Abstract LB-313: ALK1-Fc inhibits tumor growth in a VEGF pathway resistance model of renal cell carcinoma

Treatment of metastatic RCC with agents that block signaling through VEGFR2 induces disease stabilization or regression in a substantial fraction of patients (pts); however, these responses tend to be short-lived. Mice bearing 786-O and A498 human RCC xenografts treated with sunitinib or sorafenib also exhibit a period of tumor stabilization followed by the resumption of growth and restoration of angiogenesis despite continued drug administration. Thus, alternate angiogenic pathways are of interest in the treatment of RCC. Activin receptor-like kinase 1 (ALK1) is one of 7 type I TGFβ receptors which is predominantly expressed on activated vascular endothelial cells. ALK1-Fc is a soluble receptor fusion protein containing the extracellular domain of ALK1 linked to a human Ig Fc region. ALK1-Fc binds to and neutralizes the activity of bone morphogenetic protein 9 and 10 (BMP9, 10) and has demonstrated antiangiogenic activity in vivo. Currently, ALK1-Fc (ACE-041) is undergoing clinical development. We have found evidence of TGFβ pathway upregulation in tumors that have developed resistance to sunitinib. Thus, to explore the role of ALK signaling in the treatment of RCC we administered ALK1-Fc to mice bearing RCC xenografts. In the treatment naïve A498 model, administration of ALK1-Fc alone delayed tumor growth relative to vehicle: days to grow by 2 mm vehicle- 5.8 +/−0.96 days (n=5) vs ALK1-Fc- 10.8 +/− 1.7 days (n=4, p<0.01). Single agent ALK1-Fc did not show activity in the 786-O model; however combination ALK1-Fc + sunitinib slowed tumor growth to a greater extent than either agent alone or vehicle tumors in both the A498 and the 786-O tumor models. A498 tumors treated with sunitinib took 13.8+/−2.5 days (n=4) to increase by 2 mm vs the ALK1-Fc + sunitinib combination (35 +/− 12.6 days (n=4) (p=0.01)). 786-O derived tumors, treated with sunitinib took 24.7+/−8.3 days (n=3), while tumors treated with combination of ALK1-Fc + sunitinib took 43.7+/−4.2 days (n=3, p<0.03) to grow by 2 mm. Perfusion imaging of these tumors revealed that sunitinib + ALK-Fc lowers perfusion more than sunitinib treated tumors. Our data indicate that ALK1-Fc treatment can act as a single agent to delay tumor growth in at least 1 RCC xenograft model. In addition, combination therapy with ALK1-Fc and sunitinib further delays tumor growth vs either agent administered alone. The effect of the combination therapy on vessel formation and tumor perfusion are currently being investigated. The differential response to ALK1-Fc treatment in the A498 compared to the 786-O cell lines provides an opportunity to explore the molecular and pathological differences between the two models, which may allow for better insight into mechanisms of action and future pt selection. The data demonstrate that blocking ligand signaling through the endogenous ALK1 receptor, either alone or in combination with other antiangiogenic therapies, is a valid strategy for treatment of RCC.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr LB-313. doi:1538-7445.AM2012-LB-313

Acute effects of single-dose aripiprazole and haloperidol on resting cerebral blood flow (rCBF) in the human brain

Antipsychotic drugs act on the dopaminergic system (first-generation antipsychotics, FGA), but some also directly affect serotonergic function (second-generation antipsychotics, SGA) in the brain. Short and long-term effects of these drugs on brain physiology remain poorly understood. Moreover, it remains unclear whether any physiological effect in the brain may be different for FGAs and SGAs. Immediate (+3.30 h) and different effects of single-dose FGA (haloperidol, 3 mg) and a SGA (aripiprazole, 10 mg) on resting cerebral blood flow (rCBF) were explored in the same 20 healthy volunteers using a pulsed continuous arterial spin labeling (pCASL) sequence (1.5T) in a placebo-controlled, repeated measures design. Both antipsychotics increased striatal rCBF but the effect was greater after haloperidol. Both decreased frontal rCBF, and opposite effects of the drugs were observed in the temporal cortex (haloperidol decreased, aripiprazole increased rCBF) and in the posterior cingulate (haloperidol increased, aripiprazole decreased rCBF). Further increases were evident in the insula, hippocampus, and anterior cingulate after both antipsychotics, in the motor cortex following haloperidol and in the occipital lobe the claustrum and the cerebellum after aripiprazole. Further decreases were observed in the parietal and occipital cortices after aripiprazole. This study suggests that early and different rCBF changes are evident following a single-dose of FGA and SGA. The effects occur in healthy volunteers, thus may be independent from any underlying pathology, and in the same regions identified as structurally and functionally altered in schizophrenia, suggesting a possible relationship between antipsychotic-induced rCBF changes and brain alterations in schizophrenia.

Differentiating maturational and training influences on fMRI activation during music processing

Two major influences on how the brain processes music are maturational development and active musical training. Previous functional neuroimaging studies investigating music processing have typically focused on either categorical differences between "musicians versus nonmusicians" or "children versus adults." In the present study, we explored a cross-sectional data set (n=84) using multiple linear regression to isolate the performance-independent effects of age (5 to 33 years) and cumulative duration of musical training (0 to 21,000 practice hours) on fMRI activation similarities and differences between melodic discrimination (MD) and rhythmic discrimination (RD). Age-related effects common to MD and RD were present in three left hemisphere regions: temporofrontal junction, ventral premotor cortex, and the inferior part of the intraparietal sulcus, regions involved in active attending to auditory rhythms, sensorimotor integration, and working memory transformations of pitch and rhythmic patterns. By contrast, training-related effects common to MD and RD were localized to the posterior portion of the left superior temporal gyrus/planum temporale, an area implicated in spectrotemporal pattern matching and auditory-motor coordinate transformations. A single cluster in right superior temporal gyrus showed significantly greater activation during MD than RD. This is the first fMRI which has distinguished maturational from training effects during music processing.

Dissociable effects of methylphenidate, atomoxetine and placebo on regional cerebral blood flow in healthy volunteers at rest: a multi-class pattern recognition approach

The stimulant drug methylphenidate (MPH) and the non-stimulant drug atomoxetine (ATX) are both widely used for the treatment of attention deficit/hyperactivity disorder (ADHD), but their differential effects on human brain function are poorly understood. PET and blood oxygen level dependent (BOLD) fMRI have been used to study the effects of MPH and BOLD fMRI is beginning to be used to delineate the effects of MPH and ATX in the context of cognitive tasks. The BOLD signal is a proxy for neuronal activity and is dependent on three physiological parameters: regional cerebral blood flow (rCBF), cerebral metabolic rate of oxygen and cerebral blood volume. To identify areas sensitive to MPH and ATX and assist interpretation of BOLD studies in healthy volunteers and ADHD patients, it is therefore of interest to characterize the effects of these drugs on rCBF. In this study, we used arterial spin labeling (ASL) MRI to measure rCBF non-invasively in healthy volunteers after administration of MPH, ATX or placebo. We employed multi-class pattern recognition (PR) to discriminate the neuronal effects of the drugs, which accurately discriminated all drug conditions from one another and provided activity patterns that precisely localized discriminating brain regions. We showed common and differential effects in cortical and subcortical brain regions. The clearest differential effects were observed in four regions: (i) in the caudate body where MPH but not ATX increased rCBF, (ii) in the midbrain/substantia nigra and (iii) thalamus where MPH increased and ATX decreased rCBF plus (iv) a large region of cerebellar cortex where ATX increased rCBF relative to MPH. Our results demonstrate that combining ASL and PR yields a sensitive method for detecting the effects of these drugs and provides insights into the regional distribution of brain networks potentially modulated by these compounds.

High dose intermittent sorafenib shows improved efficacy over conventional continuous dose in renal cell carcinoma

BACKGROUND

Renal cell carcinoma (RCC) responds to agents that inhibit vascular endothelial growth factor (VEGF) pathway. Sorafenib, a multikinase inhibitor of VEGF receptor, is effective at producing tumor responses and delaying median progression free survival in patients with cytokine refractory RCC. However, resistance to therapy develops at a median of 5 months. In an effort to increase efficacy, we studied the effects of increased sorafenib dose and intermittent scheduling in a murine RCC xenograft model.

METHODS

Mice bearing xenografts derived from the 786-O RCC cell line were treated with sorafenib according to multiple doses and schedules: 1) Conventional dose (CD) continuous therapy; 2) high dose (HD) intermittent therapy, 3) CD intermittent therapy and 4) HD continuous therapy. Tumor diameter was measured daily. Microvessel density was assessed after 3 days to determine the early effects of therapy, and tumor perfusion was assessed serially by arterial spin labeled (ASL) MRI at day 0, 3, 7 and 10.

RESULTS

Tumors that were treated with HD sorafenib exhibited slowed tumor growth as compared to CD using either schedule. HD intermittent therapy was superior to CD continous therapy, even though the total dose of sorafenib was essentially equivalent, and not significantly different than HD continuous therapy. The tumors exposed to HD sorafenib had lower microvessel density than the untreated or the CD groups. ASL MRI showed that tumor perfusion was reduced to a greater extent with the HD sorafenib at day 3 and at all time points thereafter relative to CD therapy. Further the intermittent schedule appeared to maintain RCC sensitivity to sorafenib as determined by changes in tumor perfusion.

CONCLUSIONS

A modification of the sorafenib dosing schedule involving higher dose intermittent treatment appeared to improve its efficacy in this xenograft model relative to conventional dosing. MRI perfusion imaging and histologic analysis suggest that this benefit is related to enhanced and protracted antiangiogenic activity. Thus, better understanding of dosing and schedule issues may lead to improved therapeutic effectiveness of VEGF directed therapy in RCC and possibly other tumors.

Reduced resolution transit delay prescan for quantitative continuous arterial spin labeling perfusion imaging

Arterial spin labeling perfusion MRI can suffer from artifacts and quantification errors when the time delay between labeling and arrival of labeled blood in the tissue is uncertain. This transit delay is particularly uncertain in broad clinical populations, where reduced or collateral flow may occur. Measurement of transit delay by acquisition of the arterial spin labeling signal at many different time delays typically extends the imaging time and degrades the sensitivity of the resulting perfusion images. Acquisition of transit delay maps at the same spatial resolution as perfusion images may not be necessary, however, because transit delay maps tend to contain little high spatial resolution information. Here, we propose the use of a reduced spatial resolution arterial spin labeling prescan for the rapid measurement of transit delay. Approaches to using the derived transit delay information to optimize and quantify higher resolution continuous arterial spin labeling perfusion images are described. Results in normal volunteers demonstrate heterogeneity of transit delay across different brain regions that lead to quantification errors without the transit maps and demonstrate the feasibility of this approach to perfusion and transit delay quantification.

Optimization of background suppression for arterial spin labeling perfusion imaging

OBJECT

To present an algorithm for optimization of background suppression pulse timing for arterial spin labeling (ASL) perfusion imaging.

MATERIALS AND METHODS

An algorithm for optimization of background suppression pulse timing is proposed. Numerical optimization of timing of the background suppression pulses is investigated in both constrained and unconstrained ASL sequences. The performance of the parameters from the algorithm is evaluated in phantom and also in vivo in five human subjects.

RESULTS

The background signal is suppressed to less than 1% across a broad range of T1s with a modest number of inversion pulses using the timings acquired from the numerical optimization algorithm proposed in this study. The performance of the parameters from the algorithm is also confirmed in vivo.

CONCLUSION

Successful background suppression over a broad range of tissues is achievable. Values for optimal pulse timing in both pulsed and continuous ASL studies are reported to facilitate sequence design with different labeling parameters.

Arterial spin labeling MR imaging for characterisation of renal masses in patients with impaired renal function: initial experience

OBJECTIVES

To retrospectively evaluate the feasibility of arterial spin labeling (ASL) magnetic resonance imaging (MRI) for the assessment of vascularity of renal masses in patients with impaired renal function.

METHODS

Between May 2007 and November 2008, 11/67 consecutive patients referred for MRI evaluation of a renal mass underwent unenhanced ASL-MRI due to moderate-to-severe chronic or acute renal failure. Mean blood flow in vascularised and non-vascularised lesions and the relation between blood flow and final diagnosis of malignancy were correlated with a 2-sided homogeneous variance t-test and the Fisher Exact Test, respectively. A p value <0.05 was considered statistically significant.

RESULTS

Seventeen renal lesions were evaluated in 11 patients (8 male; mean age = 70 years) (range 57-86). The median eGFR was 24 mL/min/1.73 m(2) (range 7-39). The average blood flow of 11 renal masses interpreted as ASL-positive (134 +/- 85.7 mL/100 g/min) was higher than that of 6 renal masses interpreted as ASL-negative (20.5 +/- 8.1 mL/100 g/min)(p = 0.015). ASL-positivity correlated with malignancy (n = 3) or epithelial atypia (n = 1) at histopathology or progression at follow up (n = 7).

CONCLUSIONS

ASL detection of vascularity in renal masses in patients with impaired renal function is feasible and seems to indicate neoplasia although the technique requires further evaluation.

KEY POINTS

Arterial spin labeling may help to characterise renal masses in patients with renal failure Detection of blood flow on ASL in a renal mass supports the presence of a neoplasm Renal masses with high blood-flow levels on ASL seem to progress rapidly.

The effect of hypercarbia and hyperoxia on the total blood flow to the retina as assessed by magnetic resonance imaging

PURPOSE

The feasibility of measuring total blood flow to the retina with Arterial Spin Labeling Magnetic Resonance Imaging (ASL-MRI) has been described previously. In the present study, the hypothesis was that the reactivity that the ASL-MRI detects at the human retina is dominated by the choroidal blood flow, and thus it may serve as a useful tool for quantitative assessment of the choroidal vascular reactivity.

METHODS

Before imaging, the intraocular pressure (IOP) was measured in the study eye of nine clinically healthy subjects (four males) while the subject performed the ventilatory protocol subsequently imaged by the scanner. End-tidal CO₂ partial pressure (P(ET)CO₂) was increased to target 45 mm Hg, (baseline P(ET)CO₂ = 40 mm Hg and baseline P(ET)O₂ = 100 mm Hg). P(ET)O₂ was then increased to target 300 and 500 mm Hg while keeping P(ET)CO₂ constant at 45 mm Hg. A background-suppressed, pulsed-continuous ASL sequence was used for blood flow imaging.

RESULTS

The measured total blood flow increased significantly from 1.55 ± 0.17 μL/mm²/min at the baseline to 1.96 ± 0.18 μL/mm²/min during hypercarbia. With increasing P(ET)O₂, the measured blood flow did not change significantly relative to the hypercarbia condition but remained significantly elevated relative to the baseline. There were no significant changes in systolic, diastolic, or mean blood pressure, heart rate, or IOP during all four breathing conditions.

CONCLUSIONS

The lack of change in the ASL signal under hyperoxic conditions is consistent with the hypothesis that this noninvasive assessment technique is predominantly weighted by choroidal blood flow. The results indicate that a CO₂ provocation challenge, in combination with ASL-MRI, is a promising noninvasive approach for investigating choroidal vascular reactivity under normal and disease states.

Effects of transcranial direct current stimulation (tDCS) on human regional cerebral blood flow

Transcranial direct current stimulation (tDCS) can up- and down-regulate cortical excitability depending on current direction, however our abilities to measure brain-tissue effects of the stimulation and its after-effects have been limited so far. We used regional cerebral blood flow (rCBF), a surrogate measure of brain activity, to examine regional brain-tissue and brain-network effects during and after tDCS. We varied the polarity (anodal and cathodal) as well as the current strength (0.8 to 2.0mA) of the stimulation. Fourteen healthy subjects were randomized into receiving either anodal or cathodal stimulation (two subjects received both, one week apart) while undergoing Arterial Spin Labeling (ASL) in the MRI scanner with an alternating off-on sampling paradigm. The stimulating, MRI-compatible electrode was placed over the right motor region and the reference electrode over the contralateral supra-orbital region. SPM5 was used to process and extract the rCBF data using a 10mm spherical volume of interest (VOI) placed in the motor cortex directly underneath the stimulating scalp electrode. Anodal stimulation induced a large increase (17.1%) in rCBF during stimulation, which returned to baseline after the current was turned off, but exhibited an increase in rCBF again in the post-stimulation period. Cathodal stimulation induced a smaller increase (5.6%) during stimulation, a significant decrease compared to baseline (-6.5%) after cessation, and a continued decrease in the post-stimulation period. These changes in rCBF were all significant when compared to the pre-stimulation baseline or to a control region. Furthermore, for anodal stimulation, there was a significant correlation between current strength and the increase in rCBF in the on-period relative to the pre-stimulation baseline. The differential rCBF after-effects of anodal (increase in resting state rCBF) and cathodal (decrease in resting state rCBF) tDCS support findings of behavioral and cognitive after-effects after cathodal and anodal tDCS. We also show that tDCS not only modulates activity in the brain region directly underlying the stimulating electrode but also in a network of brain regions that are functionally related to the stimulated area. Our results indicate that ASL may be an excellent tool to investigate the effects of tDCS and its stimulation parameters on brain activity.

Amide proton transfer imaging with improved robustness to magnetic field inhomogeneity and magnetization transfer asymmetry using saturation with frequency alternating RF irradiation

Amide proton transfer (APT) imaging has shown promise as an indicator of tissue pH and as a marker for brain tumors. Sources of error in APT measurements include direct water saturation, and magnetization transfer (MT) from membranes and macromolecules. These are typically suppressed by postprocessing asymmetry analysis. However, this approach is strongly dependent on B(0) homogeneity and can introduce additional errors due to intrinsic MT asymmetry, aliphatic proton features opposite the amide peak and radiation damping-induced asymmetry. Although several methods exist to correct for B(0) inhomogeneity, they tremendously increase scan times and do not address errors induced by asymmetry of the z-spectrum. In this article, a novel saturation scheme-saturation with frequency alternating RF irradiation (SAFARI)-is proposed in combination with a new magnetization transfer ratio (MTR) parameter designed to generate APT images insensitive to direct water saturation and MT, even in the presence of B(0) inhomogeneity. The feasibility of the SAFARI technique is demonstrated in phantoms and in the human brain. Experimental results show that SAFARI successfully removes direct water saturation and MT contamination from APT images. It is insensitive to B(0) offsets up to 180 Hz without using additional B(0) correction, thereby dramatically reducing scanning time.

Optimized double inversion recovery for reduction of T₁ weighting in fluid-attenuated inversion recovery

Fluid-attenuated inversion recovery (FLAIR) is a routinely used technique in clinical practice to detect long T(2) lesions by suppressing the cerebrospinal fluid. Concerns remain, however, that the inversion pulse in FLAIR imparts T(1) weighting that can decrease the detectability and mischaracterize some lesions. Hence, FLAIR is usually acquired in conjunction with a standard T(2) to guard against these concerns. Recently, double inversion recovery (DIR) preparations have highlighted certain types of lesions by suppressing both cerebrospinal fluid and white matter but produce even stronger T(1) contrast than FLAIR. This work shows that the inversion times in a DIR sequence can be optimized to minimize unwanted T(1) weighting, enabling the acquisition of cerebrospinal fluid-suppressed images with pure T(2) weighting. This technique is referred to as T(1) -nulled DIR. The theory to determine the optimized inversion times is discussed and the results are shown by simulations, normal volunteer studies, and multiple sclerosis patient studies. T(1) -nulled DIR provides equivalent or superior contrast between gray and white matters as well as white matter and multiple sclerosis lesion at the same repetition time. Multiple sclerosis lesions appeared sharper on T(1) -nulled DIR compared to FLAIR. T(1) -nulled DIR has the potential to replace the combination of standard T(2) and FLAIR acquisitions in many clinical protocols.

Resistance of renal cell carcinoma to sorafenib is mediated by potentially reversible gene expression

PURPOSE

Resistance to antiangiogenic therapy is an important clinical problem. We examined whether resistance occurs at least in part via reversible, physiologic changes in the tumor, or results solely from stable genetic changes in resistant tumor cells.

EXPERIMENTAL DESIGN

Mice bearing two human RCC xenografts were treated with sorafenib until they acquired resistance. Resistant 786-O cells were harvested and reimplanted into naïve mice. Mice bearing resistant A498 cells were subjected to a 1 week treatment break. Sorafenib was then again administered to both sets of mice. Tumor growth patterns, gene expression, viability, blood vessel density, and perfusion were serially assessed in treated vs control mice.

RESULTS

Despite prior resistance, reimplanted 786-O tumors maintained their ability to stabilize on sorafenib in sequential reimplantation steps. A transcriptome profile of the tumors revealed that the gene expression profile of tumors upon reimplantation reapproximated that of the untreated tumors and was distinct from tumors exhibiting resistance to sorafenib. In A498 tumors, revascularization was noted with resistance and cessation of sorafenib therapy and tumor perfusion was reduced and tumor cell necrosis enhanced with re-exposure to sorafenib.

CONCLUSIONS

In two RCC cell lines, resistance to sorafenib appears to be reversible. These results support the hypothesis that resistance to VEGF pathway therapy is not solely the result of a permanent genetic change in the tumor or selection of resistant clones, but rather is due to a great extent to reversible changes that likely occur in the tumor and/or its microenvironment.

A 3T MR imaging investigation of the topography of whole spinal cord atrophy in multiple sclerosis

BACKGROUND AND PURPOSE

Spinal cord atrophy is a common feature of MS. However, it is unknown which cord levels are most susceptible to atrophy. We performed whole cord imaging to identify the levels most susceptible to atrophy in patients with MS versus controls and also tested for differences among MS clinical phenotypes.

MATERIALS AND METHODS

Thirty-five patients with MS (2 with CIS, 27 with RRMS, 2 with SPMS, and 4 with PPMS phenotypes) and 27 healthy controls underwent whole cord 3T MR imaging. The spinal cord contour was segmented and assigned to bins representing each C1 to T12 vertebral level. Volumes were normalized, and group comparisons were age-adjusted.

RESULTS

There was a trend toward decreased spinal cord volume at the upper cervical levels in PPMS/SPMS versus controls. A trend toward increased spinal cord volume throughout the cervical and thoracic cord in RRMS/CIS versus controls reached statistical significance at the T10 vertebral level. A statistically significant decrease was found in spinal cord volume at the upper cervical levels in PPMS/SPMS versus RRMS/CIS.

CONCLUSIONS

Opposing pathologic factors impact spinal cord volume measures in MS. Patients with PPMS demonstrated a trend toward upper cervical cord atrophy. However patients with RRMS showed a trend toward increased volume at the cervical and thoracic levels, which most likely reflects inflammation or edema-related cord expansion. With the disease causing both expansion and contraction of the cord, the specificity of spinal cord volume measures for neuroprotective therapeutic effect may be limited.

Sensitivity calibration with a uniform magnetization image to improve arterial spin labeling perfusion quantification

Quantification of perfusion with arterial spin labeling MRI requires a calibration of the imaging sensitivity to water throughout the imaged volume. Since this sensitivity is affected by coil loading and other interactions between the subject and the scanner, the sensitivity must be calibrated in the subject at the time of scan. Conventional arterial spin labeling perfusion quantification assumes a uniform proton density and acquires a proton density reference image to serve as the calibration. This assumption, in the form of an assumed constant brain-blood partition coefficient, incorrectly adds inverse proton density weighting to the perfusion image. Here, a sensitivity calibration is proposed by generating a uniform magnetization image whose intensity is highly independent of brain tissue type. It is shown that such a uniform magnetization image can be achieved, and brain tissue perfusion values quantified with the sensitivity calibration agree with those quantified with a proton density image when segmentation of brain tissues is performed and appropriate partition coefficients are assumed. Quantification of brain tissue water density is also demonstrated using this sensitivity calibration. This approach can improve and simplify quantification of arterial spin labeling perfusion and may have broader applications to measurement of edema and sensitivity calibration for parallel imaging.

Association cortex hypoperfusion in mild dementia with Lewy bodies: a potential indicator of cholinergic dysfunction?

Dementia with Lewy bodies (DLB) is often associated with occipital hypometabolism or hypoperfusion, as well as deficits in cholinergic neurotransmission. In this study, 11 mild DLB, 16 mild AD and 16 age-matched controls underwent arterial spin-labeled perfusion MRI (ASL-pMRI) and neuropsychological testing. Patterns of cerebral blood flow (CBF) and cognitive performance were compared. In addition, combined ASL-pMRI and ChEI drug challenge (pharmacologic MRI) was tested as a probe of cholinergic function in 4 of the DLB participants. Frontal and parieto-occipital hypoperfusion was observed in both DLB and AD but was more pronounced in DLB. Following ChEI treatment, perfusion increased in temporal and parieto-occipital cortex, and cognitive performance improved on a verbal fluency task. If confirmed in a larger study, these results provide further evidence for brain cholinergic dysfunction in DLB pathophysiology, and use of pharmacologic MRI as an in vivo measure of cholinergic function.

The relationships among MRI-defined spinal cord involvement, brain involvement, and disability in multiple sclerosis

OBJECTIVE

To determine the interrelationships between MRI-defined lesion and atrophy measures of spinal cord involvement and brain involvement and their relationships to disability in a small cohort of patients with multiple sclerosis (MS).

BACKGROUND

Although it is known that cervical spinal cord atrophy correlates with disability in MS, it is unknown whether it is the most important determinant when compared to other regions of the central nervous system (CNS). Furthermore, it is not clear to what extent brain and cord lesions and atrophy are related.

DESIGN AND METHODS

3T MRI of the whole brain and whole spinal cord was obtained in 21 patients with MS, including 18 with relapsing-remitting, one with secondary progressive, one with primary progressive, and one with a clinically isolated syndrome. Brain global gray and white matter volumes were segmented with Statistical Parametric Mapping 8. Spinal cord contour volume was segmented in whole by a semi-automated method with bins assigned to either the cervical or thoracic regions. All CNS volumes were normalized by the intracranial volume. Brain and cord T2 hyperintense lesions were segmented using a semi-automated edge finding tool.

RESULTS

Among all MRI measures, only upper cervical spinal cord volume significantly correlated with Expanded Disability Status Scale score (r =-.515, P = .020). The brain cord relationships between whole or regional spinal cord volume or lesions and gray matter, white matter, or whole brain volume or whole brain lesions were generally weak and all nonsignificant.

CONCLUSIONS AND RELEVANCE

In this preliminary study of mildly disabled, treated MS patients, cervical spinal cord atrophy most strongly correlates with physical disability in MS when accounting for a wide range of other CNS measures of lesions and atrophy, including thoracic or whole spinal cord volume, and cerebral gray, white or whole brain volume. The weak relationship between spinal cord and brain lesions and atrophy may suggest that they progress rather independently in patients with MS.

Perfusion imaging with a freely diffusible hyperpolarized contrast agent

Contrast agents that can diffuse freely into or within tissue have numerous attractive features for perfusion imaging. Here we present preliminary data illustrating the suitability of hyperpolarized (13)C labeled 2-methylpropan-2-ol (also known as dimethylethanol, tertiary butyl alcohol and tert-butanol) as a freely diffusible contrast agent for magnetic resonance perfusion imaging. Dynamic (13)C images acquired in rat brain with a balanced steady-state free precession sequence following administration of hyperpolarized 2-methylpropan-2-ol show that this agent can be imaged with 2-4 s temporal resolution, 2 mm slice thickness, and 700 μm in-plane resolution while retaining adequate signal-to-noise ratio. (13)C relaxation measurements on 2-methylpropan-2-ol in blood at 9.4 T yield T(1) = 46 ± 4s and T(2) = 0.55 ± 0.03 s. In the rat brain at 4.7 T, analysis of the temporal dynamics of the balanced steady-state free precession image intensity in tissue and venous blood indicate that 2-methylpropan-2-ol has a T(2) of roughly 2-4s and a T(1) of 43 ± 24 s. In addition, the images indicate that 2-methylpropan-2-ol is freely diffusible in brain and hence has a long residence time in tissue; this in turn makes it possible to image the agent continuously for tens of seconds. These characteristics show that 2-methylpropan-2-ol is a promising agent for robust and quantitative perfusion imaging in the brain and body.

Arterial spin labelling reveals an abnormal cerebral perfusion pattern in Parkinson's disease

There is a need for objective imaging markers of Parkinson's disease status and progression. Positron emission tomography and single photon emission computed tomography studies have suggested patterns of abnormal cerebral perfusion in Parkinson's disease as potential functional biomarkers. This study aimed to identify an arterial spin labelling magnetic resonance-derived perfusion network as an accessible, non-invasive alternative. We used pseudo-continuous arterial spin labelling to measure cerebral grey matter perfusion in 61 subjects with Parkinson's disease with a range of motor and cognitive impairment, including patients with dementia and 29 age- and sex-matched controls. Principal component analysis was used to derive a Parkinson's disease-related perfusion network via logistic regression. Region of interest analysis of absolute perfusion values revealed that the Parkinson's disease pattern was characterized by decreased perfusion in posterior parieto-occipital cortex, precuneus and cuneus, and middle frontal gyri compared with healthy controls. Perfusion was preserved in globus pallidus, putamen, anterior cingulate and post- and pre-central gyri. Both motor and cognitive statuses were significant factors related to network score. A network approach, supported by arterial spin labelling-derived absolute perfusion values may provide a readily accessible neuroimaging method to characterize and track progression of both motor and cognitive status in Parkinson's disease.

Modified pulsed continuous arterial spin labeling for labeling of a single artery

Imaging the contribution of different arterial vessels to the blood supply of the brain can potentially guide the treatment of vascular disease and other disorders. Previously available only with catheter angiography, vessel-selective labeling of arteries has now been demonstrated with pulsed and continuous arterial spin labeling methods. Pulsed continuous labeling, which permits continuous labeling on standard scanner radiofrequency hardware, has been used to encode the contribution of different vessels to the blood supply of the brain. Vessel encoding requires a longer scan and a more complex reconstruction algorithm and may be more sensitive to fluctuations in flow, however. Here a method is presented for single-artery selective labeling, in which a disk around the targeted vessel is labeled. Based on pulsed continuous labeling, this method is achieved by rotating the directions of added in-plane gradients. Numerical simulations of the simplest strategy show good efficiency but poor suppression of labeling at large distances from the target vessel. Amplitude modulation of the rotating in-plane gradients results in better suppression of distant vessels. In vivo results demonstrate highly selective labeling of individual vessels and a rapid falloff of the labeling with distance from the center of the labeling disk, in agreement with the simulations.

Blood flow quantification of the human retina with MRI

The purpose of this study was to investigate the feasibility of measuring blood flow to the retina using arterial spin labeling MRI, a quantitative, noninvasive tomographic technique. Blood flow imaging was performed in a single axial slice through both eyes of five healthy volunteers with no history of retinal diseases. The imaging was optimized to minimize the errors from motion and nonuniform magnetic fields caused by proximity to the sinuses. Key hemodynamic factors for flow quantification, including arterial transit delay and the apparent decay time of the signal, were estimated by repeated measurements with different arterial spin labeling timing. A clearly elevated signal, consistent with the anatomical location of the retina, was observed in all subjects. The measured blood flow to a 1 cm × 1.47 cm section of the retina, centered on the fovea, was 1.75 ± 0.54 µL/mm(2) /min (total blood flow of 261 ± 87 µL/min). The arterial transit delay from a labeling plane 5 cm below the slice was 1137 ± 288 ms. These results establish the feasibility of measuring blood flow to the retina with MRI, and support the future characterization of the healthy and diseased ocular circulation with this method.

Time-resolved vessel-selective digital subtraction MR angiography of the cerebral vasculature with arterial spin labeling

PURPOSE

To demonstrate an arterial spin-labeling (ASL) magnetic resonance (MR) angiographic technique that covers the entire cerebral vasculature and yields transparent-background, time-resolved hemodynamic, and vessel-specific information similar to that obtained with x-ray digital subtraction angiography (DSA) without the use of exogenous contrast agents.

MATERIALS AND METHODS

Prior institutional review board approval and written informed consent were obtained for this HIPAA-compliant study in which 12 healthy volunteers (five women, seven men; age range, 21-62 years; average age, 28 years) underwent imaging. An ASL technique in which variable labeling durations are used to acquire hemodynamic inflow information and a vessel-selective pulsed-continuous ASL technique were tested. Region-of-interest signal intensities in various vessel segments were averaged across subjects and used to quantitatively compare images. For comparison, a standard time of flight (TOF) acquisition was performed in the circle of Willis.

RESULTS

Inflow temporal resolution of 200 msec was demonstrated, revealing arterial transit times of 750, 950, and 1100 msec to consecutive segments of the middle cerebral artery from distal to the circle of Willis to deep regions of the midbrain. Selective labeling resulted in an average of eightfold suppression of contralateral vessels relative to the labeled vessel. Signal-to-noise ratios and contrast-to-noise ratios on maximum intensity projection images obtained with 88-second volumetric acquisitions (60 ± 15 [standard deviation] and 57 ± 15, respectively) and 11-second single-projection acquisitions (19 ± 5 and 17 ± 5, respectively) were comparable with standard TOF acquisitions, in which a 2.7-fold longer imaging duration for a 2.6-fold lower pixel area was used. Normal variations of the vasculature were identified with ASL angiography.

CONCLUSION

ASL angiography can be used to acquire hemodynamic vessel-specific information similar to that obtained with x-ray DSA.