MR technology: effect of even-echo rephasing on calculated T2 values and T2 images

In multiple spin-echo image sequences of blood flow, the "even-echo" phenomenon produces an absolute increase in signal magnitude from first- to second-echo images of normal vessels harboring slow flow. Distinguishing this from the apparent relatively high signal intensity seen on second-echo images in pathologic foci of stationary tissue is important to the diagnostician. Selected case material containing two tissue types was reviewed retrospectively: tissues known to harbor slow flow, such as normal veins and venous sinuses and vascular malformations, and tissues that have long transverse (T2) relaxation times and appear as intense structures on second-echo images, such as neoplasms, infarcts, and regions of demyelination. Calculations of T2 parameters were made by computer for defined regions of interest. T2 images were also generated. Visual inspection of the acquired images did not reliably distinguish increased intensity due to even-echo rephasing from the relative changes between adjacent tissues seen on second-echo images. More definitive differentiation of the even-echo phenomenon was provided by calculated values of T2 and computer-synthesized T2 images representing acquired intensity data of two-echo sequences. The synthesized images were especially useful when stationary tissue with lengthened T2 values was adjacent to or in proximity to vessels or vascular lesions. A five spin-echo image sequence was valuable for separating slow flow from stationary tissue by a technique of synthesizing T2-difference images using three consecutive echoes.     

Increased fetoplacental active renin production in pregnancy-induced hypertension

Since pregnancy-induced hypertension is associated with impaired uteroplacental blood flow, we studied fetoplacental and maternal renin production in controls and subjects with pregnancy-induced hypertension. We measured total, active, and inactive (pro-) renin in maternal serum, fetal arterial and venous blood, and chorion homogenate in eight normotensive term patients and 18 patients with pregnancy-induced hypertension. No differences in active or prorenin were found in maternal blood from normal women or patients with pregnancy-induced hypertension. In contrast, fetal artery and vein, as well as chorionic tissue, contained significantly higher active renin in pregnancy-induced hypertension compared with normal subjects. No difference in fetal or chorionic prorenin was seen in the two groups. Thus active to total renin ratio was higher in the fetus and chorion of subjects with pregnancy-induced hypertension, which suggests enhanced active renin production. These results suggest that pregnancy-induced hypertension is associated with increased activity of the renin-angiotensin system in the fetoplacental unit, which is not reflected in the maternal circulation. This may be an attempt by the fetus and chorionic membranes to maintain vascular homeostasis in the face of altered uteroplacental blood flow.     

Normal deposition of brain iron in childhood and adolescence: MR imaging at 1.5 T

Magnetic resonance (MR) images of the brain in 285 patients between the ages of 2 and 25 years were retrospectively studied to determine the appearance of brain iron accumulation. The globus pallidus, red nucleus, substantia nigra, and dentate nucleus were evaluated with long TR/TE (repetition time/echo time) spin-echo sequences and staged. All four regions in most patients were initially hyperintense compared with white matter (stage I) before becoming isointense (stage II) and subsequently hypointense (stage III). The globus pallidus was the first to reach stage III, the red nucleus and substantia nigra were next, and the dentate nucleus was last. In general, decreased signal intensity (stage III) was not seen in these regions in patients less than 10 years old; in most patients it was seen by age 25 years. The dentate nucleus decreased in signal intensity more slowly and inconsistently; only one-third of patients had reached stage III by age 25 years. The temporal sequence of normal iron deposition as detected with MR imaging is helpful not only in the diagnosis of known iron-deposition diseases but also in the detection of iron-related pathologic changes.     

Brain MR imaging in children with developmental retardation of unknown cause: results in 76 cases.

Seventy-six children with developmental retardation of unknown cause underwent MR imaging of the brain. Twenty-one (28%) had positive MR findings, including nine with atrophy, six with delayed myelination, four with multiple focal white matter lesions, three with hypoplastic white matter, and three with migration abnormalities. The frequency of abnormality was highest in nonautistic children with associated neurologic physical findings (61%) but was also significant in nonautistic children without neurologic findings (23%). We did not detect abnormalities on MR images of autistic retarded children. Delayed myelination and migration abnormalities were the predominant abnormalities in children with associated neurologic findings, whereas focal white matter lesions were more common in children without neurologic findings. Abnormalities were significantly more common in children with a small head circumference. Although MR did not have any effect on treatment or prognosis, it did aid the clinician in family counseling. MR will reveal brain abnormalities in about one third of nonautistic children with developmental retardation of unknown cause, and more often in those with neurologic deficits, seizures, or a small head size.     

Cystic intracranial lesions: magnetic resonance imaging

Thirty-three patients with cystic intracranial lesions were examined with both magnetic resonance (MR) imaging and CT scanning. The abnormalities imaged included 11 arachnoid cysts, 10 cystic tumors, six postoperative cysts, and three colloid cysts. The intensity patterns of the cyst contents as encoded with routine spin-echo imaging sequences enabled subdivision of the cysts into three categories. Arachnoid and postoperative cysts had an intensity pattern identical to cerebrospinal fluid. More proteinaceous cysts, including inflammatory cysts and nonhemorrhagic tumoral cysts, had an intermediate intensity pattern with characteristically low intensity on the short TR sequence (0.5 sec), but had clearly higher intensity than cerebrospinal fluid on the long TR sequences (2 sec). Finally, three cystic tumors with hemorrhagic fluid and three colloid cysts had a distinctly different pattern of high intensity on all four MR sequences through the same section. MR was superior to CT in characterizing intracranial cystic lesions because of its ability to categorize cysts into these three groups on the basis of the intensity pattern of cyst contents, thereby improving diagnostic specificity and patient management.     

Nonlissencephalic cortical dysplasias: correlation of imaging findings with clinical deficits.

PURPOSE: To establish correlations between MR patterns and clinical outcome in patients with nonlissencephalic cortical dysplasias. PATIENTS AND METHODS: MR and clinical data from 36 patients with cerebral cortical gyral anomalies (other than classical type I or type II lissencephaly) were retrospectively reviewed. RESULT: The five patients with diffuse cortical dysplasia, including two with congenital infections, had microcephaly and severe development delay from a very early age. Infantile spasms occurred in three of the five. Focal areas of cortical dysplasia were most common in the frontal lobes, but were seen in all areas of the brain. The most common MR appearances were 1) a thickened, irregularly bumpy cortex with shallow, wide sulci, and 2) a deep infolding of thickened cortex. The twelve patients with bilateral focal dysplasia had a high incidence of bilateral motor dysfunction (67%), delayed speech (67%), and generalized developmental delay (92%). When the dysplasia was unilateral, contralateral spastic hemiplegia or monoplegia was present in 14 of 19 patients (74%), but dysphasia was uncommon, even in patients with dysplasia in the frontal lobe of the dominant hemisphere. CONCLUSION: Surgical resection of focal areas of cortical dysplasia in patients with medically refractory seizures is becoming more common, and the neuroradiologist will play an increasingly important role in the initial diagnosis and delineation of these anomalies.