Diffusion spectrum magnetic resonance imaging (DSI) tractography of crossing fibers

MRI tractography is the mapping of neural fiber pathways based on diffusion MRI of tissue diffusion anisotropy. Tractography based on diffusion tensor imaging (DTI) cannot directly image multiple fiber orientations within a single voxel. To address this limitation, diffusion spectrum MRI (DSI) and related methods were developed to image complex distributions of intravoxel fiber orientation. Here we demonstrate that tractography based on DSI has the capacity to image crossing fibers in neural tissue. DSI was performed in formalin-fixed brains of adult macaque and in the brains of healthy human subjects. Fiber tract solutions were constructed by a streamline procedure, following directions of maximum diffusion at every point, and analyzed in an interactive visualization environment (TrackVis). We report that DSI tractography accurately shows the known anatomic fiber crossings in optic chiasm, centrum semiovale, and brainstem; fiber intersections in gray matter, including cerebellar folia and the caudate nucleus; and radial fiber architecture in cerebral cortex. In contrast, none of these examples of fiber crossing and complex structure was identified by DTI analysis of the same data sets. These findings indicate that DSI tractography is able to image crossing fibers in neural tissue, an essential step toward non-invasive imaging of connectional neuroanatomy.     

Decompressive craniectomy, reperfusion, or a combination for early treatment of acute "malignant" cerebral hemispheric stroke in rats? Potential mechanisms studied by MRI.

BACKGROUND AND PURPOSE: Both early reperfusion and decompressive craniectomy have proved beneficial in the treatment of large space-occupying "malignant" hemispheric stroke. The aim of this study was to directly compare the benefit of reperfusion with that of craniectomy and to study the effects of combined treatment in a rat model of focal cerebral ischemia. METHODS: Cerebral ischemia was introduced in 28 rats. Four groups were investigated: (1) no treatment, (2) decompressive craniectomy, (3) reperfusion, and (4) reperfusion and craniectomy as treatment at 1 hour after middle cerebral artery occlusion. Perfusion- and diffusion-weighted MRI were performed serially from 0.5 to 6 hours after middle cerebral artery occlusion. RESULTS: The 6-hour DWI-derived hemispheric lesion volumes in the reperfusion group (10.2+/-3.9%), the craniectomy group (23.0+/-6.4%), and the combination group (21.8+/-12.4) were significantly smaller than that in the control group (44.1+/-5.4%) (P<0.05). Reperfusion, craniectomy, and combined treatment led to higher perfusion in the cortex compared with the control group, whereas only reperfused animals achieved significantly higher perfusion in the basal ganglia. In 5 animals, combined reperfusion and decompressive craniectomy resulted in an early contrast media enhancement. CONCLUSIONS: Early reperfusion and craniectomy were shown to be effective in decreasing infarction volume by improving cerebral perfusion. Reperfusion remains the best therapy in malignant hemispheric stroke. Combined treatment yields no additional benefit compared with single treatment, probably because of early blood-brain barrier breakdown.     

Compromised white matter tract integrity in schizophrenia inferred from diffusion tensor imaging

BACKGROUND: Current investigations suggest that brain white matter may be qualitatively altered in schizophrenia even in the face of normal white matter volume. Diffusion tensor imaging provides a new approach for quantifying the directional coherence and possibly connectivity of white matter fibers in vivo. METHODS: Ten men who were veterans of the US Armed Forces and met the DSM-IV criteria for schizophrenia and 10 healthy, age-matched control men were scanned using magnetic resonance diffusion tensor imaging and magnetic resonance structural imaging. RESULTS: Relative to controls, the patients with schizophrenia exhibited lower anisotropy in white matter, despite absence of a white matter volume deficit. In contrast to the white matter pattern, gray matter anisotropy did not distinguish the groups, even though the patients with schizophrenia had a significant gray matter volume deficit. The abnormal white matter anisotropy in patients with schizophrenia was present in both hemispheres and was widespread, extending from the frontal to occipital brain regions. CONCLUSIONS: Despite the small sample size, diffusion tensor imaging was powerful enough to yield significant group differences, indicating widespread alteration in brain white matter integrity but not necessarily white matter volume in schizophrenia.     

More on management of choroid plexus cysts in the mid-trimester fetus

EDITORIAL COMMENT: We have published this pair of letters as a feature rather than in the correspondence column so it will not be lost to reference in the literature. Readers are also referred to a recently published review of the world literature concerning the risks of trisomies 18 and 21 in the second-trimester fetus with an isolated choroid plexus cyst (A). This study concluded that 'the likelihood of trisomy 18 was 13.8 times greater than the a priori risk in fetuses with isolated choroid plexus cysts diagnosed in the second trimester. However, the likelihood of trisomy 21 was not significantly greater than the a priori risk with isolated choroid plexus cysts.' N.B.
(A) Yoder PR, Sabbagha RE, Gross SJ, Zelop CM. The second-trimester fetus with isolated choroid plexus cysts: A meta-analysis of risk of trisomies 18 and 21. Obstet Gynecol 1999; 93: 869–872
1. Choong S, Meagher S, Management of choroid plexus cysts in the mid-trimester fetus Aust NZ J Obstet Gynecol 1999; 39: 7–11
2. Goldstein H, Philip J. A cost-benefit analysis of prenatal diagnosis by amniocentesis in Denmark. Clinical Genetics 1990; 37: 24–263
3. Gupta J, Thornton J, Lilford R. Management of fetal choroid plexus cyst. Br J Obstet Gynaecol 1997; 104: 881–886.
4. Gratton R, Hogge W, Ashton C. Choroid plexus cysts and Trisomy 18: Risk modification based on maternal age and multiple-marker screening. Am J Obstet Gynecol 1996; 175: 1493–1497
Associate Professor Lachlan de Crespigny, Head of Ultrasound, Royal Women's Hospital, Carlton, Melbourne and Associate Professor Julian Savulescu Director, Ethics Unit, The Murdoch Institute, Royal Children's Hospital, Parkville, Melbourne and Dr Leslie J Sheffield, Director of Education and Training, Victorian Clinical Genetic Services, Royal Children's Hospital, Parkville, Melbourne.     

Prenatal diagnosis and management of sacrococcygeal teratoma

Five fetuses, each with a sacrococcygeal teratoma (SCT) were delivered at the Royal Women's Hospital while 2 fetuses, each with a SCT were delivered at Monash Medical Centre in 1998. The number of cases reported in this series is higher than expected but it most likely occurred due to chance. The diagnosis was made prenatally in all cases. Three of the SCT were entirely external while the remaining 4 were external with intrapelvic extension. Rapid growth of the SCT occurred in 3 fetuses. This was associated with polyhydramnios in 2 fetuses. No fetus developed nonimmune hydrops. Six infants were liveborn (perinatal mortality rate of 14%), 3 of whom were delivered prior to 37 weeks' gestation. Two infants were delivered by classical Caesarean section. The remaining 4 infants were delivered by lower uterine segment Caesarean section. There was 1 perinatal death. This stillborn infant was delivered vaginally. The 6 surgical resections were performed between the 4th and 10th postnatal days. Histological examination confirmed the diagnosis of benign SCT in each. One infant developed a recurrence at 2 months of age and required chemotherapy.     

Better medication management for Aboriginal people with mental health disorders: a survey of providers

OBJECTIVE: To explore the experiences and training needs of service providers in relation to medication management for Aboriginal people with mental health disorders. DESIGN: Survey. SETTING: Aboriginal and mainstream health and human service organisations in metropolitan, rural and remote South Australia. SUBJECTS: Aboriginal health workers, nurses, mental health workers, substance misuse workers, managers, liaison officers, social workers, police, pharmacists, general practitioners, community workers, counsellors, paramedics, educators, family support workers and others. RESULTS: The major health service issues for Aboriginal people with mental health disorders and their carers are related to access to, and availability and appropriateness of services. Quality use of medications by Aboriginal clients is influenced by drug and alcohol misuse, cost, compliance, feelings about the value of medicines, sharing of medications and unwanted side-effects. Many workers providing services to Aboriginal people with mental health disorders lack adequate training and/or resources on mental health and safe medication management; yet, are required to provide advice or assistance on these matters. CONCLUSIONS: The survey provides new, reliable evidence relevant to mental health services and medication management for South Australian Aboriginal people. It highlights the major issues impacting on quality of care and service provision, demonstrates the wide range of health and allied workers providing medication advice and assistance to Aboriginal people, and reveals workforce development needs.     

Combined X-ray angiography and diffusion-perfusion MRI for studying stroke evolution after rt-PA treatment in rats

Clinical studies on rt-PA (recombinant tissue-type plasminogen activator) treatment of stroke showed a favorable outcome. However, there are reports of harmful effects of t-PA via the potentiation of excitotoxic injury. We used combined X-ray angiography and MRI imaging to study the balance between the beneficial effect of reperfusion and secondary detrimental effects of rt-PA. Therefore, rats (n=15) were assigned to three groups according to recanalization or lack thereof of the middle cerebral artery (MCA) and rt-PA or saline treatment in an embolic stroke model. Diffusion and perfusion MRI showed that animals had significantly improved perfusion values and final infarct size when recanalization was successful. However, final infarct volumes at 6 h post stroke onset were greater in the rt-PA group compared to controls at comparable perfusion values when the MCA did not recanalize after treatment (67.4+/-5.4 versus 47.7+/-17.9% of ipsilateral hemisphere, P=0.042). Our results demonstrate that the combination of angiography and MR-imaging is useful to further evaluate rt-PA treatment of thromboembolic stroke.     

Words matter: nomenclature and communication in perinatal medicine

The best interests of our patients are served by using language that both supports patient autonomy and is neutral. While it remains a "tentative" pregnancy (ie, before the completion of normal prenatal tests), the term "fetus" should be used. After normal prenatal testing, only in rare situations will the pregnant woman request an abortion. In such cases, it is appropriate that the term "fetal patient" or the lay terms "child" or "baby" be used. To be a "mother," however, one must have borne a child. Our language should support the autonomous views of the pregnant woman. The language proposed is not intended to be rigidly adhered to in all situations but rather is an appropriate starting point after which one needs to be responsive to the position of the pregnant woman. It is important to individualize language to cater to the views of individual patients. It is, however, time for doctors to acknowledge that their language can influence reality, particularly because they are frequently considered experts not only in prenatal diagnosis but also in morality. Doctor's language has a powerful influence over the way patients think.