause of the small-bowel obstruction in 95% (39/41) of those patients in who CT correctly showed the obstruction. CONCLUSION: Plain film radiography and CT had similar overall accuracies in showing small-bowel obstruction of various severities. Plain film radiography should remain the initial method of imaging patients with suspected small-bowel obstruction. The ability of CT to show the cause of small-bowel obstruction makes CT an important additional diagnostic tool when specific management issues must be addressed.

Adult↗
PubMed1993

Obstruction of the small intestine: accuracy and role of CT in diagnosis.

The reliability of abdominal computed tomography (CT) in the assessment of varying degrees of small bowel obstruction (SBO) was evaluated by using results at enteroclysis and clinical outcome as standards of reference. A blinded retrospective analysis was performed of the studies of 55 patients who underwent both CT and enteroclysis in the course of assessment for suspected SBO. Nine patients had no obstruction, 40 patients had obstruction due to adhesions, and six patients had tumor-related obstruction. CT results were used to identify correctly 63% (29 of 46) of those who had SBO and 78% (seven of nine) of the patients who did not. The overall accuracy of the CT interpretations to help establish diagnosis was 65% (36 of 55). When obstructions were classified into low- and high-grade partial obstruction, CT results could be used to identify correctly 81% (17 of 21) of high-grade SBOs and 48% (12 of 25) of low-grade SBOs. The procedure yielded two false-positive and 13 false-negative results for patients with low-grade obstruction, revealed masses in all six cases with tumor-related obstruction, and helped predict the correct cause in all true-positive cases.

Double-Blind Method↗
PubMed1992

Stone surface area determination techniques: a unifying concept of staghorn stone burden assessment.

The use of stone surface area measurements obtained from standard radiographs provides a more accurate and reproducible assessment of stone burden when reporting results and treatment recommendations for staghorn calculi. Techniques for determining stone surface area include use of graph paper, planimeter or computerized image analysis. The use of graph paper is inefficient while planimeters suffer from significant variation for areas less than 500 mm.2 (more than 5%). Computer image analysis is accurate, rapid and easiest to perform. Software programs compatible with microcomputers are readily available making assessment of stone surface area practical and inexpensive. Stone surface area showed close correlation to stone volume as measured by 3-dimensional computerized tomography (correlation coefficient 0.84, p = 0.005). Stone surface area determination enables more accurate reporting of treatment results and, thus, recommendations based upon stone burden. Comparison of data between institutions becomes more meaningful if stone surface area is used. Stone surface area also provides a useful basis to study and compare trends of treatment within a single institution.

Humans↗
PubMed1991

Uterine adnexal torsion: a case report.

Uterine adnexal torsion is a surgical condition that requires prompt diagnosis and intervention. An ultrasound examination demonstrating a unilaterally enlarged, hypoechoic ovary with several small spherical, peripherally located sonolucent structures in the involved ovary, in addition to a history and physical consistent with torsion, confirms the need for surgical intervention. In this article, we present a case of uterine adnexal torsion and discuss the etiologic, diagnostic and therapeutic aspects of this entity.

Adult↗
PubMed1991

The accuracy of preoperative staging for surgically resected laryngeal cancer.

A retrospective analysis was undertaken to evaluate the accuracy of preoperative staging for laryngeal cancers. T (primary tumor) stage was evaluated more accurately by the combined assessment (clinical examination plus computed tomography (CT) for all laryngeal tumors when compared to the clinical examination (75% versus 31%, p less than 0.04). Supraglottic tumors were evaluated more accurately by CT than the clinical examination (86% versus 0%, p less than 0.01). There was no difference between CT and the clinical examination when evaluating glottic and transglottic lesions. The clinical examination, CT and combined assessment equally evaluated N (regional lymph node involvement) stage. The clinical examination and CT are complementary exams that should be used in conjunction when evaluating patients with advanced laryngeal cancers.

Humans↗
PubMed1990

Calcific deposits in the heart.

Four case reports are presented which illustrate various patterns of calcific deposits in the heart. Valvular, myocardial, intracavitary, and coronary calcific deposits are illustrated, with emphasis on pathology and clinicopathologic-radiologic correlation. "Dystrophic" and "metastatic" calcifications are terms used to describe calcific deposits in abnormal and normal soft tissues, respectively. These terms are somewhat confusing in relation to the myocardium, however, as the chronologic sequence of cardiac injury is often uncertain. We suggest that these terms be avoided in relation to the heart, in favor of simple descriptive terms such as "myocardial calcific deposits." Many conditions, such as renal failure and hypercalcemia may contribute to the likelihood of soft tissue calcification, although a definite common etiology has not been identified. Likewise, soft tissue calcification has been difficult to diagnose premortem. The advent of ultrafast (cine) computed tomography may provide a quick, noninvasive, highly sensitive and specific method for diagnosis of soft tissue calcific deposits in the future.

Adult↗