Biomedical subjects

M S Peterson

Publications and source records attributed to M S Peterson.

At least 19 recordsLinked to original sources

PubMed2001

Stochastic kinetic analysis of the Escherichia coli stress circuit using sigma(32)-targeted antisense.

A stochastic Petri net model was developed for simulating the sigma(32) stress circuit in E. coli. Transcription factor sigma(32) is the principal regulator of the response of E. coli to heat shock. Stochastic Petri net (SPN) models are well suited for kinetics characterization of fluxes in biochemical pathways. Notably, there exists a one-to-one mapping of model tokens and places to molecules of particular species. Our model was validated against experiments in which ethanol (inducer of heat shock response) and sigma(32)-targeted antisense (downward regulator) were used to perturb the sigma(32) regulatory pathway. The model was also extended to simulate the effects of recombinant protein production. Results show that the stress response depends heavily on the partitioning of sigma(32) within the cell; that is, sigma(32) becomes immediately available to mediate a stress response because it exists primarily in a sequestered, inactive form, complexed with chaperones DnaK, DnaJ, and GrpE. Recombinant proteins, however, also compete for chaperone proteins, particularly when folded improperly. Our simulations indicate that when the expression of recombinant protein has a low requirement for DnaK, DnaJ, and GrpE, the overall sigma(32) levels may drop, but the level of heat shock proteins will increase. Conversely, when the overexpressed recombinant protein has a strong requirement for the chaperones, a severe response is predicted. Interestingly, both cases were observed experimentally.

Antisense Elements (Genetics)↗

PubMed2001

Radiologic diagnosis of hepatocellular carcinoma.

Substantial recent technologic improvements in CT scanning, US scanning, and MR imaging, together with advances in the understanding of the optimal application of contrast administration techniques, have facilitated advances in radiologic imaging detection for HCC diagnosis. Despite a large number of earlier publications reporting a high sensitivity for imaging detection of HCC, more recent screening studies of large cirrhotic populations confirm that only 37% to 45% of HCC tumor nodules are detected by CT scanning, US scanning, or MR imaging. Future investigation will include efforts to improve the detection of small tumors and to characterize with greater specificity the spectrum of nodular changes that occur with cirrhosis. Although several small series have attempted to characterize cirrhotic nodules by evaluating the relative arterial or portal blood supply, these preliminary results require substantiation with larger series. Continued technologic advances such as multidetector helical CT scanning and new US and MR contrast agents under investigation may improve the imaging characterization of cirrhotic nodules.

Carcinoma, Hepatocellular↗

PubMed2001

A simultaneous multichannel monophasic action potential electrode array for in vivo epicardial repolarization mapping.

While the recording of extracellular monophasic action potentials (MAPs) from single epicardial or endocardial sites has been performed for over a century, we are unaware of any previous successful attempt to record MAPs simultaneously from a large number of sites in vivo. We report here the design and validation of an array of MAP electrodes which records both depolarization and repolarization simultaneously at up to 16 epicardial sites in a square array on the heart in vivo. The array consists of 16 sintered Ag-AgCl electrodes mounted in a common housing with individual suspensions allowing each electrode to exert a controlled pressure on the epicardial surface. The electrodes are arranged in a square array, with each quadrant of four having an additional recessed sintered Ag-AgCl reference electrode at its center. A saline-soaked sponge establishes ionic contact between the reference electrodes and the tissue. The array was tested on six anesthetized open-chested pigs. Simultaneous diagnostic-quality MAP recordings were obtained from up to 13 out of 16 ventricular sites. Ventricular MAPs had amplitudes of 10-40 mV with uniform morphologies and stable baselines for up to 30 min. MAP duration at 90% repolarization was measured and shown to vary as expected with cycle length during sustained pacing. The relationship between MAP duration and effective refractory period was also confirmed. The ability of the array to detect local differences in repolarization was tested in two ways. Placement of the array straddling the atrioventricular (AV) junction yielded simultaneous atrial or ventricular recordings at corresponding sites during 1:1 and 2:1 AV conduction. Localized ischemia via constriction of a coronary artery branch resulted in shortening of the repolarization phase at the ischemic, but not the nonischemic, sites. In conclusion, these results indicate that the simultaneous multichannel MAP electrode array is a viable method for in vivo epicardial repolarization mapping. The array has the potential to be expanded to increase the number of sites and spatial resolution.

Action Potentials↗

PubMed2001

Visual search has memory.

By monitoring subjects' eye movements during a visual search task, we examined the possibility that the mechanism responsible for guiding attention during visual search has no memory for which locations have already been examined. Subjects did reexamine some items during their search, but the pattern of revisitations did notfit the predictions of the memory less search model. In addition, a large proportion of the refixations were directed at the target, suggesting that the revisitations were due to subjects' remembering which items had not been adequately identified. We also examined the patterns of fixations and compared them with the predictions of a memoryless search model Subjects' fixation patterns showed an increasing hazard function, whereas the memoryless model predicts a flat function. Lastly, we found no evidence suggesting that fixations were guided by amnesic covert scans that scouted the environment for new items during fixations. Results do not support the claims of the memorvless search model, and instead suggest that visual search does have memory.

Adult↗

PubMed2001

From the RSNA refresher courses: screening the cirrhotic liver for hepatocellular carcinoma with CT and MR imaging: opportunities and pitfalls.

The inherent distortion of the appearance of liver parenchyma by the underlying pathologic changes of cirrhosis can obscure and simulate malignancy at imaging. That hepatocellular carcinoma is the most common abdominal malignancy worldwide and occurs most often in patients with chronic liver disease and cirrhosis compounds this problem. Magnetic resonance (MR) imaging and, to a lesser extent, computed tomography (CT) can depict the underlying nodular and fibrotic changes in patients with cirrhosis, particularly when siderotic nodular regeneration is present. Application of state-of-the-art helical CT and MR imaging techniques has improved the ability to detect hepatocellular carcinoma in this population, but, even with these advances, fewer than 50% of small tumors are detected with either of these techniques in a screening population. Dynamic hepatic arterial-phase contrast material-enhanced imaging is essential with both CT and MR imaging to achieve even these levels of success. Benign lesions that simulate tumor tissue are encountered in many patients with cirrhosis and include focal fibrosis, infarcted regenerative nodules, arteriovenous shunts, hemangiomas, pseudoaneurysms, and focal transient hepatic enhancement. An awareness of the imaging characteristics of these lesions can help one avoid a mistaken diagnosis of hepatocellular carcinoma in many cases.

Carcinoma, Hepatocellular↗

PubMed2001

Radiologist performance in the diagnosis of internal hernia by using specific CT findings with emphasis on transmesenteric hernia.

PURPOSE: To evaluate the performance of radiologists in the diagnosis of internal hernia with specific computed tomographic (CT) findings. MATERIALS AND METHODS: Abdominal CT scans obtained in 42 patients were retrospectively reviewed by three radiologists. The case group consisted of 18 patients with internal hernias (two paraduodenal, 16 transmesenteric); the comparison group was 24 patients with no internal hernia. Images were reviewed in a random and blinded fashion. Individual and group performance was evaluated with receiver operating characteristic (ROC) analysis, and interobserver agreement was measured with Cronbach coefficient alpha. Individual CT signs relevant as predictors of transmesenteric hernia were identified with logistic regression analysis and ranked by their odds ratio and P values. RESULTS: Both paraduodenal hernias were diagnosed by all readers on the basis of CT signs, including a retrogastric saclike mass of small-bowel loops. Diagnosis of transmesenteric hernia was more difficult and variable, with an average accuracy of area under the ROC curve (A(z)) of 77%, sensitivity of 63%, and specificity of 76%. CT signs of transmesenteric hernia were recognized consistently (Cronbach coefficient alpha >or= 0.80) and included a cluster of dilated small-bowel segments and stretching and displacement of mesenteric vessels. Coexisting volvulus and ischemia were diagnosed with low sensitivity (46% and 43%, respectively) but high specificity (96% and 98%, respectively). CONCLUSION: Diagnosis of internal hernia with CT remains difficult. Special attention should be given to the clustering of bowel loops, the mesenteric vessels, and signs of small-bowel obstruction.

Adolescent↗

PubMed2001

Focal nodular hyperplasia: CT findings with emphasis on multiphasic helical CT in 78 patients.

PURPOSE: To evaluate features of focal nodular hyperplasia (FNH) at multiphasic helical computed tomography (CT). MATERIALS AND METHODS: Clinical, pathologic, and preoperative imaging findings were retrospectively reviewed in 78 patients. Conventional liver CT was performed in nine patients; helical multiphasic CT, in 69. Diagnosis was based on complete resection (n = 20), biopsy (n = 42), or clinical and imaging follow-up for a minimum of 6 months (n = 16). Number, size, location, margins, surface, homogeneity of enhancement, and presence of a central scar, mass effect, exophytic growth, calcification, pseudocapsule, or vessels feeding or draining the lesion were evaluated. RESULTS: CT depicted 124 tumors (mean diameter, 4.1 cm; range, 1-11 cm); 62 were small (< or =3 cm). FNHs were hypervascular and hyperattenuating to liver on 106 of 106 arterial phase scans and were isoattenuating to liver on 82 of 89 delayed scans. Of the 124 tumors, 111 enhanced homogeneously, 109 had a smooth surface, 101 were subcapsular, 89 had ill-defined margins, and 62 had a central scar that was observed more often in large lesions (40 of 62 lesions) than in small lesions (22 of 62 lesions). FNHs less frequently exerted a mass effect (43 lesions), had vessels around or within the lesion (42 lesions), demonstrated exophytic growth (40 lesions), or showed a pseudocapsule (10 lesions). Only one FNH had calcification. CONCLUSION: Helical CT demonstrates characteristic features that may allow confident diagnosis of FNH. In typical cases, neither biopsy nor further imaging is necessary.

Adolescent↗

PubMed2001

Discrimination of small hepatic hemangiomas from hypervascular malignant tumors smaller than 3 cm with three-phase helical CT.

PURPOSE: To compare the appearance of small hepatic hemangiomas at nonenhanced and contrast material-enhanced helical computed tomography (CT) with that of small (<3-cm) hypervascular malignant liver tumors and to evaluate the accuracy of multiphase helical CT for differentiating small hemangiomas from small hypervascular malignant tumors. MATERIALS AND METHODS: Radiologists reviewed multiphase helical CT liver images in 86 patients with 37 hemangiomas and 49 malignant liver tumors. They evaluated lesion type and degree of enhancement for change from arterial to portal venous phase. They rated their confidence in the discrimination of hemangiomas from malignant tumors. RESULTS: At arterial phase CT, enhancement similar to aortic enhancement was observed in 19%-32% of hemangiomas and 0%-2% of malignant tumors; globular enhancement, in 62%-68% and 4%-12%, respectively. At portal venous phase CT, enhancement similar to blood pool enhancement was observed in 43%-54% of hemangiomas and 4%-14% of malignant tumors; globular enhancement, in 46%-49% and 0%-2%, respectively. For all readers and all phases of enhancement, the area under the receiver operating characteristic curves was 0.81-0.87, indicating that inherent accuracy of CT is high and that there was no significant difference (P >.28) in overall accuracy. Readers diagnosed hemangiomas with 47%-53% mean sensitivity with all enhancement phases and diagnosed malignant lesions with 95% mean specificity. CONCLUSION: Small hemangiomas frequently show atypical appearances at CT. Two-phase helical CT does not improve sensitivity but does improve specificity for differentiating hemangiomas from hypervascular malignant tumors.

Carcinoma, Hepatocellular↗

PubMed2001

Performance of CT in detection of bowel injury.

OBJECTIVE: The objective of our study was to identify relevant and reliable CT signs of bowel injury, to determine the overall performance of CT in detection of bowel injuries, and to establish the effect of the training level of radiologists on this performance. MATERIALS AND METHODS: Abdominal CT scans of 112 patients with blunt abdominal trauma were prospectively and retrospectively reviewed. Fifty patients had proven bowel injuries (with or without other visceral injuries), whereas 62 patients had no bowel injury and comprised the comparison or control group. Thirty-one of the 62 patients in the comparison group had surgical proof of abdominal but not bowel or mesenteric injuries. The retrospective review of the 112 CT scans was performed randomly and individually by nine radiologists unaware of the diagnosis, including three faculty abdominal radiologists, three senior residents in training, and three junior residents in training. Individual performance and group performance were evaluated by receiver operating characteristic analysis, and interobserver agreement was tested. Individual CT signs as relevant predictors of bowel injury were identified by logistic regression. RESULTS: Relevant predictors of bowel injury included mesenteric infiltration, bowel wall thickening, extravasation of vascular or enteric contrast agent, and the presence free air. In the retrospective blinded review, CT showed good to excellent interobserver reliability for individual CT signs as well as for diagnosis of bowel and visceral injuries. Faculty radiologists tended to diagnose injuries with greater accuracy and confidence, but they showed significantly better performance than residents only in diagnosing duodenal perforation. For the prospective CT diagnosis of bowel injury, CT had a sensitivity of 64%, an accuracy of 82%, and a specificity of 97%. CONCLUSION: Bowel injuries are challenging to diagnose on CT. Radiologists with various levels of experience and expertise can achieve accurate and reproducible results using a variety of CT criteria.

Abdominal Injuries↗

PubMed2001

Using CT and cholangiography to diagnose biliary tract carcinoma complicating primary sclerosing cholangitis.

OBJECTIVE: The objective of our study was to determine the value of CT and cholangiography for diagnosing biliary tract carcinoma complicating primary sclerosing cholangitis. MATERIALS AND METHODS: One hundred thirteen abdominal CT examinations and cholangiograms in 45 patients with primary sclerosing cholangitis, including 18 patients with established biliary tract carcinoma, were analyzed for tumor. Four radiologists who were unaware of the presence or absence of carcinoma rated each study as to the probability of malignancy. Receiver operating characteristic curve analysis was used to assess the diagnostic performance of CT and cholangiography, the value of imaging signs, and the degree of inter-observer variation in interpretation. Sensitivity and specificity values were calculated. RESULTS: CT outperformed cholangiography in the detection of carcinoma. The average area under the receiver operating characteristic curve was 0.82 for CT and 0.57 for cholangiography (p = 0.003). Sensitivity and specificity for detecting carcinoma using CT were good, with average values of 82% and 80%, respectively. Average sensitivity and specificity for cholangiography were 54% and 53%, respectively. The most reliable sign of tumor on CT was a discrete mass. Progressive biliary dilatation on sequential studies was the most useful sign on cholangiography. Interobserver agreement assessed using the Cronbach alpha was fair for cholangiography and good for CT. CONCLUSION: CT provides good sensitivity and specificity and significantly outperforms cholangiography in detecting biliary tract carcinoma complicating primary sclerosing cholangitis. Despite limitations, CT and cholangiography provide useful information not otherwise available in the treatment of patients with primary sclerosing cholangitis.

Adult↗

PubMed2001

Influence of single and multiple onset distractors on visual search for singleton targets.

In three experiments, we examined attentional and oculomotor capture by single and multiple abrupt onsets in a singleton search paradigm. Subjects were instructed to move their eyes as quickly as possible to a color singleton target and to identify a small letter located inside of it. In Experiment 1, task-irrelevant sudden onsets appeared simultaneously on half the trials with the presentation of the color singleton target. Response times (RTs) were longer when onsets appeared in the display regardless of the number of onsets. Eye-scan strategies were also disrupted by the appearance of the onset distractors, although the proportion of trials on which the eyes were directed to the onsets was the same regardless of the number of onsets. In Experiment 2, we manipulated the time of presentation of two task-irrelevant onsets in order to further examine whether multiple onsets would be attended and fixated prior to attending a color singleton target. Again, subjects made a saccade to a task-irrelevant onset on a substantial proportion of trials prior to fixating the target. However, saccades to the second onset were rare. Experiment 3 served as a replication of Experiment 1 but without the requirement for subjects to move their eyes to detect and identify the singleton target. The RT results were consistent with those in Experiment 1; dual onsets had no larger an effect on response speed than single onset distractors. These data are discussed in terms of the interaction between top-down and bottom-up control of attention and the eyes.

Adult↗

PubMed2001

Attentional guidance of the eyes by contextual information and abrupt onsets.

Contextual cuing is a memory-based phenomenon in which previously encountered global pattern information in a display can automatically guide attention to the location of a target (Chun & Jiang, 1998), leading to rapid and accurate responses. What is not clear is how contextual cuing works. By monitoring eye movements, we investigated the roles that recognition and guidance play in contextual cuing. Recognition does not appear to occur on every trial and sometimes does not have its effects until later in the search process. When recognition does occur, attention is guided straight to the target rather than in the general direction. In Experiment 2, we investigated the interaction between memory-driven search (contextual cuing) and stimulus-driven attentional capture by abrupt onsets. Contextual cuing was able to override capture by abrupt onsets. In contrast, onsets had almost no effect on the degree of contextual cuing. These data are discussed in terms of the role of top-down and bottom-up factors in the guidance of attention in visual search.

Adult↗

PubMed2000

Evidence for distinct attentional bottlenecks in attention switching and attentional blink tasks.

E. Weichselgartner and G. A. Sperling (1987), using rapid serial visual presentation (RSVP), estimated that attention could be moved to a new spatial location within 300-400 ms. H. J. Müller and P. M. Rabbit (1989) used a spatial cuing task and found a similar time course for voluntarily redeploying attention. A separate phenomenon known as the attentional blink (AB) also follows a similar time course, yet occurs when participants attend to a single spatial location. The present study found that attention can be shifted more quickly than previously estimated and that part of the deficit observed during searches of spatially distinct RSVP streams is due to an AB. The results support some early and late selection accounts for the temporal dynamics of visual attention and suggest different bottlenecks during visual selection. The implications for visual search and visual processing are discussed.

Attention↗

PubMed2000

Antisense downregulation of sigma(32) as a transient metabolic controller in Escherichia coli: effects on yield of active organophosphorus hydrolase.

Plasmids containing an antisense fragment of the sigma(32) gene were constructed and introduced into Escherichia coli cells. Downregulation of the sigma(32)-mediated stress response was evaluated under heat shock and ethanol stress and during the production of organophosphorus hydrolase (OPH). Northern blot analyses revealed that sigma(32) sense mRNA was virtually undetected in antisense-producing cultures from 5 to 20 min after antisense induction. However, lower-molecular-weight bands were found, presumably due to partial degradation of sigma(32) mRNA. While a >10-fold increase in sigma(32) protein level was found under ethanol stress in the control cultures, antisense producing cultures resulted in a <3-fold increase, indicating downregulation of sigma(32). Correspondingly, antisense synthesis resulted in a decreased level of a sigma(32) regulated chaperone (GroEL) for the first 2 h after induction relative to control cultures without sigma(32) antisense mRNA. The total yield of OPH in the presence of sigma(32) antisense was, on average, 62% of the yield without antisense. However, during sigma(32) antisense production, a sixfold-higher specific OPH activity was observed compared to non-antisense-producing cultures.

Aryldialkylphosphatase↗

PubMed2000

Islet cell tumor of the pancreas: biphasic CT versus MR imaging in tumor detection.

PURPOSE: To compare the effectiveness of biphasic computed tomography (CT) and magnetic resonance (MR) imaging in the detection of pancreatic islet cell tumors. MATERIALS AND METHODS: Retrospective quantitative, qualitative, and receiver operating characteristic analyses of biphasic CT and MR imaging were performed in 19 patients with 26 histopathologically proved islet cell tumors. Delayed arterial dominant-phase (AP) and portal venous-phase (PVP) biphasic CT was performed after the administration of contrast material. MR imaging included T1-weighted spin-echo (SE) and T2-weighted SE or fast SE imaging, fat-saturated T1-weighted SE imaging, dynamic contrast material-enhanced T1-weighted gradient-echo imaging, and delayed enhanced T1-weighted SE imaging with or without fat saturation. RESULTS: PVP CT and delayed enhanced T1-weighted MR imaging had the highest A(z) values (0.98 and 0.97, respectively; P <.05). Delayed enhanced T1-weighted MR imaging had the highest relative sensitivity (14-15 [74%-79%] of 19 lesions), followed by PVP CT (18-19 [69%-73%] of 26 lesions), AP CT (17-19 [65%-73%] of 26 lesions), fat-saturated T1-weighted MR imaging (eight to 10 [57%-71%] of 14 lesions), T2-weighted (16-17 [62%-65%] of 26 lesions), T1-weighted (15-18 [58%-69%] of 26 lesions) MR imaging, and dynamic MR imaging (nine [56%] of 16 lesions). CONCLUSION: Biphasic (especially PVP) CT and MR imaging have similar effectiveness in the detection of islet cell tumors if fat-saturated T1-weighted and delayed enhanced T1-weighted MR imaging are included.

Adenoma, Islet Cell↗

PubMed2000

Extrahepatic metastases of hepatocellular carcinoma.

PURPOSE: To determine the relative frequency, incidence, and locations of metastases of hepatocellular carcinoma (HCC), correlate extrahepatic metastatic disease with intrahepatic tumor staging, and determine the computed tomographic (CT) manifestations of HCC metastases. MATERIALS AND METHODS: CT findings in 403 consecutive patients with HCC at our institution since 1992 were reviewed retrospectively. One hundred forty-eight patients with extrahepatic metastatic HCC were identified, and the locations, sizes, and attenuation and enhancement characteristics of the lesions were recorded. RESULTS: A majority (128 [86%] of 148) of patients with extrahepatic HCC foci had either intrahepatic stage IVA tumor (112 [76%] patients) or an intrahepatic stage III tumor (16 [11%] patients) at the occurrence of metastases. The most frequent site of the first detectable metastasis was the lung (58 [39%] patients). Tabulation of all extrahepatic metastatic sites showed the most common to be the lung in 81 (55%) patients, the abdominal lymph nodes in 60 (41%) patients, and the bone in 41 (28%) patients. CONCLUSION: The lung, abdominal lymph nodes, and bone are the most common sites of extrahepatic metastatic HCC. Most extrahepatic HCC occurs in patients with advanced intrahepatic tumor stage (stage IVA). Incidental extrahepatic lesions at CT in patients with stage I or II intrahepatic HCC are unlikely to represent metastatic HCC.

Adolescent↗

PubMed2000

Pretransplantation surveillance for possible hepatocellular carcinoma in patients with cirrhosis: epidemiology and CT-based tumor detection rate in 430 cases with surgical pathologic correlation.

PURPOSE: To determine the prevalence of clinically unsuspected hepatocellular carcinoma (HCC) with advanced cirrhosis and assess the sensitivity of helical computed tomographic (CT) surveillance for tumor detection in these patients. MATERIALS AND METHODS: Prospective direct correlation of CT findings with explanted liver specimen findings was performed in 430 transplant recipients with cirrhosis. The prevalence of clinically unsuspected HCC according to liver disease cause was evaluated. Serum alpha-fetoprotein (AFP) values in patients with and those without tumor were recorded. Prospective and retrospective CT tumor detection was evaluated with respect to CT technique and time from CT to transplantation. RESULTS: HCC was found in 59 (14%) of 430 transplant recipients without suspicion of tumor before referral for transplantation. HCC was most prevalent with hepatitis B (27%) and hepatitis C (22%). Serum AFP values were not sensitive for detection of most small tumors. With triphasic helical CT, the prospective and retrospective rates of identifying patients with tumor were 59% and 68%, respectively; the prospective and retrospective tumor nodule detection rates were 37% and 44%, respectively. Tumor detection rates were highest with CT performed within 67 days before transplantation. CONCLUSION: Clinically unsuspected HCC is most prevalent with cirrhosis secondary to hepatitis B or C, and, when evaluated at CT, is best detected with triphasic contrast material-enhanced helical imaging performed within 67 days before transplantation.

Adolescent↗

PubMed2000

Hepatic angiosarcoma: findings on multiphasic contrast-enhanced helical CT do not mimic hepatic hemangioma.

OBJECTIVE: The objective of our study was to identify multiphasic contrast-enhanced helical CT findings of angiosarcoma of the liver to determine whether this tumor could be confused with hemangioma of the liver. CONCLUSION: Angiosarcoma of the liver is a multifocal tumor with a variety of findings on multiphasic contrast-enhanced helical CT. None of the findings would usually be confused with the typical findings of hepatic hemangioma.

Adolescent↗