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Biomedical subjects

R D Howe

Publications and source records attributed to R D Howe.

7 recordsLinked to original sources
PubMed2001

Tactile imaging of breast masses: first clinical report.

HYPOTHESIS: Tactile imaging can accurately document the palpable extent of breast masses. DESIGN: Prospective nonrandomized interventional trial, comparing mass size estimates from preoperative physical examination, ultrasound, and tactile imaging with postoperative measurements of the resected masses. SETTING: A community ambulatory surgical center and a university hospital tertiary care center. PATIENTS: Twenty-three women undergoing surgical excision of breast masses. All subjects had a single, palpable, dominant mass, 0.5 to 3 cm in diameter. INTERVENTION: Prior to surgery, the size of each mass was estimated from tactile imaging using an array of pressure sensors that is stroked over the mass. Size was also estimated by ultrasound and physical examination. Immediately following resection of the mass, it was bisected, and the palpable extent was measured with a caliper. MAIN OUTCOME MEASURE: Maximum mass diameter estimates from ultrasound, physical examination, and tactile imaging, compared with the resected measurement. RESULTS: Tactile imaging estimates were repeatable (7.5% mean SD for multiple estimates of the same mass) and show good agreement with the resected measurements. Mean absolute error was 13%, and linear regression with zero intercept had a slope of 0.94, r(2) = 0.51. Physical examination and ultrasound estimates had respective mean absolute errors of 46% and 34%, regression slopes of 1.27 and 0.89, and r(2) = 0.28 and 0.37. CONCLUSIONS: Tactile imaging can provide accurate and reproducible estimates of the size of breast masses. This capability can enhance cancer surveillance for patients with benign masses (eg, due to scarring or fibrocystic changes) because previous work suggests that reliable detection of a difference in mass size by physical examination requires a 40% change in diameter. In contrast, this study suggests tactile imaging requires only a 15% change (95% confidence interval).

Breast Neoplasms↗
PubMed2001

THOMAS MCMAHON: A Dedication in Memoriam.

Thomas A. McMahon (1943-1999) was a pioneer in the field of biomechanics. He made primary contributions to our understanding of terrestrial locomotion, allometry and scaling, cardiac assist devices, orthopedic biomechanics, and a number of other areas. His work was frequently characterized by the use of simple mathematical models to explain seemingly complex phenomena. He also validated these models through creative experimentation. McMahon was a successful inventor and also published three well-received novels. He was raised in Lexington, Massachussetts, attended Cornell University as an undergraduate, and earned a PhD at MIT. From 1970 until his death, he was a member of the faculty of Harvard University, where he taught biomedical engineering. He is fondly remembered as a warm and gentle colleague and an exemplary mentor to his students.

Journal Article↗
PubMed1999

Dynamic contact of the human fingerpad against a flat surface.

This paper investigates the dynamic, distributed pressure response of the human fingerpad in vivo when it first makes contact with an object. A flat probe was indented against the fingerpad at a 20 to 40 degree angle. Ramp-and-hold and sinusoidal displacement trajectories were applied to the fingerpad within a force range of 0-2 N. The dynamic spatial distribution of the pressure response was measured using a tactile array sensor. Both the local pressure variation and the total force exhibited nonlinear stiffness (exponential with displacement) and significant temporal relaxation. The shape of the contact pressure distribution could plausibly be described by an inverted paraboloid. A model based on the contact of a rigid plane (the object) and a linear viscoelastic sphere (the fingerpad), modified to include a nonlinear modulus of elasticity, can account for the principal features of the distributed pressure response.

Adult↗
PubMed1999

Dynamic lumped element response of the human fingerpad.

The dynamic response of the fingerpad plays an important role in the tactile sensory response and precision manipulation, as well as in ergonomic design. This paper investigates the dynamic lumped element response of the human fingerpad in vivo to a compressive load. A flat probe indented the fingerpad at a constant velocity, then held a constant position. The resulting force (0-2 N) increased rapidly with indentation then relaxed during the hold phase. A quasilinear viscoelastic model successfully explained the experimental data. The instantaneous elastic response increased exponentially with position, and the reduced relaxation function included three decaying exponentials (with time constants of approximately 4 ms, 70 ms, and 1.4 s) plus a constant. The model was confirmed with data from sinusoidal displacement trajectories.

Acceleration↗
PubMed1999

Robotics for surgery.

Robotic technology is enhancing surgery through improved precision, stability, and dexterity. In image-guided procedures, robots use magnetic resonance and computed tomography image data to guide instruments to the treatment site. This requires new algorithms and user interfaces for planning procedures; it also requires sensors for registering the patient's anatomy with the preoperative image data. Minimally invasive procedures use remotely controlled robots that allow the surgeon to work inside the patient's body without making large incisions. Specialized mechanical designs and sensing technologies are needed to maximize dexterity under these access constraints. Robots have applications in many surgical specialties. In neurosurgery, image-guided robots can biopsy brain lesions with minimal damage to adjacent tissue. In orthopedic surgery, robots are routinely used to shape the femur to precisely fit prosthetic hip joint replacements. Robotic systems are also under development for closed-chest heart bypass, for microsurgical procedures in ophthalmology, and for surgical training and simulation. Although results from initial clinical experience is positive, issues of clinician acceptance, high capital costs, performance validation, and safety remain to be addressed.

Biomedical Engineering↗
PubMed1997

Identification of the mechanical impedance at the human finger tip.

Rapid transients were applied to the outstretched human index finger tip, which resulted in motion primarily at the metacarpophalangeal (MCP) joint in extension and in abduction. A second-order linear model was fit to approximately 20 milliseconds of the force and displacement data to determine the effective mechanical impedance at the finger tip. Ranges of mass, damping, and stiffness parameters were estimated over a range of mean finger tip force (2-20 N for extension, 2-8 N for abduction). Effective translational finger tip mass for each subject was relatively constant for force levels greater than 6 N for extension, and constant throughout the abduction trials. Stiffness increased linearly with muscle activation. The estimated damping ratio for extension trials was about 1.7 times the ratio for abduction.

Acceleration↗