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W Froncisz

Publications and source records attributed to W Froncisz.

At least 19 recordsLinked to original sources
PubMed1992

Theoretical studies on the control of the oxidative phosphorylation system.

The dynamic model developed in our previous publications [1,2] was used to calculate the flux control coefficients of oxidation, phosphorylation and proton leak fluxes for isolated mitochondria and for three modes of work of intact cells (hepatocytes). The results obtained were compared with experimental data, especially those measured in the frame of the 'top-down approach' of the metabolic control theory. A good agreement for mitochondria and for intact cells was found. The control of the oxygen consumption flux is shared between the ATP utilization (main controlling factor), substrate dehydrogenation, proton leak and, in some conditions, the ATP/ADP carrier. The phosphorylation subsystem seemed to be controlled mainly by itself, while the proton leak was influenced by all three subsystems. It was also shown that the large relative change in the enzyme activity during inhibitor titration of mitochondria or cells could lead to the overestimation of some flux control coefficient values in experimental measurements. An influence of some hormones (glucagon, vasopressin, adrenaline and others) on the mitochondrial respiration was also simulated. Our results suggest that these hormones stimulate the substrate dehydrogenation as well as the phosphorylation system (ATP usage and, possibly, the ATP/ADP carrier).

Adenosine Triphosphate↗
PubMed1991

An extended dynamic model of oxidative phosphorylation.

The presented model based on an earlier one (Korzeniewski, B. and Froncisz, W. (1989) Studia Biophys. 132, 173-187) simulates concentration changes in time of chemical compounds and thermodynamic forces during respiration of cell suspension in a closed chamber. A set of differential equations solved numerically describes the utilization of oxygen up to anaerobiosis and the behaviour of the system after a sudden pulse of oxygen. Flux control coefficients for most important reactions (enzymes) of oxidative phosphorylation were calculated. A good qualitative and (when a direct comparison is possible) quantitative agreement with experimental results can be observed. The following conclusions can be drawn from the simulation: (1) Wilson's steady state model is not in contradiction with sharing of the control over the respiration between some steps and displacement of the ATP/ADP carrier from equilibrium. (2) The overshoot characteristics of the delta microH+ time-course after reoxygenation can be explained without using the lag-phase kinetics of ATP-synthetase. (3) A 'hot region' (sharp changes of many parameters) can be distinguished when the oxygen concentration approaches zero; only cytochrome oxidase is clearly sensitive on oxygen concentration in all its range. (4) Control over oxidative phosphorylation is shared mainly between inputs of the system (ATP utilization and substrate dehydrogenation) and the proton leak.

Adenine Nucleotides↗
PubMed1991

Noise correlation.

Calculations and experiments that provide support for our previously stated theorem are presented: If two coils simultaneously receiving magnetic resonance signals from the same anatomic region exhibit zero mutual inductance, there can be no correlation of the noise. It is shown that correlation does not exist even in the presence of mutual inductance unless the two signal paths have amplifiers prior to signal combination. It is further found that in the presence of mutual inductance with ideal amplifiers (0 dB noise figure) in the two signal paths, there is no correlation of noise. In order to satisfy the condition of zero mutual inductance, it may be necessary to employ a decoupling circuit external to the body. A novel coil assembly, which was used in the experiments, places a single-turn surface coil in the median plane between the two loops of a counter rotating current coil. The signal-to-noise ratio can be improved by combining signals. This is in analogy to quadrature receiving coils, where the mutual inductance is zero because vector reception fields are perpendicular. In the present geometry, vector reception fields are collinear, but are parallel and antiparallel on the two sides of the coil assembly, resulting in zero mutual inductance.

Amplifiers, Electronic↗
PubMed1989

Conformation of spin-labeled melittin at membrane surfaces investigated by pulse saturation recovery and continuous wave power saturation electron paramagnetic resonance.

Melittin spin-labeled specifically with a nitroxide at positions 7, 21, 23, or the amino terminus was bound to phospholipid membranes, and the exposure of the spin label to the aqueous phase was investigated by measurement of Heisenberg exchange with chromium oxalate in the solution. The exchange frequency was determined by saturation recovery electron paramagnetic resonance (EPR) using a loop-gap resonator. This method allows use of very low concentrations (less than 1 mM) of chromium oxalate compared with conventional measurements of EPR line broadening (typically 50 mM), thus avoiding problems associated with high metal ion concentration. Differences in exchange frequency between the various positions were also estimated by continuous wave power saturation methods. In either approach, the spin label at lysine 7 was found to be the most exposed to chromium oxalate whereas that at lysine 23 was found to be the least exposed. This is consistent with a model for the membrane bound peptide in which an amphiphilic helix lies with its axis parallel to the bilayer surface and the hydrophobic moment points toward the bilayer interior.

Amino Acid Sequence↗
PubMed1989

Gated cardiac MR imaging and P-31 MR spectroscopy in humans at 1.5 T. Work in progress.

The authors describe a technique to acquire gated cardiac proton magnetic resonance images and localized hydrogen-1 and phosphorus-31 spectra with a doubly tuned surface coil probe. The probe reduces study time because the need to exchange imaging and spectroscopy coils is eliminated, while at the same time the sensitivity of singly tuned coils is retained. In addition, the probe enhances the ability of the investigator to localize cardiac spectra spatially and temporally during the cardiac cycle. Spectra were acquired from the left ventricular myocardium in five volunteers, and systolic and diastolic gated P-31 spectra were shown.

Humans↗
PubMed1988

Simultaneous image acquisition from the head (or body) coil and a surface coil.

Any number of coils can in principle be used simultaneously and independently in magnetic resonance imaging if the mutual inductances are sufficiently small. Surface coils and head or body coils have equal sensitivity at some crossover depth of the order of 6 to 10 cm. Using a 7.5-cm-diameter surface coil that was intrinsically isolated from the head coil, images were acquired simultaneously from both coils and combined to improve the signal-to-noise ratio at 6 cm depth by 2 1/2. A similar experiment with the body coil showed 2 1/2 improvement at about 8 cm depth.

Image Enhancement↗
PubMed1988

Doubly tuned local coils for MRI and MRS at 1.5 T.

We describe a doubly tuned radiofrequency (RF) local coil probe designed specifically for performing in vivo image-localized spectroscopy. The probe was designed using principles developed in connection with the counter-rotating-current (CRC) and planar-pair loop gap resonators for magnetic resonance imaging (MRI). The probe design satisfies several criteria useful for in vivo 1H/31P experiments at 1.5 T. First, sensitivity on the low-frequency mode is preserved relative to a singly tuned coil. This result was confirmed by bench-test and in vitro MR experimental data. Second, through principles of intrinsic decoupling the probe is isolated from any externally applied uniform excitation field, which is desirable for in vivo 1H imaging and solvent suppression. Third, the regions of sensitivity of the high- and low-frequency modes of the coil are similar, and therefore spectroscopic volumes of interest identified on an image will reflect the same volumes as those selected during spectroscopy. Finally, interface to the MR system is such that the high- or low-frequency circuits may be selected entirely under software control, with no requirement for changing coils or cables or moving the subject.

Humans↗
PubMed1988

Simultaneous reception from a whole-volume coil and a surface coil on a clinical MR system.

Simultaneous acquisition of signals from the same anatomic region with use of both the head or body coil and a surface coil was demonstrated on healthy volunteers with a commercial magnetic resonance imaging system and a hybrid combiner. An improvement in the signal-to-noise ratio (S/N) over that which is obtained with the surface coil alone was demonstrated at depths of 3-4 cm and greater from the surface of the body. The practical necessity of use of the hybrid combiner to add the signals created several problems, such as the inability to obtain the predicted increase in S/N in certain areas and an actual decrease in S/N close to the surface coil. These problems would have been avoided with the use of two separate data channels. The only problem intrinsic to the method is a "wraparound" of structures and motion artifacts onto the field of view.

Humans↗
PubMed1987

Quadrature detection surface coil.

A surface coil assembly consisting of two interleaved coplanar resonators that are intrinsically decoupled from each other is described for imaging at 1.5 T. Vector reception fields on-axis at 3 cm depth are orthogonal and of equal magnitude. Both components of magnetization were received and combined resulting in a 2 1/2 improvement in signal-to-noise for temporomandibular joint images.

Humans↗
PubMed1987

A complication in prescan strategy when using surface coils.

The "prescan" process for setting the gain of an MRI scanner can be confounded by an effect arising from the spatial variation of the angle between the vector reception field of a local or surface coil and the excitation field of a whole-body coil. It is most pronounced when the phase-encoding direction is parallel to the plane of the coil but not along the magnetic field. The largest signal is shown to reside in a data row that is shifted from the one that corresponds to zero phase-encoding gradient. The effect depends on the field-of-view and the dimensions of the receiving coil. Strategies are suggested by which manufacturers of scanners can cope with this intrinsic problem. In the meantime, users of surface coils should be aware of the difficulty.

Magnetic Resonance Imaging↗
PubMed1987

An evaluation of paramagnetic broadening agents for spin probe studies of intact mammalian cells.

Six transition metal ion complexes have been examined for their effects on the cell survival as well as their effectiveness in inducing the broadening of the electron spin resonance (ESR) spectra of nitroxide spin probes. These paramagnetic species are Ni(EDTA), Ni(DTPA), potassium tris(oxalato) chromate (chromium oxalate), K3Fe(CN)6, Cu(DTPA), and NiCl2. At 100 mM concentration, the typical concentration used in cell studies to broaden the extracellular nitroxide ESR signal, only Ni(EDTA) and Ni(DTPA) are found to be non-toxic to Chinese hamster ovary cells. The relative cytotoxicities of the six metal ion complexes are Cu(DTPA) greater than K3Fe(CN)6 greater than NiCl2 greater than chromium oxalate greater than Ni(DTPA) greater than Ni(EDTA). Thus, potassium ferricyanide and NiCl2, two most commonly used paramagnetic broadening agents, are relatively toxic to the cell. In contrast, among the six paramagnetic species tested here, chromium oxalate appears to be the most effective agent at non-toxic concentrations in inducing the broadening of the ESR spectra of both cationic and neutral nitroxide spin probes. By considering both their cytotoxicity and their effectiveness in causing line broadening of the nitroxide ESR spectra, chromium oxalate is a good paramagnetic broadening agent for spin probe studies of intact mammalian cells.

Animals↗
PubMed1987

Enlarged parathyroid glands: high-resolution local coil MR imaging.

Twenty-two patients with primary hyperparathyroidism underwent high-resolution magnetic resonance (MR) imaging with local (surface) coils for preoperative localization of enlarged parathyroid glands. The MR studies were interpreted prospectively and the results compared with findings at surgery and the results of computed tomography (CT), ultrasonography (US), and thallium-technetium scintigraphy (TTS). The sensitivity and specificity of MR imaging were .74 and .88, respectively. The sensitivity/specificity for the other modalities were as follows: 74/.95 for CT, .59/.82 for US, and .82/.98 for TTS. Enlarged parathyroid glands displayed a medium-intensity signal on T1-weighted images and a marked increase in intensity on T2-weighted images, but the degree of increase varied considerably.

Adenoma↗
PubMed1987

Failed temporomandibular joint prostheses: MR imaging.

Magnetic resonance (MR) imaging with surface coils was performed on 43 temporomandibular joints with disk prostheses in 28 patients who had pain, dysfunction, or both after implantation of the prostheses. Fracture was diagnosed prospectively as a discontinuity of the prosthesis on the MR examination; the sensitivity and specificity of MR imaging for this diagnosis was determined on the basis of these studies. All patients underwent surgery, after which the final diagnosis was made. MR imaging was found to have a sensitivity of 0.81 and a specificity of 0.91. Other MR findings included an abnormal amount of soft tissue surrounding the disk, thinning of the disk, osteophytes, and erosion of the condyle. An as yet unexplained artifact was frequently seen and obscured the prostheses in four of the six false-negative studies. The one false-positive case resulted from the interpretation of a markedly thinned but intact region of the prosthesis as a fracture.

Female↗
PubMed1987

MR imaging of the carpal tunnel: normal anatomy and preliminary findings in the carpal tunnel syndrome.

MR imaging was performed through the carpal tunnel in 18 wrists of nine normal volunteers and compared with cryomicrotome sections from cadaver wrists. MR reliably imaged the flexor retinaculum and carpal bones and thus defined the borders of the carpal tunnel. In all cases the median nerve was seen as an ovoid structure of moderate signal intensity and was easily distinguished from the flexor tendons of the hands running in the carpal tunnel. The tendons were separated from each other by their tendon sheaths, and this allowed for identification of the various tendons. Anatomic variations encountered in the normal volunteers included anomalous positioning of the origin of the lumbrical muscles within the carpal tunnel in two, persistent median arteries in two, and interposition of the median nerve between the flexor pollicis longus and the superficial flexor tendon to the index finger in one. Preliminary observations in 10 wrists of patients with carpal tunnel syndrome include segmental and diffuse swelling of the median nerve in six, distortion of the nerve in one, and thickening of the tendon sheaths in one. We conclude that MR imaging accurately and reliably displays the normal anatomy of the carpal tunnel and can detect morphologic changes in patients with carpal tunnel syndrome.

Adult↗
PubMed1987

High-resolution MR imaging of the normal rotator cuff.

The shoulders of six normal volunteers were imaged with high-resolution MR in the axial, sagittal, and coronal planes. An angled pair of counter-rotating current loop-gap resonators designed specifically for the shoulder was used as a local coil. All images were compared with corresponding cryomicrotome sections from cadaver shoulders. The rotator cuff was analyzed in detail. It appeared as a complex, heterogeneous band to tissue superficial to the humeral head. The areas of low signal intensity corresponded to the central tendons of the four rotator cuff muscles. These tendons could be distinguished from each other as well as from the intervening components of the cuff, which have a moderate intensity. We concluded that MR is capable of imaging the normal rotator cuff and of separating the various components. This may allow for improved precision in the diagnosis of rotator cuff disorders.

Adult↗
PubMed1987

MR imaging of the shoulder: diagnosis of rotator cuff tears.

Twenty-five patients with known or suspected tears of the rotator cuff in 26 shoulders underwent MR imaging. All patients also underwent arthrography or surgery. MR visualized abnormalities consistent with a tear in 20 of the 22 tears diagnosed by arthrography or surgery. In most cases, tears were seen as regions of increased signal intensity within the cuff on long-TR pulse sequences, although two cases simply showed an almost complete absence of normal cuff. The MR appearance of the two cases with partial tears was similar to that of full-thickness tears. Of the four cases with normal arthrograms, one case had MR findings consistent with a tear. We conclude that MR has good potential for the noninvasive diagnosis of rotator cuff tears. Its ultimate role in this diagnosis must await prospective studies comparing its accuracy with that of sonography, CT, and arthrography.

Adult↗