Gastrointestinal complications of AIDS: radiologic findings.
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Acquired Immunodeficiency Syndrome↗
Biomedical subjects
M A Bernstein
Publications and source records attributed to M A Bernstein.
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↗
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↗
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↗
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↗
The effect of combination treatment with cis-platinum and low dose rate 125I radiation in a murine brachytherapy model.
We studied the effect of combination treatment with cis-platinum during low dose rate irradiation from 125I sources in the RIF-1 murine flank tumor model. Cell survival measured with a colony forming efficiency assay was used as the experimental endpoint. Sources implanted into tumors delivered 25 Gy of radiation to isodosed annuli of tissue at a dose rate of 1.3 Gy/hr. When 3 mg/kg of cis-platinum was administered 24, 12, and 1 hr before or 0, 12 and 24 hr after irradiation, the effect on cell kill was additive. Thus in the RIF-1 model there is no particular advantage gained by treatment with the combinations of cis-platinum and 125I radiation used in these studies.
Animals↗
Small colonic polyps: a reappraisal of their significance.
With the advent of fiberoptic endoscopy and modern radiographic techniques, the majority of detected polyps are less than 1 cm. During a seven-month period, we studied 140 patients who had radiographically demonstrated colonic polyps that were confirmed by pathologic study. Tissue specimens were obtained by proctoscopy, colonoscopy, or surgery. There were 222 polyps of which 144 (65%) were 1 cm or less in size, with the preponderance (80%) of these being adenomatous. Of the 82 polyps that ranged in size from 6-10 mm, 68 (83%) were adenomas, including one carcinoma and five villous adenomas. Forty-seven (72%) of the diminutive polyps (less than or equal to 5 mm) were adenomatous, including two with atypia. Our results correspond to those of several recent endoscopic studies, reporting that a small colonic polyp is most likely to be adenomatous, and that it possesses the potential for growth and malignant transformation. The detection of small polyps during barium enema examination is thus warranted, particularly in the proximal colon where the majority are adenomatous. The clinical management of polyps is becoming more aggressive, and the removal of even small lesions (less than or equal to 5 mm) is now performed if they are found incidentally during colonoscopy.
Adenoma↗
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↗
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↗
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↗
Angle-dependent utilization of gradient hardware for oblique MR imaging.
A straightforward method for calculating maximum gradient amplitudes for the frequency-encoding, phase-encoding, and section-select functions in oblique magnetic resonance (MR) imaging is presented. The calculated amplitude values depend on the prescribed angulation and on which of the three functions are simultaneously active. The derived expressions are optimal in most cases, and when not optimal, they still offer substantial improvement over calculations that do not incorporate angular information. Both matrix-based and geometric interpretations are presented.
Humans↗
Breath-hold MR measurements of blood flow velocity in internal mammary arteries and coronary artery bypass grafts.
Breath-hold velocity-encoded cine MR (VENC-MR) imaging is a feasible method for measuring phasic blood flow velocity in small vessels that move during respiration. The purposes of the current study are to compare breathhold VENC-MR measurements of flow velocities in the internal mammary arteries (IMA) with nonbreath-hold measurements and to characterize the systolic and diastolic flow velocity curves in a cardiac cycle in native IMA and IMA grafts. Flow velocity in 30 native IMA and 8 IMA grafts were evaluated with a breath-hold VENC-MR sequence with K-space segmentation and view-sharing reconstruction (TR/TE = 16/9 msec, VENC = 100 cm/s). In 10 native IMA, nonbreath-hold VENC-MR images were acquired as well for comparison. Breath-hold VENC-MR imaging showed significantly higher systolic and diastolic peak velocities in native IMA (43.1 cm/second +/- 15.0 and 10.0 cm/second +/- 4.8), in comparison to those of nonbreath-hold VENC-MR imaging (27.6 cm/second +/- 10.2 and 7.3 cm/second +/- 3.9, P < .05). The diastolic/systolic peak velocity ratio in the IMA grafts (.88 +/- .41) was significantly higher than that in native IMA (.24 +/- .08, P < .01). Interobserver variability in the flow velocity measurement was less than 4%. Breath-hold VENC-MR imaging demonstrated higher peak flow velocity in the IMA than nonbreath-hold VENC-MR imaging. This technique is a rapid and effective method for the noninvasive assessment of blood flow velocity in IMA grafts.
Adult↗
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↗
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↗
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↗
Measurement of coronary blood flow and flow reserve using magnetic resonance imaging.
PURPOSE: It was the purpose of this study to demonstrate the feasibility of performing coronary artery flow and coronary flow reserve (CFR) measurements in normal human volunteers using a magnetic resonance (MR) phase contrast technique. MATERIALS AND METHODS: Coronary flow rate, flow velocity, peak flow and CFR were determined at rest and during pharmacologically induced hyperemia in 10 healthy volunteers. The flow measurements were obtained during a single breath-hold by using a fast, prospectively gated, segmented k-space gradient-echo phase contrast acquisition with view sharing (FASTCARD PC) that was modified to improve sampling of the diastolic flow. Data were processed using the standard phase difference (PD) processing techniques as well as a new complex difference (CD) flow measurement method intended to improve the accuracy of flow measurements in small vessels. RESULTS: Mean hyperemic flow velocity (40 +/- 16 cm/s) and blood flow (3.9 +/- 1.5 ml/s) rates differed significantly from resting velocity (13 +/- 6.6 cm/s) and flow (1.1 +/- 0.4 ml/s) measurements (p < 0.0001). PD methods consistently measured larger flow rates at rest (24% larger, p < 0.0005) and stress (29% larger, p < 0.0001). CFR, calculated as the ratio of the mean PD flows (4.7 +/- 2.8), was higher than CFR calculated as the ratio of mean CD flows (4.2 +/- 1.8); however, the differences did not reach statistical significance (p = 0.07). Flow measurements performed in adjacent slices of the same vessel correlated well (r = 0.88). CONCLUSIONS: Coronary flow and CFR measurements using the MR techniques are feasible and are similar to those reported in the literature for healthy volunteers.
Adult↗
Fat signal suppression in head and neck imaging using fast spin-echo-IDEAL technique.
We present our initial experience with the use of a modified 3-point Dixon technique to obtain reliable fast spin-echo T1- and T2-weighted fat-suppressed images in the soft-tissue neck. The method has less sensitivity to magnetic field inhomogeneity than frequency-selective radiofrequency fat saturation and provides uniform fat suppression even near tissue-tissue and air-tissue interfaces. Clinical advantages and limitations of the method are discussed and several examples are shown.
Head and Neck Neoplasms↗
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↗