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Biomedical subjects

A Jesmanowicz

Publications and source records attributed to A Jesmanowicz.

At least 19 recordsLinked to original sources
PubMed1992

Eyelid anatomy revisited. Dynamic high-resolution magnetic resonance images of Whitnall's ligament and upper eyelid structures with the use of a surface coil.

We used a new radiofrequency surface coil and complementary software in eyelid magnetic resonance imaging. This custom-designed coil allows visualization of the eyelid structures in submillimeter resolution, providing detailed delineation of such structures as the orbital septum, levator aponeurosis, Müller's muscle, and orbital septa. The effect of Whitnall's ligament on the levator aponeurosis can be observed as a "tenting" of the aponeurosis; the change in vector force is persistent in upgaze and downgaze. This technology will allow accurate dynamic studies of eyelid anatomy in patients with various anatomically based eyelid diseases, before and after surgery, making it possible to test in vivo longstanding theories of normal and pathologic eyelid physiology.

Eyelids↗
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↗
PubMed1991

Coil optimization for MRI by conjugate gradient descent.

A flexible iterative algorithm is presented for optimizing gradient and radio frequency coils for MRI. It is based on a model using discrete current elements and direct Biot-Savart calculation of the fields. An error function is defined over a region of interest (ROI) and is minimized by conjugate gradient descent. The choice of error function allows optimization of the field uniformity, the inductance, and the efficiency of the coil in any combination. Neither the coil nor the ROI is restricted to any particular geometry. A 40-turn cylindrical z-gradient coil of radius a and length 4a, designed for ROI of radius 0.7a and length 2a has an average error in the gradient fields generated of 0.85%, an inductance of 0.014a mH/cm, and an efficiency of 6.65a-2 Gcm/A. A 16-turn birdcage-like RF coil of radius 5 cm, designed for a ROI of radius 4 cm has an average error of 0.79%.

Algorithms↗
PubMed1991

High-resolution, short echo time MR imaging of the fingers and wrist with a local gradient coil.

The many fibrous tissues of the wrist and hand have short T2s, and, because of the small size of the tissues, their magnetic resonance (MR) imaging necessitates use of the high spatial resolution obtainable with fields of view as small as 2 cm x 2 cm x 1 mm. The authors demonstrate that the use of a local xyz gradient coil, positioned off-center in a clinical MR imager to facilitate patient positioning, permits acquisition of high-resolution images in spin-echo (SE) and gradient-recalled-echo (GRE) sequences with echo time (TE) as short as 6 msec (SE) or 3 msec (GRE). The authors compare this method for obtaining high-resolution images with the alternative method of using normal gradient strengths and increased pulse duration. The effects on image quality of TE, bandwidth, gradient strength, and chemical shift artifacts are presented. Images obtained with the local gradient coil of the carpal tunnel, carpal bones, and proximal interphalangeal joint in healthy volunteers are shown.

Finger Joint↗
PubMed1991

Interdigital (Morton) neuroma: high-resolution MR imaging with a solenoid coil.

Fifteen patients (17 feet) with symptoms suggestive of plantar interdigital neuroma underwent magnetic resonance (MR) imaging at 1.5 T with a solenoid forefoot coil with an 8-cm field of view. Surgery was subsequently performed on six feet. Fifteen interdigital masses were identified with MR imaging. Five of these, in feet that underwent surgery, were pathologically confirmed neuromas. In the remaining foot that underwent surgery, flexor tendon injury with probable inflammatory reaction was demonstrated with MR imaging but was interpreted as indeterminate for neuroma. No neuronal was identified at surgery, which otherwise confirmed the MR imaging findings. Neuromas were most conspicuous on T1-weighted images as foci of decreased signal intensity well demarcated from adjacent fat tissue. The lesions were poorly seen on T2-weighted images, where they appeared isointense or slightly hypointense to fat tissue in all cases. Prominent regions of increased signal intensity, presumably representing fluid in intermetatarsal bursae, were seen proximal to 10 of the 15 masses found with MR imaging.

Foot↗
PubMed1990

Facial surface coil for MR imaging.

A local-reception counter-rotating-current coil for magnetic resonance imaging at 1.5 T was developed. It consists of two parallel coaxial racetrack-shaped loops. The planes of the loops are orthogonal to the surface of the body, and the space between the loops is open. The separation between the loops allows the device to fit over the nose and mouth for oral-maxillofacial imaging without the threat of occlusion to the patient's air passages. The sensitivity of this coil is similar to that of conventional surface coils of the same dimensions. The two active current elements conform to other anatomic objects including the eyes and anterior portion of the neck.

Face↗
PubMed1990

MR imaging of the tarsal tunnel and related spaces: normal and abnormal findings with anatomic correlation.

The tarsal tunnel syndrome may be caused by extrinsic or intrinsic pressure on the posterior tibial nerve or its terminal branches. The specific symptoms depend on the extent of nerve involvement, and compression distal or proximal to the tarsal tunnel may result in variants of the syndrome. To define better the capability of MR imaging for evaluating this entity, we performed MR imaging on three normal subjects and correlated the images with cryomicrotome sections. Six patients with symptoms suggestive of tarsal tunnel syndrome also were studied with MR. In all normal subjects, MR images showed the flexor retinaculum and the structures passing deep to the retinaculum: the tibialis posterior tendon, flexor digitorum longus tendon, flexor hallucis longus tendon, and the posterior tibial neurovascular bundle. The medial calcaneal sensory branch(es) and the medial and lateral plantar nerves also were delineated. Mechanical causes of compression were shown in all six symptomatic patients. The pathologic entities included two neurilemomas, tenosynovitis involving all three tendons, a ganglion cyst arising from the flexor hallucis longus tendon sheath, posttraumatic fibrosis, and post-traumatic fibrosis with associated posttraumatic neuroma. The MR findings were confirmed surgically in five cases. MR imaging can accurately depict the contents of the tarsal tunnel and the courses of the terminal branches of the posterior tibial nerve. In our small series, MR imaging accurately showed the lesions responsible for tarsal tunnel syndrome.

Ankle↗
PubMed1989

Piezoelectric-controlled tuning capacitor for surface coils.

The design of a piezoelectric-controlled trimmer capacitor and its use as a tuning element of an MRI surface coil at 63.8 MHz are described. It is found that image quality does not depend strongly on match of the coil to the transmission line but that tuning can be a significant factor. The work is intended to lead eventually to an automatic frequency control circuit in which the capacitor serves as the active element in holding the resonant frequency of the nuclei and the resonant frequency of the coil in coincidence.

Equipment Design↗
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

Enhancement of parallel MR image acquisition by rotation of the plane of section.

The technique of simultaneous acquisition of magnetic resonance images from two different locations was combined with a modification of a commercially available oblique multisection method. By angling the sections slightly from the coronal plane and rotating the subject, simultaneous sections can be obtained within the given repetition time through both regions without a loss of the signal-to-noise ratio that would result from the use of true coronal sections. The technique has allowed simultaneous imaging of both shoulders and, with rotation of the subject, both knees.

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

Evulsion of the retina associated with optic nerve evulsion.

We examined two patients with optic nerve evulsion as well as nasal peripapillary retinal and retinal pigment epithelial evulsion after ocular trauma. Fluorescein angiography demonstrated an intact peripapillary choriocapillaris, loss of peripapillary retina and retinal pigment epithelium, and complete disruption of retinal perfusion. We have postulated a mechanism for traumatic peripapillary retinal evulsion involving severe anterior displacement and abduction of the globe that may explain how the disruptive force was transmitted to the nasal retinal nerve fiber layer. We have provided a clinical correlation with magnetic resonance imaging of the optic nerve and globe of a normal individual.

Adult↗