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Biomedical subjects

Rafael Rojas

Publications and source records attributed to Rafael Rojas.

At least 19 recordsLinked to original sources
PubMed2005

Experimental development of a petal resonator surface coil.

A surface coil for MRI was designed and built based on the principles of the petal resonator proposed by Mansfield [J Phys D Appl Phys 21 (1988) 1643]. This resonator coil design was named the petal resonator surface (PERES) coil and is composed of an eight-petal coil array and a central circular coil. A minimum separation of three times the petal coil radius is necessary to significantly decrease the mutual inductance. An analytical function for the PERES Signal-to-noise ratio (SNR) is obtained based on the quasistatic method. Theoretical plots of SNR enhancement yielded 26% and 35% more SNR over the circular coil and phased-array coils. Imaging experiments were first performed using a spectroscopy phantom on a 1.5-T commercial imager. Subsequently, brain images of healthy volunteers were obtained. Clinical MR imager compatibility allows this resonator coil to be used with conventional pulse sequences and imaging protocols. This coil design offers a new alternative to existing surface coils because it significantly increases the SNR.

Brain Mapping↗
PubMed2005

[Neutrophilic eccrine hidradenitis secondary to thioguanine in a neutropenic patient].

Neutrophilic eccrine hidradenitis (NEH) is an infrequent, self-limited inflammatory dermatosis characterized by a neutrophilic infiltrate around the eccrine glands. Clinically, it presents with different types of lesions. NEH occurs most frequently in patients who have undergone chemotherapy for hematologic neoplasms. We present a case of NEH in a 70-year-old neutropenic male who received thioguanine for acute myeloid leukemia. The erythematous plaques disappeared in 3-4 weeks. The histological findings were compatible with NEH. Skin cultures ruled out infectious causes.

Aged↗
PubMed2005

Neuroimaging in drug and substance abuse part II: opioids and solvents.

The central nervous system is one of the primary targets for the detrimental effects of drugs of abuse. Diagnostic imaging, especially MRI, plays an important role in the detection of complications associated with drug abuse. We present the imaging findings associated with the abuse of opioids and other morphine derivatives, as well, as solvents. Of the morphine derivatives, heroin is the most commonly abused. Several CNS pathologic effects have been described in association with its abuse. These include neurovascular complications such as microvascular ischemic changes or ischemic stroke. A rare form of leukoencephalopathy has been described in those abusers who inhale heroin vapors. Other neurologic complications include atrophy and various infectious processes. Solvent inhalation is a common practice among adolescents and young adults secondary to its ease of access and low cost. The most important component of industrial solvents is toluene. Complications of toluene abuse may be either acute, showing no neuroradiological changes, or chronic, characterized by cerebral and cerebellar demyelination as well as atrophy.

Administration, Inhalation↗
PubMed2005

Neuroimaging in drug and substance abuse part I: cocaine, cannabis, and ecstasy.

Multiple neurological complications of cocaine abuse have been described including both ischemic and hemorrhagic cerebrovascular events, atrophy in the case of chronic abuse, and an increase in incidence of congenital malformations in the setting of maternal use. The abuse of cannabis may cause a number of neurovascular changes that, in turn, may result in ischemic events, however, a direct connection between these has not been fully established. The use of MDMA (ecstasy), a popular recreational drug, has been related to ischemic and hemorrhagic cerebrovascular events, as well as atrophy. Neuroimaging studies are vital in the assessment of the extent of neurologic damage in these patients.

Atrophy↗
PubMed2005

Magnetic resonance imaging findings in substance abuse: alcohol and alcoholism and syndromes associated with alcohol abuse.

Alcohol abuse is common among the population and results in significant diseases that shorten life span. Ethanol may result in chronic brain changes such as atrophy but may also result in neurologic disease that may be acute or chronic and sometimes life threatening. Accompanying vitamin deficiencies may lead to Wernicke's encephalopathy and changes in serum osmosis may lead to several acute demyelinating disorders. In addition, pregnant women who consume alcohol place their babies at high risk for the fetal alcohol syndrome. In this article we review these disorders and emphasize their imaging features.

Alcohol-Induced Disorders, Nervous System↗
PubMed2005

Sinonasal hemangiopericytomas: clinicopathologic and imaging findings.

Hemangiopericytomas are rare soft-tissue neoplastic lesions that can arise in any part of the body. They are mesenchymal tumors that account for 3 to 5% of all soft-tissue sarcomas and 1% of all vascular tumors. They originate in extravascular cells (pericytes). Some 15 to 30% of all hemangiopericytomas occur in the head and neck; of these, approximately 5% occur in the sinonasal area. We describe our brief retrospective review of 7 histologically proven cases of sinonasal hemangiopericytoma, and we discuss the imaging characteristics and clinical and pathologic findings in these patients.

Adult↗
PubMed2004

Control of Epstein-Barr virus load and lymphoproliferative disease by maintenance of CD8+ T lymphocytes in the T lymphocyte-depleted graft after bone marrow transplantation.

Of 100 bone marrow transplant recipients, 30 (30%) received a CD4(+) lymphocyte-depleted graft (1x10(6) CD8(+) T lymphocytes/kg of body weight). Replication of Epstein-Barr virus (EBV) was observed in 40 patients (40%). The use of a CD4(+) lymphocyte-depleted graft was the only independent risk factor for replication of EBV (relative risk, 11.5; 95% confidence interval, 5.8-22.8; P<.0001). Nevertheless, EBV load in those patients was not higher than in the rest of patients, and the low EBV load prevented the development of lymphoproliferative disease. These results suggest that the presence of CD8(+) T lymphocytes in the bone marrow graft can control EBV load, thereby reducing the risk of developing lymphoproliferative disease.

Antibodies, Viral↗
PubMed2004

Odontogenic keratocysts in nevoid basal cell carcinoma (Gorlin's) syndrome: CT and MRI evaluation.

We describe the imaging findings in a 13-year-old boy with nevoid basal cell carcinoma syndrome (NBCCS). The initial imaging work-up included plain radiographs and computed tomography (CT) of the facial area and mandible. CT detected large expansile cystic changes on both sides of the body and angle of the mandible. When the patient's condition worsened, magnetic resonance imaging (MRI) was performed to further characterize the nature of the lesions and to rule out intracranial anomalies. We agree with others who have published previous reports that although CT is valuable in elucidating osseous craniofacial anomalies associated with NBCCS, MRI is superior in demonstrating the internal composition and structure of the odontogenic keratocysts that are commonly seen in this syndrome.

Adolescent↗
PubMed2004

Apical petrositis.

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Bone Diseases↗