Dual-energy contrast-enhanced digital mammography: Glandular dose estimation using a Monte Carlo code and voxel phantom.

PURPOSE: To estimate the mean glandular dose of contrast enhanced digital mammography, using the EGSnrc Monte Carlo code and female adult voxel phantom. METHODS: Automatic exposure control of full field digital mammography system was used for the selection of the X-ray spectrum and the exposure settings for dual energy imaging. Measurements of the air-kerma and of the half value layers were performed and a Monte Carlo simulation of the digital mammography system was used to compute the mean glandular dose, for breast phantoms of various thicknesses, glandularities and for different X-ray spectra (low and high energy). RESULTS: For breast phantoms of 2.0-8.0 cm thick and 0.1-100% glandular fraction, CC view acquisition, from AEC settings, can result in a mean glandular dose of 0.450 ± 0.022 mGy -2.575 ± 0.033 mGy for low energy images and 0.061 ± 0.021 mGy - 0.232 ± 0.033 mGy for high energy images. In MLO view acquisition mean glandular dose values ranged between 0.488 ± 0.007 mGy - 2.080 ± 0.021 mGy for low energy images and 0.065 ± 0.012 mGy - 0.215 ± 0.010 mGy for high energy images. CONCLUSION: The low kV part of contrast enhanced digital mammography is the main contributor to total mean glandular breast dose. The results of this study can be used to provide an estimated mean glandular dose for individual cases.

Dual-energy contrast-enhanced digital mammography: patient radiation dose estimation using a Monte Carlo code.

Mammography is a standard procedure that facilitates breast cancer detection. Initial results of contrast-enhanced digital mammography (CEDM) are promising. The purpose of this study is to assess the CEDM radiation dose using a Monte Carlo code. EGSnrc MC code was used to simulate the interaction of photons with matter and estimate the glandular dose (Dg). A voxel female human phantom with a 2-8-cm breast thickness range and a breast glandular composition of 50 % was applied. Dg values ranged between 0.96 and 1.45 mGy (low and high energy). Dg values for a breast thickness of 5.0 cm and a glandular fraction of 50 % for craniocaudal and mediolateral oblique view were 1.12 (low energy image contribution is 0.98 mGy) and 1.07 (low energy image contribution is 0.95 mGy), respectively. The low kV part of CEDM is the main contributor to total glandular breast dose.

Evidence-based medicine and radiology.

In the early 1990's, a group of physician-epidemiologists developed ways of efficiently tracking down and appraising literature and wrote them up in order to help other doctors, with no or with minimal formal epidemiological training. Today Evidence-Based Medicine (EBM) integrates clinical experience and patient values with the best available research information in order to expand research evidence and to provide sensible answers to medical questions in clinical decision making. Although EBM does not provide the answer to every clinical question, it provides us valuable additional evidence helpful in decision making. EBM process includes five steps: answerable questions asking; accessing for the best information; information appraisal for validity and relevance; data application to patient care and finally evaluation of the performance. The purpose of this paper is to help radiologists who have no postgraduate specialist training in research to become familiar with EBM and to find solutions that are based on best current evidence for problems arising in their practice.

How to optimize radiological images captured from digital cameras, using the Adobe Photoshop 6.0 program.

Over the past decade, the technology that permits images to be digitized and the reduction in the cost of digital equipment allows quick digital transfer of any conventional radiological film. Images then can be transferred to a personal computer, and several software programs are available that can manipulate their digital appearance. In this article, the fundamentals of digital imaging are discussed, as well as the wide variety of optional adjustments that the Adobe Photoshop 6.0 (Adobe Systems, San Jose, CA) program can offer to present radiological images with satisfactory digital imaging quality.

Neurotrophin-3 is required for the survival-differentiation of subsets of developing enteric neurons.

Neurotrophin-3 (NT-3) promotes enteric neuronal development in vitro; nevertheless, an enteric nervous system (ENS) is present in mice lacking NT-3 or TrkC. We thus analyzed the physiological significance of NT-3 in ENS development. Subsets of neurons developing in vitro in response to NT-3 became NT-3 dependent; NT-3 withdrawal led to apoptosis, selectively in TrkC-expressing neurons. Antibodies to NT-3, which blocked the developmental response of enteric crest-derived cells to exogenous NT-3, did not inhibit neuronal development in cultures of isolated crest-derived cells but did so in mixed cultures of crest- and non-neural crest-derived cells; therefore, the endogenous NT-3 that supports enteric neuronal development is probably obtained from noncrest-derived mesenchymal cells. In mature animals, retrograde transport of (125)I-NT-3, injected into the mucosa, labeled neurons in ganglia of the submucosal but not myenteric plexus; injections of (125)I-NT-3 into myenteric ganglia, the tertiary plexus, and muscle, labeled neurons in underlying submucosal and distant myenteric ganglia. The labeling pattern suggests that NT-3-dependent submucosal neurons may be intrinsic primary afferent and/or secretomotor, whereas NT-3-dependent myenteric neurons innervate other myenteric ganglia and/or the longitudinal muscle. Myenteric neurons were increased in number and size in transgenic mice that overexpress NT-3 directed to myenteric ganglia by the promoter for dopamine beta-hydroxylase. The numbers of neurons were regionally reduced in both plexuses in mice lacking NT-3 or TrkC. A neuropoietic cytokine (CNTF) interacted with NT-3 in vitro, and if applied sequentially, compensated for NT-3 withdrawal. These observations indicate that NT-3 is required for the normal development of the ENS.

Promotion of the development of enteric neurons and glia by neuropoietic cytokines: interactions with neurotrophin-3.

Neurotrophin-3 (NT-3) is known to promote enteric neuronal and glial development. Ciliary neurotrophic factor (CNTF) and leukemia inhibitory factor (LIF) were investigated to test the hypothesis that the development of subsets of enteric neurons and/or glia is also affected by a neuropoietic cytokine, by itself, or together with NT-3. Crest-derived cells, immunoselected from the fetal rat gut (E14) with antibodies to p75NTR, were found by RT-PCR and immunocytochemistry (after culture) to express both alpha (CNTER alpha) and beta components (gp130 and LIFR beta) of the tripartite CNTF receptor. In situ, myenteric ganglia below the esophagus were CNTFR alpha-immunoreactive by E16-E18. In vitro, CNTF and LIF induced in crest-derived cells nuclear translocation of STAT3 (signal transducer and activator of transcription 3), a concentration-dependent increase in expression of neuronal or glial markers, and a decrease in expression of the precursor marker, nestin. LIFR beta was expressed by more cells than CNTFR alpha; therefore, although the factors were equipotent, the maximal effect of LIF > CNTF. The cytokines and NT-3 were additive in promoting neuronal but not glial development. Specifically, the development of neurons expressing NADPH-diaphorase activity (an early marker found in inhibitory motor neurons) was promoted by CNTF and NT-3. These observations support the idea that a ligand for the tripartite CNTF receptor complex plays a role in ENS development.

Age-dependent differences in the effects of GDNF and NT-3 on the development of neurons and glia from neural crest-derived precursors immunoselected from the fetal rat gut: expression of GFRalpha-1 in vitro and in vivo.

No enteric neurons or glia develop in the gut below the rostral foregut in mice lacking glial cell line-derived neurotrophic factor (GDNF) or Ret. We analyzed the nature and age dependence of the effects of GDNF and, for comparison, those of NT-3, on the in vitro development of the precursors of enteric neurons and glia. Positive and negative immunoselection with antibodies to p75(NTR) were used to isolate crest-derived and crest-depleted populations of cells from the fetal rat bowel at E12, 14, and 16. Cells were typed immunocytochemically. GDNF stimulated the proliferation of nestin-expressing precursor cells isolated at E12, but not at E14-16. GDNF promoted the development of peripherin-expressing neurons (E12 >> E14-16) and expression of TrkC. GDNF inhibited expression of S-100-expressing glia at E14-16. NT-3 did not affect cells isolated at E12, never stimulated precursors to proliferate, and promoted glial as well as neuronal development at E14-16. GFRalpha-1 was expressed both by crest- and non-crest-derived cells, although only crest-derived cells anchored GFRalpha-1 and GFRalpha-2 (GFRalpha-1 >> GFRalpha-2). GDNF increased the number of neurons anchoring GFRalpha-1. GFRalpha-1 is immunocytochemically detectable in neurons of the E13 intestine and persists in adult neurons of both plexuses. We suggest that GDNF stimulates the proliferation of an early (E12) NT-3-insensitive precursor common to enteric neurons and glia; by E14, this common precursor is replaced by specified NT-3-responsive neuronal and glial progenitors. GDNF exerts a neurotrophic, but not a mitogenic, effect on the neuronal progenitor. The glial progenitor is not maintained by GDNF.

The alpha1 subunit of laminin-1 promotes the development of neurons by interacting with LBP110 expressed by neural crest-derived cells immunoselected from the fetal mouse gut.

A plasmalemmal protein, LBP110, which binds to the alpha1 chain of laminin-1, is acquired by the neural crest-derived precursors of enteric neurons after they colonize the gut. We tested the hypothesis that laminin-1 interacts with LBP110 to promote enteric neuronal development. The effects of laminin-1 on neuronal development were studied in cultures of cells immunoselected from fetal mouse gut (E14-15) with antibodies to LBP110 or p75NTR, a marker for enteric crest-derived cells. No matter which antibody was used, the development of cells expressing neuronal markers was increased three- to fourfold by culturing the cells on a laminin-1-containing substrate. To determine whether this effect of laminin-1 is due to the selective adherence of a neurocompetent subset of precursors, immunoselected cells were permitted to preadhere to poly-D-lysine. Addition of soluble laminin-1 24 h later promoted neuronal but not glial development. The laminin-1-induced increment in neuronal development was abolished both by a peptide containing the sequence of the LBP110-binding domain, IKVAV, and by antibodies to laminin alpha1 that recognize the IKVAV domain. Neither reagent affected the total number of cells. In contrast, the response to laminin-1 was not affected by control peptides, preimmune sera, or antibodies to laminin beta1. Laminin-1 transiently induced the expression of nuclear Fos immunoreactivity; this action was blocked specifically by the IKVAV peptide. These data are consistent with the hypothesis that LBP110 interacts with the IKVAV domain of laminin alpha1 to promote the differentiation of neurons from enteric crest-derived precursors.

Neurotrophin-3 as an essential signal for the developing nervous system.

Rapid advances in characterization of the biological actions mediated by the third member of the neurotrophin family, neurotrophin-3 (NT-3), have been made recently in vitro as well as in situ. These have been made possible by the cloning of the genes for NT-3 and for its transducing receptor tyrosine kinase TrkC. This article will focus on the roles of NT-3 in the nervous system. In situ localization of NT-3 consistent with that of its receptor is manifested at all developmental stages studied and into adulthood. Through TrkC, NT-3 signals a number of trophic effects, ranging from mitogenesis, promotion of survival, or differentiation, depending on the developmental stage of the target cells. The sites of action of NT-3 reside primarily in the peripheral nervous system (PNS), various areas of the central nervous system (CNS), and in the enteric system (ENS). Analyses of the phenotypes of transgenic mice lacking NT-3 or injection of embryos with a blocking antibody have so far revealed the essential role of NT-3 in development of specific populations of the PNS, and in particular of proprioceptive, nodose, and auditory sensory neurons and of sympathetic neurons. The actions of NT-3 also extend to modulation of transmitter release at several types of synapses in the periphery as well as in the adult CNS. In addition, NT-3 may play a role in the development of tissues other than the nervous system, such as the cardiovascular system. Future investigations will widen the understanding of the many roles of NT-3 on both neuronal and nonneuronal cells.

Neurotrophin-3 induces neural crest-derived cells from fetal rat gut to develop in vitro as neurons or glia.

The precursor cells that form the enteric nervous system (ENS) are multipotent when they arrive in the gut from the neural crest. Their differentiation thus depends on signals from the enteric microenvironment. Crest-derived cells were isolated from the fetal rat bowel by immunoselection at E14 with NC-1/HNK-1 antibodies and secondary antibodies coupled to magnetic beads. NC-1/HNK-1-immunoreactive cells were enriched approximately 36-fold. The NC-1/HNK-1-selected population and the residual population were plated at equal cell density and maintained in a defined medium for 6-7 d. The total number of cells found in the cultures of the residual cells was three- to fourfold that in cultures of immunoselected cells. Neurotrophin-3 (NT-3), but not nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), or neurotrophin-4/5 (NT-4/5), was found to increase the proportion of neurons (neurofilament-immunoreactive or neuron-specific enolase-immunoreactive) or glia (S-100-immunoreactive) (from 6.6 +/- 0.9% to 15.2 +/- 1.4%; p < 0.001). This effect was concentration dependent (from 1 to 40 ng/ml) and observed only in the cultures of immunoselected cells. NT-3 also enhanced neurite outgrowth. NT-3 increased neither cell number nor bromodeoxyuridine incorporation and thus was not mitogenic. Exposure of immunoselected cells to NT-3 rapidly and transiently induced the appearance of nuclear Fos immunoreactivity. Transcripts coding for TrkC, the transducing receptor for NT-3, were identified in the fetal rat gut (E14-E16) and in the immunoselected population of cells using reverse transcriptase and the polymerase chain reaction. It is concluded that NT-3 specifically promotes the differentiation of enteric crest-derived cells as neurons or glia and may thus play a role in the development and/or maintenance of the ENS.

Neural crest-derived cells isolated from the gut by immunoselection develop neuronal and glial phenotypes when cultured on laminin.

The neural crest-derived cells that colonize the bowel are different from their predecessors in the premigratory crest. A procedure, which utilized the immunoselection of cells with a magnet, was thus devised to obtain crest-derived precursors from developing gut. Primary antibodies against cell surface antigens, NC-1 in chick, quail, and rat, or antibodies to a 110-kDa laminin binding protein (alpha-110) in mouse, were used in conjunction with secondary antibodies coupled to magnetic beads. Immediately after immunoselection with NC-1, almost all of the selected cells were NC-1-immunoreactive. Neurons and glia, identified immunocytochemically with antibodies to specific markers, developed preferentially in cultures of immunoselected cells. Some of the phenotypes expressed by neurons arising in vitro were appropriate for the bowel (serotonin- and vasoactive intestinal peptide-immunoreactive); however, catecholaminergic neurons, which are not present in the enteric nervous system, also differentiated in the cultures. Neuronal development, as well as neurite outgrowth, were promoted by laminin. Cells selected with alpha-110 from the fetal murine bowel preferentially gave rise in vitro to neurons and glia. These data suggest that the population of crest-derived cells that colonizes the gut is multipotent, that development of catecholaminergic neurons in situ is prevented by the intact enteric microenvironment, that laminin is important in the formation of enteric ganglia, and that the 110-kDa laminin binding protein is expressed on the surfaces of the immediate precursors of enteric neurons and glia.

From neural crest to bowel: development of the enteric nervous system.

The ENS resembles the brain and differs both physiologically and structurally from any other region of the PNS. Recent experiments in which crest cell migration has been studied with DiI, a replication-deficient retrovirus, or antibodies that label cells of neural crest origin, have confirmed that both the avian and mammalian bowel are colonized by émigrés from the sacral as well as the vagal level of the neural crest. Components of the extracellular matrix, such as laminin, may play roles in enteric neural and glial development. The observation that an overabundance of laminin develops in the presumptive aganglionic region of the gut in ls/ls mutant mice and is associated with the inability of crest-derived cells to colonize this region of the bowel has led to the hypothesis that laminin promotes the development of crest-derived cells as enteric neurons. Premature expression of a neuronal phenotype would cause crest-derived cells to cease migrating before they complete the colonization of the gut. The acquisition by crest-derived cells of a nonintegrin, nerve-specific, 110 kD laminin-binding protein when they enter the bowel may enable these cells to respond to laminin differently from their pre-enteric migrating predecessors. Crest-derived cells migrating along the vagal pathway to the mammalian gut are transiently catecholaminergic (TC). This phenotype appears to be lost rapidly as the cells enter the bowel and begin to follow their program of terminal differentiation. The appearance and disappearance of TC cells may thus be an example of the effects of the enteric microenvironment on the differentiation of crest-derived cells in situ. Crest-derived cells can be isolated from the enteric microenvironment by immunoselection, a method that takes advantage of the selective expression on the surfaces of crest-derived cells of certain antigens. One neurotrophin, NT-3, promotes the development of enteric neurons and glia in vitro. Because trkC is expressed in the developing and mature gut, it seems likely that NT-3 plays a critical role in the development of the ENS in situ. Although the factors that are responsible for the development of the unique properties of the ENS remain unknown, progress made in understanding enteric neuronal development has recently accelerated. The application of new techniques and recently developed probes suggest that the accelerated pace of discovery in this area can be expected to continue.

Transforming growth factor beta has neurotrophic actions on sensory neurons in vitro and is synergistic with nerve growth factor.

Transforming growth factor beta (TGF beta) influences the growth and differentiation of a wide variety of nonneuronal cells (nnc) during embryogenesis and in response to wounding. In the present study TGF beta 1 and TGF beta 2 were examined for their neurotrophic actions on neonatal rat dorsal root ganglion (DRG) neurons with ganglionic nnc in dissociated cultures. TGF beta 1 and TGF beta 2 each increased both neuronal survival and levels of the peptide neurotransmitter substance P (SP) expressed per neuron as well as per culture. TGF beta 1 was maximally effective at a concentration of 40 pM, whereas TGF beta 2 was about 10-fold less potent. Survival effects promoted by simultaneous treatment with both factors were not additive. TGF beta 1 also changed the morphology and distribution of DRG nnc which resulted in clustering of DRG neurons on top of the nnc. Cotreatment of the cultures with two different anti-nerve growth factor (NGF) antibodies eliminated the neurotrophic effects of TGF beta 1. However, treatment with TGF beta 1 did not alter NGF mRNA expression in the cultures nor did it change the amount of NGF in the medium. Further, TGF beta 1 greatly enhanced survival effects and SP stimulation promoted by exogenous NGF at concentrations up to 100 ng/ml. The neurotrophic effects of TGF beta 1 were significantly attenuated by decreasing the proportion of the ganglionic nnc, suggesting a role for these cells in mediating TGF beta 1 action on the neurons. It is hypothesized that the neurotrophic activity of TGF beta depended upon the presence of molecules immunologically related to NGF and that the effects of TGF beta were synergistic with NGF. These observations suggest that TGF beta may play a role in the differentiation and regeneration of DRG neurons in vivo.

Transforming growth factor alpha, but not epidermal growth factor, promotes the survival of sensory neurons in vitro.

Transforming growth factor alpha (TGF alpha) is a mitogenic polypeptide that is structurally homologous to epidermal growth factor (EGF) and appears to bind to the same receptor in all systems tested previously. In the present study, TGF alpha was found to enhance survival and neurite outgrowth of cultured neonatal rat dorsal root ganglion (DRG) neurons in a dose-dependent manner. This effect was observed with TGF alpha concentrations as low as 17.8 pM. By contrast, EGF at concentrations up to 83 nM was ineffective. Moreover, EGF did not antagonize the TGF alpha survival-promoting effect unless present in large excess (500-fold the concentration for which TGF alpha is effective); even in this case, only partial antagonism was achieved. Survival of neurons from nodose, trigeminal, and sympathetic ganglia was not increased by TGF alpha. Both a subpopulation of DRG neurons and of macrophages in the cultures bound iodinated TGF alpha. This binding was inhibited by excess unlabeled TGF alpha but not EGF. Our data are consistent with the possibilities that the actions of TGF alpha on DRG neurons occur indirectly via unidentified neurotrophic molecules other than NGF as well as directly on the neurons themselves. Thus, TGF alpha, in contrast to EGF, may act as a survival or maintenance factor for a subset of rat sensory neurons. Mediation of this neurotrophic effect appears to occur via a new form of TGF alpha receptor.

Purine analogs inhibit nerve growth factor-promoted neurite outgrowth by sympathetic and sensory neurons.

Past studies have shown that purine analogs block certain, but not all, responses of cultured rat PC12 pheochromocytoma cells to nerve growth factor (NGF). In the present work, newborn rat sympathetic and sensory neurons were exposed to NGF in the presence or absence of the purine analogs 6-thioguanine and 2-aminopurine. These compounds reversibly suppressed NGF-dependent neurite outgrowth by the neurons and did so at concentrations comparable to those effective on PC12 cells. In contrast to their effects on neurites, neither compound significantly blocked NGF-promoted neuronal survival. Similar effects were seen with cultures of chick embryo sympathetic ganglia. These findings show that purine analog effects on NGF responses can be extended to mammalian and avian neurons. Moreover, the differential effects of the analogs on neurite outgrowth and survival indicate that these 2 actions of NGF can be dissected from one another and may represent different mechanistic pathways.