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1.
Phys Med Biol ; 54(12): 3659-76, 2009 Jun 21.
Artigo em Inglês | MEDLINE | ID: mdl-19478374

RESUMO

A compact dedicated 3D breast SPECT-CT (mammotomography) system is currently under development. In its initial prototype, the cone-beam CT sub-system is restricted to a fixed-tilt circular rotation around the patient's pendant breast. This study evaluated stationary-tilt angles for the CT sub-system that will enable maximal volumetric sampling and viewing of the breast and chest wall. Images of geometric/anthropomorphic phantoms were acquired using various fixed-tilt circular and 3D sinusoidal trajectories. The iteratively reconstructed images showed more distortion and attenuation coefficient inaccuracy from tilted cone-beam orbits than from the complex trajectory. Additionally, line profiles illustrated cupping artifacts in planes distal to the central plane of the tilted cone-beam, otherwise not apparent for images acquired with complex trajectories. This indicates that undersampled cone-beam data may be an additional cause of cupping artifacts. High-frequency objects could be distinguished for all trajectories, but their shapes and locations were corrupted by out-of-plane frequency information. Although more acrylic balls were visualized with a fixed-tilt and nearly flat cone-beam at the posterior of the breast, 3D complex trajectories have less distortion and more complete sampling throughout the reconstruction volume. While complex trajectories would ideally be preferred, negatively fixed-tilt source-detector configuration demonstrates minimally distorted patient images.


Assuntos
Tomografia Computadorizada de Feixe Cônico/instrumentação , Mamografia/instrumentação , Técnica de Subtração/instrumentação , Tomografia Computadorizada de Emissão de Fóton Único/instrumentação , Desenho de Equipamento , Análise de Falha de Equipamento , Imagens de Fantasmas , Reprodutibilidade dos Testes , Sensibilidade e Especificidade , Integração de Sistemas
2.
Phys Med Biol ; 52(3): 603-16, 2007 Feb 07.
Artigo em Inglês | MEDLINE | ID: mdl-17228108

RESUMO

A dual modality computed mammotomography (CmT) and single photon emission computed tomography (SPECT) system for dedicated 3D breast imaging is in development. Using heavy K-edge filtration, the CmT component narrows the energy spectrum of the cone-shaped x-ray beam incident on the patient's pendant, uncompressed breast. This quasi-monochromatic beam is expected to improve discrimination of tissue with similar attenuation coefficients while restraining absorbed dose to below that of dual view mammography. Previous simulation studies showed the optimal energy that maximizes dose efficiency for a 50/50% adipose/glandular breast is between 30 and 40 keV. This study experimentally validates these results using pre-breast and post-breast spectral measurements made under tungsten tube voltages between 40 and 100 kVp using filter materials with K-edge values ranging from 15 to 70 keV. Different filter material thicknesses are used, approximately equivalent to the 200th and 500th attenuating value layer (VL) thickness. Cerium (K = 40.4 keV) filtered post-breast spectra for 8-18 cm breasts are measured for a range of breast compositions. Figures of merit include mean beam energy, spectral full-width at tenth-maximum, beam hardening and dose for the range of breast sizes. Measurements corroborate simulation results, indicating that for a given dose, a 200th VL of cerium filtration may have optimal performance in the dedicated mammotomography paradigm.


Assuntos
Neoplasias da Mama/diagnóstico por imagem , Mamografia/instrumentação , Tomografia Computadorizada por Raios X/instrumentação , Fenômenos Biofísicos , Biofísica , Desenho de Equipamento , Feminino , Humanos , Mamografia/métodos , Mamografia/estatística & dados numéricos , Imagens de Fantasmas , Tomografia Computadorizada por Raios X/métodos , Tomografia Computadorizada por Raios X/estatística & dados numéricos
3.
Genesis ; 34(4): 228-35, 2002 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-12434332

RESUMO

Due to the internal nature of mammalian development, much of the research performed is of a static nature and depends on interpolation between stages of development. This approach cannot explore the dynamic interactions that are essential for normal development. While roller culture overcomes the problem of inaccessibility of the embryo, the constant motion of the medium and embryos makes it impossible to observe and record development. We have developed a static mammalian culture system for imaging development of the mouse embryo. Using this technique, it is possible to sustain normal development for periods of 18-24 h. The success of the culture was evaluated based on the rate of embryo turning, heart rate, somite addition, and several gross morphological features. When this technique is combined with fluorescent markers, it is possible to follow the development of specific tissues or the movement of cells. To highlight some of the strengths of this approach, we present time-lapse movies of embryonic turning, somite addition, closure of the neural tube, and fluorescent imaging of blood circulation in the yolk sac and embryo.


Assuntos
Técnicas de Cultura/métodos , Embrião de Mamíferos/embriologia , Desenvolvimento Embrionário , Ar , Animais , Meios de Cultura , Desenvolvimento Embrionário e Fetal , Feminino , Masculino , Camundongos , Microscopia de Vídeo , Gravidez , Ratos , Soro , Temperatura , Fatores de Tempo
4.
Development ; 125(11): 1991-8, 1998 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-9570764

RESUMO

Analysis of the regulatory regions of the Hox genes has revealed a complex array of positive and negative cis-acting elements that control the spatial and temporal pattern of expression of these genes during embryogenesis. In this study we show that normal expression of the murine Hoxa4 gene during development requires both autoregulatory and retinoic acid-dependent modes of regulation. When introduced into a Hoxa4 null background, expression of a lacZ reporter gene driven by the Hoxa4 regulatory region (Hoxa4/lacZ) is either abolished or significantly reduced in all tissues at E10. 5-E12.5. Thus, the observed autoregulation of the Drosophila Deformed gene is conserved in a mouse homolog in vivo, and is reflected in a widespread requirement for positive feedback to maintain Hoxa4 expression. We also identify three potential retinoic acid response elements in the Hoxa4 5' flanking region, one of which is identical to a well-characterized element flanking the Hoxd4 gene. Administration of retinoic acid to Hoxa4/lacZ transgenic embryos resulted in stage-dependent ectopic expression of the reporter gene in the neural tube and hindbrain. When administered to Hoxa4 null embryos, however, persistent ectopic expression was not observed, suggesting that autoregulation is required for maintenance of the retinoic acid-induced expression. Finally, mutation of the consensus retinoic acid response element eliminated the response of the reporter gene to exogenous retinoic acid, and abolished all embryonic expression in untreated embryos, with the exception of the neural tube and prevertebrae. These data add to the evidence that Hox gene expression is regulated, in part, by endogenous retinoids and autoregulatory loops.


Assuntos
Proteínas de Ligação a DNA , Regulação da Expressão Gênica no Desenvolvimento , Genes Homeobox , Proteínas de Homeodomínio/biossíntese , Sequências Reguladoras de Ácido Nucleico , Tretinoína/metabolismo , Animais , Sistema Nervoso Central/embriologia , Sequência Consenso , Cruzamentos Genéticos , Indução Embrionária , Desenvolvimento Embrionário e Fetal , Retroalimentação , Feminino , Camundongos , Camundongos Transgênicos , Dados de Sequência Molecular , Gravidez , Rombencéfalo/embriologia , Fatores de Tempo , Fatores de Transcrição
5.
Dev Dyn ; 211(3): 269-91, 1998 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-9520114

RESUMO

Megacolon occurs in neonatal and adult transgenic mice that overexpress the Hoxa-4 gene. Abnormalities, which are restricted to the terminal colon of these mice, include a hypoganglionosis, abnormal enteric ganglia with a structure appropriate for extra-enteric peripheral nerve and not the enteric nervous system (ENS), and gaps in the longitudinal muscle occupied by ganglia. To investigate the developmental origin of these abnormalities, we analyzed the development of the pelvis and terminal colon in Hoxa-4 transgenic mice. Morphological abnormalities were detected as early as E13. These included an enlargement of the mucosa and the bowel wall, a thickening of the enteric mesenchyme, and the ectopic location of pelvic ganglion cells, which initially clustered on the dorsolateral wall of the hindgut. As the bowel enlarged, these ectopic cells become ventrolateral and, between days E17 and E18.5, appeared to become incorporated into the gut, leaving neuron-filled gaps in the longitudinal muscle layer. The ectopic ganglia retained extra-enteric characteristics, including the presence of capillaries, basal laminae, collagen fibers, and catecholaminergic neurons, even after their incorporation into the bowel. It is proposed that the abnormal and ectopic expression of the Hoxa-4 transgene in the colon causes signalling molecule(s) of the enteric mesenchyme to be overproduced and that the overabundance of these signals leads to mucosal enlargement and misdirection of migrating pelvic neuronal progenitors.


Assuntos
Colo/anormalidades , Colo/embriologia , Proteínas de Ligação a DNA , Sistema Nervoso Entérico/anormalidades , Sistema Nervoso Entérico/embriologia , Proteínas de Homeodomínio/fisiologia , Animais , Colo/inervação , Desenvolvimento Embrionário e Fetal , Sistema Nervoso Entérico/ultraestrutura , Gânglios/citologia , Gânglios/ultraestrutura , Proteínas de Homeodomínio/genética , Mucosa Intestinal/embriologia , Megacolo/embriologia , Mesoderma , Camundongos , Camundongos Transgênicos , Neurônios/ultraestrutura , Pelve/embriologia , Fatores de Transcrição , Tirosina 3-Mono-Oxigenase/análise
6.
Mech Dev ; 63(2): 145-57, 1997 May.
Artigo em Inglês | MEDLINE | ID: mdl-9203138

RESUMO

The intron of the mouse Hoxa-4 gene acts as a strong homeotic response element in Drosophila melanogaster leg imaginal discs. This activity depends on homeodomain binding sites present within a 30 bp conserved element, HB1, in the intron. A similar arrangement of homeodomain binding sites is found in many other potential homeotic target genes. HB1 activity in Drosophila imaginal discs is activated by Antennapedia and more posterior homeotic genes, but is not activated by more anterior genes. Testing a reporter gene construct with mutated binding sites in mouse embryos shows that HB1 is also active in the expression domains of posterior Hox genes in the mouse neural tube.


Assuntos
Proteínas de Ligação a DNA , Drosophila/genética , Regulação da Expressão Gênica no Desenvolvimento , Proteínas de Homeodomínio/fisiologia , Proteínas Nucleares , Animais , Proteína do Homeodomínio de Antennapedia , Sequência de Bases , Sequência Conservada/fisiologia , Proteínas de Drosophila , Elementos Facilitadores Genéticos/fisiologia , Genes Reporter , Hibridização In Situ , Proteínas de Insetos/fisiologia , Íntrons/fisiologia , Camundongos , Camundongos Transgênicos , Fatores de Transcrição/fisiologia
7.
Dev Dyn ; 198(1): 28-53, 1993 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-7904838

RESUMO

Congenital megacolon develops in transgenic mice that overexpress the homeobox-containing gene, Hoxa-4. The current study was done to identify abnormalities of the terminal colon that might account for the phenotype. The terminal bowel of transgenic mice was compared with that of control and lethal spotted (ls/ls) mice, a strain in which megacolon also develops. The terminal colon of the transgenic mice contained fewer ganglia than that of controls, but was hypoganglionic, rather than aganglionic like that of ls/ls mice. The neurons present in the adult transgenic colon were significantly increased in size and a subset of very large neurons (> 40 microns in maximum diameter) were observed. Electron microscopic studies of young adult transgenic mice revealed that the ganglia and nerves of the myenteric plexus had the ultrastructure of extraenteric peripheral nerve rather than that of the enteric nervous system (ENS). The myenteric ganglia in the transgenic animals contained Schwann cells associated with a basal lamina that enveloped axons completely and individually, instead of glia. Although collagen is excluded from the ganglia and thin nerve fibers of the normal ENS, a collagen-containing endoneurium surrounded each of the axon-Schwann cell units of the abnormal nerve fibers of the transgenic colon. Some of the neurons of the transgenic mice were located in these nerve bundles rather than in ganglia. There were also smooth muscle abnormalities in the terminal bowel of the transgenic mice. Wide gaps were present in the longitudinal muscle of the transgenic mice; these gaps contained ganglia that were in contact with the adventitia. These longitudinal smooth muscle cells were more irregular than those of controls and they contained fewer puncta adherens; moreover, a larger proportion of the volume of the cytoplasm of transgenic smooth muscle cells was occupied by organelles. Finally, an extensive thickening and reduplication of the basal lamina surrounding the smooth muscle cells of the muscularis mucosa was observed in the transgenic colon and resembled that found in ls/ls mice. These data suggest that both smooth muscle and the innervation of the terminal bowel of neonatal Hoxa-4 transgenic mice are structurally abnormal. Although some of the abnormalities seen in Hoxa-4 transgenic mice are similar to those which arise in ls/ls mice, the two conditions are not identical. In both animals, the data are consistent with the hypothesis that the defects arise as a result of a defective interaction between the precursors of enteric neurons and smooth muscle.


Assuntos
Sistema Nervoso Entérico/anormalidades , Doença de Hirschsprung/patologia , Acetilcolinesterase/análise , Animais , Animais Recém-Nascidos , Sistema Nervoso Entérico/enzimologia , Sistema Nervoso Entérico/ultraestrutura , Expressão Gênica/fisiologia , Genes Homeobox/genética , Doença de Hirschsprung/genética , Masculino , Camundongos , Camundongos Transgênicos
8.
Development ; 117(3): 823-33, 1993 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-8100763

RESUMO

The murine homeobox-containing gene Hox-1.4 is expressed in restricted patterns during embryogenesis and in male germ cells. To begin identification of the cis-acting elements regulating this expression, transgenic mice were generated carrying a chimeric construct that contained approx. 4 kb of 5' flanking sequence and approx. 1 kb of structural gene, fused in frame to the E. coli lacZ gene. This construct directed expression of the resulting Hox-1.4,beta-galactosidase fusion protein in a pattern that reproduced virtually the complete embryonic and adult sites of expression of the endogenous gene. Embryonic expression of the fusion protein was first detected in mesoderm at day 8.0 of gestation (E 8.0). Between gestational ages E 8.5 to E 12.5, beta-gal expression was observed in the somites, the lateral walls of the posterior myelencephalon, the dorsal region and ventral wall of the spinal cord, spinal ganglia and prevertebrae and their surrounding mesenchyme, between presumptive ribs, as well as in mesenchymal layers in the lung, kidney and portions of the gut. Expression was also noted in the pancreas and in the supporting cells and sheath around subsets of peripheral nerves, sites that had not been detected previously. Adult expression was observed in testes, specifically in meiotic and post-meiotic male germ cells. In contrast, transgenic mice carrying 5' deletions of the construct which leave approx. 1.2 kb or approx. 2.0 kb of Hox-1.4 sequence 5' to the embryonic promoter, did not exhibit beta-gal staining. These deletion experiments defined at least one cis-acting control element necessary for the expression of the Hox-1.4 gene to a 2 kb region located 2 to 4 kb 5' of the embryonic transcription start site.


Assuntos
Proteínas de Ligação a DNA/genética , Expressão Gênica/genética , Genes Homeobox/genética , Proteínas de Homeodomínio , Óperon Lac/genética , Camundongos Transgênicos/genética , Animais , Escherichia coli/genética , Imuno-Histoquímica , Masculino , Camundongos , Camundongos Transgênicos/embriologia , Deleção de Sequência , Espermatogênese/genética , Testículo/embriologia , Fatores de Transcrição , beta-Galactosidase/genética
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