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Biomedical subjects

M A Bernstein

Publications and source records attributed to M A Bernstein.

17 recordsLinked to original sources
PubMed1992

A data adaptive reprojection technique for MR angiography.

Inability to detect vessel overlap and vascular loops can compromise the interpretation of magnetic resonance angiograms. A data-adaptive ray tracing (DART) technique was developed to produce the appropriate variations in signal intensity at points of vessel overlap in order to simulate the standard angiographic representation of vessels. In this technique a threshold is utilized to identify vessels in the image slices composing a 3D angiographic data set. A mask, which defines regions slightly larger than the vessel boundaries, is obtained by blurring the vessel information surviving the initial threshold. This mask is converted to binary form prior to multiplication by the original angiographic data set. Following application of an additional threshold to the masked data, line integrals through the regions defined by the mask are performed to obtain an angiographic signal proportional to the integrated vessel signal as in conventional angiography. This integrated reprojection is then uniquely combined with a maximum intensity pixel (MIP) reprojection to produce the final DART image. The application of the DART technique to 2D time-of-flight and 3D phase-contrast angiograms successfully enabled the identification of over-lapping vessels and vascular loops. DART was also found to produce less vessel narrowing than the MIP technique.

Algorithms↗
PubMed1989

A method for correctly setting the rf flip angle.

Currently the accepted method for setting the correct rf power levels to achieve 90 degrees and 180 degrees rf pulses for MR imaging is to peak the echo amplitude of a rf spin-echo sequence. The echo amplitude of this alpha-2 alpha pulse sequence is proportional to sin3 (alpha) and has a relatively broad maximum. Recently another method for setting the rf flip angle by maximizing the ratio of the stimulated echo to the primary echo amplitudes (in a 3 alpha sequence) demonstrated accuracy similar to that of the spin-echo method using a shorter repetition time. We present a new, more sensitive, and more accurate method for setting the correct rf power levels for 90 degrees and 180 degrees rf pulses. In this method, based upon the stimulated echo pulse sequence, we are able to accurately set the rf power to within +/- 0.1 dB by minimizing the signal amplitude of the third spin echo. This null method works for both selective and nonselective rf pulses of flip angle 90 degrees or 180 degrees, allowing the user to accurately adjust the relative amplitudes of the four rf pulse types within a single pulse sequence.

Calibration↗
PubMed1989

Multiple short-echo (2.5-ms) quantitation of in vivo sodium T2 relaxation.

The MR behavior of the sodium-23 nucleus in vivo is a complex problem which has generated considerable interest over the last 20 years. Early studies on excised tissue samples revealed that the sodium nucleus exhibited a two-component T2 relaxation. This biexponential T2 relaxation was characterized by a short component with a T2 = 0.7-4.8 ms, and a long component with a T2 = 7.0-26.0 ms. We have developed a 3D pulse sequence capable of performing multiple Hahn echo in vivo sodium-23 imaging at echo times as short as 2.5 ms. This sequence obtains the shorter spin echo times by presaturating the spins outside of the desired imaging region, allowing the use of nonselective rf pulses. Using this sequence we have been able to quantify the long and short T2 components of normal brain tissue, vitreous humor of the eye, and a rabbit VX-2 carcinoma. We found that gray matter and white matter of normal brain have a monoexponential T2 relaxation with T2 = 17.6 +/- 2.4 ms. The vitreous humor T2 relaxation is also monoexponential with T2 = 56.8 +/- 2.1 ms. However, we find that some of the rabbit VX2 carcinomas exhibit a biexponential T2 decay with a short component of 3.3 +/- 4.6 ms and a long component of 22.0 +/- 9.0 ms.

Absorption↗
PubMed1988

Acute recurrent appendicitis with appendicolith.

Appendiceal disease can be acute, acute recurrent, or chronic. Acute appendicitis is the most common form. Acute recurrent appendicitis is more common than chronic appendicitis. In children the clinical manifestations of appendicitis are variable. Patients who have an appendicolith usually develop appendicitis, often with perforation. A case is presented of 3-year follow-up of a patient with an appendicolith and acute recurrent appendicitis. The literature about appendicoliths is reviewed. In the appropriate clinical setting, a history of prior episodes of similar right lower quadrant pain does not preclude the diagnosis of appendiceal disease. Awareness of the less common forms of appendicitis is important so that appropriate treatment is not delayed.

Appendectomy↗
PubMed1987

Thoracic manifestations of AIDS.

Of 67 hospitalized AIDS patients, 39 had pulmonary pathology. More than half of these patients died of pulmonary disease. Pneumocystis carinii, cytomegalovirus, Cryptococcus neoformans and Mycobacterium avium-intracellulare were the most common pulmonary pathogens, and Kaposi's sarcoma was the most common neoplasm. Infections and neoplasms frequently coexist in the thorax of an AIDS patient. The chest radiograph may be normal in an AIDS patient with active Pneumocystis pneumonia.

Acquired Immunodeficiency Syndrome↗
PubMed1986

Detection of hemangiomas using whole-body imaging with technetium-99m labeled RBCs.

Hemangiomas are easily, quickly and relatively noninvasively detected using whole-body imaging with Tc-99m labeled RBCs. A case in which this method was used to confirm known lesions and detect additional unsuspected lesions is described. This method can also be useful in the detection and evaluation of other types of vascular malformations, such as arteriovenous communications. The lesions must be of sufficient size and flow to be seen. Applications include the examination of patients known to have one vascular malformation in a search for additional lesions and the screening of relatives of patients with familial conditions that include hemangiomas.

Adolescent↗
PubMed1986

Changing concepts of colonic polyps: clinical and radiographic implications.

The relationship of colonic polyps to carcinoma of the colon provides a basis for their importance. Recent advances in the detection of colonic polyps, including double contrast barium examination and colonoscopy, have provided a method for more extensive study of colonic polyps. Studies using these newer techniques indicate that many traditional concepts of colonic polyps were inaccurate. The relationships of polyp size to histology, polyp location to age, and the phenomenon of colon polyp clustering are important to both the immediate treatment of the polyp and to the long-term follow-up of the patient. The use of hemoccult stool screening as a technique for screening for colonic pathology is also of significance to the radiologist. The changing relationships of various parameters of colon polyps bring into question the utility of many of the currently recommended screening procedures for colon pathology. Undoubtedly, this will impact on the practice of radiology.

Aged↗
PubMed1985

Distribution of colonic polyps: increased incidence of proximal lesions in older patients.

Several recent studies have shown a proximal shift in the distribution of colonic carcinoma compared to older studies. Because of the association between polyps and cancer, the authors evaluated the distribution of colonic polyps in 3,664 consecutive patients who had a colon examination over a period of 14 months. A total of 967 colorectal polyps were found in 633 patients. In all, 502 polyps (52%) were proximal to the rectosigmoid. Older patients had significantly more right-sided polyps and fewer rectosigmoid lesions. Large polyps occurred more frequently in the right colon, and this was also statistically significant. Gender has no effect on polyp distribution. The authors conclude that the importance of screening for polyps, particularly on the right side of the colon, increases with age.

Adult↗
PubMedDate not supplied

Encoding strategies for three-direction phase-contrast MR imaging of flow.

Three encoding strategies for the measurement of flow velocities in arbitrary directions with phase-contrast magnetic resonance imaging are presented; their noise and dynamic range performance are compared by means of theoretical analysis and computer simulation. A six-point measurement strategy is shown to be quite inefficient in terms of velocity variance per unit time. A simple four-point method exhibits equal dynamic range; its noise depends on flow direction but on average is equal to that of the six-point method. An alternate, balanced four-point method has noise that is direction independent and has, depending on implementation, possibly lower noise levels. Either four-point method is more efficient and is preferred over the six-point approach.

Blood Flow Velocity↗
PubMedDate not supplied

Comparison of phase-difference and complex-difference processing in phase-contrast MR angiography.

The two main phase-contrast reconstruction methods are phase difference and complex difference. The signal-to-noise ratio properties and relative advantages of the two techniques are discussed. It is argued that each processing method has applications in which it is superior, and guidelines are provided to determine those applications. It is demonstrated theoretically and experimentally that only the complex-difference method is well suited for processing phase-contrast slabs with use of a projection dephaser gradient.

Angiography↗
PubMedDate not supplied

Minimizing TE in moment-nulled or flow-encoded two- and three-dimensional gradient-echo imaging.

A method for minimizing field-echo delay in moment-nulled gradient-echo imaging is presented. Even though ramps are accounted for, the analysis yields simple closed-form solutions. The method is then generalized to the section-select waveform for three-dimensional volume imaging and to flow encoding for phase-contrast imaging. Three strategies for first-moment selection in phase-contrast imaging are discussed, including a new strategy that always yields the minimum echo delay. Trapezoidal and triangular gradient lobe shapes are analyzed.

Algorithms↗
PubMedDate not supplied

Pulse sequence generated oblique magnetic resonance imaging: applications to cardiac imaging.

A pulse sequence procedure for producing oblique magnetic resonance images is described. Using this procedure we present a new, accurate method to obtain true short-axis views and true long-axis views (both parallel and perpendicular to the septal plane) of the heart. The method is accurate regardless of the orientation of patient's heart. The method does not require the patient to be rotated, nor otherwise moved, and does not require any additional hardware. The method is experimentally verified with both human and phantom studies. The phantom study indicates accuracy of approximately 1 degree with a commercial scanner that reports angular measurements to a precision of 1 degree. Application of the short-axis views to measurement of left ventricular volume, and possible advantages of Gauss-Legendre integration for this measurement are discussed. Finally, multiphase oblique cardiac images are presented.

Biophysical Phenomena↗
PubMedDate not supplied

Oblique magnetic resonance imaging of the bronchi.

The trachea and main bronchi of a supine patient in a magnetic resonance (MR) scanner are not contained in a single standard coronal plane, but instead intersect this coronal plane at some angle, usually 20 degrees - 35 degrees. We have developed a new MR imaging protocol to determine the oblique imaging plane which best contains the trachea and main bronchi. The resulting oblique images simplify anatomical identification, and allow the user to select additional oblique planes which cut any desired portion of main bronchus in true cross section. Accurate lumen shapes and areas may then be extracted from these cross-sectional images. The method does not require the patient to be moved or rotated, and does not require hardware modification. We demonstrate the clinical application of the protocol with both a normal volunteer and a patient with an endobronchial tumor. The use of gradient echo pulse sequences together with this protocol to distinguish between vessels and bronchi is presented. We provide phantom verification to demonstrate the quantitative accuracy of the method to provide lumen areas.

Humans↗
PubMedDate not supplied

Improved detectability in low signal-to-noise ratio magnetic resonance images by means of a phase-corrected real reconstruction.

We show that for magnetic resonance (MR) images with signal-to-noise ratio (SNR) less than 2 it is advantageous to use a phase-corrected real reconstruction, rather than the more usual magnitude reconstruction. We discuss the results of the phase correction algorithm used to experimentally verify the result. We supplement the existing literature by presenting closed form expressions (in an MR context) for the probability distribution and first moments of the signal resulting from a magnitude reconstruction.

Algorithms↗
PubMedDate not supplied

Artifacts from pulsatile flow in MR imaging.

Previous investigators have examined the effect of blood flow on the apparent blood vessel signal intensity. These studies reported flow brightening and darkening effects within vessels. In this paper we have investigated another type of flow artifact, which originates from the pulsatile nature of blood flow. These flow artifacts have characteristic bright and dark "ghosting" patterns which appear close to small vessels, usually arteries, which are bright in slow flow. Similar to the amplitude-of-motion artifacts caused by patient motion (e.g., breathing and cardiac motion) the ghosting artifacts due to pulsatile flow are best characterized as frequency modulated spectral sidebands. The pulsatile artifacts can have both dark and bright structures and usually appear close to the "moving" vessel that generates the artifact. In this paper we present a study of the chief features of these pulsatile flow artifacts, and we develop a theoretical description of their origins in terms of "accidental" velocity-encodings that occur strongly in most magnetic resonance imaging sequences.

Blood Flow Velocity↗