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PubMed1987

The dynamic response of cat gastrocnemius motor units investigated by ramp-current injection into their motoneurones.

1. The isometric force developed by single motor units in response to injection of ramp-and-hold currents into their motoneurones was recorded from the common tendon of the gastrocnemius muscles of the cat. The average rate of rise of the force (force-slope) produced by the ramp-evoked discharge, was found to grow almost linearly with the rate of current injection (current-slope) up to a saturation value (maximal force-slope). 2. The slope of the function which links the force slope to the current-slope is the gain (dF/dI) of the motor unit under dynamic conditions. The value of the dynamic gain, measured in the linear region of growth, displays a large variability, i.e. for each nanoampere of current injected, the force developed is as much as 40 times larger in the strongest than in the weakest motor units. Such large gain differences, however, are drastically reduced if the force is expressed as a percentage of the maximal tetanic tension, Ft: per nanoampere injected, most of the units deliver from 1.0 to 3.0% of Ft. 3. The maximal force-slope which each unit could reach exhibits a large variability, ranging from 0.06 to 4.0 g ms-1. Like the dynamic gain, the maximal force-slope is positively related to Ft. 4. It was found that the dynamic sensitivity of the motoneurone, i.e. the increase of the firing rate per unitary increase of the current-slope, governs the fractional growth of the force-slope, whereas the motor unit contraction time determines the firing rate at which maximal force-slope is reached. Together, the two factors co-operate in defining, for each motor unit, the range of input-slopes within which the force-slope is regulated. 5. The motoneurones which supply the weak motor units, those with the lowest dynamic gain, have higher dynamic sensitivity and lower rheobase than those innervating the strong motor units. This suggests that weak motor units need less synaptic current both to be recruited and to reach the maximal speed of force development when their input is supraliminal.

Action Potentials↗
PubMed2006

Static and dynamic gamma-motor output to ankle flexor muscles during locomotion in the decerebrate cat.

In locomotion, the flexor muscles of the leg are mainly concerned with the relatively constant task of raising the foot, whereas the extensors have the more variable task of support and propulsion at different speeds. This suggests that the way in which the fusimotor system works may differ between the two muscle groups. Observations previously made of the static and dynamic gamma-motor firing patterns in the ankle extensor medial gastrocnemius (MG) have therefore been repeated in the flexor tibialis anterior (TA). One or more single gamma-motor axons, dissected from a small filament of TA nerve, were recorded simultaneously with a number of single spindle afferents in dorsal rootlets. Cats were decerebrated and locomoted spontaneously on a treadmill. Identification of each gamma-motor axon depended on relating the changes in firing caused by midbrain stimulation to the changes in static and dynamic behaviour of the spindle afferents in response to repetitive ramp and hold stretches. Static gamma axons all showed a smooth modulation in frequency, increasing in phase with muscle shortening, superimposed on a minimum frequency of about 20-30 impulses s(-1). Dynamic gamma axons showed interrupted firing with the frequency rising abruptly from zero at the onset of shortening, and falling again to zero shortly after the onset of lengthening. The frequency during the active periods was relatively constant, even when movement amplitudes varied. The basic similarity in the static and dynamic gamma discharge patterns for the two muscles suggests that the strategy of gamma-motor control is common to both flexors and extensors. The static gamma pattern is thought to be a 'temporal template' of the expected movement, effectively expanding the dynamic response range of the spindles in active movements. The dynamic gamma pattern sensitizes the primary afferents to detect the onset of muscle lengthening and to detect departures from the intended movement trajectory.

Action Potentials↗
PubMed2006

Dynamic clamp: a powerful tool in cardiac electrophysiology.

Dynamic clamp is a collection of closely related techniques that have been employed in cardiac electrophysiology to provide direct answers to numerous research questions regarding basic cellular mechanisms of action potential formation, action potential transfer and action potential synchronization in health and disease. Building on traditional current clamp, dynamic clamp was initially used to create virtual gap junctions between isolated myocytes. More recent applications include the embedding of a real pacemaking myocyte in a simulated network of atrial or ventricular cells and the insertion of virtual ion channels, either simulated in real time or simultaneously recorded from an expression system, into the membrane of an isolated myocyte. These applications have proven that dynamic clamp, which is characterized by the real-time evaluation and injection of simulated membrane current, is a powerful tool in cardiac electrophysiology. Here, each of the three different experimental configurations used in cardiac electrophysiology is reviewed. Also, directions are given for the implementation of dynamic clamp in the cardiac electrophysiology laboratory. With the growing interest in the application of dynamic clamp in cardiac electrophysiology, it is anticipated that dynamic clamp will also prove to be a powerful tool in basic research on biological pacemakers and in identification of specific ion channels as targets for drug development.

Action Potentials↗
PubMedDate not supplied

Dynamic details of disparity convergence eye movements.

Classically, the primary tool for quantifying the dynamics of vergence and other eye movements has been the main sequence. The main sequence is a plot of peak velocity versus response amplitude and is particularly useful for comparing the dynamics of a large number of eye movements over a range of response amplitudes. However, the main sequence represents only the equivalent first-order behavior of a response and does not describe its dynamics in detail. Since the main sequence is based on only two points on the dynamic trajectory, it is sensitive to measurement artifacts and noise. A new methodology is presented which quantifies the equivalent second-order dynamics of eye movements using a larger region of the transient response. These new indexes were applied to vergence eye movements and were found to differentiate between subtle, but important differences in movement dynamics.

Biomedical Engineering↗
PubMed1998

Static and dynamic bending responses of the human cervical spine.

The quasi-static and dynamic bending responses of the human mid-lower cervical spine were determined using cadaver intervertebral joints fixed at the base to a six-axis load cell. Flexion bending moment was applied to the superior end of the specimen using an electrohydraulic piston. Each specimen was tested under three cycles of quasi-static load-unload and one high-speed dynamic load. A total of five specimens were included in this study. The maximum intervertebral rotation ranged from 11.0 to 15.4 deg for quasi-static tests and from 22.9 to 34.4 deg for dynamic tests. The resulting peak moments at the center of the intervertebral joint ranged from 3.8 to 6.9 Nm for quasi-static tests and from 14.0 to 31.8 Nm for dynamic tests. The quasi-static stiffness ranged from 0.80 to 1.35 Nm/deg with a mean of 1.03 Nm/deg (+/- 0.11 Nm/deg). The dynamic stiffness ranged from 1.08 to 2.00 Nm/deg with a mean of 1.50 Nm/deg (+/- 0.17 Nm/deg). The differences between the two stiffnesses were statistically significant (p < 0.01). Exponential functions were derived to describe the quasi-static and dynamic moment-rotation responses. These results provide input data for lumped-parameter models and validation data for finite element models to better investigate the biomechanics of the human cervical spine.

Aged↗
PubMed1999

A poroelastic continuum model of the cupula partition and the response dynamics of the vestibular semicircular canal.

Using mixture theory, an axisymmetric continuum model is presented describing the response dynamics of the vestibular semicircular canals to canal-centered head rotation in which the cupula partition is modeled as a poroelastic mixture of interpenetrating solid and fluid constituents. The solid matrix of the cupula is assumed to behave as a linear elastic material, whereas the fluid constituent is assumed to be Newtonian. A regular perturbation analysis of the fluid dynamics in the canal provides a dynamic boundary condition, which acts across the cupula partition. Numerical solution of the coupled system of momentum equations provides the spatio-temporal displacement fields for both the fluid and solid constituents of the cupula. Results indicate that at frequencies above 1 Hz, the fluid constituent is dynamically entrained by the solid matrix such that their motions are bound as if to exist as a single component. The resulting high-frequency response is consistent with the macromechanical response predicted by single-component viscoelastic models of the cupula. Below 1 Hz, the dynamic coupling between the fluid and solid constituents weakens and the transcupular differential pressure is sufficient to force fluid through the mixture with little deformation of the solid matrix. Results are sensitive to the precise value of the cupular permeability. One of the most important distinctions between the present analysis and previous impermeable models of the cupula arises at the micromechanical level in terms of the local fluid flow that is predicted to occur within the cupula and around the ciliary bundles and sensory hair cells. Another important result reveals that the permeation dynamics predicted below 1 Hz gives rise to the same low-frequency macromechanical response as would occur with an impermeable viscoelastic structure having a much greater stiffness. Current estimates of the mechanical stiffness of the cupula, based solely on afferent nerve data, may therefore overestimate the true value intrinsic to the solid matrix by as much as an order of magnitude.

Animals↗
PubMed2002

A method for geometrical verification of dynamic intensity modulated radiotherapy using a scanning electronic portal imaging device.

In order to guarantee the safe delivery of dynamic intensity modulated radiotherapy (IMRT), verification of the leaf trajectories during the treatment is necessary. Our aim in this study is to develop a method for on-line verification of leaf trajectories using an electronic portal imaging device with scanning read-out, independent of the multileaf collimator. Examples of such scanning imagers are electronic portal imaging devices (EPIDs) based on liquid-filled ionization chambers and those based on amorphous silicon. Portal images were acquired continuously with a liquid-filled ionization chamber EPID during the delivery, together with the signal of treatment progress that is generated by the accelerator. For each portal image, the prescribed leaf and diaphragm positions were computed from the dynamic prescription and the progress information. Motion distortion effects of the leaves are corrected based on the treatment progress that is recorded for each image row. The aperture formed by the prescribed leaves and diaphragms is used as the reference field edge, while the actual field edge is found using a maximum-gradient edge detector. The errors in leaf and diaphragm position are found from the deviations between the reference field edge and the detected field edge. Earlier measurements of the dynamic EPID response show that the accuracy of the detected field edge is better than 1 mm. To ensure that the verification is independent of inaccuracies in the acquired progress signal, the signal was checked with diode measurements beforehand. The method was tested on three different dynamic prescriptions. Using the described method, we correctly reproduced the distorted field edges. Verifying a single portal image took 0.1 s on an 866 MHz personal computer. Two flaws in the control system of our experimental dynamic multileaf collimator were correctly revealed with our method. First, the errors in leaf position increase with leaf speed, indicating a delay of approximately 0.8 s in the control system. Second, the accuracy of the leaves and diaphragms depends on the direction of motion. In conclusion, the described verification method is suitable for detailed verification of leaf trajectories during dynamic IMRT.

Algorithms↗
PubMed2000

Dynamic and omni wedge implementation on an Elekta SL linac.

The concommitant use of a multileaf collimator (MLC) and a wedge can result in conflicts in the optimal collimator angle if both MLC and wedge are fixed relative to one another. This is particularly true of linacs in which a single wedge orientation is provided. In this paper, a solution is provided that makes use of two orthogonal universal wedges (omni wedge). Although this technique can be applied regardless of the means by which the wedged fields are implemented, the measurements reported in this paper were performed using a fixed, internal mechanical wedge coupled with a dynamic wedge, formed by the motion of one of the backup jaws. An implementation of a dynamic wedge for the Elekta SL series of linear accelerators is presented. Results of measurements of the dosimetric characteristics of both the particular implementation of the dynamic wedge and of the omni field are presented. For the dynamic wedge, measurements were made of the wedge factor and dose profile as a function of field size and depth. In addition, the effects of variables, such as dynamic delivery technique and direction of diaphragm motion, on the dynamic wedge profiles were studied and discussed. For the omni wedge, measurements were made of the degree to which the mathematical formalism for describing an omni wedge matches the measured isodose distributions. Comparisons between mechanical wedge dose distributions and the omni wedge were also made.

Dose-Response Relationship, Radiation↗
PubMed2005

A feasibility study of Dynamic Phantom scanner for quality assurance of photon beam profiles at various gantry angles.

The effect of gantry rotation on beam profiles of photon and electron beams is an important issue in quality assurance for radiotherapy. To address variations in the profiles of photon and electron beams at different gantry angles, a Dynamic Phantom scanner composed of a 20 x 12 x 6 cm3 scanning Lucite block was designed as a cross-beam-profile scanner. To our knowledge, differences between scanned profiles acquired at different gantry angles with a small size Lucite block and those acquired a full-size (60 x 60 x 50 cm3) water phantom have not been previously investigated. We therefore performed a feasibility study for a first prototype Dynamic Phantom scanner without a gantry attachment mount. Radiation beams from a Varian LINAC 21EX and 2100C were used. Photon beams (6 MV and 18 MV) were shaped by either collimator jaws or a Varian 120 Multileaf (MLC) collimator, and electron beams (6 MeV, 12 MeV, and 20 MeV) were shaped by a treatment cone. To investigate the effect on profiles by using a Lucite block, a quantitative comparison of scanned profiles with the Dynamic Phantom and a full-size water phantom was first performed at a 0 degrees gantry angle for both photon and electron beams. For photon beam profiles defined by jaws at 1.0 cm and 5.0 cm depths of Lucite (i.e., at 1.1 cm and 5.7 cm depth of water), a good agreement (less than 1% variation) inside the field edge was observed between profiles scanned with the Dynamic Phantom and with a water phantom. The use of Lucite in the Dynamic Phantom resulted in reduced penumbra width (about 0.5 mm out of 5 mm to 8mm) and reduced (1% to 2%) scatter dose beyond the field edges for both 6 MV and 18 MV beams, compared with the water phantom scanner. For profiles of the MLC-shaped 6 MV photon beam, a similar agreement was observed. For profiles of electron beams scanned at 2.9 cm depth of Lucite (i.e., at 3.3 cm depth of water), larger disagreements in profiles (3% to 4%) and penumbra width (3 mm to 4 mm out of 12 mm) were observed. Additional profiles with the gantry at 90 degrees and 270 degrees were performed for both MLC- and jaw-shaped photon beams and electron beams to evaluate the effect of gantry rotation. General good agreement is seen (less than 1 % variation) at all field sizes for collimator-shaped 6 MV and 18 MV photon beams. Similar variations observed for MLC-shaped photon beams indicate that the uncertainty in MLC position is similar to that for the collimator jaws. We conclude that the Dynamic Phantom scanner is a useful device for the routine quality assurance on beam profiles of photon beams and for constancy check on electron beams at various gantry angles. Caution should be taken when using this device to acquire basic electron dosimetry data.

Equipment Design↗
PubMed2005

Dynamic soft tissue mobilisation increases hamstring flexibility in healthy male subjects.

OBJECTIVES: The purpose of this study was to investigate the effect of dynamic soft tissue mobilisation (STM) on hamstring flexibility in healthy male subjects. METHODS: Forty five males volunteered to participate in a randomised, controlled single blind design study. Volunteers were randomised to either control, classic STM, or dynamic STM intervention. The control group was positioned prone for 5 min. The classic STM group received standard STM techniques performed in a neutral prone position for 5 min. The dynamic STM group received all elements of classic STM followed by distal to proximal longitudinal strokes performed during passive, active, and eccentric loading of the hamstring. Only specific areas of tissue tightness were treated during the dynamic phase. Hamstring flexibility was quantified as hip flexion angle (HFA) which was the difference between the total range of straight leg raise and the range of pelvic rotation. Pre- and post-testing was conducted for the subjects in each group. A one-way ANCOVA followed by pairwise post-hoc comparisons was used to determine whether change in HFA differed between groups. The alpha level was set at 0.05. RESULTS: Increase in hamstring flexibility was significantly greater in the dynamic STM group than either the control or classic STM groups with mean (standard deviation) increase in degrees in the HFA measures of 4.7 (4.8), -0.04 (4.8), and 1.3 (3.8), respectively. CONCLUSIONS: Dynamic soft tissue mobilisation (STM) significantly increased hamstring flexibility in healthy male subjects.

Adolescent↗
PubMed1999

Disturbances of dynamic balance in phasic cervical dystonia.

OBJECTIVE: To quantitatively assess control of balance under static and dynamic conditions in patients with tonic and phasic cervical dystonia. METHODS: Ten patients with purely tonic cervical dystonia with fixed postural deviation and 20 patients with cervical dystonia with phasic head movements were investigated at least 3 months after botulinum toxin injections. Seventeen age matched volunteers served as controls. Static posturography was performed on a force platform; dynamic equilibrium was studied on a stabilometer, which requires the subject to continuously adapt upright posture to an unstable tilting surface. Measurements of maximum amplitude and linear displacement of the pivot were taken with open and closed eyes. RESULTS: Sway path values in static posturography were not significantly different between patients with cervical dystonia and controls. On dynamic posturography, patients with phasic cervical dystonia showed significantly higher platform measures (maximum amplitude and linear displacement of the pivot) with eyes open and closed By contrast, none of the dynamic platform measures differed significantly between patients with tonic cervical dystonia and controls. CONCLUSIONS: Normal measures of dynamic equilibrium in tonic cervical dystonia argue against a primary abnormality of balance control in cervical dystonia. Impaired dynamic equilibrium in phasic cervical dystonia is likely to reflect a disruption of vestibular input due to repetitive, involuntary head oscillations.

Adult↗
PubMed2003

Confinement effects on the slow dynamics of a supercooled polymer melt: Rouse modes and the incoherent scattering function.

Results of large-scale molecular-dynamics simulations of a supercooled polymer film are presented (F. Varnik, J. Baschnagel, K. Binder, J. Phys. IV 10, 239 (2000)). The dynamic and static properties of the system are studied for a wide range of film thicknesses (from 3 to about 55 times the bulk radius of gyration) and temperatures (from the normal liquid state to the supercooled region). The system is confined between two completely smooth and purely repulsive walls. Motivated by the previous results on the enhancement of the local relaxation dynamics due to the confinement (F. Varnik, J. Baschnagel, K. Binder, Eur. Phys. J. E 8, 175 (2002); Phys. Rev. E. 65, 021507 (2002)), we now study the effect of the walls on the dynamics of the Rouse modes. It has been reported from Monte Carlo studies of the Bond Fluctuation Model (BFM) that, contrary to the enhancement of the "cage dynamics" (exemplified by a faster relaxation of the incoherent scattering function in the film), Rouse modes exhibit a slower relaxation in the confined system (C. Mischler, J. Baschnagel, K. Binder, Adv. Colloid Interface Sci. 94, 197 (2001)). However, we do not observe such a discrepancy for our continuum model: At a given temperature, the relaxation of a given Rouse mode is faster in the film than in the bulk in accordance with the acceleration of the dynamics around the cage.

Computer Simulation↗
PubMed1998

Ultrafast solvation dynamics explored by femtosecond photon echo spectroscopies.

Chemical reaction and optical dynamics in the liquid phase are strongly affected by specific solute-solvent interactions. The dynamical part of this coupling leads to energy fluctuations. The associated energy gap dynamics can be probed by using various nonlinear optical spectroscopies. We discuss various forms of photon echo--time-integrated, time-gated, and heterodyne-detected photon echo--as well as Fourier transform spectral interferometry. It is shown that for solutions of the dye molecule DTTCI, a system-bath correlation function can be acquired that provides a quantitative description of all (non)linear spectroscopic experiments. The deduced correlation function is projected onto the multimode Brownian oscillator model, which allows for a physical interpretation of the multiple-time correlation function and a determination of the spectral density relevant to the solvation process. The following applications of photon echo to condensed phase dynamics are discussed: enhanced vibrational mode suppression, Liouville pathways interference, and dynamical Stokes shift. Recent results of echo-peak shift experiments on the hydrated electron are also presented. The review concludes that photon echo should be useful as a novel tool to explore transition state dynamics.

Journal Article↗
PubMed2006

Progress in the theory of mixed quantum-classical dynamics.

Quantum-classical Liouville dynamics can be used to study the properties of open quantum systems that are coupled to bath or environmental degrees of freedom whose dynamics can be approximated by classical equations of motion. In contrast to many open quantum system approaches, quantum-classical dynamics provides a detailed description of the bath molecules. Such a description is especially appropriate for the study of quantum rate processes, such as proton and electron transport, where the detailed dynamics of the bath has a strong influence on the quantum rate. The quantum-classical Liouville equation can also serve as a starting point for the derivation of reduced descriptions where all or some of the bath degrees of freedom are projected out. Quantum-classical Liouville dynamics can be simulated in terms of an ensemble of surface-hopping trajectories whose character differs from that in other surface-hopping schemes. The results of studies of proton transfer in condensed phase and reactive dynamics in a dissipative environment are presented to illustrate applications of the formalism.

Journal Article↗
PubMed2002

Functional and morphologic evaluation of congenital urinary tract dilatation by using combined static-dynamic MR urography: findings in kidneys with a single collecting system.

PURPOSE: To assess combined static-dynamic magnetic resonance (MR) urography in the evaluation of congenital urinary tract dilatation in infants and children. MATERIALS AND METHODS: Sixty-two patients with urinary tract dilatation underwent prospective examination with combined static-dynamic MR urography. A combination examination involved use of a static T2-weighted three-dimensional inversion-recovery fast spin-echo sequence and a dynamic T1-weighted two-dimensional fast field-echo sequence with gadopentetate dimeglumine-DTPA and furosemide application. Twelve additional patients underwent examination with only static MR urography. Thus, both image quality and morphologic features were assessed in 74 patients with the use of MR urography. The results were compared with those of ultrasonography and, when available, conventional urography or surgery. In 62 patients, the dynamic sequence was used to calculate split renal function from renograms generated from parenchymal regions of interest and to assess urinary excretion from whole-kidney renograms. Results were compared with those of diuretic renal scintigraphy (DRS) for split function (Spearman rank correlation coefficient) and urinary excretion (kappa coefficient). RESULTS: Stenoses at the ureteropelvic (n = 33) and ureterovesical (n = 31) junctions and within the ureter (n = 3) and nonstenotic dilatation (n = 23) were clearly depicted, while the normal urinary tract (n = 51) was depicted in its entirety in 47 of 51 examinations. Image quality was considered good or excellent in 95% of the kidney-ureter units. For split renal function, dynamic MR urography and DRS showed significant correlation (r = 0.92, P <.001). For urinary excretion, MR urography and DRS showed strong agreement (kappa = 0.67), with concordant classification of urinary excretion in 59 (81%) of 73 abnormal kidney-ureter units and in all 47 (100%) normal kidney-ureter units. CONCLUSION: Combined static-dynamic MR urography provides high-quality depiction of the urinary tract in infants and children, while allowing accurate determination of single-kidney function and reliable evaluation of urinary excretion.

Child↗
PubMed2003

Imaging of osteoid osteoma with dynamic gadolinium-enhanced MR imaging.

PURPOSE: To compare dynamic gadolinium-enhanced T1-weighted magnetic resonance (MR) imaging with nonenhanced T1-weighted and T2-weighted MR imaging and thin-section computed tomography (CT) for the demonstration of osteoid osteomas. MATERIALS AND METHODS: The images of 11 patients with pathologically proven osteoid osteomas who underwent nonenhanced MR imaging, dynamic gadolinium-enhanced MR imaging, and CT were retrospectively reviewed. Images obtained with all three techniques were scored for conspicuity of the osteoid osteoma relative to the surrounding bone. Time-enhancement curves were generated from signal intensity measurements of these lesions and the adjacent bone marrow. The mean imaging scores of the four techniques were compared, and the statistical significance was calculated by using a linear model with terms for method and patient. Pairwise comparisons were made by using the Tukey-Kramer adjustment for multiple comparisons. RESULTS: Compared with CT, dynamic gadolinium-enhanced MR imaging demonstrated the osteoid osteoma equally well in eight of 11 patients and with better conspicuity in three of 11 patients, although this difference was not statistically significant (P =.69). The dynamic gadolinium-enhanced MR images demonstrated the osteoid osteomas significantly better than the nonenhanced T1-weighted (P <.001) and T2-weighted (P <.001) MR images. On the dynamic gadolinium-enhanced MR images, nine (82%) of 11 patients had peak enhancement of the osteoid osteoma in the arterial phase with early partial washout, compared with slower, progressive enhancement of the adjacent marrow. This resulted in greatest lesion to marrow contrast material enhancement in the arterial phase. One osteoid osteoma had peak enhancement in the venous phase, and one showed progressive enhancement through all phases to 150 seconds. CONCLUSION: Osteoid osteomas can be imaged with greater conspicuity by using dynamic gadolinium-enhanced instead of nonenhanced MR imaging and with conspicuity equal to or better than that obtained with thin-section CT.

Adolescent↗
PubMed2004

Soft-tissue tumors: value of static and dynamic gadopentetate dimeglumine-enhanced MR imaging in prediction of malignancy.

PURPOSE: To prospectively evaluate static and dynamic gadopentetate dimeglumine-enhanced magnetic resonance (MR) imaging relative to nonenhanced MR imaging in differentiation of benign from malignant soft-tissue lesions and to evaluate which MR imaging parameters are most predictive of malignancy, with associated interobserver variability. MATERIALS AND METHODS: One hundred forty consecutive patients (78 male patients [median age, 51 years], 62 female patients [median age, 53 years]) with a soft-tissue mass underwent nonenhanced static and dynamic contrast material-enhanced MR imaging. Diagnosis was based on histologic findings in surgical specimens (86 of 140), findings at core-needle biopsy (43 of 140), or results of all imaging procedures with clinical follow-up (11 of 140). Multivariate logistic regression analysis was used to identify the best combination of MR imaging parameters that might be predictive of malignancy. Subjective overall performance of two observers was evaluated with receiver operating characteristic analysis. RESULTS: For subjective overall diagnosis, area under the receiver operating characteristic curve, a measure for diagnostic accuracy, was significantly larger for combined nonenhanced and contrast-enhanced MR imaging than it was for nonenhanced MR imaging alone, with no significant difference between observers. Multivariate analysis of all lesions revealed that combined nonenhanced static and dynamic contrast-enhanced MR imaging parameters were significantly superior to nonenhanced MR imaging parameters alone and to nonenhanced MR imaging parameters combined with static contrast-enhanced MR imaging parameters in prediction of malignancy. The most discriminating parameters were presence of liquefaction, start of dynamic enhancement (time interval between start of arterial and tumor enhancement), and lesion size (diameter). Results for extremity lesions were the same, with one exception: With dynamic contrast-enhanced MR imaging parameters, diagnostic performance of one observer did not improve. CONCLUSION: Static and dynamic contrast-enhanced MR imaging, when added to nonenhanced MR imaging, improved differentiation between benign and malignant soft-tissue lesions.

Adolescent↗
PubMed2006

Diagnostic architectural and dynamic features at breast MR imaging: multicenter study.

PURPOSE: To prospectively determine the prevalence and predictive value of three-dimensional (3D) and dynamic breast magnetic resonance (MR) imaging and contrast material kinetic features alone and as part of predictive diagnostic models. MATERIALS AND METHODS: The study protocol was approved by the institutional review board or ethics committees of all participating institutions, and informed consent was obtained from all participants. Although study data collection was performed before HIPAA went into effect, standards that would be compliant with HIPAA were adhered to. Data from the International Breast MR Consortium trial 6883 were used in the analysis. Women underwent 3D (minimum spatial resolution, 0.7 x 1.4 x 3 mm; minimal temporal resolution, 4 minutes) and dynamic two-dimensional (temporal resolution, 15 seconds) MR imaging examinations. Readers rated enhancement shape, enhancement distribution, border architecture, enhancement intensity, presence of rim enhancement or internal septations, and the shape of the contrast material kinetic curve. Regression was performed for each feature individually and after adjustment for associated mammographic findings. Multivariate models were also constructed from multiple architectural and dynamic features. Areas under the receiver operating characteristic curve (Az values) were estimated for all models. RESULTS: There were 995 lesions in 854 women (mean age, 53 years +/- 12 [standard deviation]; range, 18-80 years) for whom pathology data were available. The absence of enhancement was associated with an 88% negative predictive value for cancer. Qualitative characterization of the dynamic enhancement pattern was associated with an Az value of 0.66 across all lesion architectures. Focal mass margins (Az = 0.76) and signal intensity (Az = 0.70) were highly predictive imaging features. Multivariate models were constructed with an Az value of 0.880. CONCLUSION: Architectural and dynamic features are important in breast MR imaging interpretation. Multivariate models involving feature assessment have a diagnostic accuracy superior to that of qualitative characterization of the dynamic enhancement pattern.

Adolescent↗