Diffusion tensor imaging of brain development

Understanding early human brain development is of great clinical importance, as many neurological and neurobehavioral disorders have their origin in early structural and functional cerebral organization and maturation. Diffusion tensor imaging (DTI), a recent magnetic resonance (MR) modality which assesses water diffusion in biological tissues at a microstructural level, has revealed a powerful technique to explore the structural basis of normal brain development. In fact, the tissue organization can be probed non-invasively, and the age-related changes of diffusion parameters (mean diffusivity, anisotropy) reveal crucial maturational processes, such as white matter myelination. Nevertheless, the developing human brain presents several challenges for DTI applications compared with the adult brain. DTI may further be used to detect brain injury well before conventional MRI, as water diffusion changes are an early indicator of cellular injury. This is particularly critical in infants in the context of administration of neuroprotective therapies. Changes in diffusion characteristics further provide early evidence of both focal and diffuse white matter injury in association with periventricular leukomalacia in the preterm infant. Finally, with the development of 3D fiber tractography, the maturation of white matter connectivity can be followed throughout infant development into adulthood with the potential to study correlations between abnormalities on DTI and ultimate neurologic/cognitive outcome.     

Diffusion tensor imaging of normal brain development

Diffusion tensor imaging (DTI) is an MRI technique that can measure the macroscopic structural organization in brain tissues. DTI has been shown to provide information complementary to relaxation-based MRI about the changes in the brain’s microstructure. In the pediatric population, DTI enables quantitative observation of the maturation process of white matter structures. Its ability to delineate various brain structures during developmental stages makes it an effective tool with which to characterize both the normal and abnormal anatomy of the developing brain. This review will highlight the advantages, as well as the common technical pitfalls of pediatric DTI. In addition, image quantification strategies for various DTI-derived parameters and the normal brain developmental changes associated with these parameters are discussed.     

MR imaging of abdominopelvic involvement in neurofibromatosis type 1: a review of 43 patients

Background: Plexiform neurofibromas are a frequent complication of neurofibromatosis type 1. This article discusses MR imaging findings and distribution of plexiform neurofibromas in the abdomen and pelvis. Objective: To define the most prevalent patterns of involvement and MR imaging findings in abdominopelvic neurofibromatosis type 1. Materials and methods: We reviewed the MR appearance of abdominopelvic lesions in 23 male and 20 female patients (median age: 16 years) with type 1 neurofibromatosis. The patients were part of a multi-institutional study of 300 patients. Imaging included coronal or sagittal, and axial short tau inversion recovery images. Results: The most common abdominopelvic involvement was in the abdominopelvic wall (n=28, 65%) and lumbosacral plexus (n=27, 63%). Retroperitoneal involvement was frequent (n=15, 35%). Lesions were less often intraperitoneal (21%) (P=0.001). Pelvic disease (n=27, 63%), neural canal involvement (n=18, 42%), and hydronephrosis (n=4, 9%) were also noted. Target-like appearance of plexiform lesions was noted in more than half the patients. Conclusion: Abdominopelvic involvement in neurofibromatosis type 1 is primarily extraperitoneal. Although lesions are most prevalent in the abdominopelvic wall and lumbosacral plexus, retroperitoneal and pelvic involvement is common and usually affects important organs. MR imaging added information in the initial and follow-up clinical evaluation of these patients.     

Diffusion tensor imaging and fiber tractography in brain malformations

Diffusion tensor imaging (DTI) is an advanced MR technique that provides qualitative and quantitative information about the micro-architecture of white matter. DTI and its post-processing tool fiber tractography (FT) have been increasingly used in the last decade to investigate the microstructural neuroarchitecture of brain malformations. This article aims to review the use of DTI and FT in the evaluation of a variety of common, well-described brain malformations, in particular by pointing out the additional information that DTI and FT renders compared with conventional MR sequences. In addition, the relevant existing literature is summarized.     

Unidentified bright objects in neurofibromatosis type 1: Conventional MRI in the follow-up and correlation of microstructural lesions on diffusion tensor images

Purpose

To evaluate the evolution of unidentified bright objects (UBOs) in individuals with neurofibromatosis type 1 (NF1) by serial magnetic resonance imaging (MRI), and to relate this to regional fractional anisotropy (FA).

Materials and Methods

The signal pattern of the T2-weighted sequences in the basal ganglia, thalamus, brain stem, and cerebellum for 27 NF1 individuals and a control group were analyzed by diffusion tensor imaging (DTI). The presence or absence of UBOs in 2 consecutive MRI examinations was related to FA.

Results

We demonstrated significant differences in FA for the basal ganglia, cerebellum, and thalamus between NF1 patients and controls (P ≤ 0.05), even with a reduction or disappearance of UBOs.

Conclusions

MRI allows for adequate monitoring of the temporal and spatial distribution of UBOs in patients with NF1. DTI confirmed changes in FA despite the disappearance or reduction of UBOs, thereby confirming the hypothesis that microstructural damage occurs in specific brain regions of NF1 patients.     

Reduced artefacts and improved assessment of hyperintense brain lesions with BLADE MR imaging in patients with neurofibromatosis type 1

Background

Assessment of small brain lesions in children is often compromised by pulsation, flow or movement artefacts. MRI with a rotating blade-like k-space covering (BLADE, PROPELLER) can compensate for these artefacts.

Objective

We compared T2-weighted FLAIR images that were acquired with different k-space trajectories (conventional Cartesian and BLADE) to evaluate the impact of BLADE technique on the delineation of small or low-contrast brain lesions.

Materials and methods

The subject group comprised 26 children with neurofibromatosis type 1 (NF 1), who had been routinely scanned at 1.5 T for optic pathway gliomas with both techniques and who had the typical hyperintense brain lesions seen in NF 1. Four experienced radiologists retrospectively compared unlabelled 4-mm axial images with respect to the presence of artefacts, visibility of lesions, quality of contour and contrast.

Results

Both techniques were comparable in depicting hyperintense lesions as small as 2 mm independent of contrast and edge definition. Pulsation and movement artefacts were significantly less common with BLADE k-space trajectory. In 7 of 26 patients (27%), lesions and artefacts were rated as indistinguishable in conventional FLAIR, but not in BLADE FLAIR images.

Conclusion

BLADE imaging significantly improved the depiction of lesions in T2-W FLAIR images due to artefact reduction especially in the posterior fossa.     

Diffusion tensor imaging demonstrates brainstem and cerebellar abnormalities in congenital central hypoventilation syndrome

Congenital central hypoventilation syndrome (CCHS) patients show reduced breathing drive during sleep, decreased hypoxic and hypercapnic ventilatory responses, and autonomic and affective deficits, suggesting both brainstem and forebrain injuries. Forebrain damage was previously described in CCHS, but methodological limitations precluded detection of brainstem injury, a concern because genetic mutations in CCHS target brainstem autonomic nuclei. To assess brainstem and cerebellar areas, we used diffusion tensor imaging-based measures, namely axial diffusivity, reflecting water diffusion parallel to fibers, and sensitive to axonal injury, and radial diffusivity, measuring diffusion perpendicular to fibers, and indicative of myelin injury. Diffusion tensor imaging was performed in 12 CCHS and 26 controls, and axial and radial diffusivity maps were compared between groups using analysis of covariance (covariates; age and gender). Increased axial diffusivity in CCHS appeared within the lateral medulla and clusters with injury extended from the dorsal midbrain through the periaqueductal gray, raphé, and superior cerebellar decussation, ventrally to the basal-pons. Cerebellar cortex and deep nuclei, and the superior and inferior cerebellar peduncles showed increased radial diffusivity. Midbrain, pontine, and lateral medullary structures, and the cerebellum and its fiber systems are injured in CCHS, likely contributing to the characteristics found in the syndrome.     

神经纤维瘤病1型脑内MRI异常信号分析

No abstract available     

Diffusion tensor imaging and tractography of Rasmussen encephalitis

A 5-year-old girl presented with intractable seizures and nonfocal hemispheric slowing on EEG. Blood, urine, and CSF laboratory values were all normal. MR imaging of the brain demonstrated diffuse volume loss of the entire left hemisphere. Clinical and imaging findings were consistent with the diagnosis of Rasmussen encephalitis. Diffusion tensor imaging demonstrated increased ADC values and decreased fractional anisotropy (FA) of the affected (left) hemisphere. Tractography data showed decreased numbers of lines drawn in the affected hemisphere, with fewer lines drawn at higher FA thresholds, relative to the contralateral hemisphere, or to normal age-matched controls. Diffusion tensor imaging offers an adjunct MR imaging modality in diagnosis and monitoring of this rare condition.     

Diffusion tensor imaging of midline posterior fossa malformations

Background Diffusion tensor imaging and tractography have been used to evaluate a variety of brain malformations. However, these studies have focused mainly on malformations involving the supratentorial compartments. There is a paucity of data on diffusion tensor imaging of posterior fossa malformations.Objective To describe the color vector maps and modified or abnormal tracts of midline posterior fossa malformations.Materials and Methods Diffusion tensor imaging was performed in one patient with rhombencephalosynapsis and two with Joubert syndrome. Color vector maps of fractional anisotropy were used to place a region of interest for seed point of fiber tracking.Results The vermis was severely hypoplastic or absent in rhombencephalosynapsis and Joubert syndrome. In rhombencephalosynapsis, vertically oriented fibers were visualized in the midportion of the cerebellum. The location of the deep cerebellar nuclei could be inferred from the amiculum and were medially located in rhombencephalosynapsis. In the two patients with Joubert syndrome, the horizontally arranged superior cerebellar peduncles were well demonstrated on the color vector maps. Failure of the superior cerebellar peduncles to decussate in the mesencephalon was also well demonstrated on both color vector maps and tractography. The deep cerebellar nuclei were more laterally located in Joubert syndrome.Conclusion The use of tractography in midline posterior fossa malformations expands our understanding of these malformations.     

Pseudoarthrosis in neurofibromatosis type 1

Neurofibromatosis type 1 (NF1) is the most common neurocutaneous disease. The clinical manifestations are diverse. Some of the skeletal changes are most relevant to the patient. We report on 9 patients with NF1 who presented with typical pseudarthrosis. In 8 of these children the lower extremity was involved. In 2 cases lesions of both tibia and fibula were found, in one case even over long segments with a fully instable leg. One child had a complete pseudarthrosis of the radius and ulna. This report analyses the bony changes, the operations performed and the possible technical improvements to be made. The present study as well as other recent studies suggest that bony lesions should be operated early using microsurgical methods.     

MR imaging of the fetal brain

Fetal MRI is clinically performed to evaluate the brain in cases where an abnormality is detected by prenatal sonography. These most commonly include ventriculomegaly, abnormalities of the corpus callosum, and abnormalities of the posterior fossa. Fetal MRI is also increasingly performed to evaluate fetuses who have normal brain findings on prenatal sonogram but who are at increased risk for neurodevelopmental abnormalities, such as complicated monochorionic twin pregnancies. This paper will briefly discuss the common clinical conditions imaged by fetal MRI as well as recent advances in fetal MRI research.     

Diffusion tensor imaging of the cortical plate and subplate in very-low-birth-weight infants

Background  

Many intervention studies in preterm infants aim to improve neurodevelopmental outcome, but short-term proxy outcome measurements are lacking. Cortical plate and subplate development could be such a marker.     

Diffusion tensor imaging in infants with basal ganglia-thalamic lesions.

We performed diffusion tensor imaging in two infants with neonatal hypoxic-ischemic encephalopathy. MRI revealed basal ganglia-thalamic lesions in both patients during the neonatal period. Patient 1 had severe neurological sequelae, whereas patient 2 achieved normal development. Conventional MRI at 12 months of age showed abnormal high-intensity areas in bilateral basal ganglia and thalami in patient 1, whereas no abnormal intensities were recognized in patient 2. Diffusion tensor tractography demonstrated poor depiction of white matter tracts above the level of centrum semiovale in patient 1. Region of interest analysis showed that fractional anisotropy of white matter of centrum semiovale and deep white matter was markedly reduced in patient 1 compared with patient 2, although apparent diffusion coefficient was not largely different between them. Our study suggested that abnormalities of diffusion property will be more widely present than those of conventional MRI. Diffusion tensor imaging will be useful to detect white matter abnormalities in normal-appearing white matter on conventional MRI.     

Diffusion tensor imaging in children and adolescents with tuberous sclerosis

Background: Tuberous sclerosis (TS) is characterised by benign hamartomatous lesions in many organs. Diffusion tensor imaging (DTI) can detect microstructural changes in pathological processes. Objective: To determine apparent diffusion coefficient (ADC) and fractional anisotropy (FA) maps in children with TS and to investigate the diffusion properties in cortical tubers, white-matter lesions, perilesional white matter, and contralateral normal-appearing white matter, and to compare the results with ADC and FA maps of normal age- and sex-matched volunteers. Materials and methods: Seven children and adolescents (age range 2–20 years) suffering from TS were included. MRI was performed on a 1.5-T scanner using a transmit/receive coil with T1-W and T2-W spin-echo and FLAIR sequences. DT images were acquired by using a single-shot echo-planar pulse sequence. Diffusion gradients were applied in six different directions with a b value of 1,000 s/mm². Results: ADC was higher in cortical tubers than in the corresponding cortical location of controls. ADC values were higher and FA values were lower in white-matter lesions and perilesional white matter than in both the contralateral normal-appearing white matter of patients and in controls. There were no significant differences for both ADC and FA values in the normal-appearing white matter of patients with TS compared to controls. Conclusions: DTI provides important information about cortical tubers, white-matter abnormalities, and perilesional white matter in patients with TS.     

Diffusion tensor imaging and tractography of the kidney in children: feasibility and preliminary experience

Background

Functional magnetic resonance urography (fMRU) provides morphological and functional information based on perfusion. Diffusion tensor imaging (DTI) complements fMRU by measuring renal microstructure and provides insight into the relationship between renal structure and function.

Objective

To evaluate the feasibility and utility of renal DTI and tractography in the setting of fMRU in children.

Materials and methods

We prospectively enrolled 9 children (6 boys, 3 girls) with a mean age of 4.3 years (range 6 months to 14.8 years). All children were examined with MRI at 3.0 tesla. DTI was acquired with an echo-planar sequence (TR/TE?=?2,300/69 ms, b?=?300 s/mm²) with 12 non-collinear directions and 3 signal averages. Functional MRU results were used to group the moieties as normal or abnormal. Regions of interest were placed in the medulla and cortex to measure DTI parameters of microstructure. DTI tractography measures of parenchymal volume were compared to fMRU-derived volumes.

Results

We analyzed 19 moieties (13 normal; 6 abnormal). Tractography of normal moieties showed numerous tracks with a radial arrangement and convergence into pyramids. Abnormal moieties did not show the radial arrangement or converging architecture and had tracks that were loosely arranged and left hollow spaces. Tractography volume correlated with MRU parenchymal volume (r ²?=?0.93, P?<?0.005) and abnormal moieties exhibited greater tractography volume than normal moieties (P?<?0.005). Tractography volume also correlated with age of the child (P?<?0.001). In normal moieties, the medulla had higher fractional anisotropy (0.401 +/?0.05) than the cortex (0.183 +/? 0.03) (P?<?0.001); fractional anisotropy in these regions did not change with age (P?>?0.1). There were no differences in apparent diffusion coefficient values between the cortex and medulla (P?>?0.5). We observed a trend of increasing apparent diffusion coefficient values with age in the cortex and medulla, which did not reach statistical significance (cortex: r²?=?0.21, P?>?0.1; medulla: r²?=?0.135, P?>?0.1).

Conclusion

DTI with tractography is feasible in children and can complement the functional information obtained from fMRU.     

Plexiform neurofibroma in type 1 neurofibromatosis

A 13-year-old African-American girl was admitted to the hospital for surgery. She was diagnosed with Type I neurofibromatosis at the age of 1 year after she was noted to have multiple café au lait spots. Her past medical history included a history of neurofibroma in the base of the brain, treated with radiation therapy and ventriculoperitoneal shunt, as well as a recent diagnosis of bilateral optic gliomas, treated with chemotherapy. Family history was negative for neurofibromatosis.     

Diagnostic delay in neurofibromatosis type 1

Since 1985 a multidisciplinary team in the Sophia Children's University Hospital in Rotterdam provides diagnostic follow up and genetic counselling services for neurofibromatosis type 1 (NF1) patients and their families. Parents of 68 affected children as well as 24 affected parents were interviewed. Of the affected children, 50% and 33% of the affected adults were treated for symptoms related to NF1 before a specific diagnosis was made. Although the disease is fully penetrant by the age of 5 years, 35% of the affected children had not been diagnosed by this age. Parents stated a preference for early diagnosis of NF1. Diagnosis of NF1 did not seem to be a reason to refrain from having children. The general attitude towards prenatal diagnosis was positive; however few parents would actually terminate an affected pregnancy. Conclusion Overall delay in diagnosis of NF1 is significant. Knowledge of symptoms should make an early diagnosis possible with beneficial effects for the patient and family members. Received: 25 July 1996 / Accepted: 21 October 1996