Systematic differences between lean and obese adolescents in brain spin-lattice relaxation time: a quantitative study

BACKGROUND AND PURPOSE

Emerging evidence suggests that obese adolescents show changes in brain structure compared with lean adolescents. In addition, obesity impacts body development during adolescence. We tested a hypothesis that T1, a marker of brain maturation, can show brain differences associated with obesity.

MATERIALS AND METHODS

Adolescents similar in sex, family income, and school grade were recruited by using strict entry criteria. We measured brain T1 in 48 obese and 31 lean adolescents by quantitative MR imaging at 1.5T. We combined MPRAGE and inversion-recovery sequences with normalization to standard space and automated skull stripping to obtain T1 maps with a symmetric voxel volume of 1 mm(3).

RESULTS

Sex, income, triglycerides, total cholesterol, and fasting glucose did not differ between groups, but obese adolescents had significantly lower HDL, higher LDL, and higher fasting insulin levels than lean adolescents. Intracranial vault volume did not differ between groups, but obese adolescents had smaller intracranial vault-adjusted brain parenchymal volumes. Obese adolescents had 4 clusters (>100 contiguous voxels) of T1 relaxation that were significantly different (P < .005) from those in lean adolescents. Three of these clusters had longer T1s in obese adolescents (in the orbitofrontal and parietal regions), and 1 cluster had shorter T1s, compared with lean adolescents.

CONCLUSIONS

Our results suggest that obesity may have a significant impact on brain development, especially in the frontal and parietal lobes. It is unclear if these changes persist into adulthood or whether they indicate that obese subjects follow a different developmental trajectory during adolescence.

Measuring brain volume by MR imaging: impact of measurement precision and natural variation on sample size requirements

BACKGROUND AND PURPOSE

To determine the sample size needed to provide adequate statistical power in studies of brain volume by MR imaging, we examined the precision and variability of measurements in healthy controls.

MATERIALS AND METHODS

A cohort of 52 people (mean age, 25.1 years) was examined at weeks 0 and 12 at 1.5 T. We used an axial multisection T1-weighted sequence and a contiguous proton-attenuation/T2-weighted sequence. Data were registered to a probabilistic brain atlas, and an automated atlas-based program was used to segment brain tissue by type and by lobe. We assumed that there were no changes in volume because there were no intervening neurologic events. Sample sizes required to yield 80% statistical power in detecting a significant difference in volume were calculated for various experimental designs, assuming a patient-control volume difference of 5% or 2%.

RESULTS

The precision of most measurements was excellent, but required sample sizes were larger than anticipated. If the goal was to detect a 5% difference in whole brain volume in a 2-sample cross-sectional study, the required sample was 73 patients and 73 controls because brain volume varies between individuals in a way that is not informative about disease effects. For a similar 2-sample longitudinal study, the required sample size was just 5 patients and 5 controls.

CONCLUSIONS

Our results argue strongly for longitudinal studies in preference to cross-sectional studies, especially as research budgets decline. Our findings also suggest that there may be more uncertainty than expected in published MR imaging brain volume studies.

Effect of therapeutic ionizing radiation on the human brain

We test a hypothesis that fractionated radiation therapy within a therapeutic dose range is associated with a dose-related change in normal brain, detectable by quantitative magnetic resonance imaging. A total of 33 patients were examined by quantitative magnetic resonance imaging to measure brain tissue spin-lattice relaxation time (T1) before treatment, and at various times during and after radiation therapy. A T1 map was generated at each time point, and radiation therapy isodose contours were superimposed on the corresponding segmented T1 map. Changes in white matter and gray matter T1 were analyzed as a function of radiation therapy dose and time since treatment, controlling for patient age and tumor site. In white matter, a dose level of more than 20 Gy was associated with a dose-dependent decrease in T1 over time, which became significant 6 months after treatment. There was no significant change in T1 of gray matter over time, at radiation therapy doses of less than 60 Gy. However, GM in close proximity to the tumor had a lower T1 before therapy. Our results represent the first radiation dose-response data derived from pediatric brain in vivo. These findings confirm that white matter is more vulnerable to radiation-induced change than is gray matter, and suggest that T1 mapping is sensitive to radiation-related changes over a broad dose range (20 to 60 Gy). Human white matter T1 is not sensitive to radiation therapy of less than 20 Gy, and gray matter T1 is unchanged over the dose range used to treat human brain tumor. The reduction of gray matter T1 near the tumor could result from compression of cortical parenchyma near the growing tumor mass, or from tumor cell invasion directly into the parenchyma. If brain T1 is a surrogate for radiation effect, reducing the volume of normal white matter receiving more than 20 Gy could be an important treatment planning goal.

A radiation hybrid map of mouse genes

A comprehensive gene-based map of a genome is a powerful tool for genetic studies and is especially useful for the positional cloning and positional candidate approaches. The availability of gene maps for multiple organisms provides the foundation for detailed conserved-orthology maps showing the correspondence between conserved genomic segments. These maps make it possible to use cross-species information in gene hunts and shed light on the evolutionary forces that shape the genome. Here we report a radiation hybrid map of mouse genes, a combined project of the Whitehead Institute/Massachusetts Institute of Technology Center for Genome Research, the Medical Research Council UK Mouse Genome Centre, and the National Center for Biotechnology Information. The map contains 11,109 genes, screened against the T31 RH panel and positioned relative to a reference map containing 2,280 mouse genetic markers. It includes 3,658 genes homologous to the human genome sequence and provides a framework for overlaying the human genome sequence to the mouse and for sequencing the mouse genome.

Prospective evaluation of the brain in asymptomatic children with neurofibromatosis type 1: relationship of macrocephaly to T1 relaxation changes and structural brain abnormalities

BACKGROUND AND PURPOSE

Mutation of the neurofibromatosis type 1 (NF-1) gene may be associated with abnormal growth control in the brain. Because macrocephaly could be a sign of abnormal brain development and because 30% to 50% of children with NF-1 display macrocephaly in the absence of hydrocephalus, we sought to determine the relationship between macrocephaly and other brain abnormalities in young subjects with NF-1. These subjects were free of brain tumor, epilepsy, or other obvious neurologic problems.

METHODS

We prospectively screened 18 neurologically asymptomatic subjects with NF-1, ages 6 to 16 years, using clinical measures, psychometric testing, conventional MR imaging, and quantitative MR imaging to measure T1.

RESULTS

Cranial circumference was 2 or more SDs above the age norm in seven (39%) of 18 subjects, a frequency of macrocephaly 17-fold higher than normal. Conventional MR imaging showed abnormalities in all 18 children, although there were more extensive abnormalities in subjects with macrocephaly. Macrocephaly in NF-1 was associated with enlargement of multiple brain structures, and brain T1 in macrocephalic subjects was reduced with respect to controls in the genu, frontal white matter, caudate, putamen, thalamus, and cortex. In normocephalic subjects, T1 was reduced only in the genu and splenium. Volumetric analysis showed that macrocephaly was associated specifically with enlargement of white matter volume.

CONCLUSION

Neurologically asymptomatic children with NF-1 showed macrocephaly, cognitive deficit, enlarged brain structures, and abnormally low brain T1. Macrocephaly in children with NF-1 may be associated with characteristic alterations in brain development, marked by more widespread and significant changes in T1, greater enlargement of midline structures, and greater volume of white matter.

Improved cerebrovascular patency following therapy in patients with sickle cell disease: initial results in 4 patients who received HLA-identical hematopoietic stem cell allografts

To test whether magnetic resonance angiography can document the evolution of vasculopathy in patients with sickle cell disease, we reviewed records to identify all patients who underwent magnetic resonance angiography from 1993 to 1999. Of 512 angiographies performed, 105 were of sickle cell disease patients, and 24 sickle cell disease patients 7 years of age or older underwent baseline and follow-up examinations. Films were paired by patient, blinded as to examination date and treatment, and quantitatively compared. Four patients who received allogeneic bone marrow transplantation were compared to 7 patients who received other therapy and to 13 untreated patients. Quantitative analysis revealed a 10% increase in the measured diameter of 64 vessels (p = 0.001) following any treatment. Patients who had undergone allogeneic bone marrow transplantation exhibited a 12% increase in the lumen of 22 vessels (p = 0.041), whereas patients treated with chronic transfusion or hydroxyurea exhibited an 8% increase in 42 vessels (p = 0.016). In 2 patients with severe stenosis, the artery normalized after transplantation, and the blood flow rate was reduced in all patients who underwent transplantation. In untreated patients, there was a trend for the size of the arterial lumen to decrease, which is consistent with disease progression. Results suggest that treatment can reverse progression of vasculopathy. Bone marrow transplantation may enable stenoses to heal and can substantially reduce cranial blood velocity, suggesting that allogeneic bone marrow transplantation may prevent infarction or brain damage.

Effect of ionizing radiation on the human brain: white matter and gray matter T1 in pediatric brain tumor patients treated with conformal radiation therapy

OBJECTIVE

To test a hypothesis that fractionated radiation therapy (RT) to less than 60 Gy is associated with a dose-related change in the spin-lattice relaxation time (T1) of normal brain tissue, and that such changes are detectable by quantitative MRI (qMRI).

METHODS

Each of 21 patients received a qMRI examination before treatment, and at several time points during and after RT. A map of brain T1 was calculated and segmented into white matter and gray matter at each time point. The RT isodose contours were then superimposed upon the T1 map, and changes in brain tissue T1 were analyzed as a function of radiation dose and time following treatment. We used a mixed-model analysis to analyze the longitudinal trend in brain T1 from the start of RT to 1 year later. Predictive factors evaluated included patient age and clinical variables, such as RT dose, time since treatment, and the use of an imaging contrast agent.

RESULTS

In white matter (WM), a dose level of greater than 20 Gy was associated with a dose-dependent decrease in T1 over time, which became significant about 3 months following treatment. In gray matter (GM), there was no significant change in T1 over time, as a function of RT doses < 60 Gy. However, GM in close proximity to the tumor had an inherently lower T1 before therapy. Neither use of a contrast agent nor a combination of chemotherapy plus steroids had a significant effect on brain T1.

CONCLUSION

Results suggest that T1 mapping may be sensitive to radiation-related changes in human brain tissue T1. WM T1 appears to be unaffected by RT at doses less than approximately 20 Gy; GM T1 does not change at doses less than 60 Gy. However, tumor appears to have an effect upon adjacent GM, even before treatment. Conformal RT may offer a substantial benefit to the patient, by minimizing the volume of normal brain exposed to greater than 20 Gy.

Hybrid artificial neural network segmentation of precise and accurate inversion recovery (PAIR) images from normal human brain

This paper presents a novel semi-automated segmentation and classification method based on raw signal intensities from a quantitative T1 relaxation technique with two novel approaches for the removal of partial volume effects. The segmentation used a Kohonen Self Organizing Map that eliminated inter- and intra-operator variability. A Multi-layered Backpropagation Neural Network was able to classify the test data with a predicted accuracy of 87.2% when compared to manual classification. A linear interpolation of the quantitative T1 information by region and on a pixel-by-pixel basis was used to redistribute voxels containing a partial volume of gray matter (GM) and white matter (WM) or a partial volume of GM and cerebrospinal fluid (CSF) into the principal components of GM, WM, and CSF. The method presented was validated against manual segmentation of the base images by three experienced observers. Comparing segmented outputs directly to the manual segmentation revealed a difference of less than 2% in GM and less than 6% in WM for pure tissue estimations for both the regional and pixel-by-pixel redistribution techniques. This technique produced accurate estimates of the amounts of GM and WM while providing a reliable means of redistributing partial volume effects.

Fast adipose tissue (FAT) assessment by MRI

We report a method of fast adipose tissue (FAT) assessment to characterize the quantity, and distribution of abdominal adipose tissue. Whole-volume coverage of the abdomen was obtained using 31 contiguous transverse T(1)-weighted images from 16 obese females. A radiologist manually traced all adipose tissue volumes in the images, while a physiologist used an automated method to measure adipose tissue in a single image at the level of the umbilicus. Automated analysis of the umbilicus-level image was significantly correlated with values obtained by manual analysis of the entire abdomen (p < 0. 001). There was good agreement between the automated umbilicus-level image method and the manual whole abdomen method for subcutaneous adipose tissue (r(2) = 0.958), visceral adipose tissue (r(2) = 0. 753), and total adipose tissue (r(2) = 0.941). The automated method required 6 min vs 2 h for the manual method.

More than meets the eye: significant regional heterogeneity in human cortical T1

Segmented k-space acquisition of data was used to decrease the acquisition time and to increase the imaging resolution of the precise and accurate inversion recovery (PAIR) method of measuring T(1). We validated the new TurboPAIR method by measuring T(1) in 158 regions of interest in 12 volunteers, using both PAIR and TurboPAIR. We found a 3% difference between methods, which could be corrected by linear regression. After validation, the TurboPAIR method was used to test a hypothesis that there is significant regional heterogeneity in cortical T(1). We measured cortical gray matter T(1) in 11 right-handed volunteers, in 48 regions of interest scattered over frontal and parietal cortex, and in 46 ROIs along the central sulcus (CS). We found that T(1) in the CS is less than T(1) elsewhere in the cortex (p<0.001), and that there is considerable hemispheric asymmetry in T(1) in gray matter, but not in white matter. In central gray structures (caudate, thalamus, nucleus pulvinarus), and in the posterior CS (sensory cortex), right hemisphere T(1) was significantly greater than left hemisphere T(1) (p< or =0.004). In cortical gray matter of the frontal lobe and anterior CS (motor cortex), left hemisphere T(1) was significantly greater than right hemisphere T(1) (p< or =0.003). These findings demonstrate that there is considerable regional heterogeneity in human cortical T(1) that is unexplained by differences in tissue iron content, but may be evidence of an inherent anatomic asymmetry of the brain.

The correlation between phase shifts in gradient-echo MR images and regional brain iron concentration

The purpose of this study was to investigate the relationship between the magnetic susceptibility of brain tissue and iron concentration. Phase shifts in gradient-echo images (TE = 60 ms) were measured in 21 human subjects, (age 0.7-45 years) and compared with published values of regional brain iron concentration. Phase was correlated with brain iron concentration in putamen (R2 = 0.76), caudate (0.72), motor cortex (0.68), globus pallidus (0.59) (all p < 0.001), and frontal cortex (R2 = 0.19, p = 0.05), but not in white matter (R2 = 0.05,p = 0.34). The slope of the regression (degrees/mg iron/g tissue wet weight) varied over a narrow range from -1.2 in the globus pallidus and frontal cortex to -2.1 in the caudate. These results suggest that magnetic resonance phase reflects iron-induced differences in brain tissue susceptibility in gray matter. The lack of correlation in white matter may reflect important differences between gray and white matter in the cellular distribution and the metabolic functions of iron. Magnetic resonance phase images provide insight into the magnetic state of brain tissue and may prove to be useful in elucidating the relationship between brain iron and tissue relaxation properties.

Radiation hybrid map of the mouse genome

Radiation hybrid (RH) maps are a useful tool for genome analysis, providing a direct method for localizing genes and anchoring physical maps and genomic sequence along chromosomes. The construction of a comprehensive RH map for the human genome has resulted in gene maps reflecting the location of more than 30,000 human genes. Here we report the first comprehensive RH map of the mouse genome. The map contains 2,486 loci screened against an RH panel of 93 cell lines. Most loci (93%) are simple sequence length polymorphisms (SSLPs) taken from the mouse genetic map, thereby providing direct integration between these two key maps. We performed RH mapping by a new and efficient approach in which we replaced traditional gel- or hybridization-based assays by a homogeneous 5'-nuclease assays involving a single common probe for all genetic markers. The map provides essentially complete connectivity and coverage across the genome, and good resolution for ordering loci, with 1 centiRay (cR) corresponding to an average of approximately 100 kb. The RH map, together with an accompanying World-Wide Web server, makes it possible for any investigator to rapidly localize sequences in the mouse genome. Together with the previously constructed genetic map and a YAC-based physical map reported in a companion paper, the fundamental maps required for mouse genomics are now available.

A YAC-based physical map of the mouse genome

A physical map of the mouse genome is an essential tool for both positional cloning and genomic sequencing in this key model system for biomedical research. Indeed, the construction of a mouse physical map with markers spaced at an average interval of 300 kb is one of the stated goals of the Human Genome Project. Here we report the results of a project at the Whitehead Institute/MIT Center for Genome Research to construct such a physical map of the mouse. We built the map by screening sequenced-tagged sites (STSs) against a large-insert yeast artificial chromosome (YAC) library and then integrating the STS-content information with a dense genetic map. The integrated map shows the location of 9,787 loci, providing landmarks with an average spacing of approximately 300 kb and affording YAC coverage of approximately 92% of the mouse genome. We also report the results of a project at the MRC UK Mouse Genome Centre targeted at chromosome X. The project produced a YAC-based map containing 619 loci (with 121 loci in common with the Whitehead map and 498 additional loci), providing especially dense coverage of this sex chromosome. The YAC-based physical map directly facilitates positional cloning of mouse mutations by providing ready access to most of the genome. More generally, use of this map in addition to a newly constructed radiation hybrid (RH) map provides a comprehensive framework for mouse genomic studies.

A high-density integrated genetic linkage and radiation hybrid map of the laboratory rat

The laboratory rat (Rattus norvegicus) is a key animal model for biomedical research. However, the genetic infrastructure required for connecting phenotype and genotype in the rat is currently incomplete. Here, we report the construction and integration of two genomic maps: a dense genetic linkage map of the rat and the first radiation hybrid (RH) map of the rat. The genetic map was constructed in two F2 intercrosses (SHRSP x BN and FHH x ACI), containing a total of 4736 simple sequence length polymorphism (SSLP) markers. Allele sizes for 4328 of the genetic markers were characterized in 48 of the most commonly used inbred strains. The RH map is a lod >/= 3 framework map, including 983 SSLPs, thereby allowing integration with markers on various genetic maps and with markers mapped on the RH panel. Together, the maps provide an integrated reference to >3000 genes and ESTs and >8500 genetic markers (5211 of our SSLPs and >3500 SSLPs developed by other groups). [Bihoreau et al. (1997); James and Tanigami, RHdb (http:www.ebi.ac.uk/RHdb/index.html); Wilder (http://www.nih.gov/niams/scientific/ratgbase); Serikawa et al. (1992); RATMAP server (http://ratmap.gen.gu.se)] RH maps (v. 2.0) have been posted on our web sites at http://goliath.ifrc.mcw.edu/LGR/index.html or http://curatools.curagen.com/ratmap. Both web sites provide an RH mapping server where investigators can localize their own RH vectors relative to this map. The raw data have been deposited in the RHdb database. Taken together, these maps provide the basic tools for rat genomics. The RH map provides the means to rapidly localize genetic markers, genes, and ESTs within the rat genome. These maps provide the basic tools for rat genomics. They will facilitate studies of multifactorial disease and functional genomics, allow construction of physical maps, and provide a scaffold for both directed and large-scale sequencing efforts and comparative genomics in this important experimental organism.

Diffuse T1 reduction in gray matter of sickle cell disease patients: evidence of selective vulnerability to damage?

The objective of our study was to test the hypothesis that subtle brain abnormality can be present in pediatric sickle cell disease (SCD) patients normal by conventional MR imaging (cMRI). We examined 50 SCD patients to identify those patients who were normal by cMRI. Quantitative MR imaging (qMRI) was then used to map spin-lattice relaxation time (T1) in a single slice in brain tissue of all 50 patients and in 52 healthy age-similar controls. We also used a radiofrequency (RF) pulse to saturate blood spins flowing into the T1 map slice, to characterize the effect of blood flow on brain T1. Abnormalities were noted by cMRI in 42% (21/50) of patients, with lacunae in 32%, and encephalo malacia in 20%. Brain T1 in patients normal by cMRI was significantly lower than controls, in caudate, thalamus, and cortex (p < or =0.007), and regression showed that gray matter T1 abnormality was present in caudate and cortex by age 4 (p < or =0.002). In patients abnormal by cMRI, T1 reductions in gray matter were larger and more significant. White matter T1 was not significantly increased except in patients abnormal by cMRI. RF saturation in a slab below the T1 map produced no significant change in T1, compared to RF saturation in a slab above the T1 map, suggesting that inflow of untipped spins in blood does not cause an artifactual shortening of T1. Gray matter T1 abnormality was present in patients normal by cMRI, while white matter T1 abnormality was present only in patients also abnormal by cMRI. These findings suggest that gray matter is selectively vulnerable to damage in pediatric SCD patients and that white matter damage occurs later in the disease process. Our inability to find an effect from saturation of inflowing blood implies that rapid perfusion cannot account for T1 reduction in gray matter.

Levels of high energy phosphate in the dorsal skin of the foot in normal and diabetic adults: the role of 31P magnetic resonance spectroscopy and direct quantification with high pressure liquid chromatography

Determining viability of tissues and wound-healing potential in diabetic patients remains a significant challenge. Current methods for preoperative assessment of wound-healing potential (pressures in the ankle, temperature of tissues, transcutaneous measurements of oxygen, and systemic nutritional status) are indirect, in that they characterize the delivery of oxygen or other nutrients to the cells. A noninvasive means to measure adenosine triphosphate (ATP) and phosphocreatine (PCr), the fundamental high energy phosphate substrates of oxidative energy-metabolism in the skin, has been devised by using magnetic resonance spectroscopy (MRS). The signal-to-noise ratio of bioenergetic metabolites in the skin was 86% lower in five patients with diabetes who had ischemia of the lower extremity compared with five control subjects (P < 0.0001), suggesting that the concentration of high energy metabolites in diabetic patients was reduced. The ratio of ATP/phosphocreatine (PCr) in patients with diabetes was also significantly lower than in controls (P < 0.01). Chewing a single piece of nicotine gum reduced the measured concentrations of ATP and PCr in control subjects by an average of 18% and by an average of 75% in subjects with diabetes. To verify these results in a second experiment, skin was harvested from the surgical wound sites in eight patients with diabetes undergoing elective amputation, eight patients with diabetes undergoing elective foot surgery, and ten age-matched control (nondiabetic) patients undergoing elective foot surgery. Analysis of ATP and PCr using high pressure liquid chromatography corroborated MRS findings, showing a significant reduction in ATP and PCr in diabetic skin. Depression of metabolites was more severe in the patients with diabetes undergoing amputation than in the ones undergoing elective surgery. Results demonstrate depression of metabolites in the skin of patients with diabetes and suggest that MRS with 31p may be useful in characterizing metabolites in the skin.

Subtle brain abnormalities in children with sickle cell disease: relationship to blood hematocrit

Our objective was to test a hypothesis that subtle brain abnormality can be present in pediatric sickle cell disease (SCD) patients who are clinically free of stroke. We prospectively compared 50 patients with 52 healthy age-similar controls, using quantitative magnetic resonance imaging. A previously validated precise and accurate inversion-recovery method was used to measure T1 in a slice at the basal ganglia. We also used the Wechsler test to measure intelligence quotient (IQ) in a randomly selected subset of 27 patients. Brain T1 was significantly lower in patients in every gray matter structure evaluated but in none of the white matter structures. Regression suggests that T1 in caudate, nucleus pulvinares, and cerebral cortex was abnormal by age 4 years. Psychometric testing showed that 33% of patients were functioning in the range of mild mental deficiency (IQ, 50-70), compared with a published prevalence of 1.45% in inner-city black children. Thus, in our patients, SCD was associated with a 23-fold increase in the risk of mild mental deficiency. Full-scale IQ of SCD patients was a function of hematocrit (Hct), and when Hct was used to stratify patients, those with an Hct of less than 27% had significantly lower psychometric test scores, and significantly lower gray matter T1, than those with an Hct of 27 or more. Both cognitive deficits and subtle T1 abnormalities were associated with a low Hct, and both could be present when conventional magnetic resonance imaging findings were normal. Our findings suggest that chronic hypoxia of brain tissue can occur in SCD patients free of clinical stroke.

Effect of a gadodiamide contrast agent on the reliability of brain tissue T1 measurements

To determine whether brain spin-lattice relaxation time (T1) can routinely be measured after contrast-agent injection, we measured T1 by a precise and accurate inversion-recovery (PAIR) method in five brain tumor patients, before and again after contrast-agent injection. The T1 in at least 20 regions of interest (ROIs) was measured in each patient, avoiding areas of contrast enhancement visible by conventional MR imaging. Contrast-agent injection reduced T1 in 51 regions of interest in white matter by less than 1% (not significant), and in 50 regions of interest in gray matter by less than 2% (p = 0.001). Pixel-by-pixel plots demonstrate that T1 is reduced substantially in extra-parenchymal tissues, but not in brain tissues. Therefore, T1 mapping with the precise and accurate inversion-recovery method can routinely be done after contrast injection. Our results suggest that the precise and accurate inversion-recovery method is not sensitive to the T1 of blood in the presence of an intact blood-brain barrier, although a substantial T1 reduction does occur in the absence of a blood-brain barrier.

Tpm1, a locus controlling IL-12 responsiveness, acts by a cell-autonomous mechanism

Th phenotype development is controlled not only by cytokines but also by other parameters including genetic background. One site of genetic variation between murine strains that has direct impact on Th development is the expression of the IL-12 receptor. T cells from B10.D2 and BALB/c mice show distinct control of IL-12 receptor expression. When activated by Ag, B10.D2 T cells express functional IL-12 receptors and maintain IL-12 responsiveness. In contrast, under the same conditions, BALB/c T cells fail to express IL-12 receptors and become unresponsive to IL-12, precluding any Th1-inducing effects if subsequently exposed to IL-12. Previously, we identified a locus, which we termed T cell phenotype modifier 1 (Tpm1), on murine chromosome 11 that controls this differential maintenance of IL-12 responsiveness. In this study, we have produced a higher resolution map around Tpm1. We produced and analyzed a series of recombinants from a first-generation backcross that significantly narrows the genetic boundaries of Tpm1. This allowed us to exclude from consideration certain previous candidates for Tpm1, including IFN-regulatory factor-1. Also, cellular analysis of F1(B10.D2 x BALB/c) T cells demonstrates that Tpm1 exerts its effect on IL-12 receptor expression in a cell-autonomous manner, rather than through influencing the extracellular milieu. This result strongly implies that despite the proximity of our locus to the IL-13/IL-4 gene cluster, these cytokines are not candidates for Tpm1.

Correction of errors caused by imperfect inversion pulses in MR imaging measurement of T1 relaxation times

Spin-lattice (T1) relaxation times were measured by an inversion-recovery magnetic resonance imaging method with a slice-selective inversion pulse (SIP), a non-selective rectangular inversion pulse (RIP), or a B1-insensitive adiabatic inversion pulse (AIP). Data analysis either assumed perfect inversion (two-parameter fit) or allowed for imperfect inversion (three-parameter fit). Imperfect inversion pulses caused low T1 values in phantoms with a two-parameter fit, while three-parameter T1 estimates were accurate over the range 430-2670 ms. A difference of approximately 10% between two-parameter and three-parameter T1 values in normal human brain tissue was attributed to B1 inhomogeneity with the slice-selective inversion pulse and rectangular inversion pulse, to the slice profile with the slice-selective inversion pulse, and to T2 effects for the adiabatic inversion pulse. Any T1 method that relies on accurate flip angles may have a significant systematic error in vivo. Phantom accuracy does not ensure accuracy in vivo, because phantoms may have a more homogeneous B1 field and a longer T2 than do biological samples.

Age-related changes in brain T1 are correlated with iron concentration

Age-related changes in brain T1 from 115 healthy subjects (range, 4.5-71.9 yr) were analyzed in relation to published regional brain iron concentration in cortex, caudate, putamen, and frontal white matter. The relaxation rate in these structures was linear with respect to iron concentration (P < 0.001). The iron relaxivity, k1 (s(-1)/mg iron/g wet weight), was much higher in cortex (5.5) and white matter (6.1) than in caudate (1.7) and putamen (1.0). These results are consistent with evidence that iron is an important factor in determining the relaxation properties of brain tissue. Iron relaxivity may reflect regional differences in the physical state of brain iron or in the interaction of brain iron with tissue water.

Evidence of cranial artery ectasia in sickle cell disease patients with ectasia of the basilar artery

GOAL

To determine if children with sickle cell disease (SCD) and basilar artery ectasia show evidence of general arterial ectasia.

METHODS

A novel method was used to analyze the base images normally used to reconstruct a magnetic resonance angiogram (MRA). A signal intensity threshold was set empirically to exclude pixels from subcutaneous fat, then base images for each patient were evaluated for the number and relative size of vessel profiles. Data from three SCD patients, imaged before and after transfusion, were analyzed to determine sensitivity of the method to blood flow. We then compared 11 SCD patients with basilar ectasia to 11 age-matched SCD patients with a normal basilar, after excluding patients with clinical stroke.

FINDINGS

Before transfusion, patients have an apparent blood volume 48% higher than after (P<.001). Transfusion reduces apparent blood volume because flow rate is reduced by transfusion and MRA is flow-sensitive. But apparent blood volume was not significantly lower in any individual vessel size class, suggesting that fast flow simply increases vessel conspicuity. Patients with basilar ectasia have an apparent blood volume 62% higher than normal (P<.001). Although this could be due to faster blood flow, apparent blood volume was higher specifically in vessels > or =2 mm in diameter (P<.001), suggesting that small arteries can become generally ectatic in patients with basilar ectasia.

CONCLUSIONS

Basilar ectasia is associated with an increased blood flow rate, generalized arterial ectasia, or both phenomena. This suggests that basilar volume measurements may supplement blood flow velocity measurements as an indicator of stroke risk.

Abnormalities of the central nervous system in very young children with sickle cell anemia

OBJECTIVE

To determine whether abnormalities of the CNS are present in very young children with sickle cell anemia.

STUDY DESIGN

Thirty-nine children with hemoglobin SS between the ages of 7 and 48 months were examined with magnetic resonance imaging (MRI) and magnetic resonance angiography (MRA). No child had a history of clinical stroke, although 3 had a history of seizures (2 neonatal). Twenty-one patients underwent developmental testing with the Bayley or McCarthy Scales.

RESULTS

The overall prevalence of CNS abnormalities in asymptomatic children was 4 of 36 (11%, confidence interval 3, 26%). One patient had a silent infarct observed on MRI and a stenotic lesion on MRA; 3 other patients had stenotic lesions on MRA. The 3 patients who had a history of seizures all had lesions consistent with infarcts on MRI. Of the asymptomatic patients who had psychometric testing, 1 of 18 was developmentally delayed. One of 3 with a history of seizures had mild developmental delay.

CONCLUSIONS

Very young children with sickle cell anemia (and no history of clinical stroke) have infarction in the brain and/or stenosis of major cerebral arteries, similar to those reported in older children. These findings indicate a need for larger studies to define the incidence of CNS lesions in this age group and to determine the need for early therapeutic intervention to prevent CNS sequelae of sickle cell disease.

Quantitative MRI of the brain in children with sickle cell disease reveals abnormalities unseen by conventional MRI

Conventional MRI (cMRI) has shown that brain abnormalities without clinical stroke can manifest in patients with sickle cell disease (SCD). We used quantitative MRI (qMRI) and psychometric testing to determine whether brain abnormalities can also be present in patients with SCD who appear normal on cMRI. Patients 4 years of age and older with no clinical evidence of stroke were stratified by cMRI as normal (n = 17) or abnormal (n = 13). Spin-lattice relaxation time (T1) of gray and white matter structures was measured by the precise and accurate inversion recovery (PAIR) qMRI method. Patient cognitive ability was assessed with a standard psychometric instrument (WISC-III or WISC-R). In all 30 patients with SCD, qMRI T1 was lower than in 24 age- and race-matched controls, in cortical gray matter (P < .0006) and caudate (P < .0009), as well as in the ratio of gray-to-white matter T1 (P < .008). In the 17 patients who were shown to be normal by cMRI, qMRI T1 was still lower than in controls, in both cortical gray matter (P < .02) and caudate (P < .004). Histograms of voxel T1 show that the proportion of voxels with T1 values intermediate between gray and white matter (ie, consistent with encephalomalacia) was 9% higher than controls in patients shown to be normal by cMRI (P < .05) and 15% higher than controls in patients shown to be abnormal by cMRI (P < .0005). The full scale intelligence quotient (FSIQ) of all patients with SCD was 75, compared to the FSIQ of 88 in a historical control group of patient siblings (P < .001). The FSIQ of patients shown to be normal by cMRI was 79, significantly lower than the FSIQ of patient siblings (P < .04). The FSIQ of 71 in patients shown to be abnormal by cMRI was significantly lower than both the patient siblings (P < .005) and the patients shown to be normal by cMRI (P < .04). Patients shown to be abnormal by cMRI scored lower than patients shown to be normal by cMRI, specifically on the subtests of vocabulary (P = .003) and information (P = .03). Cognitive impairment is thus significant, even in patients with SCD who were shown to be normal by cMRI, suggesting that cMRI may be insensitive to subtle neurologic damage that can be detected by qMRI. Because cognitive impairment can occur in children normal by cMRI, our findings imply that prophylactic therapy may be needed earlier in the course of SCD to mitigate neurologic damage.

Establishing norms for age-related changes in proton T1 of human brain tissue in vivo

The goal of this study was to determine the expected normal range of variation in spin-lattice relaxation time (T1) of brain tissue in vivo, as a function of age. A previously validated precise and accurate inversion recovery method was used to map T1 transversely, at the level of the basal ganglia, in a study population of 115 healthy subjects (ages 4 to 72; 57 male and 58 female). Least-squares regression analysis shows that T1 varied as a function of age in pulvinar nucleus (R2 = 56%), anterior thalamus (R2 = 51%), caudate (R2 = 50%), frontal white matter (R2 = 47%), optic radiation (R2 = 39%), putamen (R2 = 36%), genu (R2 = 22%), occipital white matter (R2 = 20%) (all p < 0.0001), and cortical gray matter (R2 = 53%) (p < 0.001). There were no significant differences in T1 between men and women. T1 declines throughout adolescence and early adulthood, to achieve a minimum value in the fourth to sixth decade of life, then T1 begins to increase. Quantitative magnetic resonance imaging provides evidence that brain tissue continues to change throughout the lifespan among healthy subjects with no neurologic deficits. Age-related changes follow a strikingly different schedule in different brain tissues; white matter tracts tend to reach a minimum T1 value, and to increase again, sooner than do gray matter tracts. Such normative data may prove useful for the early detection of brain pathology in patients.

Ectasia of the basilar artery in children with sickle cell disease: Relationship to hematocrit and psychometric measures

GOAL

To determine whether children with sickle cell disease (SCD), but without clinical evidence of cerebrovascular disease, have vasculopathy shown by quantitative magnetic resonance angiography (MRA).

METHODS

In a retrospective review of MRA films, we compared 47 SCD patients with 49 control patients. Time-of-flight three-dimensional T1-weighted gradient-echo images were reconstructed, by maximum-intensity projection, to show the basilar artery in coronal view, and basilar volume was calculated from measurements made on films. Basilar volume was correlated with hematocrit and with results of cognitive testing.

FINDINGS

Mean basilar artery volume was 74% larger in SCD patients than in controls (P<.001). If the upper limit of normal is defined as mean adult volume +2 SD (< or =427 mm(3)), 2% (1 of 43) of controls but 37% (17 of 46) of SCD patients exceed this value (chi(2)=19.0; P<.001). Basilar volume correlated inversely with hematocrit (r=-.60; P<.0001), with full-scale IQ (r=-.62; P<.005), and with freedom from distractability (r=-.61; P<.006) in SCD patients. Analysis of basilar artery tissue from a 5-year-old SCD patient showed that basilar dilatation can be associated with pathological changes typical of hypertension.

CONCLUSIONS

Approximately 37% of a heterogenous group of pediatric SCD patients had ectasia of the basilar artery. Quantitative MRA is sensitive to subtle vasculopathy that can go undetected in the qualitative analysis more commonly done. Data suggest that there is a substantial elevation of arteriolar blood volume in pediatric SCD patients, and that such patients may share disease features in common with adult hypertension.

Effects of p53 mutations on apoptosis in mouse intestinal and human colonic adenomas

We have examined the effects of inactivation of the p53 tumor suppressor gene on the incidence of apoptotic cell death in two stages of the adenoma-to-carcinoma progression in the intestine: in early adenomas where p53 mutations are rare and in highly dysplastic adenomas where loss of p53 occurs frequently. Homozygosity for an inactivating germ-line mutation of p53 had no effect on the incidence or the rate of progression of ApcMin/+-induced adenomas in mice and also did not affect the frequency of apoptosis in the cells of these adenomas. To examine the effect of p53 loss on apoptosis in late-stage adenomas, we compared the incidence of apoptotic cell death before and after the appearance of highly dysplastic cells in human colonic adenomas. The appearance of highly dysplastic cells, which usually coincides during colon tumor progression with loss of heterozygosity at the p53 locus, did not correlate with a reduction in the incidence of apoptosis. These studies suggest that p53 is only one of the genes that determine the incidence of apoptotic in colon carcinomas and that wild-type p53 retards the progression of many benign colonic adenoma to malignant carcinomas by mechanism(s) other than the promotion of apoptosis.

Fat-saturated contrast-enhanced T1-weighted MRI in evaluation of osteosarcoma and Ewing sarcoma

To assess contrast-enhanced (C+), fat-saturated (FatSat), T1-weighted (T1W) imaging in the characterization of the soft tissue mass associated with primary bone tumors, we compared it with T2-weighted (T2W) imaging in patients with osteosarcoma (n = 36) and Ewing sarcoma family of tumors (Ewing sarcoma; n = 11). Periosseous tumor compared with normal muscle had greater contrast-to-noise ratio (CNR) on the FatSat T1W C+ image than on T2W for 81% (38/47; P < .0001) of patients. The CNR of periosseous tumor compared with subcutaneous fat was greater on FatSat T1W C+ for 98% (46/47; P < .0001). Radiologists found it easier to evaluate neurovascular bundle proximity to tumor with FatSat T1W C+ images than with T2W for 64% of patients (30/47; P < .0001). They judged FatSat T1W C+ superior to T2W for periosseous tumor conspicuity and visualization of soft tissue necrosis in 62% (29/47; P < .0001). In patients with osteosarcoma or Ewing sarcoma, FatSat T1W C+ imaging may replace T2W imaging for soft tissue mass evaluation, especially if contrast is being used for dynamic enhancement.

Age-related changes in the pediatric brain: quantitative MR evidence of maturational changes during adolescence

PURPOSE

To determine whether a quantitative MR imaging method to map spin-lattice relaxation time (T1) can be used to characterize maturational changes in the normal human brain.

METHODS

An inversion-recovery technique was used to map T1 transversely at the level of the basal ganglia in a study population of 19 healthy children (4 to 10 years old) and 31 healthy adolescents (10 to 20 years old), and in a normative population of 20 healthy adults (20 to 30 years old).

RESULTS

Nonparametric analysis of variance showed that T1 decreases with age in the genu, frontal white matter, caudate, putamen, anterior thalamus, pulvinar nucleus, optic radiation, cortical gray matter (all P < .0001), and occipital white matter. There was a significant reduction in T1 between childhood (mean age, 7.1 +/- 1.4) and adolescence (mean age, 13.5 +/- 2.6) in all brain structures, but there was also a significant reduction in T1 between adolescence (mean age, 13.5 +/- 2.6) and adulthood (mean age, 26.5 +/- 3.4) in all brain structures except occipital white matter. Regression shows that T1 declines to within the range (mean +/- 2 SD) of young adult T1 values by about 2 years in the occipital white matter, by about 4 years in the genu, by 11 years in the cortical gray matter, by 11 years in the frontal white matter, and by 13 years in the thalamus.

CONCLUSION

Brain structures mature at strikingly different rates, yet the ratio of gray matter T1 to white matter T1 does not change significantly with age. Thus, conventional MR imaging methods based on inherent contrast are insensitive to these changes. Age-related changes tend to reach completion sooner in white matter than in gray matter tracts. Such normative data are essential for studies of specific pediatric disorders and may be useful for assessing brain maturation in cases of developmental delay.

Phenotype of mice lacking functional Deleted in colorectal cancer (Dcc) gene

The DCC (Deleted in colorectal cancer) gene was first identified as a candidate for a tumour-suppressor gene on human chromosome 18q. More recently, in vitro studies in rodents have provided evidence that DCC might function as a receptor for the axonal chemoattractant netrin-1. Inactivation of the murine Dcc gene caused defects in axonal projections that are similar to those observed in netrin-1-deficient mice but did not affect growth, differentiation, morphogenesis or tumorigenesis in mouse intestine. These observations fail to support a tumour-suppressor function for Dcc, but are consistent with the hypothesis that DCC is a component of a receptor for netrin-1.

Genetic mapping of a murine locus controlling development of T helper 1/T helper 2 type responses

Genetic background of the T cell can influence T helper (Th) phenotype development, with some murine strains (e.g., B10.D2) favoring Th1 development and others (e.g., BALB/c) favoring Th2 development. Recently we found that B10.D2 exhibit an intrinsically greater capacity to maintain interleukin 12 (IL-12) responsiveness under neutral conditions in vitro compared with BALB/c T cells, allowing for prolonged capacity to undergo IL-12-induced Th1 development. To begin identification of the loci controlling this genetic effect, we used a T-cell antigen receptor-transgenic system for in vitro analysis of intercrosses between BALB/c and B10.D2 mice and have identified a locus on murine chromosome 11 that controls the maintenance of IL-12 responsiveness, and therefore the subsequent Th1/Th2 response. This chromosomal region is syntenic with a locus on human chromosome 5q31.1 shown to be associated with elevated serum IgE levels, suggesting that genetic control of Th1/Th2 differentiation in mouse, and of atopy development in humans, may be expressed through similar mechanisms.

Genetic susceptibility to Leishmania: IL-12 responsiveness in TH1 cell development

The genetic background of T lymphocytes influences development of the T helper (TH) phenotype, resulting in either resistance or susceptibility of certain mouse strains to pathogens such as Leishmania major. With an in vitro model system, a difference in maintenance of responsiveness of T cells to interleukin-12 (IL-12) was detected between BALB/c and B10.D2 mice. Although naive T cells from both strains initially responded to IL-12, BALB/c T cells lost IL-12 responsiveness after stimulation with antigen in vitro, even when cocultured with B10.D2 T cells. Thus, susceptibility of BALB/c mice to infection with L. major may derive from the loss of the ability to generate IL-12-induced TH1 responses rather than from an IL-4-induced TH2 response.

Quantitative MR imaging of children with sickle cell disease: striking T1 elevation in the thalamus

Nineteen patients with sickle cell disease (SCD) were examined with conventional MR imaging (cMRI), including T1- and T2-weighted sequences and MR angiography (MRA). qMRI mapping of T1 was also done using a precise and accurate inversion-recovery (PAIR) technique optimized and validated previously. In addition, 21 healthy African-American control subjects had the qMRI examination. Nonparametric Kruskal-Wallis analysis of variance of control subjects, of SCD patients without stroke, and of SCD patients with stroke showed that T1 increased with disease severity in the thalamus, frontal white matter, genu, and occipital white matter. T1 was significantly longer in SCD patients without stroke (n = 13) than in control subjects (n = 21) in the thalamus and frontal white matter. In addition, T1 values were significantly longer in SCD patients with stroke than in patients without stroke in the genu and frontal white matter. Abnormality of the thalamus was identified by qMRI in a substantial fraction of patients read as normal by both cMRI and MRA, suggesting that it may be possible to use T1 elevation to identify a subset of patients with SCD who are at elevated risk for stroke.

Statistical error mapping for reliable quantitative T1 imaging

We developed a statistically based error image for rapid appreciation of unreliable regions in quantitative water proton T1 images. The chi-squared error and co-efficient of variation of the fitted parameter were used to estimate uncertainties in the goodness-of-fit to mono-exponential T1 relaxation and the reliability of the calculated T1, respectively, for each pixel. Errors exceeding a statistical threshold based on a .1 acceptance criterion were displayed as a color-coded overlay on the T1 image. Error maps of quantitative T1 images from 31 healthy volunteers showed a characteristic error structure; few pixels within the parenchyma had excessive errors. Clinical cases with stroke and sickle cell disease showed deviations from the normal pattern in the spatial distribution and magnitude of chi-squared errors. Disease states may deviate from mono-exponential T1 relaxation more than normal brain does. The color-coded error map is a valuable tool for investigators using quantitative MR imaging to determine tissue relaxation parameters.

Growth rate, labeling index, and radiation survival of cells grown in the Matrigel thread in vitro tumor model

Six rodent cell lines (36B10 rat glioma cells, 9L rat gliosarcoma cells, V79 Chinese hamster lung fibroblasts, EMT6/UW and EMT6/Ro mouse mammary sarcoma cells, and RIF-1 mouse fibrosarcoma cells) were tested for growth in cylindrical threads of Matrigel. These cells grew in the threads with doubling times of 17-23 h, reaching maximum cell densities on the order of 10(8) cells/ml. Histological sections of these threads showed a heterogeneous cell distribution: cells grew to confluence at the thread surface and at somewhat lower cell densities in the thread core. [H-3]thymidine labeling index and radiation sensitivity were measured for 9L and EMT6/UW cells in Matrigel threads. For both cell types, the labeling index in Matrigel was lower than observed in cell monolayers, with higher labeling indexes at the thread periphery than in the thread core. When these threads were grown in stirred medium, lower thread diameters, higher cell yields per thread, and higher labeling indices were obtained. EMT6 cell monolayers coated with Matrigel were less radiosensitive than cells in uncoated monolayers. This protective effect was eliminated by irradiating in the presence of 1 mg/ml misonidazole. EMT6 cells consume nearly three times as much oxygen (mole/cm3-sec) as do 9L cells, which are equally radiosensitive in monolayers with or without a Matrigel coating. The radiation sensitivity of EMT6/UW cells in Matrigel threads was similar to that for monolayers of plateau phase cells, whereas for 9L cells, the response in threads was more similar to exponentially growing cells. We conclude that Matrigel threads provide an alternative in vitro model for studying the radiation response of cells in a three-dimensional geometry.

Age-related changes in proton T1 values of normal human brain

To determine whether there were age-related changes in the brain tissue of 55 healthy adult volunteers (29 men, 26 women; 18-72 years old) without known brain abnormalities, a standard inversion-recovery technique was optimized for precise and accurate T1 measurement within the constraints of a 15-minute examination. Measurements of water proton T1 were obtained in eight brain regions. T1 increased with age in the genu (P < .001) (analysis of variance), frontal white matter (P < .05), occipital white matter (P < .05), putamen (P < .001), and thalamus (P << .001). A significant decrease in T1 with age was found in cortical gray matter (P < .05). Thus, age-related changes in T1 are present in a healthy population, even if extremes of age are excluded, suggesting that T1 values generally increase with age. However, increases in T1 were also observed in the genu, putamen, and thalamus of a substantial fraction of volunteers less than 35 years old. Aging healthy persons can show subtle, nonsymptomatic brain changes, suggesting that brain aging is associated with occult processes that can begin at a relatively early age.

Precise and accurate measurement of proton T1 in human brain in vivo: validation and preliminary clinical application

Precise and accurate inversion-recovery (PAIR) magnetic resonance (MR) measurements of T1 were obtained in eight brain regions and cerebrospinal fluid of 26 healthy volunteers. Accuracy of the technique was assessed by measuring T1 in small fluid volumes with the PAIR technique and with two independent spectroscopic techniques. The mean difference between T1 measured with PAIR and with the two spectroscopic techniques was 3.1% +/- 1.3. The precision (reproducibility) of measurements with the PAIR technique was excellent. The coefficient of variation (CV) across 16 measurements in a head phantom was 2.0%, compared with a CV of 2.7% across 45 separate measurements in a single subject. The within-subject CV was 1.8% +/- 0.6 in white matter and 1.4% +/- 1.0 in basal ganglia. The between-subject CV in 26 healthy volunteers was 3.6% +/- 0.6 in white matter and 4.1% +/- 1.9 in basal ganglia. Comparison between a patient with an active recurrent brain tumor and an age-matched patient with an inactive brain tumor showed that T1 was significantly elevated throughout the brain of the active-tumor patient, especially in white matter tracts, even though no tumor or edema was detected in the white matter on standard MR images. Comparisons between five brain tumor patients and four healthy volunteers of similar age showed that T1 was significantly and substantially elevated throughout the white matter tracts and in the caudate nucleus, putamen, and thalamus. These results are consistent with the hypothesis that white matter tracts are selectively vulnerable to edema and that T1 increases in white matter are a sensitive indicator of patient status or tumor aggressiveness.

A genetic map of the mouse with 4,006 simple sequence length polymorphisms

We have constructed a genetic map of the mouse genome containing 4,006 simple sequence length polymorphisms (SSLPs). The map provides an average spacing of 0.35 centiMorgans (cM) between markers, corresponding to about 750 kb. Approximately 90% of the genome lies within 1.1 cM of a marker and 99% lies within 2.2 cM. The markers have an average polymorphism rate of 50% in crosses between laboratory strains. The markers are distributed in a relatively uniform fashion across the genome, although some deviations from randomness can be detected. In particular, there is a significant underrepresentation of markers on the X chromosome. This map represents the two-thirds point toward our goal of developing a mouse genetic map containing 6,000 SSLPs.

Discrete signal processing of dynamic contrast-enhanced MR imaging: statistical validation and preliminary clinical application

A high-resolution image-based method was developed to analyze dynamic contrast agent-enhanced magnetic resonance images quantitatively. This method determines the initial rate of contrast agent accumulation, the delayed rate of accumulation, and the maximum enhancement in each pixel. These three parameters allow characterization of the dynamic signal features. Simulated noisy test sets of dynamic enhancement curves have shown this method to yield a fast and accurate characterization of the dynamic signal. Clinical examples of both qualitative image parameter maps and quantitative statistical analysis of the parameter distributions demonstrated the quality and potential of the technique. The technique is designed to yield imaging and quantitative information on contrast agent accumulation that can be useful in detecting residual tumor and evaluating response to therapy, while requiring less than 7 minutes of imaging time and 5 minutes of processing time per study.

In vivo measurement of tumor blood oxygenation by near-infrared spectroscopy: immediate effects of pentobarbital overdose or carmustine treatment

Near-infrared (NIR) spectroscopy was used to measure blood oxygen saturation (SO2) in vivo, in normal rat brain and in subcutaneously-implanted rat 9L gliosarcoma. Changes in cranial and tumor blood SO2 were measured during lethal pentobarbital overdose. After sacrifice, SO2 of cranial blood fell rapidly to a mean of 5.0% of the pre-sacrifice values, whereas SO2 of tumor blood stabilized at a mean of 72.4% of the pre-sacrifice values. This suggests that oxygen consumption by tumor is very low compared to brain. Cranial blood had a higher SO2 than tumor blood before sacrifice (p = 0.03), and a lower SO2 after sacrifice (p = 0.02). The magnitude of the change in SO2 after sacrifice was greater in normal brain than in tumor (p = 0.02), showing that brain tissue uses a greater proportion of the oxygen in ischemic blood than does tumor tissue. To determine the effect of carmustine (BCNU) treatment on tumor and cranial blood SO2, we compared BCNU-treated rats with sham-treated rats. Continuous NIR measurements before and immediately following treatment (ie. over 30-60 min) showed that tumor blood SO2 tended to increase after BCNU treatment, whereas SO2 tended to decrease following sham-treatment. The difference in SO2 between treated and control tumors was significant at 60 min (p = 0.02). Thus BCNU treatment can potentially result in immediate increases in tumor oxygenation. The increase in treated tumor blood SO2 occurred despite the fact that there was no change in cranial blood SO2 even at day 4 following treatment. Tumor blood SO2 was inversely correlated with tumor size (p = 0.001), confirming that blood is more poorly oxygenated in large tumors.

A genetic linkage map of the mouse: current applications and future prospects

Technological advances have made possible the development of high-resolution genetic linkage maps for the mouse. These maps in turn offer exciting prospects for understanding mammalian genome evolution through comparative mapping, for developing mouse models of human disease, and for identifying the function of all genes in the organism.

Relationship of perfusion to edema in the 9L gliosarcoma

The relationship between tumor perfusion and edema was analyzed, with edema characterized as tumor wet/dry weight ratio. Perfusion of subcutaneous 9L gliosarcoma was measured by injection of 133Xe in saline into the tumor core, followed by gamma camera imaging of 133Xe washout kinetics. A significant inverse correlation was found between edema and tumor perfusion (p < 0.0002), suggesting that edema can limit tumor perfusion, perhaps through a mechanism of increased interstitial fluid pressure. The perfusion rate of highly edematous tumors was reduced to less than 10% of the perfusion rate of less edematous tumors (p < 0.001). It was also found that tumor edema increased significantly with increasing tumor volume (p < 0.001), which could account for the finding that perfusion declined significantly with increasing tumor volume (p < 0.02). These findings are potentially important because it is possible to quantify tumor edema in vivo, with millimeter resolution, using 1H magnetic resonance imaging (MRI). Thus MRI may provide a non-invasive technique for characterizing tumor perfusion or tumor drug delivery.

Applications of magnetic resonance spectroscopy to the investigation of neuropsychiatric disorders

Magnetic resonance spectroscopy (MRS) can noninvasively characterize tissue composition and metabolism in vivo without the need for radioactive isotope administration. For the neuropsychiatrist interested in the functional basis of disease, MRS offers an investigative tool capable of studying a wide variety of neuropsychiatric disorders. This report provides an overview of how MRS works, current and potential clinical applications for specific psychiatric populations, and limitations of the technology.

Edema and tumor perfusion: characterization by quantitative 1H MR imaging

Tumor perfusion is of central importance to the clinical oncologist because it has a direct effect on the success of cancer therapy. Yet determining whether a tumor is well or poorly perfused is difficult without the use of invasive techniques, because the variables that affect tumor perfusion are poorly understood. Quantitative MR imaging of tumor edema may provide a means of characterizing tumor perfusion, of studying heterogeneity of perfusion within the tumor mass, or of monitoring changes in tumor perfusion after therapy. A combination of factors often results in production of a large amount of edema within cranial or extracranial tumors. Any tumor that is encapsulated, whether by a fibrous tumor capsule or by a structure such as the cranium, will have an elevation in interstitial fluid pressure because dissipation of fluid is hindered. Elevated pressure of interstitial fluid acts to occlude tumor capillaries, so edema can cause a striking reduction of tumor perfusion. Because MR imaging can potentially be used for quantitative imaging of tumor edema, it may provide a means of indirectly measuring tumor perfusion. A review of the literature suggests that diffusion-weighted MR imaging may be better than T1- or T2-weighted MR imaging for quantitative imaging of tumor edema. I do not propose that diffusion-weighted imaging can measure perfusion directly; rather I hypothesize that a diffusion-weighted image can be correlated with tumor edema. Because edema indirectly regulates perfusion through the mechanism of interstitial fluid pressure, I propose an indirect correlation between the diffusion-weighted image and regional tissue perfusion. If the relationship between tumor perfusion and the pharmacokinetics of chemotherapeutic agents is better understood, MR imaging of tumor edema may even aid in predicting the delivery of drugs to a tumor.

In vivo phosphorus NMR spectroscopy of skin using a crossover surface coil

A modified crossover surface coil with minimal B1 field penetration was used for collection of skin phosphorus NMR spectra. Projection imaging experiments show that the coil-sensitive volume is uniform at the phosphorus frequency, but strikingly nonuniform at the proton frequency. Experiments with an in vitro phosphorus phantom, designed to simulate skin and underlying tissue, demonstrated that 45.1% (+/- 1.2%) of total signal was derived from Sprague-Dawley rat skin and 19.3% (+/- 1.4%) of total signal was derived from Fischer-344 rat skin. 31P MR spectra of rat skin in vivo permitted resolution of four phosphorus compounds: nucleoside triphosphates, phosphocreatine (PCr), inorganic phosphate (Pi), and phosphomonoester. Spectra collected after skin flap surgery in Fischer-344 rats showed a 50.1% (+/- 7.6%) reduction in the ratio of PCr/Pi within 30 min of surgery, compared to presurgical PCr/Pi levels (P less than 0.01). Skin phosphorus spectra are potentially useful for assessment of skin flap and skin graft viability.

Characterization of tumor hypoxia by 31P MR spectroscopy

Tumor hypoxia is of considerable importance to the oncologist in selecting and optimizing cancer therapy, because hypoxia can determine the effectiveness of various therapies. The relationship between tumor hypoxia and tumor bioenergetics, assessed by 31P MR spectroscopy, is examined to determine whether 31P MR spectroscopy can be clinically useful to measure or characterize tumor hypoxia. Work with experimental tumors has suggested that several different types of hypoxia may exist and that 31P MR spectroscopy cannot be used to characterize all types. Metabolic hypoxia is the level of hypoxia that results in mitochondrial impairment in cells, and it is associated with declining cellular bioenergetic status, which can be measured by enzymatic assay of adenosine triphosphate (ATP). Because 31P MR spectroscopy is sensitive to levels of ATP, it is potentially sensitive to metabolic hypoxia in vivo and may provide a rapid and noninvasive technique for characterizing metabolic hypoxia in tumors. Radiobiologic hypoxia is the level of hypoxia that results in attenuated cell death due to radiation, because radiotoxicity is directly related to tissue levels of oxygen. Radiobiologic hypoxia of tumors thus has more impact on choice of therapy, yet the relationship between metabolic hypoxia and radiobiologic hypoxia remains to be elucidated. An analysis of published data suggests that 31P MR spectroscopy is directly sensitive to metabolic hypoxia in tumors, but it is only indirectly sensitive to radiobiologic hypoxia in tumors. Therefore, 31P MR spectroscopy may be unable to quantify the cell fraction of a tumor that has radiobiologic hypoxia. However, preliminary data suggest that MR spectroscopy may prove useful for determining the effectiveness of therapeutic interventions designed to manipulate radiobiologic hypoxia in tumors or for monitoring the kinetics of tumor reoxygenation after treatment.