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V S Lee

Publications and source records attributed to V S Lee.

At least 19 recordsLinked to original sources
PubMed2006

Single breath-hold T1 measurement using low flip angle TrueFISP.

A method for estimating T1 using a single breath-hold, segmented, inversion recovery prepared, true fast imaging with steady-state precession (sIR-TrueFISP) acquisition at low flip angle (FA) was implemented in this study. T1 values measured by sIR-TrueFISP technique in a Gd-DTPA-doped water phantom and the human brain and abdomen of healthy volunteers were compared with the results of the standard IR fast spin echo (FSE) technique. A good correlation between the two methods was observed (R2=0.999 in the phantom, and R2=0.943 in the brain and abdominal tissues). The T1 values of the tissues agreed well with published results. sIR-TrueFISP enables fast measurements of T1 to be obtained within a single breath-hold with good accuracy, which is particularly important for chest and abdominal imaging.

Algorithms↗
PubMed2004

Statistical factorial analysis on the material property sensitivity of the mechanical responses of the C4-C6 under compression, anterior and posterior shear.

A systematic approach using factorial analysis was conducted on the C4-C6 finite element model to analyse the influence of six spinal components (cortical shell, vertebral body, posterior elements, endplate, disc annulus and disc nucleus) on the internal stresses and external biomechanical responses under compression, anterior and posterior shear. Results indicated that the material properties variation of the disc annulus has a significant influence on both the external biomechanical responses and internal stress of the disc annulus and its neighboring hard bones. The study reveals for the first time, the significant influence of the cancellous bone under compression, while variation in the cortical shell modulus has a high influence under anterior and posterior shear. The study also reveals that the effects of interaction between two main components are insignificant.

Adaptation, Physiological↗
PubMed2001

Optimal dose of Gd-DTPA in dynamic MR studies.

The relationship between the administered dose d of Gd-DTPA and the accuracy of measurements of the glomerular filtration rate G and the cardiac output O was investigated. For a wide range of values the concentration of Gd-DTPA can be uniquely derived from MR signals and precontrast longitudinal relaxation time. Fixed and random errors in these measured variables were analyzed. Depending on noise level and the level of renal function, errors in G reach a minimum for d = 1.4-2.8 mmol. Random errors in G are relatively insensitive to d as long as d > 1.5 mmol. These results establish the feasibility of dynamic MR measurements using doses of Gd-DTPA that are several times lower than current standards.

Cardiac Output↗
PubMed2001

MR renography with low-dose gadopentetate dimeglumine: feasibility.

PURPOSE: To develop a low-dose magnetic resonance (MR) renographic method performed with and without an angiotensin converting enzyme (ACE) inhibitor and in conjunction with gadolinium-enhanced MR angiography in patients with suspected renovascular disease. MATERIALS AND METHODS: Thirty-two patients underwent MR renography (turbo fast low-angle shot sequence: repetition time, 5 msec; echo time, 2.3 msec; flip angle, 15 degrees; one coronal image acquired every 2 seconds for 4 minutes) following intravenous injection of 2 mL of gadopentetate dimeglumine, which was repeated following intravenous injection of an ACE inhibitor. Contrast material-enhanced MR angiography was also performed. On the basis of renographic findings, renal cortex and renal medulla enhancement curves and normalized enhancement ratios were analyzed. RESULTS: The cortex and medulla showed an early transient period of enhancement within 20 seconds (vascular phase). During 1-2 minutes, a second, gradual increase in medullary enhancement, reflecting transit of filtered contrast material, was observed that was significantly greater in patients with a serum creatinine level less than 2 mg/dL (177 micromol/L) than in those with a level of 2 mg/dL or greater (P < .01). After injection of the ACE inhibitor, patients with elevated creatinine levels showed low renal medullary enhancement regardless of the presence of renal artery stenosis (RAS). However, in patients with creatinine less than 2 mg/dL, medullary enhancement ratios after injection of the ACE inhibitor were consistently lower in patients with RAS of 50% or greater than in those without stenosis (P = .02 to .08). CONCLUSION: Low-dose MR renography can be performed in the clinical setting before and after injection of an ACE inhibitor, and its potential use for evaluating decreased renal function as a consequence of RAS is promising.

Angiotensin-Converting Enzyme Inhibitors↗
PubMed2001

Siderotic nodules in the cirrhotic liver at MR imaging with explant correlation: no increased frequency of dysplastic nodules and hepatocellular carcinoma.

PURPOSE: To determine the sensitivity of magnetic resonance (MR) imaging for detection of siderotic nodules in patients with cirrhosis and whether the frequency of hepatocellular carcinoma (HCC) and dysplastic nodules is greater if siderotic nodules are present. MATERIALS AND METHODS: MR imaging (1.5 T) was performed within 0-117 days (mean, 30 days) before liver transplantation in 77 patients. Two readers retrospectively evaluated gradient-echo (GRE) (echo time [TE], > or = 9 and 4-5 msec) and turbo short inversion time inversion-recovery or T2-weighted images for low-signal-intensity nodules. Whole-explant pathologic correlation was available in every case. RESULTS: At explantation, 28 (36%) of 77 patients had HCC, 25 (32%) had dysplastic nodules, and nine (12%) had both; 35 (45%) patients had siderotic nodules. The sensitivity of GRE imaging with 9-msec or longer TE for the detection of siderotic nodules was 80% (28 of 35) but decreased to 31% (11 of 35) with 4-5-msec TE. Frequency of HCC was not significantly higher (P =.27) in patients with (43% [15 of 35]) than in patients without (31% [13 of 42]) siderotic nodules. Frequency of dysplastic nodules also was not significantly higher (P =.42) in patients with (37% [13 of 35]) than in patients without (29% [12 of 42]) siderotic nodules. CONCLUSION: Sensitivity of MR imaging for the detection of siderotic nodules was improved with use of GRE pulse sequences with longer TEs of 9 msec or greater (80%) versus 4-5 msec (31%); however, there was no significant increased frequency of HCC or dysplastic nodules in patients with pathologically proved siderotic nodules.

Adult↗
PubMed2001

Dynamic contrast-enhanced three-dimensional MR imaging of liver parenchyma: source images and angiographic reconstructions to define hepatic arterial anatomy.

PURPOSE: To assess the accuracy of an interpolated breath-hold T1-weighted three-dimensional (3D) gradient-echo (GRE) magnetic resonance (MR) imaging sequence with near-isotropic pixel size (</=2.3 mm) for evaluation of hepatic arterial anatomy variants during dynamic liver parenchymal imaging and to report patterns of hepatic arterial anatomy. MATERIALS AND METHODS: Liver MR imaging, including an interpolated breath-hold 3D GRE sequence with fat suppression (4.2/1.8 [repetition time msec/echo time msec], 12 degrees flip angle), was performed in 207 consecutive patients before and after gadopentetate dimeglumine administration. Of the 207 patients, 202 (98%) had technically satisfactory studies clearly defining the hepatic arterial system. The first contrast material-enhanced GRE acquisition was timed for optimal arterial enhancement with a timing examination. In a retrospective review, hepatic arteries were evaluated on the basis of arterial phase images interpreted by two independent readers using transverse source images complemented by multiplanar reconstructions. Twenty-three patients also underwent digital subtraction angiography, which was a reference standard for comparison. RESULTS: Conventional hepatic arterial anatomy was demonstrated in 135 (67%) of 202 patients. In the 23 patients with angiographic correlation, no discrepancy was noted between MR imaging and digital subtraction angiographic findings. CONCLUSION: Hepatic arterial anatomy can be reliably demonstrated during liver parenchymal imaging with an optimally timed contrast-enhanced isotropic 3D GRE sequence.

Angiography, Digital Subtraction↗
PubMed2001

Hepatocellular carcinoma and dysplastic nodules in patients with cirrhosis: prospective diagnosis with MR imaging and explantation correlation.

PURPOSE: To determine the sensitivity and specificity of magnetic resonance (MR) imaging for detection of hepatocellular carcinoma (HCC) and dysplastic nodules (DNs) by using explantation correlation in patients with cirrhosis and no known HCC. MATERIALS AND METHODS: Seventy-one patients without a known history of HCC who underwent MR imaging and subsequent transplantation within 90 days were examined. Breath-hold turbo short inversion time inversion-recovery and/or T2-weighted turbo spin-echo MR images were obtained. Dynamic two- or three-dimensional gadolinium-enhanced gradient-echo MR images were obtained in the hepatic arterial, portal venous, and equilibrium phases. Prospective MR image interpretations were compared directly with explanted liver pathologic results. RESULTS: Eleven (15%) of 71 patients had hepatic malignancies; MR imaging enabled diagnosis of tumor in six (54%) of 11 patients. On a lesion-by-lesion basis, MR imaging depicted 11 of 20 hepatic neoplasms, for an overall sensitivity of 55%. MR imaging depicted four (80%) of five lesions larger than 2 cm, six (50%) of 12 lesions 1-2 cm, and one (33%) of three lesions smaller than 1 cm. MR imaging depicted only nine (15%) of 59 DNS: The specificities of MR imaging for detection of HCC and DNs on a per patient basis were 60 (86%) of 70 patients and 53 (85%) of 62 patients, respectively. CONCLUSION: MR imaging is insensitive for the diagnosis of small (<2-cm) HCCs and DNS:

Adult↗
PubMed2001

MR imaging as the sole preoperative imaging modality for right hepatectomy: a prospective study of living adult-to-adult liver donor candidates.

OBJECTIVE: Our aim was to investigate the feasibility of MR imaging as a comprehensive preoperative imaging test for examination of liver donor candidates for adult-to-adult right lobe transplantation. SUBJECTS AND METHODS: Twenty-five consecutive donor candidates were examined at 1.5 T using a torso phased array coil with breath-hold T1- and T2-weighted imaging of the abdomen, MR cholangiography using T2-weighted turbo spin-echo imaging, and MR angiography and venography of the liver using two interpolated three-dimensional spoiled gradient-echo sequences (average dose of gadolinium contrast material, 0.17 mmol/kg). Images were interpreted for liver parenchymal and extrahepatic abnormalities; measurements of right and left lobe liver volumes; definition of hepatic arterial, portal venous, and hepatic venous anatomy; and definition of the biliary branching pattern. Findings were compared with those of conventional angiography in 13 patients, 11 of whom also had surgical findings for comparison. RESULTS: Nine patients were excluded as candidates for donation on the basis of MR imaging findings that included parenchymal or extrahepatic abnormalities in five patients, vascular anomalies in two, and biliary anomalies in three. Two patients who did not undergo surgery underwent conventional angiography that confirmed MR angiographic findings except for a small (<2 mm) accessory left hepatic artery missed on MR imaging. Of the nine patients who underwent successful right hepatectomy, all MR imaging findings were corroborated intraoperatively. In two patients, right hepatectomy was aborted at laparotomy because of intraoperative cholangiography findings; in one of them, the biliary finding was unsuspected on MR imaging. CONCLUSION: A comprehensive MR imaging examination has the potential to serve as the sole preoperative imaging modality for living adult-to-adult liver donor candidates provided improvements in definition of intrahepatic biliary anatomy can be achieved.

Adult↗
PubMed2001

Real-time interactive duplex MR measurements: application in neurovascular imaging.

OBJECTIVE: Real-time interactive duplex MR imaging is a new phase-contrast MR imaging technique that enables the quantification and display of flow velocities in real time without the need for cardiac gating. We investigated the feasibility and reliability of the technique to assess hemodynamic information both in vitro and in vivo in the carotid arteries and in the venous sinuses. SUBJECTS AND METHODS: Real-time interactive duplex MR measurements (TR/TE, 53/27; flip angle, 90 degrees; encoding velocity, 100 or 150 cm/sec) were performed in vitro with a steady-flow phantom and in 10 healthy volunteers in whom common and internal carotid artery velocities were measured. In eight volunteers, velocity measurements were also performed in the superior sagittal sinus during both normal breathing and hyperventilation. Time-velocity plots were analyzed qualitatively and quantitatively and compared with findings from conventional segmented k-space phase-contrast MR imaging and Doppler sonography. RESULTS: Velocity determinations for real-time duplex MR and conventional phase-contrast MR imaging showed an in vitro correlation of 0.99 and an in vivo correlation of 0.83 (carotid arteries) and 0.76 (venous sinus). Velocity measurements in the carotid arteries with real-time MR imaging were significantly lower than those obtained with conventional phase-contrast MR (averaged, 7.8%; p = 0.003) or sonography (23.7%, p < 0.001), likely because of volume averaging. Small but significant velocity changes occurring in the venous sinus during hyperventilation were reliably identified with both MR techniques. CONCLUSION: Real-time interactive duplex MR imaging can be effectively applied in neurovascular imaging to obtain hemodynamic information.

Adult↗
PubMed2001

Vascular and extravascular complications of liver transplantation: comprehensive evaluation with three-dimensional contrast-enhanced volumetric MR imaging and MR cholangiopancreatography.

OBJECTIVE: Our purpose was to evaluate a comprehensive MR imaging strategy for recipients of liver transplants that relies on dynamic interpolated three-dimensional (3D) MR imaging for simultaneous vascular, parenchymal, and extrahepatic imaging. MATERIALS AND METHODS: Twenty-three consecutive adult patients underwent 30 MR imaging examinations between 2 days and 99 months (mean, 15 months) after transplantation using a breath-hold 3D gradient-echo sequence (TR range/TE range, 3.7-4.7/1.8-1.9; flip angle, 12-30 degrees ) with an intermittent fat-saturation pulse and interpolation in the section-select direction to enable pixel size 3 mm or less in all dimensions. Unenhanced and triphasic contrast-enhanced 3D imaging (average dose, 0.13 mmol/kg of gadopentetate dimeglumine) was performed. A subset of patients (n = 13) also underwent MR cholangiopancreatography using half-Fourier single-shot turbo spin-echo imaging. MR imaging examinations were correlated with digital subtraction angiography (n = 8), contrast-enhanced cholangiography (n = 9), sonography (n = 13), and histopathology (n = 14). RESULTS: MR imaging revealed abnormal findings in 27 (90%) of 30 examinations, including vascular disease in nine, biliary complications in four, and evidence of intra- or extra-hepatic hepatocellular carcinoma recurrence in six. Digital subtraction angiography confirmed seven MR angiography examinations but suggested disease overestimation in one. Contrast-enhanced cholangiography confirmed findings of MR cholangiopancreatography in seven cases but suggested disease underestimation in two. CONCLUSION: Dynamic interpolated 3D MR imaging combined with dedicated MR cholangiopancreatography can provide a comprehensive assessment of vascular, biliary, parenchymal, and extrahepatic complications in most recipients of liver transplants.

Adult↗
PubMed2001

Volumetric MR imaging of the liver and applications.

Recent improvements in MR technology have enabled the development of volumetric three-dimensional (3D) imaging methods for fat-suppressed T1-weighted images of the entire upper abdomen with pixel sizes of approximately 2 mm in all dimensions and with acquisition times of less than 25 seconds for breath-hold imaging. When performed with a timing scheme, dynamic contrast-enhanced volumetric imaging of the liver can be performed with selective imaging during the arterial phase and portal venous phase of enhancement. The volumetric data sets can be reconstructed in any oblique plane, enabling improved detection, localization, and characterization of small liver lesions. The combination of high-resolution isotropic pixels and accurate timing also permits angiographic reconstructions of the 3D images, producing MR angiography and venography that can be useful in therapeutic planning, such as for catheter-based interventions or surgical resections or transplantation. Additionally, with use of a hepatobiliary contrast agent such as mangafodipir, T1-weighted volumetric MR cholangiography can be performed in patients with nonobstructed systems for depiction of intrahepatic biliary anatomy.

Bile Ducts↗
PubMed2000

Pelvic arteriovenous malformations: gadolinium-enhanced three-dimensional MR angiography findings.

Pelvic arteriovenous malformations (PAV-Ms) are rare disorders traditionally diagnosed by conventional angiography. Breath-hold three-dimensional gadolinium-enhanced MR angiography (3D-Gd-MRA) is a state-of-the-art alternative for vascular imaging. We describe the 3D-Gd-MRA findings in two patients with PAVMs. The 3D-Gd-MRA approach provides a noninvasive and versatile method for evaluation of PAVMs that enables both angiographic assessment of the malformations and evaluation of visceral involvement, which can preclude surgical intervention.

Adult↗
PubMed2000

Variability of Doppler US measurements along the common carotid artery: effects on estimates of internal carotid arterial stenosis in patients with angiographically proved disease.

PURPOSE: To determine the effect of variability of common carotid arterial (CCA) velocities on velocity ratios used to assess internal carotid arterial (ICA) stenosis. MATERIALS AND METHODS: Doppler ultrasonographic (US) velocity measurements were obtained at three levels in the CCA and in the carotid bulb and ICA in all patients referred for carotid US between September 1996 and October 1997. Only ICAs (n = 98, in 57 patients) without ipsilateral CCA disease at angiography were analyzed. The range of CCA peak systolic velocities (PSVs) and end diastolic velocities (EDVs) and velocity ratios were calculated for each CCA measurement. For each ICA/CCA velocity ratio, receiver operating characteristic analysis was performed. RESULTS: CCA PSV and EDV ranges averaged 23.1 cm/sec +/- 15.7 (SD) and 5.1 cm/sec +/- 3.6, respectively. For a given side, the difference averaged 1.0 +/- 1.3 for PSV ratios and 2.7 +/- 6.9 for EDV ratios, depending on where CCA measurements were taken. By using a threshold of 60% stenosis as indication for endarterectomy, variability in CCA velocities could have altered recommendations in 16 (28%) of 57 patients. Receiver operating characteristic analysis showed that ratios made by using the three CCA velocities or their mean were not significantly different. CONCLUSION: Variability in velocity measurements along the course of the CCA in patients with ICA disease can be substantial and can result in inaccuracies in assessment of carotid stenosis.

Aged↗
PubMed2000

Hepatic MR imaging with a dynamic contrast-enhanced isotropic volumetric interpolated breath-hold examination: feasibility, reproducibility, and technical quality.

PURPOSE: To evaluate the feasibility, reproducibility, and technical quality of a dynamic contrast material-enhanced isotropic three-dimensional (3D) volumetric interpolated breath-hold hepatic magnetic resonance (MR) imaging examination. MATERIALS AND METHODS: Fifty patients underwent 3D spoiled gradient-echo imaging (4.2/1.8 [repetition time msec/echo time msec]; flip angle, 12 degrees; interpolation in three directions; intermittent fat saturation; pixel size </= 2.5 mm in all dimensions) before and dynamically after administration of gadopentetate dimeglumine, with the first enhanced acquisition timed for hepatic arterial dominance by using a test bolus of contrast material. Qualitative and quantitative measures of image quality were determined. Patterns of arterial and venous anatomy were assessed. Ten patients (20%) underwent repeat imaging within 6 months, and reproducibility was evaluated. RESULTS: Hepatic contrast-to-noise ratios for nonenhanced and arterial, portal venous, and equilibrium phase studies averaged 13.0 +/- 12.6 (SD), 17.4 +/- 11.8, 30.4 +/- 16.2, and 28.6 +/- 21.1, respectively. During arterial phase, the liver enhanced a mean of 29% of the maximal enhancement as measured during portal venous phase. Hepatic vascular anatomic variants were comparable in distribution to those cited in published articles. Repeat studies were not significantly different in image quality when compared with original studies. CONCLUSION: High-quality arterial phase 3D volumetric interpolated breath-hold images can be obtained reliably and reproducibly when timed by using a test dose of contrast material.

Adipose Tissue↗
PubMed2000

Residential randon exposure and lung cancer risk in Misasa, Japan: a case-control study.

In order to investigate an association between residential radon exposure and risk of lung cancer, a case-control study was conducted in Misasa Town, Tottori Prefecture, Japan. The case series consisted of 28 people who had died of lung cancer in the years 1976-96 and 36 controls chosen randomly from the residents in 1976, matched by sex and year of birth. Individual residential radon concentrations were measured for 1 year with alpha track detectors. The average radon concentration was 46 Bq/m3 for cases and 51 Bq/m3 for controls. Compared to the level of 24 or less Bq/m3, the adjusted odds ratios of lung cancer associated with radon levels of 25-49, 50-99 and 100 or more Bq/m3, were 1.13 (95% confidence interval; 0.29-4.40), 1.23 (0.16-9.39) and 0.25 (0.03-2.33), respectively. None of the estimates showed statistical significance, due to small sample size. When the subjects were limited to only include residents of more than 30 years, the estimates did not change substantially. This study did not find that the risk pattern of lung cancer, possibly associated with residential radon exposure, in Misasa Town differed from patterns observed in other countries.

Adult↗
PubMed2000

Angiotensin-converting enzyme inhibitor-enhanced phase-contrast MR imaging to measure renal artery velocity waveforms in patients with suspected renovascular hypertension.

OBJECTIVE: We investigated the usefulness of phase-contrast MR imaging to measure renal artery velocity waveforms as an adjunct to renal MR angiography. We also examined whether an angiotensin-converting enzyme (ACE) inhibitor improves the diagnostic accuracy of waveform analysis. SUBJECTS AND METHODS: Thirty-five patients referred for MR angiography of renal arteries underwent non-breath-hold oblique sagittal velocity-encoded phase-contrast MR imaging through both renal hila (TR/TE, 24/5; flip angle, 30 degrees; signal averages, two; encoding velocity, 75 cm/sec) before and after i.v. administration of an ACE inhibitor (enalaprilat). We analyzed velocity waveforms using established Doppler sonographic criteria. A timing examination with a test bolus of gadolinium contrast material was performed to ensure optimal arterial enhancement during breath-hold gadolinium-enhanced three-dimensional gradient-echo MR angiography. RESULTS: MR phase-contrast waveform pattern analysis was 50% (9/18) sensitive and 78% (40/51) specific for the detection of renal artery stenosis equal to or greater than 60% as shown on MR angiography. Sensitivity (67%, 12/18) and specificity (84%, 42/50) increased slightly, but not significantly, after i.v. administration of an ACE inhibitor. Also, the accuracy of quantitative criteria such as acceleration time and acceleration index did not improve after the administration of ACE inhibitor. CONCLUSION: Renal hilar velocity waveforms, measured using non-breath-hold MR phase-contrast techniques with or without an ACE inhibitor, are insufficiently accurate to use in predicting renal artery stenosis.

Adult↗