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Biomedical subjects

D M Weber

Publications and source records attributed to D M Weber.

At least 37 records · Page 2Linked to original sources
PubMed1993

Quantitative velocity images from thick slab 2D phase contrast.

Thick slab two-dimensional phase contrast (2D PC) angiography provides a large amount of anatomical information in a short acquisition time. Quantitative velocity information is, however, destroyed by the necessary projection dephasing gradient. We present a 2D PC acquisition scheme which retains quantitative velocity information in a thick slab acquisition. A thick slab acquisition produces an image which is a projection through an entire vessel. Accurate velocity measurements must take into account the intravoxel phase cancellation caused by a distribution of velocities within the vessel. In addition to the description of the data acquisition scheme, we outline a method for determining the mean velocity within a vessel having a laminar flow distribution. It is shown that without the consideration for intravoxel phase cancellation, the mean velocity measurement from thick slab images overestimates the true mean velocity by 10%.

Blood Flow Velocity↗
PubMed1993

Generalized matched filtering for time-resolved MR angiography of pulsatile flow.

Generating flow-specific images (arteriograms, venograms) with optimal signal-to-noise ratios for time-resolved MR angiography is a conditional maximum problem, and its solutions are generalized matched filters. We have investigated six matched filters, corresponding to all possible combinations of three flow suppression conditions and two signal-to-noise ratio maximization procedures. Four of these matched filters correspond to previously described methods: the subtractive matched filter, the standard deviation, the global venous eigenimage and the global arterial eigenimage. The two others are referred to here as the local venous eigenimage and the local arterial eigenimage. These six matched filters have been applied to 2D time-resolved phase contrast angiographic data. The local arterial eigenimage is found to be the most effective in suppressing undesired venous flow and preserving desired arterial flow.

Blood Flow Velocity↗
PubMed1993

MR angiography using velocity-selective preparation pulses and segmented gradient-echo acquisition.

We describe a cardiac-gated MR angiographic imaging method that employs velocity-selective preparation (VSP) pulses in conjunction with segmented gradient-echo acquisition and subtraction to produce images that, ideally, contain no signal from stationary tissues and display vessels with a signal intensity that is dependent on the velocity of the blood in the vessels. The novel features of this method are a) it acquires several phase-encoding values/application of a single VSP pulse, b) it uses subtraction to eliminate signal that is not sufficiently suppressed by the VSP pulses, and c) it uses VSP pulses that are synchronized with the cardiac cycle so it can be used to produce ghost-free images of pulsatile blood. An advantage of this sequence is that it detects a signal that, after preparation, is relatively unaffected by changes in blood velocity. This leads to a large signal-to-noise ratio for all the phase-encoding values, a reduction of ghosting artifacts, and the ability to visualize blood that is in motion for only a short time during the cardiac cycle. Because the signal is prepared during peak flow, venous signal can be suppressed by making the sequence sensitive to high velocities. An additional advantage of this sequence is that it permits sampling with a short TE because the velocity-encoding gradient can be applied in a preparatory interval. Signal loss that results from dephasing during the longer TE preparation interval can be reduced or eliminated by allowing the dephased spins to flow out of the region of complex flow, and perhaps out of the field-of-view, by introducing a delay between the finish of the VSP pulse and the beginning of data acquisition.

Blood Flow Velocity↗
PubMed1993

Preoperative evaluation of giant cell tumors of the radius with magnetic resonance angiography.

We report three clinical cases of giant cell tumor of the distal radius in which reconstructions were performed with vascularized fibular grafts. Magnetic resonance angiography, a newer and noninvasive technique, was used in addition to preoperative magnetic resonance imaging. All patients had routine digital subtraction arteriography, with which magnetic resonance angiography compared favorably, demonstrating the carpal arch anatomy and other major vessels at the tumor site. In two patients the trifurcation vessels of both legs were also studied with magnetic resonance angiography before fibular harvest. In one case, the fibula graft was successfully harvested on the basis of the magnetic resonance angiographic findings. In the other case, digital subtraction arteriography had been done to evaluate suspected peripheral vascular disease. In that case magnetic resonance angiography correlated well with the digital subtraction arteriographic study, showing bilateral anterior tibial artery occlusions and patent posterior tibial and peroneal arteries. Magnetic resonance angiography has the potential to replace conventional angiography in preoperative evaluation of upper-extremity tumors.

Adult↗
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↗
PubMed1992

Peripheral MR angiography with variable velocity encoding. Work in progress.

An electrocardiographically triggered two-dimensional phase-contrast (PC) magnetic resonance angiographic pulse sequence was developed in which velocity encoding (VENC) was varied throughout an acquisition in response to changes in blood velocity during the cardiac cycle. This was done to better capture signal in the peripheral vasculature, where pulsatile flow degrades images. After reconstruction, a matched filter addition technique was applied to the cardiac phase images to obtain a single high-quality static image. Images were obtained of six healthy volunteers--with and without varying VENC--and contrast-to-noise ratio (C/N) calculations were performed for the added images. Varying VENC significantly improved vascular signal from small and large vessels (P less than .02), but it was most helpful for small vessels, for which the C/N increased by as much as 260% (average increase, 149%). These preliminary findings suggest that variable VENC can enhance the signal from the small and large peripheral blood vessels in cardiac-gated PC acquisitions.

Angiography↗
PubMed1991

Spontaneous lymphocyte proliferation in HTLV-I/II infection reflects preferential activation of CD8 and CD16/56 cell subsets.

Previous studies have shown that lymphocytes from HTLV-infected persons spontaneously proliferate when cultured in vitro. We investigated which cell subsets become activated in this response. Mononuclear cells from 16 HTLV-seropositive former blood donors and 9 seronegative controls were cultured for 7 days; activation was then assessed by measuring DNA synthesis in cultured cells and by monitoring CD25 expression by CD3, CD4, CD8, CD19, and CD16/56 lymphocyte subsets. Of the 16 cultures of HTLV + donor cells, 10 showed spontaneous proliferation (Prol + group) and 6 did not (Prol - group). Cytofluorometric analysis revealed a significant increase in the fractions of CD8 cells and CD16/56 cells expressing CD25 for the Prol + group, compared to the Prol- and control groups. Similarly, the fractions of CD25 cells expressing CD8 or CD16/56 were significantly increased in the Prol + group. Although neither the fraction of CD4 cells expressing CD25 nor the fraction of CD25 cells expressing CD4 were increased for the Prol + group, the modal fluorescence intensity value for CD25 expression by CD4 cells was increased, suggesting some CD4 cell activation occurred as well. Blastoid cells were, on average, 79% CD25 +, whereas the sum of CD4 + CD25 + (27%), CD8 + CD25 + (30%), CD19 + CD25 + (3%), and CD16/56 + CD25 + (35%) subsets was 95%; the presence of 17% CD8 + CD16/56 + cells accounted for most of this discrepancy. These findings indicate that spontaneous lymphocyte proliferation in HTLV infection reflects preferential activation of CD8 and CD16/56 cell subsets, apparently including the minor CD8 + CD16/56 + subset.

Antigens, CD↗
PubMed1991

Geometric quantitative coronary arteriography. A comparison of unsubtracted and dual energy-subtracted images.

The application of dual energy (DE) subtraction techniques to quantitative coronary arteriography (QCA) has the advantage of removing the tissue signal surrounding the vessel profile. We have compared the performance of two geometric QCA algorithms on DE-subtracted and -unsubtracted images to determine, for each, if DE subtraction is advantageous. The two algorithms under study were an edge detection algorithm and a Fourier analysis-based algorithm. For each algorithm, linear regression analysis was performed of measured cross-sectional area (CSA) versus actual CSA of coronary vessel phantoms. The edge detection algorithm was found to have improved precision (P less than .05) when applied to the DE-subtracted images. The Fourier analysis algorithm, however, was not effected by the DE subtraction. Among the unsubtracted image results, the Fourier measurements were more accurate (P less than .05) than the edge detection measurements. We conclude that the benefits to edge detection QCA of DE tissue subtraction outweigh the disadvantages of increased image noise and possible misregistration artifacts. However, the Fourier algorithm is relatively insensitive to tissue signal variations.

Algorithms↗
PubMed1990

Quantitative dual-energy coronary arteriography.

Subtraction techniques for digital cardiac imaging have been hampered by misregistration artifacts. The use of dual-energy imaging is being evaluated as a means for reducing these artifacts. Results reported previously indicate that the dual-energy technique may be useful for applications such as exercise ventriculography and general quantification tasks. The purpose of the current study is to investigate the use of dual-energy subtraction imaging for quantitative coronary arteriography. In vivo coronary vessel phantoms (0.2 to 7 mm2 in cross-sectional area) were used to study the potential advantages of tissue suppressed energy subtracted images over unsubtracted images for quantification of absolute vessel cross-sectional area when cardiac motion is present. Estimates of lumen cross-sectional area (N = 20) were determined using videodensitometric analysis of selected energy subtracted and unsubtracted images. Linear regression analysis of measured and actual cross-sectional area showed energy subtracted image data (slope = 1.06, intercept = 0.48 mm2, r = 0.99) to have improved accuracy (P less than .05) and precision (P less than .05) over unsubtracted image data (slope = 1.24, intercept = 1.07 mm2, r = 0.95).

Angiography, Digital Subtraction↗
PubMed1987

Functional differences between small and large luteal cells of the late-pregnant vs. nonpregnant cow.

This paper describes an in vitro model for the study of two types of steroidogenic luteal cells from cows in different physiological states. Two different populations of enzymatically dispersed bovine luteal cells were separated on the basis of size in a Cel-Sep Sedimentation Chamber. The separated small (12.5-23 micron in diameter) and large (greater than 23 micron in diameter) luteal cells of late-pregnant cows (Days 190-280) contained the distinct morphological characteristics previously defined for these two populations of cells. Cells were evaluated for progesterone (P4) production during a 3-h incubation with and without bovine luteinizing hormone (bLH, 10 ng/ml). Both small and large luteal cells from the late-pregnant cow were found to contain equal levels of P4 at Time 0 and increased but equal levels of P4 after a 3-h incubation. Neither cell type showed an increase in P4 production in response to the addition of bLH (p greater than 0.05). Since these results differed from earlier reports for luteal cells of the nonpregnant cow, small and large luteal cells of the mid-cycle (Day 14) were incubated, and the levels of P4 production were compared with P4 levels from the late pregnant cow. In agreement with previous reports for nonpregnant cows, progesterone content at Time 0 was 7-fold higher in large cells than in small cells (p less than 0.05), and after 3 h of incubation, 13-fold higher (p less than 0.05). Although the small cells responded to the presence of bLH in the incubation medium with a 4-fold increase in P4 production, this increase was not significant (p greater than 0.05). The large cell did not respond to bLH. However, the large cell type continued to contain and produce more P4 than did the small cells treated with bLH. This study indicates that both the small and large luteal cells of late-pregnancy are able to produce P4. However, the large luteal cell of the estrous cycle produces greater quantities of P4 than does the small luteal cell or the large luteal cell of late pregnancy.

Animals↗
PubMed1976

Occlusive arterial disease in the lower leg and foot.

In approaching a patient suspected of peripheral vascular disease the following signs and symptoms are of key importance (16): 1) Pain in the extremity which is induced by exercise and relieved by rest; pain which is influenced by posture is localized to one digit, is unilateral or is paroxysmal. 2) Impaired pulsations of peripheral arteries. 3) Abnormal color of the skin, particularly when affected by raising or lowering the part. 4) Gangrene, ulceration, impaired nail and hair growth, excessive calluses, or paronychial infections. 5) Unusual warmth or coldness. 7) Swelling, atrophy, or difference in length of extremity. 8) Ausculatory evidence of arteriovenous fistula. 9) Cyanosis or unusual pallor of digits when immersed in cold water. 10) Peripheral neuritis.

Age Factors↗