Automated segmentation of MR imaging to determine normative central nervous system cerebrospinal fluid volumes in healthy volunteers.

An accurate non-invasive method to determine total body cerebrospinal fluid volume has a number of potential diagnostic and therapeutic applications. Herein we describe a technique for automated segmentation of total body MRI data to determine cranial and spinal CSF volume in 15 healthy adults. These in vivo estimates of CSF volume exceed the standard reported volume of 150mL in human adults and provide normative data for diagnosis of disease states such as hydrocephalus and therapy including pharmacologic dosimetry. No correlation was observed between patient height or weight and total body CSF volume.

Variability in assessing treatment response: metastatic colorectal cancer as a paradigm.

PURPOSE: The cutoff values currently used to categorize tumor response to therapy are neither biologically based nor tailored for measurement reproducibility with contemporary imaging modalities. Sources and magnitudes of discordance in response assessment in metastatic colorectal cancer (mCRC) are unknown. EXPERIMENTAL DESIGN: A subset of patients' CT images of chest, abdomen, and pelvis were randomly chosen from a multicenter clinical trial evaluating insulin-like growth factor receptor type 1-targeted therapy in mCRC. Using Response Evaluation Criteria in Solid Tumors (RECIST), three radiologists selected target lesions and measured "uni" (maximal diameter), "bi" (product of maximal diameter and maximal perpendicular diameter), and "vol" (volume) on baseline and 6-week posttherapy scans in the following ways: (i) each radiologist independently selected and measured target lesions and (ii) one radiologist's target lesions were blindly remeasured by the others. Variability in relative change of tumor measurements was analyzed using linear mixed effects models. RESULTS: Three radiologists independently selected 138, 101, and 146 metastatic target lesions in the liver, lungs, lymph nodes, and other organs (e.g., peritoneal cavity) in 29 patients. Of 198 target lesions total, 33% were selected by all three, 28% by two, and 39% by one radiologist. With independent selection, the variability in relative change of tumor measurements was 11% (uni), 19% (bi), and 22% (vol), respectively. When measuring the same lesions, the corresponding numbers were 8%, 14%, and 12%. CONCLUSIONS: The relatively low variability in change of mCRC measurements suggests that response criteria could be modified to allow more accurate and sensitive CT assessment of anticancer therapy efficacy.

(11)C-MK-8278 PET as a tool for pharmacodynamic brain occupancy of histamine 3 receptor inverse agonists.

UNLABELLED: The histamine 3 (H3) receptor is a presynaptic autoreceptor in the central nervous system that regulates the synthesis and release of histamine and modulates the release of other major neurotransmitters. H3 receptor inverse agonists (IAs) may be efficacious in the treatment of various central nervous system disorders, including excessive daytime sleepiness, attention deficit hyperactivity disorder, Alzheimer disease, ethanol addiction, and obesity. METHODS: Using PET and a novel high-affinity and selective radioligand (11)C-MK-8278, we studied the tracer biodistribution, quantification, and brain H3 receptor occupancy (RO) of MK-0249 and MK-3134, 2 potential IA drugs targeting cerebral H3 receptors, in 6 healthy male subjects (age, 19-40 y). The relationship among H3 IA dose, time on target, and peripheral pharmacokinetics was further investigated in 15 healthy male volunteers (age, 18-40 y) with up to 3 PET scans and 3 subjects per dose level. RESULTS: The mean effective dose for (11)C-MK-8278 was 5.4 ± 1.1 µSv/MBq. Human brain kinetics showed rapid high uptake and fast washout. Binding potential values can be assessed using the pons as a reference region, with a test-retest repeatability of 7%. Drug RO data showed low interindividual variability per dose (mean RO SD, 2.1%), and a targeted 90% RO can be reached for both IAs at clinically feasible doses. CONCLUSION: (11)C-MK-8278 is a useful novel PET radioligand for determination of human cerebral H3 receptor binding and allows highly reproducible in vivo brain occupancy of H3-targeting drugs, hereby enabling the evaluation of novel compounds in early development to select doses and schedules.