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Biomedical subjects

M A Haider

Publications and source records attributed to M A Haider.

8 recordsLinked to original sources
PubMed2004

Triple-phase MDCT of hepatocellular carcinoma.

OBJECTIVE: The purpose of this study was to describe the appearances of hepatocellular carcinoma including intralesional contrast washout using a triple-phase liver protocol on an MDCT scanner. MATERIALS AND METHODS: Fifty-one patients with newly diagnosed hepatocellular carcinoma underwent standardized triple-phase CT using a multidetector scanner. Pathologic proof was obtained in 35 patients (69%); in 16 patients (31%), hepatocellular carcinoma was diagnosed on clinical and laboratory findings. Two radiologists independently reviewed the CT studies for the appearance and attenuation of the lesions. Intralesional washout of contrast material was evaluated subjectively and objectively. Statistical analysis was performed using Fisher's exact test to analyze the relationships between tumor appearance and alpha-fetoprotein level, tumor grade, and risk factor. Correlation between tumor size and appearance was analyzed using the Student's t test and Wilcoxon's rank sum test. RESULTS: The most common enhancement pattern for hepatocellular carcinoma was hypervascularity on hepatic arterial phase images with a mosaic pattern on both arterial and portal venous images; this finding was seen in 86% and 78% of lesions by the two observers, respectively. A hypervascular component was seen in 96% of lesions by both observers, and the observers recorded 86% and 63% of lesions as showing washout, respectively. Objective washout was present in 76% of lesions. Both subjective and objective washout correlated with an elevated alpha-fetoprotein level (p = 0.01). CONCLUSION: The appearances of hepatocellular carcinoma on images obtained using MDCT scanners are similar to those described for images obtained using single-detector helical scanners. However, the prevalence of hypervascular hepatocellular carcinoma on MDCT images is higher than previously described on single-detector helical images and most lesions showed washout on portal venous MDCT images.

Adult↗
PubMed2001

Perineural cysts presenting as complex adnexal cystic masses on transvaginal sonography.

OBJECTIVE: This study describes the sonographic features of sacral perineural cysts that initially presented as adnexal complex cystic masses on transvaginal sonography. CONCLUSION: Perineural cysts may have a complex cystic appearance, including septation and internal debris, on transvaginal sonography. The extraovarian, extraperitoneal, and posterior location on real-time sonography are suggestive features.

Adnexal Diseases↗
PubMed2000

An axisymmetric boundary integral model for incompressible linear viscoelasticity: application to the micropipette aspiration contact problem.

The micropipette aspiration test has been used extensively in recent years as a means of quantifying cellular mechanics and molecular interactions at the microscopic scale. However, previous studies have generally modeled the cell as an infinite half-space in order to develop an analytical solution for a viscoelastic solid cell. In this study, an axisymmetric boundary integral formulation of the governing equations of incompressible linear viscoelasticity is presented and used to simulate the micropipette aspiration contact problem. The cell is idealized as a homogeneous and isotropic continuum with constitutive equation given by three-parameter (E, tau 1, tau 2) standard linear viscoelasticity. The formulation is used to develop a computational model via a "correspondence principle" in which the solution is written as the sum of a homogeneous (elastic) part and a nonhomogeneous part, which depends only on past values of the solution. Via a time-marching scheme, the solution of the viscoelastic problem is obtained by employing an elastic boundary element method with modified boundary conditions. The accuracy and convergence of the time-marching scheme are verified using an analytical solution. An incremental reformulation of the scheme is presented to facilitate the simulation of micropipette aspiration, a nonlinear contact problem. In contrast to the halfspace model (Sato et al., 1990), this computational model accounts for nonlinearities in the cell response that result from a consideration of geometric factors including the finite cell dimension (radius R), curvature of the cell boundary, evolution of the cell-micropipette contact region, and curvature of the edges of the micropipette (inner radius a, edge curvature radius epsilon). Using 60 quadratic boundary elements, a micropipette aspiration creep test with ramp time t* = 0.1 s and ramp pressure p*/E = 0.8 is simulated for the cases a/R = 0.3, 0.4, 0.5 using mean parameter values for primary chondrocytes. Comparisons to the half-space model indicate that the computational model predicts an aspiration length that is less stiff during the initial ramp response (t = 0-1 s) but more stiff at equilibrium (t = 200 s). Overall, the ramp and equilibrium predictions of aspiration length by the computational model are fairly insensitive to aspect ratio a/R but can differ from the half-space model by up to 20 percent. This computational approach may be readily extended to account for more complex geometries or inhomogeneities in cellular properties.

Biomechanical Phenomena↗
PubMed1997

A mathematical approximation for the solution of a static indentation test.

The classical contact problem of the indentation of a thin compressible linear elastic layer bonded to a rigid substrate is considered. Closed-form mathematical approximations of the deformation are presented for the cases of plane indentation by a rectangular block and three dimensional indentation by a plane-ended (axisymmetric) cylinder. The approximations are analyzed in the context of a static indentation test by comparison of applied load values to those obtained using a classical integral transform solution. In the case of plane indentation, the mathematical and classical predictions agree to within 2% relative error for aspect ratios between 0.1 and 1.0 and apparent Poisson ratio between 0.0 and 0.3. Comparisons for the axisymmetric case indicate a similar pattern. The main advantage of the new approach is that it yields closed-form approximations of the static indentation solution which can also capture the essential singular behavior.

Animals↗
PubMed1995

The role of intraoperative ultrasonography in planning the resection of hepatic neoplasms.

OBJECTIVE: Both intraoperative ultrasonography (US) and computed tomography with arterial portography (CTAP) may be used in planning segment-oriented liver resection in patients with primary or secondary hepatic neoplasms. This study was conducted to determine if intraoperative US findings substantially alter surgical plans based on CTAP findings alone. PATIENTS AND METHODS: Patients with potentially resectable hepatic lesions were considered for the study; judgement as to whether a lesion was resectable was based on a clinical evaluation and CTAP. Over the period Apr. 4, 1991, to Oct. 1, 1993, 24 consecutive patients with hepatic lesions were examined; of these, 22 (13 men and 9 women with a mean age of 60.1 years) underwent US during resection, 1 did not undergo surgery and 1 was found at surgery to have carcinomatosis. The true nature of the lesions was verified pathologically or by follow-up imaging and assays for carcinoembryonic antigen. RESULTS: The surgical plan based on CTAP findings alone was altered by the intraoperative US findings in 9 (41%) of the 22 patients. A total of 60 intrahepatic abnormalities were evaluated: 49 malignant lesions and 11 artifacts. The specificity (100%) and negative predictive value (73.3%) for intraoperative US were significantly greater than for CTAP (specificity of 9.1% and negative predictive value of 14.1%). CONCLUSION: In a substantial proportion of patients undergoing hepatic resection, intraoperative US alters the surgical plan based on CTAP and provides additional specificity in the evaluation of liver lesions. This method of imaging is therefore justified for patients undergoing liver resection.

Female↗