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Lawrence C Chow

Publications and source records attributed to Lawrence C Chow.

15 recordsLinked to original sources
PubMed2005

Vascular mapping of the leg with multi-detector row CT angiography prior to free-flap transplantation.

PURPOSE: To retrospectively evaluate multi-detector row computed tomographic (CT) angiography in determining donor- and recipient-site arterial suitability for successful vascularized free-flap transplantation. MATERIALS AND METHODS: The institutional review board granted approval; informed consent was waived, and the study was HIPAA compliant. Lower extremities of 20 (12 male, eight female; mean age, 51 years; range, 10-84 years) patients undergoing vascularized free-flap procedures were examined at multi-detector row CT angiography. In five patients, legs were assessed as potential fibular free-flap donors for mandibular, maxillary, or radial reconstruction. In 15 patients, legs were assessed as recipient sites for free flaps. Vascular maps obtained with volume rendering, maximum intensity projections, and curved planar reformations were generated, and assessment was made in the depiction of calf vessels and presence of stenosis, occlusion, and anatomic anomaly. Findings of CT angiography, physical examination, and surgery were compared, where applicable, and successful CT-based prediction of the surgical intervention was assessed. Immediate and long-term (>70 days) viability of the graft was assessed in all patients. RESULTS: CT angiography depicted the entirety of all four major calf arteries in 29 of 32 legs scanned. In three legs, external-fixation hardware obscured some segments. There were no discrepancies between CT findings and those identified at the time of surgery. Arterial abnormalities, including stenosis, occlusion, and variant anatomy, were seen in 12 lower extremities in 10 patients. Only two were suspected on the basis of physical examination findings. In five of 20 patients, CT findings resulted in changes to the surgical plan. There was a 100% immediate viability of all grafts, which remained well vascularized between 70 days and 37 months after the procedure. CONCLUSION: Multi-detector row CT angiography provides a noninvasive means of preoperatively assessing lower extremity arteries for abnormalities, which could jeopardize graft viability or pedal arterial supply after free-flap procedures.

Aged↗
PubMed2005

Measurement of renal extraction fraction with contrast-enhanced CT.

Study was approved by the institutional review board, and informed patient consent was waived. A method for minimization of sources of variability in measuring single-kidney extraction fraction (EF) was determined retrospectively with contrast material-enhanced computed tomography (CT). Ten adults underwent CT of the kidneys; precontrast scans were obtained, followed by postcontrast scanning 2 minutes after contrast material injection. Single-kidney EF was then calculated for each patient with the formula EF = (CT(A) - CT(V))/(CT(A) - CT(PRE)), where CT(A) and CT(V) are the postcontrast CT values (in Hounsfield units) of the systemic blood and renal venous blood, respectively, and CT(PRE) is the precontrast CT value of the blood. Both conventional two-dimensional and volumetric three-dimensional regions of interest were used for determining mean CT values of the blood. By using the volumetric regions of interest, left and right renal EF values averaged 17.3% and 18.0%, respectively, for two observers, compared with the accepted value of 15%-20%. This latter technique also minimized right-left kidney and interobserver variability in the measurement of EF.

Adult↗
PubMed2005

Estimation of renal extraction fraction based on postcontrast venous and arterial differential T1 values: an error analysis.

An error analysis for quantifying single kidney extraction fraction (EF) via differential T1 measurements in the renal vein (RV) and renal artery (RA) is presented. Sources of error include blood flow effects, the effect of a short repetition time (TR), and the impact of uncertainties in the T1 estimates on the final EF calculations. Blood flow effects were investigated via simulation. For a range of blood velocities in the renal vein that may be found in kidney disease, incomplete refreshment of blood between readouts results in significant errors in T1 estimation. For a .5-cm slice, 110-ms sampling interval, and T1 of 600 ms, T1 estimation to within 5% of true T1 requires an average through-plane velocity of 6.75 cm/s for parabolic flow, and 3.5 cm/s for plug flow. Improvement can be achieved by accurately estimating the fraction of blood that has not refreshed between readouts (f(old)), while the quality of the T1 estimate varies with the accuracy of f(old) estimation. Shortening of the TR was investigated using phantom and in vivo studies. T1 was estimated to within 3% of the true value on phantoms, and within 5% of the true value for flowing blood for TR = 2T1. The estimated EF is shown to be very sensitive to the difference between T(1RA) and T(1RV). To achieve 10% or 20% uncertainty in the EF estimate, T1 in the renal vein and renal artery must be estimated to within approximately 1% or 2%. Because of limitations on measurement accuracy and precision, this method appears to be impractical at this time.

Blood Flow Velocity↗
PubMed2005

The sonographic features of papillary thyroid carcinomas: pictorial essay.

Papillary thyroid carcinoma (PTC) is the most common thyroid malignancy in children and adults, with an incidence of 22,000 cases per year in the United States. Differentiating PTC from more frequently occurring benign thyroid nodules has proved challenging as there may be significant overlap in their clinical presentation and sonographic appearance. That said, high-resolution ultrasound provides a safe and affordable way of identifying and characterizing thyroid nodules and guiding percutaneous biopsies. Although no single sonographic feature is pathognomonic for PTC, certain features should raise suspicion and the combination of several features may be even more suggestive. In this pictorial essay, we describe the high-resolution sonographic features of pathologically proven PTCs. The nodule number, echo texture, internal architecture, calcifications, margins, contours, vascularity, and lymph nodes are considered. While the classic sonographic description of PTC is a solitary, hypoechoic solid nodule with microcalcifications and intrinsic vascularity, in practice, PTC may manifest with a myriad of sonographic appearances making biopsy necessary for a definitive diagnosis.

Biopsy, Fine-Needle↗
PubMed2004

Pulmonary nodules on multi-detector row CT scans: performance comparison of radiologists and computer-aided detection.

PURPOSE: To compare the performance of radiologists and of a computer-aided detection (CAD) algorithm for pulmonary nodule detection on thin-section thoracic computed tomographic (CT) scans. MATERIALS AND METHODS: The study was approved by the institutional review board. The requirement of informed consent was waived. Twenty outpatients (age range, 15-91 years; mean, 64 years) were examined with chest CT (multi-detector row scanner, four detector rows, 1.25-mm section thickness, and 0.6-mm interval) for pulmonary nodules. Three radiologists independently analyzed CT scans, recorded the locus of each nodule candidate, and assigned each a confidence score. A CAD algorithm with parameters chosen by using cross validation was applied to the 20 scans. The reference standard was established by two experienced thoracic radiologists in consensus, with blind review of all nodule candidates and free search for additional nodules at a dedicated workstation for three-dimensional image analysis. True-positive (TP) and false-positive (FP) results and confidence levels were used to generate free-response receiver operating characteristic (ROC) plots. Double-reading performance was determined on the basis of TP detections by either reader. RESULTS: The 20 scans showed 195 noncalcified nodules with a diameter of 3 mm or more (reference reading). Area under the alternative free-response ROC curve was 0.54, 0.48, 0.55, and 0.36 for CAD and readers 1-3, respectively. Differences between reader 3 and CAD and between readers 2 and 3 were significant (P < .05); those between CAD and readers 1 and 2 were not significant. Mean sensitivity for individual readings was 50% (range, 41%-60%); double reading resulted in increase to 63% (range, 56%-67%). With CAD used at a threshold allowing only three FP detections per CT scan, mean sensitivity was increased to 76% (range, 73%-78%). CAD complemented individual readers by detecting additional nodules more effectively than did a second reader; CAD-reader weighted kappa values were significantly lower than reader-reader weighted kappa values (Wilcoxon rank sum test, P < .05). CONCLUSION: With CAD used at a level allowing only three FP detections per CT scan, sensitivity was substantially higher than with conventional double reading.

Adolescent↗
PubMed2004

Parallel imaging of the abdomen.

Parallel imaging holds great potential for improving the quality of diagnostic abdominal MRI. The increased imaging speed afforded by parallel imaging can be translated into the obvious benefits of reduced scan time with set resolution and coverage, improved spatial resolution with set imaging time and coverage, increased anatomic coverage for a set imaging time and resolution, or some combination of the above. Additionally, the reduction in scan time can also allow some sequences that normally require multiple breath-holds to be performed with only one, or simply make breath-hold imaging possible for more patients. The decreased echo-train length allows for truer T2-weighting, less magnetic susceptibility artifact, and less blurring with echo-train imaging. Dynamic contrast-enhanced sequences can be acquired with improved temporal or spatial resolution. All of these potential advantages come with the trade-off of decreased signal-to-noise ratio, but for many patients, the benefits far outweigh the drawbacks and can vastly improve the diagnostic quality of abdominal MRI.

Artifacts↗
PubMed2003

Multidetector CT of pancreatic adenocarcinoma: diagnostic advances and therapeutic relevance.

Detection and staging of pancreatic malignancies remains a challenge for radiologists. Considering the poor prognosis of pancreatic adenocarcinoma, accurate preoperative staging is the key to a possibly curative surgical treatment. Contrast-enhanced helical CT has been the most commonly used for evaluation of pancreatic cancer in many institutions, although it suffers from many limitations. With the fast pace of advances in multidetector CT (MDCT), and the beginning clinical implementation of 16-row scanners, improvements in spatial resolution in the z-axis with near-isotropic imaging provide exquisite multiplanar reconstructions of pancreatic anatomy. This article provides an overview of current MDCT technique and protocols for assessment of pancreatic adenocarcinoma, and describes new 3D-display methods for effective visualization of large data sets provided by MDCT.

Carcinoma, Pancreatic Ductal↗
PubMed2003

Single breath-hold diffusion-weighted imaging of the abdomen.

PURPOSE: To generate high quality diffusion-weighted images (DWI) and corresponding isotropic ADC maps of the abdomen with full organ (kidneys) coverage in a single breath-hold. MATERIALS AND METHODS: DWI was performed in 12 healthy subjects with an asymmetric, spin-echo, single-shot EPI readout on a system with high performance gradients (40 mT/minute). The isotropic diffusion coefficient was measured from maps and SNR was determined for both diffusion-weighted and reference images in the liver, spleen, pancreas, and kidneys. In six patients, single-axis diffusion encoding along three orthogonal axes (12 NEX) was employed to assess anisotropic diffusion in kidneys. RESULTS: This technique yielded images of quality and resolution which compares favorably to that of prior work. SNR ranged from 27.0 in liver to 44.1 in kidneys for the diffusion-weighted images, and from 19.6 in liver to 39.0 in kidneys in reference images. ADCs obtained in the renal medulla, renal cortex, liver, spleen, and pancreas were (2091 +/- 55) x 10(-6), (2580 +/- 53) x 10(-6), (1697 +/- 52) x 10(-6), (1047 +/- 82) x 10(-6), and (2605 +/- 168) x 10(-6) mm(2)/second, respectively (mean +/- SE). Apparent diffusion coefficient (ADC) in the renal medulla and cortex were significantly different by paired t-test (P = 4.22 x 10(-10)). Renal medulla and cortex yielded anisotropy indices (AI) of 0.129 and 0.067, respectively. CONCLUSIONS: 1) Single-shot SE EPI DWI in the abdomen with this technique provides high quality images and maps with full organ coverage in a single breath-hold; 2) ADCs obtained in the renal medulla and cortex are significantly different; and 3) diffusion within the renal medulla is moderately anisotropic.

Abdomen↗
PubMed2003

Early experience with computed tomographic angiography in microsurgical reconstruction.

Preoperative angiography is frequently used in the planning of microsurgical reconstruction. However, several potentially devastating complications can result from angiography, including arterial occlusion and pseudoaneurysm. Computed tomographic angiography is a relatively new technique that can provide detailed information about vascular anatomy as well as soft and bony tissue without the risks of traditional angiography. In addition, three-dimensional image reconstruction uniquely demonstrates anatomical relationships among blood vessels, bones, and soft tissue. Fourteen computed tomographic angiograms were obtained in 10 patients undergoing microsurgical reconstruction of the head and neck, lower extremity, or upper extremity. The average patient age was 46.9 years (range, 22 to 67 years). Charges related to the computed tomographic procedure were compared with those of conventional preoperative imaging for microsurgical repair. At our institution, the average computed tomographic angiogram charge was 1140 US dollars, whereas the average charge for traditional arteriography was 3900 US dollars. When compared with intraoperative evaluation, computed tomographic angiograms demonstrated clinically relevant surgical anatomy. No complications were noted for the radiographic procedure or after free flap reconstruction. Computed tomographic angiography provides high-resolution, three-dimensional arterial, venous, and soft-tissue imaging without the risks of traditional angiogram and at a lower cost.

Adult↗
PubMed2002

CT angiography of the arterial system.

CTA has become an important diagnostic tool in the evaluation of vascular diseases in virtually all parts of the body. Whereas CTA is able to provide images depicting exquisite anatomic detail, careful scanning technique and selection of scan parameters are critical for high quality studies. The choices to be made when prescribing a scan can seem daunting at first, but if one applies the principles outlined previously, CTA can be a relatively easy, fast, and safe diagnostic technique that is effective in the majority of patients with vascular disease.

Angiography↗
PubMed2002

Isoattenuating pancreatic adenocarcinoma at multi-detector row CT: secondary signs.

PURPOSE: To assess the frequency of isoattenuating pancreatic adenocarcinoma with multi-detector row computed tomography (CT) and determine whether there are specific secondary signs that aid in detection. MATERIALS AND METHODS: Fifty-three patients with pancreatic adenocarcinoma underwent contrast material-enhanced biphasic multi-detector row CT with curved planar reformation. Tumors were initially deemed isoattenuating or hypoattenuating to normal pancreatic parenchyma on the basis of visual inspection, and the degree of attenuation was confirmed by calculating the mean attenuation differences between normal pancreatic parenchyma and tumor (tumor-pancreas contrast) during the pancreatic phase. Indirect signs of pancreatic tumor were tabulated in patients with an isoattenuating tumor. RESULTS: Of the 53 patients, six (11%) had isoattenuating tumors with a mean tumor-pancreas contrast of 9.25 HU +/- 11.3 during the pancreatic phase and 4.15 HU +/- 8.5 during the portal venous phase. The secondary signs of pancreatic tumor in these six patients included an interrupted pancreatic duct (n = 5), dilated biliary and pancreatic ducts (n = 1), atrophic distal pancreatic parenchyma (n = 3), and mass effect and/or convex contour abnormality (n = 3). The mean tumor-pancreas contrast for the remaining 47 patients was 74.76 HU +/- 35.61 during the pancreatic phase. CONCLUSION: With no visible tumor-pancreas contrast for isoattenuating tumors, indirect signs such as mass effect, atrophic distal parenchyma, and an interrupted duct sign are important indicators for the presence of tumor.

Adenocarcinoma↗
PubMed2002

Local staging of pancreatic carcinoma with multi-detector row CT: use of curved planar reformations initial experience.

PURPOSE: To evaluate the utility of curved planar reformations compared with standard transverse images in the assessment of pancreatic tumors. MATERIALS AND METHODS: Forty-three patients suspected of having pancreatic tumors underwent contrast material-enhanced biphasic multi-detector row computed tomography (CT). Curved planar reformations were generated along the pancreatic duct, common bile duct, and major mesenteric vessels. Three blinded independent readers assessed the curved planar reformations and transverse images separately for the presence of tumor, resectability, and vascular involvement. The results were compared with those of a consensus panel who evaluated the curved planar reformations and transverse images together along with clinical data and surgical findings. RESULTS: Of 43 patients, 20 had pancreatic malignancies as judged by the consensus panel and proven at biopsy and/or clinical follow-up. For tumor detection, transverse images and curved planar reformations had an average sensitivity of 95.0% and 98.4% (P >.05), respectively, and an average specificity of 90.9% and 91.3% (P >.05), respectively. For tumor resectability, transverse images and curved planar reformations had an average sensitivity of 85.7% and 71.4% (P >.05), respectively, and an average specificity of 85.2% and 84.3% (P >.05), respectively. Average interpretation time was 6.4 minutes with transverse images and 4.1 minutes with curved planar reformations. CONCLUSION: Curved planar reformations are equivalent to transverse images in the detection of pancreatic tumors and determination of surgical resectability.

Adenocarcinoma↗
PubMed2002

[Radiological study of temporal bone in children with profound deafness before cochlear implant: CT vs magnetic resonance imaging].

OBJECTIVE: To evaluate the clinical application of magnetic resonance imaging (MRI) and CT in children with profound deafness before cochlear implant and their impact on surgical decision. METHODS: The pre-operative CT and MRI data from 71 children with bilateral profound deafness planned for cochlear implant were studied. RESULTS: 12 patients showed enlarged vestibular aqueduct (16.9%); 14 patients had Mondini malformation (19.7%); 3 patients demonstrated enlarged internal auditory meatus (4.2%); and 2 patients were suspected to have fistulae (2.8%) on both CT and MRI examinations. In comparison between MRI and CT, unilateral cochlear fibrosis was detected in 5 patients(7%) by MRI, but none by CT scans. Bilateral dehiscent facial nerve was detected in 1 patient(1.4%) by CT scan, while MRI was normal. CONCLUSION: CT and MRI are essential for the pre-operative planning of cochlear implant, especially in patients with enlarged vestibular aqueduct, Mondini malformation, enlarged internal auditory meatus and suspected fistulae. These two imaging modalities are complementary to each other in cases with cochlear fibrosis and facial nerve dehiscence.

Child↗
PubMedDate not supplied

CT angiography of the subclavian artery: utility of curved planar reformations.

Despite advances in the diagnosis and treatment of peripheral vascular occlusive disease, an ever-aging population continues to provide scores of new cases requiring medical care. While traditional angiography has been the mainstay of diagnosis for many years, newer, less invasive techniques such as CT angiography with three-dimensional reformation are rapidly establishing themselves as first-line diagnostic modalities. We present a case of severe left subclavian artery stenosis that demonstrates the utility of curved planar reformation in providing a concise visual summary of the pertinent anatomy and abnormalities.

Angiography↗