Dual phase hepatic CT: influence of scanning direction on liver attenuation

OBJECTIVE

We measured changes in hepatic attenuation during arterial and portal phase acquisition of hepatic CT in the craniocaudal and caudocranial directions.

SUBJECTS AND METHODS

In 10 of 20 patients undergoing dual phase helical CT during staging for colorectal cancer, images in both phases were obtained in the craniocaudal direction. Ten patients underwent imaging in the caudocranial direction. Attenuation values in the aorta and in the peripheral and central liver regions of interest were measured on each slice. Central and peripheral liver attenuation was also measured in 10 additional patients undergoing unenhanced CT.

RESULTS

Both peripheral and central regions of interest revealed progressively increasing attenuation during the arterial phase, irrespective of scanning direction. During the portal phase, hepatic attenuation was stable in the craniocaudal direction but decreased in the caudocranial direction (p < 0.05, Wilcoxon's signed rank sum test). Central hepatic attenuation was lower than peripheral attenuation in unenhanced livers and in enhanced livers during both phases of caudocranial acquisition. We determined no significant difference during the arterial phase of enhancement in the craniocaudal direction.

CONCLUSION

The direction of acquisition does not influence sequential liver enhancement during the arterial phase. Craniocaudal acquisition produces more stable enhancement during the portal phase. Differences in attenuation between the central and peripheral areas of the liver are probably unrelated to contrast administration.

Phosphorylation of dynamin I on Ser-795 by protein kinase C blocks its association with phospholipids

Dynamin I is phosphorylated in nerve terminals exclusively in the cytosolic compartment and in vitro by protein kinase C (PKC). Dephosphorylation is required for synaptic vesicle retrieval, suggesting that its phosphorylation affects its subcellular localization. An in vitro phospholipid binding assay was established that prevents lipid vesiculation and dynamin lipid insertion into the lipid. Dynamin I bound the phospholipid in a concentration-dependent and saturable manner, with an apparent affinity of 230 +/- 51 nM. Optimal binding occurred with mixtures of phosphatidylserine and phosphatidylcholine of 1:3 with little binding to phosphatidylcholine or phosphatidylserine alone. Phospholipid binding was abolished after dynamin I phosphorylation by PKC and was restored after dephosphorylation by calcineurin. Matrix-assisted laser desorption/ionization-time of flight mass spectrometry revealed the phosphorylation site in PKCalpha-phosphorylated dynamin I as a single site at Ser-795, located near a binding site for the SH3 domain of p85, the regulatory subunit of phosphatidylinositol 3-kinase. However, phosphorylation had no effect on dynamin binding to a bacterially expressed p85-SH3 domain. Thus, phosphorylation of dynamin I on Ser-795 prevents its association with phospholipid, providing a basis for the cytosolic localization of the minor pool of phospho-dynamin I that mediates synaptic vesicle retrieval in nerve terminals.

Phosphorylation of a new brain-specific septin, G-septin, by cGMP-dependent protein kinase

The septins are a family of GTPase enzymes, some of which are required for the cytokinesis stage of cell division and others of which are associated with exocytosis. We purified and cloned the cDNA for a 40-kDa protein from rat brain that is a substrate for type I cGMP-dependent protein kinase (PKG). The amino acid sequences of two tryptic peptides of P40 showed high homology to the septins. Molecular cloning revealed the 358-amino acid P40 to be a new member of the septin family. P40 was named G-septin, as it is phosphorylated in vitro by PKG, but relatively poorly by the related cAMP-dependent protein kinase and not by protein kinase C. Two splice variants of G-septin (alpha and beta) were found with distinct N and C termini, but a common GTPase domain. G-septin lacks the C-terminal coiled-coil domain characteristic of all other mammalian septins and uniquely has two predicted phosphorylation site motifs for type I PKG. Photoaffinity labeling with [alpha-(32)P]GTP confirmed that G-septin is a GTP-binding protein. Northern blotting showed that G-septin mRNA (5.0 kilobases) is highly expressed in brain and undetectable in 12 other tissues, indicating that the G-septins are primarily neuronal proteins. Very low levels of 6.0-, 3.4-, and 2.6-kilobase transcripts were found in testis. Our results reveal a new class of brain-specific septins that may be regulated by PKG in neurons.

MRI of liver: a comparison of CNR enhancement using high dose and low dose ferumoxide infusion in patients with colorectal liver metastases

The purpose of this study was to compare the effects of high dose (HD) and low dose (LD) ferumoxides infusions on lesion-to-liver contrast-to-noise ratio (CNR) using four different T(2)-weighted MR sequences. Seventy-three patients with known colorectal liver metastases underwent T(2)-weighted fast spin echo (FSE) imaging before and after ferumoxides. After ferumoxides, T(2)-weighted dual echo (DE) and T(2)-weighted GRE FLASH images were also obtained. To evaluate the relationship between TE length and lesion-to-liver CNR, the same FLASH sequence was repeated in 18 LD patients after lengthening the TE. Ferumoxides was administered at a dose of 15 micromol/kg (HD) and 7.5 micromol/kg (LD) in 45 and 28 patients, respectively. The effects of HD and LD ferumoxides infusions were measured as the percentage signal intensity change (PSIC) in the liver and lesions, lesion-to-liver CNR and the change in lesion-to-liver CNR (DeltaCNR). In both LD and HD groups, all CNR values obtained after SPIO were significantly greater than those observed with unenhanced FSE (p < 0.01). There was no significant difference between the mean CNR values obtained with either dose for any sequence. With the FLASH sequence, CNR increased progressively with longer TE. At the longest TE of 26 ms, mean CNR was higher than that recorded with any of the other sequences. Although mean liver PSIC was significantly greater in the HD group than in the LD group (p < 0.01) because the mean lesion PSIC was also greater in the HD group, the mean DeltaCNR after ferumoxides was not significantly different in the two groups. LD SPIO enhanced MR significantly increases lesion-to-liver CNR compared with unenhanced images. At 1. 0 T, HD and LD ferumoxides infusions produce comparable lesion-to-liver CNR. Our results suggest that at 1.0 T ferumoxides may be administered at a dose of 7.5 micromol/kg without loss of image quality.

Signaling through sphingolipid microdomains of the plasma membrane: the concept of signaling platform

Transmembrane signaling requires modular interactions between signaling proteins, phosphorylation or dephosphorylation of the interacting protein partners and temporary elaboration of supramolecular structures, to convey the molecular information from the cell surface to the nucleus. Such signaling complexes at the plasma membrane are instrumental in translating the extracellular cues into intracellular signals for gene activation. In the most straightforward case, ligand binding promotes homodimerization of the transmembrane receptor which facilitates modular interactions between the receptor's cytoplasmic domains and intracellular signaling and adaptor proteins. For example, most growth factor receptors contain a cytoplasmic protein tyrosine kinase (PTK) domain and ligand-mediated receptor dimerization leads to cross phosphorylation of tyrosines in the receptor's cytoplasmic domains, an event that initiates the signaling cascade. In other signaling pathways where the receptors have no intrinsic kinase activity, intracellular nonreceptor PTKs (i.e. Src family PTKs, JAKs) are recruited to the cytoplasmic domain of the engaged receptor. Execution of these initial phosphorylations and their translation into efficient cellular stimulation requires concomitant activation of diverse signaling pathways. Availability of stable, preassembled matrices at the plasma membrane would facilitate scaffolding of a large array of receptors, coreceptors, tyrosine kinases and other signaling and adapter proteins, as it is the case in signaling via the T cell antigen receptor. The concept of the signaling platform has gained usage to characterize the membrane structure where many different membrane-bound components need to be assembled in a coordinated manner to carry out signaling. The structural basis of the signaling platform lies in preferential assembly of certain classes of lipids into distinct physical and functional compartments within the plasma membrane. These membrane microdomains or rafts (Figure 1) serve as privileged sites where receptors and proximal signaling molecules optimally interact. In this review, we shall discuss first how signaling platforms are assembled and how receptors and their signaling machinery could be functionally linked in such structures. The second part of our review will deal with selected examples of raft-based signaling pathways in T lymphocytes and NK cells to illustrate the ways in which rafts may facilitate signaling.

Imaging liver metastases: current limitations and future prospects

The diagnosis of liver metastasis relies on imaging. The sensitivity of ultrasound, CT and magnetic resonance techniques for detecting liver metastases can only be assessed in comparison with surgical inspection, intraoperative ultrasound and pathological examination, all methods that are of uncertain accuracy in detecting very small lesions. With current imaging technology, we should detect virtually all liver metastases 2 cm or larger in size, and most of those 1-2 cm in size. Even with optimum imaging, at present we detect only about one-half of metastatic nodules smaller than 1 cm in patients undergoing liver resection and pathological correlation. Improvements in the earlier detection of metastases will probably require a fundamentally different approach from that of conventional anatomical methods. Micrometastases produce alterations in blood flow that may be recognized by radionuclide or Doppler perfusion methods.

Ca(2+) influx inhibits dynamin and arrests synaptic vesicle endocytosis at the active zone

Ca(2+) entry into nerve terminals through clusters of voltage-dependent Ca(2+) channels (VDCCs) at active zones creates a microdomain of elevated intracellular free Ca(2+) concentration ([Ca(2+)](i)) that stimulates exocytosis. We show that this VDCC-mediated [Ca(2+)](i) elevation has no specific role in stimulating endocytosis but can inhibit endocytosis evoked by three different methods in isolated mammalian nerve terminals. The inhibition can be relieved by using either VDCC antagonists or fast, but not slow, binding intracellular Ca(2+) chelators. The Ca(2+)-dependent inhibition of endocytosis is mimicked in vitro by a low-affinity inhibition of dynamin I vesiculation of phospholipids. Increased [Ca(2+)](i) also inhibits dynamin II GTPase activity and receptor-mediated endocytosis in non-neuronal cells. VDCC-meditated Ca(2+) entry inhibits dynamin-mediated endocytosis at the active zone and provides neurons with a mechanism to clear recycling vesicles to nonactive zone regions during periods of high activity.

Hepatic lesion detection after superparamagnetic iron oxide enhancement: comparison of five T2-weighted sequences at 1.0 T by using alternative-free response receiver operating characteristic analysis

PURPOSE

To compare the accuracy of five T2-weighted sequences in the detection of liver lesion at magnetic resonance (MR) imaging after superparamagnetic iron oxide (SPIO) enhancement.

MATERIALS AND METHODS

Forty-nine candidates for hepatic resection with known coloretal metastases were examined. Before SPIO enhancement, fast spin-echo (SE) images were obtained. After enhancement, the same fast SE sequence and long; TR/short TE, short TE, long TR/TE, and T2-weighted fast low-angle shot (FLASH) sequences were used. All images were viewed independently by four observers who were blinded to the results of the other imaging sequences, the results of the other observers, and the findings at surgery and histopathologic examination. Four weeks after the initial reading, the combined long TR/short TE and long TR/TE dual-echo images were also viewed as an additional set. The alternative free response receiver operating characteristic (ROC) method was used to analyze the results, which were correlated with findings at surgery, intraoperative ultrasonography, and histopathologic examination.

RESULTS

Irrespective of lesion size, the accuracy of all sequences after enhancement was significantly greater than that of the nonenhanced fast SE sequence (P < .01). Dual-echo and FLASH sequences were significantly more accurate than the enhanced fast SE sequence (P < .03 or P < .02, respectively). For all lesions, lesions smaller than 1 cm, and lesions 1 cm or larger, mean accuracies were as follows: dual-echo, 0.75, 0.54, and 0.93; FLASH, 0.75, 0.54, and 0.95; and enhanced fast SE, 0.72, 0.49, and 0.92.

CONCLUSION

At 1.0 T, dual-echo and FLASH sequences are the most accurate pulse sequences after SPIO enhancement.

Mechanisms of synaptic vesicle recycling illuminated by fluorescent dyes

The recycling of synaptic vesicles in nerve terminals involves multiple steps, underlies all aspects of synaptic transmission, and is a key to understanding the basis of synaptic plasticity. The development of styryl dyes as fluorescent molecules that label recycling synaptic vesicles has revolutionized the way in which synaptic vesicle recycling can be investigated, by allowing an examination of processes in neurons that have long been inaccessible. In this review, we evaluate the major aspects of synaptic vesicle recycling that have been revealed and advanced by studies with styryl dyes, focussing upon synaptic vesicle fusion, retrieval, and trafficking. The greatest impact of styryl dyes has been to allow the routine visualization of endocytosis in central nerve terminals for the first time. This has revealed the kinetics of endocytosis, its underlying sequential steps, and its regulation by Ca2+. In studies of exocytosis, styryl dyes have helped distinguish between different modes of vesicle fusion, provided direct support for the quantal nature of exocytosis and endocytosis, and revealed how the probability of exocytosis varies enormously from one nerve terminal to another. Synaptic vesicle labelling with styryl dyes has helped our understanding of vesicle trafficking by allowing better understanding of different synaptic vesicle pools within the nerve terminal, vesicle intermixing, and vesicle clustering at release sites. Finally, the dyes are now being used in innovative ways to reveal further insights into synaptic plasticity.

The enhancement of audience participation in telemedicine education by the use of electronic voting

The rotation of trainee registrars in obstetrics and gynaecology to peripheral centres in South Australia was introduced for the first time in January 1998. A pilot study of the use of telemedicine to maintain the trainees' involvement in the established weekly training sessions conducted at the Women's and Children's Hospital (WCH) was also commenced at the same time. Sessions were problem based and required the trainees to be actively involved throughout. An electronic voting system (EVS) was used by the WCH audience, with the results of all responses being seen at the peripheral centres. Initial evaluation of the EVS as an educational tool was sufficiently positive to justify further studies of its use in this environment. The availability of voting units at the peripheral sites, used in conjunction with the main centre, will provide an exciting opportunity for further research.

How easily do topical antibiotics pass through tympanostomy tubes?--an in vitro study

BACKGROUND

Despite potential ototoxicity, eardrops containing aminoglycosides remain in widespread use in the presence of indwelling tympanostomy tubes (grommets). It is unclear how readily they pass into the middle ear during administration, nor whether this is affected by middle ear secretions.

MATERIALS AND METHODS

The trans-tympanic pressure required to force antibiotic solutions through a tympanostomy tube in an artificial middle ear model was investigated with six ototopical preparations and two sizes of tube. To assess the effect of middle ear secretions, tympanostomy tubes removed from patients ears were investigated in addition to new tubes. The intra-canal pressure generated during tragal massage was also measured.

RESULTS

Pressures required for leakage of solutions differed significantly between solutions (P=0.001) and tube sizes, smaller lumen tubes requiring higher trans-tympanic pressure for leakage to occur. The presence of middle ear secretions reduced the pressure required for leakage of solution. Tragal massage generated pressures of over 20 cm of H20 which would be enough to force solution into the middle ear in all tube/solution combinations.

DISCUSSION

Some antibiotic solution is likely to leak into the middle ear during most applications of antibiotic solution. Although the risk is small, this suggests the possibility of ototoxicity, previously demonstrated in animal experiments. The relatively low incidence of this occurrence in clinical practice is thought to be related to inter-species anatomical variations.

Dynamic contrast-enhanced MR imaging and dual-phase helical CT in the preoperative assessment of suspected pancreatic cancer: a comparative study with receiver operating characteristic analysis

OBJECTIVE

The purpose of this study was to compare dynamic contrast-enhanced MR imaging and dual-phase helical CT in the preoperative assessment of patients with suspected pancreatic carcinoma.

SUBJECTS AND METHODS

Thirty-three consecutive surgical candidates (20 men, 13 women; 39-81 years old) were included. MR imaging comprised fast spin-echo (TR/TE 4000/91), fat-suppressed T1-weighted spin-echo (500/15), and T1-weighted breath-hold gradient-echo fast low-angle shot (100/4; flip angle, 80 degrees) images before and after the administration of gadopentetate dimeglumine. Helical CT used 5-mm collimation with a pitch of 1:1.5-1.7; images were obtained 20 and 65-70 sec after injection of 150 ml of contrast material. Two pairs of interpreters who were unaware of the results of the other imaging method independently scored each examination for the presence of a lesion and for surgical resectability using a five-point scale. Results were correlated with surgery (n = 25) or consensus review (n = 8). Receiver operating characteristic methodology was used to analyze the results for resectability, and positive predictive values were calculated.

RESULTS

Both MR imaging and helical CT revealed 29 of 31 lesions. In determining lesion resectability, the mean areas under the receiver operating characteristic curves were 0.96 and 0.81 (p = .01) and the positive predictive values were 86.5% and 76% (p = .02) for MR imaging and helical CT, respectively.

CONCLUSION

MR imaging and helical CT performed equally well in lesion detection. MR imaging was significantly better in the assessment of resectability of pancreatic tumors.

Phosphorylation of splicing factor SF1 on Ser20 by cGMP-dependent protein kinase regulates spliceosome assembly

Splicing factor 1 (SF1) functions at early stages of pre-mRNA splicing and contributes to splice site recognition by interacting with the essential splicing factor U2AF65 and binding to the intron branch site. We have identified an 80 kDa substrate of cGMP-dependent protein kinase-I (PKG-I) isolated from rat brain, which is identical to SF1. PKG phosphorylates SF1 at Ser20, which inhibits the SF1-U2AF65 interaction leading to a block of pre-spliceosome assembly. Mutation of Ser20 to Ala or Thr also inhibits the interaction with U2AF65, indicating that Ser20 is essential for binding. SF1 is phosphorylated in vitro by PKG, but not by cAMP-dependent protein kinase A (PKA). Phosphorylation of SF1 also occurs in cultured neuronal cells and is increased on Ser20 in response to a cGMP analogue. These results suggest a new role for PKG in mammalian pre-mRNA splicing by regulating in a phosphorylation-dependent manner the association of SF1 with U2AF65 and spliceosome assembly.

Effects of losartan and captopril on QT dispersion in elderly patients with heart failure. ELITE study group

Differences in QT dispersion (a predictor for sudden death) were observed in a subgroup of patients in the ELITE heart failure study of losartan compared with captopril, and may explain improved survival with losartan.

Calcium-induced p56(Lck) phosphorylation in human T lymphocytes via calmodulin dependent kinase

We report that stimulation of both primary human and Jurkat T lymphocytes with the calcium ionophore ionomycin, or A23187, results in the phosphorylation of p56(Lck) as determined by shifts in mobility of p56(Lck) on immunoblots. The shifts in the mobility of p56(Lck) induced by ionomycin could be blocked by preincubation of the cells with EGTA, demonstrating the requirement for extracellular calcium in this response. Although increases in intracellular calcium have been shown to modulate CD45 activity, phosphorylation of p56(Lck) was not mediated via CD45. Ionomycin stimulation of J45. 01 cells, a CD45-negative Jurkat cell derivative, also resulted in p56(Lck) mobility shifts. Instead, this response appears to be mediated via a calmodulin-dependent kinase. This response could be blocked by calmidazolium, an inhibitor of calmodulin, and KN-93, an inhibitor of calmodulin-dependent kinases (CaM-Kinase). KN-92, an inactive analog of KN-93, failed to block this response. These studies demonstrate a new role for calcium and CaM-Kinase in human T-lymphocytes and describe a novel mechanism by which p56(Lck) can be modulated.

Calcium-induced ERK activation in human T lymphocytes

We have previously shown that stimulation of B lymphocytes with calcium ionophores lead to the phosphorylation and enzymatic activation of ERK2. We have now determined that stimulation of human primary and Jurkat T lymphocytes with ionomycin also results in the activation of ERK1 and 2 as determined by; shifts in the mobility of this enzyme on SDS PAGE gels, the binding of an antibody that recognizes only the activated form of this enzyme, and increased ability to phosphorylate myelin basic protein (MBP). Another calcium ionophore, A23187, also induced activation of ERK1 and 2 in human primary and Jurkat T lymphocytes demonstrating that this is a general effect of calcium ionophores and is not limited to ionomycin. The activation of ERK1 and 2 by calcium ionophores was rapid, transient, and occurred in a dose-dependent manner. Activation of ERK1 and 2 by increases in intracellular calcium were blocked by the MEK inhibitor PD98059. These data point to a new role for calcium fluxes in T lymphocytes.

Interpretation of selected accident and emergency radiographic examinations by radiographers: a review of 11000 cases

Two specially trained radiographers took part in the radiologists' rota for "cold" reporting skeletal radiographs of patients who attended the Accident and Emergency (A&E) Department at times when there was no "hot" reporting service operating, and who were not admitted for treatment or referred to fracture clinics for follow-up. These radiographs had initially been seen by A&E medical staff. At the end of an 18 month period during which the two radiographers reported on 11,322 skeletal examinations, a retrospective search was made to detect interpretive errors. The radiological history of all 11,322 patients was reviewed over a follow-up period of at least 3 months subsequent to the attendance reported by the radiographers. 48% of patients did not re-attend, 42% re-attended for unrelated examinations, and 10% re-attended for repeat examinations of the same anatomical area, or for different procedures (bone scintigraphy or CT) related to the original injury. The second (or subsequent) report was discrepant with that of the first attendance in only 29 cases out of 1103. Of these 29 patients, 13 had occult fractures which were undetectable at first attendance even in retrospect, six had new injuries accounting for the new findings, six had been the subject of false positive calls at an earlier visit, one had a fracture of the hamate missed at first attendance, and in three cases no consensus could be reached as to the cause of the discrepancy, owing to incomplete films or insufficient clinical data. Analysis of the patients' postcodes showed at least 89% were of local origin and only 1% were from outside Yorkshire, suggesting that the review should have identified the great majority of erroneous reports. It is concluded that appropriately trained and supervised radiographers can successfully undertake diagnostic reporting of selected skeletal examinations on A&E patients.

Phosphorylation of proteins in chick ciliary ganglion under conditions that induce long-lasting changes in synaptic transmission: phosphoprotein targets for nitric oxide action

Production of nitric oxide and the activation of protein kinases are required for long-term potentiation of synaptic transmission at the giant synapses in chicken ciliary ganglion. In the present study, we investigated the ability of nitric oxide to regulate the phosphorylation of endogenous proteins under conditions that induced long-term potentiation in intact ciliary ganglion and the protein kinases responsible for the phosphorylation of these proteins in lysed ciliary ganglion. Using Calcium Green-1 we showed that the nitric oxide donor sodium nitroprusside did not change the intraterminal Ca2+ dynamics in ciliary ganglion. Two dimensional phosphopeptide analysis of 32Pi-labelled intact ciliary ganglion showed that the sodium nitroprusside (300 microM) increased the phosphorylation of several phosphopeptides (P50a, P50b and P41) derived from proteins at 50,000 and 41,000 mol. wts which we have called nitric oxide-responsive phosphoproteins. A similar stimulation of phosphorylation was achieved by 8-bromo-cyclic AMP (100 microM), which also induced long-term potentiation, but not by phorbol dibutyrate (2 microM) that does not induce long-term potentiation in ciliary ganglion. When subcellular fractions from lysed ciliary ganglion were labelled in vitro by [gamma-32P]ATP in the presence of purified cGMP-dependent, cAMP-dependent or Ca2+-phospholipid-dependent protein kinases, we identified cyclic GMP-dependent protein kinase substrates that gave rise to phosphopeptides co-migrating with P50a, P50b and P41 from 32Pi-labelled intact ciliary ganglion. P50a and P41 were derived from soluble proteins while P50b was derived from a membrane-associated protein. The proteins giving rise to P50a, P50b and P41 were also substrates for cyclic AMP-dependent protein kinase, but not for calcium and phospholipid-dependent protein kinase in vitro, suggesting that nitric oxide-responsive phosphoproteins are convergence points in information processing in vivo and their phosphorylation might represent an important mechanism in nitric oxide-mediated synaptic plasticity in ciliary ganglion.

MR imaging of the liver and spleen: a comparison of the effects on signal intensity of two superparamagnetic iron oxide agents

We compared the effects of two superparamagnetic iron oxide (SPIO) contrast agents, ferumoxides and SHU-555A, in MR imaging of the liver and spleen. Thirty-six patients with known malignant lesions of the liver underwent T2W turbo spin-echo (TSE) and T1WGRE FLASH opposed-phase imaging before and after SPIO injection on a 1.0 T MR system. Post-ferumoxides images were obtained in 18 patients 90 min after infusion of 15 micrommol Fe/kg of the agent. In 18 other patients SHU-555A was administered as a rapid bolus at a dose of 7.0-12.9 micrommol Fe/kg. T1WGRE FLASH images were obtained immediately, 30 s and 480 s and T2WTSE images 10 min after injection. Signal intensity of the liver, spleen, and malignant liver lesions before and after SPIO was measured with operator-defined regions of interest. The effects of ferumoxides and SHU-555A were measured as the percentage signal intensity change (PSIC) and in the malignant liver lesions additionally as changes in lesion-to-liver contrast-to-noise ratio (deltaDCNR). On T2W TSE images, there was no significant difference between the two agents in signal loss of liver parenchyma (p > 0.05). The signal loss in the spleen produced by ferumoxides was greater than with SHU-555A (p < 0.05). Both SPIO agents produced a significant increase in the CNR of malignant liver lesions. Delta CNR was slightly greater with ferumoxides than with SHU-555A (p < 0.05). On T1WGRE FLASH images, a slight decrease of liver SI induced by both agents was found on late post-SPIO images. No significant difference of liver PSIC between the two SPIO agents was noted on T1W images. The SI of spleen was significantly increased with both agents on T1W images and no difference in PSIC of spleen was noted (p > 0.05). The T1 and T2 effects produced by ferumoxides and SHU-555A were comparable in the liver although ferumoxides produced a stronger T2 effect in the spleen.

Variation between experienced observers in the interpretation of accident and emergency radiographs

Skill mix and role extension initiatives have highlighted the difficulty of establishing quality standards for the accuracy of plain film reporting. An acceptable performance might be one which is indistinguishable from that of a group of experienced consultant radiologists. In order to assess the feasibility of setting such a standard, the variation between experienced observers must first be established. This study examines the variation found between three observers with the three major types of plain film examination. 402 plain film examinations (205 skeletal, 100 chest and 97 abdominal) performed on accident and emergency patients were reported retrospectively and independently by three experienced radiologists. The clinical data supplied on the request cards were available to the readers. Each examination was categorized by each reader as being normal, as showing significant abnormality relevant to the current clinical problem, or as showing insignificant or irrelevant abnormality. Concordance between all three readers was found in 51%, 61% and 74% of abdominal, chest and skeletal radiographs, respectively. Weighted kappa values confirmed that the level of agreement between pairs of observers was higher with skeletal radiographs (kappa w = 0.76-0.77) than with chest (kappa w = 0.63-0.68), or abdominal (kappa w = 0.50-0.78) examinations. However, the frequency of major disagreements (at least one reader reporting "normal" and one reporting "relevant abnormality") was similar for abdominal (11%), chest (12%) and skeletal (10%) radiographs. When the reports were reclassified into only two groups--either significantly abnormal or not--pairs of observers disagreed on 9-10% of skeletal, 11-19% of chest and 8-18% of abdominal cases. The average incidence of errors per observer was estimated to be in the range 3-6%. The magnitude of interobserver variation in plain film reporting is considerable, and must be taken into account when designing assessment techniques and setting quality standards for this activity.

Hepatic lesion detection: comparison of MR imaging after the administration of superparamagnetic iron oxide with dual-phase CT by using alternative-free response receiver operating characteristic analysis

PURPOSE

To compare the performance of magnetic resonance (MR) imaging after the administration of superparamagnetic iron oxide (SPIO) and dual-phase computed tomography (CT) in the depiction of liver metastases.

MATERIALS AND METHODS

Fifty-one hepatic resection candidates with known colorectal metastases were examined. MR imaging comprised fast spin-echo (SE) T2-weighted imaging, T1-weighted gradient-echo (GRE) fast low-angle shot imaging before SPIO enhancement, dual-echo SE imaging, T2-weighted fast low-angle shot imaging, and T1-weighted GRE imaging after SPIO enhancement. CT was performed with 8-mm collimation and 1:1 pitch; imaging commenced 20 seconds and 65-70 seconds after injection of 150 mL of contrast medium. All images were reviewed independently by four blinded observers. The alternative-free response receiver operating characteristic (ROC) method was used to analyze the results, which were correlated with findings from surgery, intraoperative ultrasonography, and histopathologic studies in 31 patients and with consensus review together with all other imaging and clinical follow-up in 20 patients. Sensitivities were also calculated.

RESULTS

The mean sensitivity of MR was significantly higher than that of CT (p < .02): 79.8% for MR and 75.3% for CT for all lesions, and 80.6% for MR and 73.5% for CT for malignant lesions. The mean areas under the alternative-free response ROC curves were 0.83 for MR and 0.78 for CT (difference not significant).

CONCLUSION

SPIO-enhanced MR imaging was more sensitive than dual-phase CT in the depiction of colorectal metastases.

Differential regulation of MAP kinase activity by corticotropin-releasing hormone in normal and neoplastic corticotropes

Corticotropin-releasing hormone (CRH) plays an important role in regulating the development and function of hypothalamic-pituitary-adrenal axis. The mechanisms by which CRH regulates tissue-specific growth, differentiation and gene expression remain to be established. In the present study, we show that CRH differentially regulates MAP kinase activity in normal ovine anterior pituitary cells and mouse corticotrope AtT20 cells. Incubation of ovine normal anterior pituitary cells with CRH increased MAP kinase activity, an effect mimicked by cAMP and inhibited by the protein kinase A inhibitor H89. In contrast, incubation of mouse pituitary tumor AtT20 cells with CRH inhibited MAP kinase activity, an effect also mimicked by forskolin and inhibited by H89. This decrease in MAP kinase activity occurred with a time course similar to the increase seen in normal anterior pituitary cells. Furthermore, both effects of CRH on MAP kinase activity were inhibited by atrial natriuretic peptide (ANP). ANP also reversed the inhibition of DNA synthesis induced by CRH in AtT20 cells. Thus, CRH may differentially regulate cell growth in sheep normal anterior pituitary and mouse tumor corticotropes by modulating MAP kinase activity through a mechanism dependent on cAMP production and subject to regulation by ANP.

Multiple leiomyosarcomas of both donor and recipient origin arising in a heart-lung transplant patient

The occurrence of Epstein-Barr virus-associated smooth-muscle tumors in immunocompromised patients has been reported, particularly in the pediatric population. In posttransplantation tumors, the tissue of origin has been either donor or recipient. Mixed-genotype sarcomas within the same patient have not yet been reported. We describe the occurrence of multiple leiomyosarcomas of both donor (arising in the lung allograft) and recipient (arising in the host liver) origin in a 15-year-old boy 3 years after heart-lung transplantation. Analysis of premortem lung tumors demonstrated the presence of Epstein-Barr virus DNA. Despite decreasing immunosuppression and commencing acyclovir, the patient died of systemic Pseudomonas infection. Immunohistochemical analysis revealed that both lung and liver tumors were negative for the Epstein-Barr virus receptor (CD21), and suggests that Epstein-Barr virus entry into the cells was not via this receptor but via an alternate mechanism such as cell fusion.

Mixed-lineage kinase 2-SH3 domain binds dynamin and greatly enhances activation of GTPase by phospholipid

Mixed-lineage kinase 2 (MLK2) is a cytoplasmic protein kinase expressed at high levels in mammalian brain. The MLK2 structure is composed of a Src homology 3 (SH3) domain, two leucine zippers, a basic motif, a Cdc42/Rac interactive binding motif and a large C-terminal domain rich in proline, serine and threonine residues. To begin to define the role of MLK2 in mammalian brain, we used an MLK2-SH3 domain-glutathione S-transferase fusion protein (GST-MLK2-SH3) to isolate MLK2-binding proteins from rat brain extract. This analysis revealed that the major MLK2-SH3-domain-binding protein in rat brain is the GTPase dynamin. By using two different forms of the dynamin proline-rich domain as affinity ligands, the binding site for MLK2-SH3 was mapped to the C-terminal region of dynamin between residues 832 and 864. In GTPase assays, the addition of MLK2-SH3 stimulated the activity of purified dynamin I by 3-fold over the basal level, whereas the addition of a known dynamin activator, phosphatidylserine (PtdSer), stimulated a 6-fold increase. When MLK2-SH3 was added to the assay together with PtdSer, however, dynamin GTPase activity accelerated by more than 23-fold over basal level. An MLK2 mutant (MLK2-W59A-SH3), with alanine replacing a conserved tryptophan residue in the SH3 domain consensus motif, had no effect on dynamin activity, either alone or in the presence of PtdSer. In the same assay the SH3 domain from the regulatory subunit of phosphatidylinositol 3'-kinase stimulated a similar synergistic acceleration of dynamin GTPase activity in the presence of PtdSer. These results suggest that synergy between phospholipid and SH3 domain binding might be a general mechanism for the regulation of GTP hydrolysis by dynamin.