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Biomedical subjects

D L Burk

Publications and source records attributed to D L Burk.

At least 37 records · Page 2Linked to original sources
PubMed1990

MRI of aggressive fibromatosis: frequent appearance of high signal intensity on T2-weighted images.

Magnetic resonance imaging of seven patients with eight pathologically proven desmoid tumor tumors was performed and retrospectively reviewed. On T2-weighted images, all but one lesion demonstrated increased signal intensity relative to muscle, and had signal intensity similar to that of fat. The signal was heterogenous in six of these seven lesions. In a patient with synchronous multicentric lesions, light microscopy correlation revealed increased cellularity in one lesion with increased signal intensity and dense collagenous elements in a second lesion, with decreased signal intensity. High signal intensity appears to be typical but nonspecific, and in following these patients could indicate recurrent tumor, superimposed inflammatory process or granulation tissue.

Abdominal Neoplasms↗
PubMed1990

Bone marrow findings on magnetic resonance images of the knee: accentuation by fat suppression.

Long TR/double spin-echo magnetic resonance images of the knee were obtained with and without the use of fat suppression techniques in seven patients with high signal intramedullary lesions. Comparison between images was performed qualitatively and quantitatively. Contrast-to-noise ratios between focal defects and surrounding fatty marrow were higher with fat suppression in all cases. The mean contrast-to-noise ratio for images obtained with fat suppression was 53.6, while for images obtained without fat suppression the mean contrast-to-noise ratio was 17.3 (p less than 0.01).

Adipose Tissue↗
PubMed1990

Variable flip angle imaging and fat suppression in combined gradient and spin-echo (GREASE) techniques.

Conventional "proton density" and "T2-weighted" spin-echo images are susceptible to motion induced artifact, which is exacerbated by lipid signals. Gradient moment nulling can reduce motion artifact but lengthens the minimum TE, degrading the "proton density" contrast. We designed a pulse sequence capable of optimizing proton density and T2-weighted contrast while suppressing lipid signals and motion induced artifacts. Proton density weighting was obtained by rapid readout gradient reversal immediately after the excitation RF pulse, within a conventional spin-echo sequence. By analyzing the behavior of the macroscopic magnetization and optimizing excitation flip angle, we suppressed T1 contribution to the image, thereby enhancing proton density and T2-weighted contrast with a two- to four-fold reduction of repetition time. This permitted an increased number of averages to be used, reducing motion induced artifacts. Fat suppression in the presence of motion was investigated in two groups of 8 volunteers each by (i) modified Dixon technique, (ii) selective excitation, and (iii) hybrid of both. Elimination of fat signal by the first technique was relatively uniform across the field of view, but it did not fully suppress the ghosts originating from fat motion. Selective excitation, while sensitive to the main field inhomogeneity, largely eliminated the ghosts (0.21 +/- 0.05 vs. 0.29 +/- 0.06, p less than 0.01). The hybrid of both techniques combined with bandwidth optimization, however, showed the best results (0.17 +/- 0.04, p less than 0.001). Variable flip-angle imaging allows optimization of image contrast which, along with averaging and effective fat suppression, significantly improves gradient- and spin-echo imaging, particularly in the presence of motion.

Adipose Tissue↗
PubMed1990

Magnetic resonance imaging of bone marrow: diagnostic value in diffuse hematologic disorders.

Magnetic resonance imaging (MRI) has value in characterizing normal and abnormal bone marrow because of its ability to distinguish fat from other tissues. Due to this advantage, hematologic disorders resulting in alterations of the normal cellular and fatty marrow distribution can be appreciated. In this article, the role of MRI in diffuse hematologic disorders is emphasized. At birth, almost all marrow is cellular, but by age 25, cellular marrow is restricted to the axial skeleton and proximal femoral and humeral metaphysis. The remainder is fatty, consisting of 80% fat, 15% water, and 5% protein. With increased need for hematopoiesis, reconversion from fatty to cellular marrow occurs in many diffuse disease states. Diffuse diseases that affect bone marrow production are divided into four categories representing conditions that affect the pluripotent hematopoietic stem cell. These include stem cell failure resulting in aplastic anemia, uncontrolled stem cell proliferation as exemplified by polycythemia vera, stem cell dysplasia such as sickle cell anemia, and malignant transformations or replacement. The MRI appearance of these disorders is discussed in this article. The use of spin-echo (SE) sequences is the most common approach to bone marrow imaging. With T1-weighted SE images, fatty marrow will appear bright and cellular marrow, with lower fat content, will exhibit a lower density signal. With T2-weighted SE pulse sequences, contrast between fatty marrow and cellular marrow decreases. Contrast between fatty and cellular marrow is enhanced with chemical shift imaging, including Dixon out-of-phase imaging, as emphasized in this article. MRI presents a more global view of the bone marrow than biopsy material and should provide a better understanding of diffuse hematologic disease progression and resolution.

Bone Marrow↗
PubMed1990

Recent advances in magnetic resonance imaging of the knee.

The examination of the knee has rapidly become the most important non-neurologic application of MR imaging. The widespread availability of high signal-to-noise knee coils has made routine imaging with T2-weighted sequences in both coronal and sagittal planes possible in 30 minutes. The spin-echo sequence remains the most important imaging technique, although many newer sequences have also been applied to the knee, with varying degrees of success. Important pitfalls in diagnosis, such as high signal intensity in the posterior horn of the medial meniscus and the transverse meniscal ligament, displaced buckethandle meniscal tears, and discoid menisci, can be recognized with experience. Common clinical problems that are encountered include meniscal cysts, osteonecrosis, and bone bruises. Detection of subtle injuries of the medial collateral ligament, patellar tendon, and anterior cruciate ligament requires careful observation. Intra-articular loose bodies can be reliably detected with MR imaging, and it should be recognized that localized pigmented villonodular synovitis can sometimes simulate the appearance of a loose body. MR imaging is a valuable noninvasive procedure that is complementary to arthroscopy in the evaluation of diseases of the knee.

Humans↗
PubMed1989

Biochemical events essential to the recombination activity of Escherichia coli RecA protein. I. Properties of the mutant RecA142 protein.

We have characterized the biochemical properties of Escherichia coli RecA142 protein, the product of a recA allele that is phenotypically defective in genetic recombination. In vitro, this mutant RecA protein is totally defective in DNA heteroduplex formation. Despite this defect, RecA142 protein is not deficient in all other biochemical activities. RecA142 protein is proficient in single-strand (ss) DNA binding ability, ssDNA-dependent ATPase activity, and DNA-free self-association (although the first 2 properties show a greater sensitivity to NaCl concentration than does the wild-type protein). However, RecA142 protein is deficient in four properties: (1) its ssDNA-dependent ATPase activity is completely inhibited by ssDNA binding (SSB) protein, demonstrating that RecA142 protein is unable to compete effectively with SSB protein for ssDNA binding sites; (2) it is unable to promote the coaggregation of ssDNA and double-strand (ds) DNA; (3) its M13 dsDNA-dependent ATPase activity is attenuated to approximately 5% of the level of the wild-type protein; (4) it is unable fully to develop characteristics of the high-affinity ssDNA-binding state that is normally induced by ATP. The first three deficiencies correspond to defects in the presynaptic, synaptic and postsynaptic steps of the in vitro DNA strand exchange reaction, respectively; the fourth is the likely fundamental basis for defects 1 and 3. Therefore, one or more of these properties must be important to both the in vitro and in vivo processes.

Adenosine Triphosphatases↗
PubMed1989

The effect of peptides and monoclonal antibodies that bind to platelet glycoprotein IIb-IIIa complex on the development of clot tension.

The development of tension in platelet-rich clots is a manifestation of fibrin polymer binding to platelets as well as platelet contractile activity. Arg-Gly-Asp(RGD)-containing peptides of fibrinogen alpha-chain and gamma-400-411 of fibrinogen gamma chain increased clot tension considerably, especially when it developed under isometric conditions. Morphometry revealed increased confluence of oriented fibrin and platelet aggregates. Monoclonal antibodies directed against different epitopes on the glycoprotein IIb-IIIa complex had varying effects on clot tension development. Monoclonal antibodies A2A9 and 7E3 inhibited clot tension while T10 and 10E5 increased it. Since neither peptides nor antibodies affected the platelet actomyosin ATPase activity, their effect on tension must reflect the interaction between platelets and polymerizing fibrin. We conclude that gamma-400-411 and RGD-peptides increase platelet-polymerizing fibrin interaction. This suggests that clot tension requires a platelet receptor for polymerizing fibrin, which is different from the fibrinogen receptor domain required for aggregation. The results with the monoclonal antibodies support this hypothesis.

Antibodies, Monoclonal↗
PubMed1989

Variable-flip-angle spin-echo MR imaging of the pelvis: more versatile T2-weighted images.

Dependence on T1 contrast can be reduced by changing the excitation flip angle. The authors compared T2-weighted spin-echo images (with 30 degrees and 90 degrees flip angles) of the male and female pelvis in 22 individuals. In six women imaged with a 1,000/80 sequence (repetition time msec/echo time msec), signal difference-to-noise ratios (SD/Ns) were higher with a 30 degree flip angle than with a 90 degree angle for urine/fat (mean, 15.2 vs -6.2; P less than .05) and endometrium/myometrium (13.8 vs 9.0, P less than .05). In eight additional examinations, a 1,000/80 sequence with a 30 degree flip angle and two signal averages had less motion artifact (1.2 vs 2.7, P less than .01) than a 2,000/80 sequence with a 90 degree angle and one signal average (4.5 minutes each); SD/Ns were similar. In a third series of experiments, contiguous sections without cross talk, obtained by interleaving two 1,000/100, 30 degrees-flip-angle acquisitions, had better contrast than contiguous sections obtained at 2,400/100 with a 90 degree flip angle (10 minutes each), with SD/Ns of urine/fat of 28.5 versus 16.1 (P less than .01) and SD/Ns of endometrium/myometrium of 15.5 versus 7.8 (P less than .05). Reducing the flip angle can improve examination time, contrast, or motion artifact suppression or eliminate cross talk in T2-weighted spin-echo MR imaging of the pelvis.

Female↗
PubMed1989

Rotator cuff tears: prospective comparison of MR imaging with arthrography, sonography, and surgery.

Thirty-eight patients with suspected rotator cuff tears were examined at 1.5 T by using a loop-gap resonator surface coil. The MR findings were compared prospectively in a blinded fashion with the results from double-contrast arthrography in all 38 patients, high-resolution sonography in 23 patients, and surgery in 16 patients. In the total group of 38 patients, MR imaging detected 22 of 22 tears and 14 of 16 intact cuffs as determined by arthrography. In the 16 surgically proved cases, MR and arthrography showed identical results, with 92% sensitivity in the diagnosis of 12 tears and 100% specificity in the diagnosis of four intact cuffs. In a subgroup of 23 patients, sonography detected nine of 15 tears and seven of eight intact cuffs as determined by comparison with arthrography. In 10 surgically proved cases, sonography was 63% sensitive in the diagnosis of eight rotator cuff tears and 50% specific in the diagnosis of two intact cuffs. For the diagnosis of rotator cuff tears, MR imaging is comparable to arthrography in both sensitivity and specificity. In this study, sonography was not as accurate in the diagnosis of rotator cuff tears as were the other two techniques. These results suggest that MR imaging should be considered the noninvasive test of choice for patients with suspected rotator cuff disease.

Arthrography↗
PubMed1989

Sampling bandwidth and fat suppression: effects on long TR/TE MR imaging of the abdomen and pelvis at 1.5 T.

In MR imaging, the sampling bandwidth is the rate at which the signal is digitized by the analog-to-digital converter. Reducing the sampling bandwidth can decrease noise in long TE images at the expense of increases in the artifacts of chemical-shift misregistration and motion. We compared 39 pairs of axial images with bandwidths of 32 kHz and 8-10 kHz. In 23 of these comparison studies (six female pelvis, seven male pelvis, 10 abdomen), all other variables were held constant, and in 16 comparisons (10 female pelvis, six male pelvis), signal from fat was suppressed in images with reduced bandwidth. Six patients with 11 liver lesions were included in those undergoing abdominal imaging. In three patients, fat was suppressed in images of the abdomen. The contrast-to-noise ratio was greater with reduced bandwidth for urine vs fat (24.5 vs 17.2; p less than .05) and central vs peripheral parts of the prostate gland (34.1 vs 22.7; p less than .02). In the abdomen, the contrast-to-noise ratio was increased between liver and right kidney (36.6 vs 25.2; p less than .01) and between liver and lesion (30.2 vs 18.2; p less than .005), but the motion-induced artifact was worse. An increase in chemical-shift misregistration did not affect the appearance of the internal structure of the uterus, prostate gland, or liver, but it made examination of the ovaries, seminal vesicles, and extrahepatic tissues difficult. The chemical-shift artifact in pelvic images could be eliminated by suppressing signal from fat with frequency-selective saturation pulses, but results were less satisfactory in the abdomen. When reduced bandwidth and fat suppression were combined, the contrast-to-noise ratio was improved for endometrium vs myometrium (22.9 vs 15.2; p less than .05) and central vs peripheral parts of the prostate gland (62.7 vs 28.5; p less than .02). Reduction of the sampling bandwidth is a promising technique for imaging the pelvis with small field of view and long TR/TE, but it currently appears less promising for images in the upper abdomen at 1.5 T. The increased chemical-shift artifact caused by reduced bandwidth can be eliminated by suppressing signal from fat.

Abdomen↗
PubMed1988

Spondyloarthropathy of the cervical spine in long-term hemodialysis.

Changes stimulating osteomyelitis have recently been described in patients undergoing long-term hemodialysis. These consist of disk-space narrowing and irregularity of adjacent end plates. However, the characteristic prevertebral mass and clinical evidence of infection are often absent. In the appropriate clinical situation, although plain radiography and computed tomography have been helpful, magnetic resonance imaging may be more definitive in excluding infection and may obviate biopsy. The authors' imaging experience with five patients with this entity forms the basis of this report.

Aged↗
PubMed1988

Hyaline cartilage-origin bone and soft-tissue neoplasms: MR appearance and histologic correlation.

Magnetic resonance (MR) images and histologic studies of 16 chondroid-matrix lesions were reviewed to determine if any distinctive morphologic or signal features might be discerned. Ten biopsy-proved nonchondroid bone lesions were compared in terms of configuration and signal characteristics. The tumor matrix had a distinctive appearance of homogeneous high signal intensity in a defined lobular configuration on images of all hyaline cartilage lesions obtained with a long repetition time and a long echo time. The areas of hyperintensity relative to muscle corresponded to areas of hyaline cartilage matrix with its uniform composition, low cellularity, and high water content; the lobular morphologic characteristic had an identical histologic correlate. The chondroblastomas, clear-cell chondrosarcoma, and synovial chondromatosis demonstrated a much more cellular stroma, with only scattered islands of chondroid matrix, and were isointense or hypointense compared with muscle on all MR sequences. The distinctive lobular, high-intensity MR appearance was not seen in the ten nonchondroid bone lesions.

Adolescent↗
PubMed1988

Radiographically negative avascular necrosis: detection with MR imaging.

To correlate the morphologic appearance on magnetic resonance (MR) images of radiographically negative avascular necrosis (AVN) of the femoral head with that on computed tomographic (CT) and radionuclide scans, the radiographic and clinical records of 24 patients were reviewed retrospectively. In 18 patients the MR signal intensity features were monitored by means of serial imaging. All MR studies included T1-weighted (short repetition time [TR], short echo delay time [TE] ) imaging and T2-weighted imaging (long TR, long TE). Thirty-one hips were determined with MR to be involved by AVN; 27 were staged on the basis of signal intensity characteristics within the low-intensity rim. Core decompression was performed on 18 hips. Afterward, progression of disease occurred in only one hip. Fourteen of the 16 asymptomatic patients (88%) had early-stage focal lesions. CT scans were obtained in 15 patients and radionuclide scans in 21. Ten hips at radionuclide imaging and five at CT appeared normal when MR results were distinctly abnormal. MR can depict early radiographically negative AVN in asymptomatic individuals. At this early stage, the lesions in this series appear to be nonprogressive after treatment.

Adult↗
PubMed1988

Motion artifact reduction in MR imaging of the abdomen: gradient moment nulling versus respiratory-sorted phase encoding.

Two currently available methods of reducing motion-induced artifact on magnetic resonance (MR) images, respiratory-sorted phase encoding (RSPE) and gradient moment nulling (GMN), were compared in images of the upper abdomen obtained with long repetition and long echo times. For ten subjects, two series of axial MR images were obtained with identical parameters except that RSPE was used in one and GMN in the other. Images were evaluated by three independent radiologists, and region-of-interest measurements were obtained to calculate signal-difference-to-noise ratios (SD/Ns) for liver versus gallbladder and liver versus the right kidney. Maximum ghost intensity and the standard deviation of motion-induced noise were also calculated. GMN was superior to RSPE for motion artifact reduction in all ten cases. The SD/N for liver versus both gallbladder and right kidney was significantly higher with GMN. Presaturation pulses applied outside the volume of interest reduced aortic and inferior vena cava signal and virtually eliminated artifact from these vessels but did not noticeably affect signal from intrahepatic vessels. GMN combined with presaturation pulses is a highly effective method of motion artifact reduction in the upper abdomen.

Abdomen↗
PubMed1988

Avascular necrosis versus other diseases of the hip: sensitivity of MR imaging.

Magnetic resonance (MR) imaging of the hip has been useful in the examination of patients for the presence of avascular necrosis (AVN). In the detection of AVN, MR imaging is more sensitive than computed tomography or nuclear scintigraphy. This study assessed the usefulness of MR imaging in the differentiation of AVN from other hip diseases. Twenty-two cases of non-AVN hip disease were matched with 23 biopsy-proved cases of AVN and ten normal controls. MR images were rated in a blinded manner by five experienced radiologists, and receiver operating characteristic (ROC) analysis was performed on the data. In the discrimination of AVN from other hip diseases or from normality, the A(z) value (the area under the ROC curve) was 98.6. With a specificity of 98%, MR imaging was 97% sensitive in the differentiation of AVN from normality, 85% sensitive in the differentiation of AVN from non-AVN disease, and 91% sensitive in the differentiation of AVN from both conditions. MR imaging may therefore help discriminate between AVN and other hip diseases.

Diagnosis, Differential↗
PubMed1988

Meniscal and ganglion cysts of the knee: MR evaluation.

Meniscal and ganglion cysts frequently present as palpable masses of the knee but occur at different locations than do popliteal cysts. Meniscal cysts also may be discovered incidentally on studies performed for suspected internal derangement. Sixteen cystic lesions of the knee were evaluated with MR, including 11 meniscal cysts and five ganglion cysts. Scans were performed at 1.5 T by using a transmit/receive extremity coil or a receive-only surface coil. Standard spin-echo imaging, including at least one long-TR/asymmetric-TE sequence, was performed in all cases. In six patients, gradient-echo, reduced flip-angle sequences also were done. All meniscal cysts (but none of the ganglion cysts) were associated with horizontal meniscal tears. Cysts were visualized best on the long-TR/TE images; meniscal tears were seen best on the short-TR/TE and long-TR/short-TE images. Meniscal tears and cysts were also seen well on the fast-scanning sequences. Septations were noted in four meniscal cysts and in four ganglion cysts on the long-TR/TE images. Long-TR/TE images were also useful in showing the relationship between the cyst and joint capsule in three of the ganglion cysts. MR imaging is an effective, noninvasive method for evaluating cystic lesions of the knee. Meniscal cysts are always associated with underlying horizontal meniscal tears, which can be detected with MR. Ganglion cysts are not associated with meniscal tears, but may have connections to the joint capsule, which can be detected with MR.

Humans↗
PubMed1988

MR imaging of soft-tissue hemangiomas: correlation with pathologic findings.

Soft-tissue hemangiomas have been described in MR imaging, but a histopathologic correlation to better understand the MR appearance has not been reported. Five patients with intramuscular soft-tissue hemangiomas were imaged in orthogonal planes on a 1.5-T system with spin-echo (SE) short-TR/TE sequences (600/20) and long-TR/TE sequences (2500/20-80). Complete intact surgical specimens were obtained, and gross and histopathologic findings were compared with MR findings. A striated-septated configuration with a high signal intensity on long-SE sequences (TE greater than 75 msec) correlated with endothelial-lined vascular channels separated by fibrous and/or fatty linear strands. An awareness of the morphologic MR pattern of soft-tissue hemangiomas may aid in recognition of these lesions.

Adolescent↗