Dark Matter Search Results from the PICO-60 C_{3}F_{8} Bubble Chamber.

New results are reported from the operation of the PICO-60 dark matter detector, a bubble chamber filled with 52 kg of C_{3}F_{8} located in the SNOLAB underground laboratory. As in previous PICO bubble chambers, PICO-60 C_{3}F_{8} exhibits excellent electron recoil and alpha decay rejection, and the observed multiple-scattering neutron rate indicates a single-scatter neutron background of less than one event per month. A blind analysis of an efficiency-corrected 1167-kg day exposure at a 3.3-keV thermodynamic threshold reveals no single-scattering nuclear recoil candidates, consistent with the predicted background. These results set the most stringent direct-detection constraint to date on the weakly interacting massive particle (WIMP)-proton spin-dependent cross section at 3.4×10^{-41} cm^{2} for a 30-GeV c^{-2} WIMP, more than 1 order of magnitude improvement from previous PICO results.

Dark Matter Search Results from the PICO-2L C3F8 Bubble Chamber.

New data are reported from the operation of a 2 liter C3F8 bubble chamber in the SNOLAB underground laboratory, with a total exposure of 211.5 kg days at four different energy thresholds below 10 keV. These data show that C3F8 provides excellent electron-recoil and alpha rejection capabilities at very low thresholds. The chamber exhibits an electron-recoil sensitivity of <3.5×10(-10) and an alpha rejection factor of >98.2%. These data also include the first observation of a dependence of acoustic signal on alpha energy. Twelve single nuclear recoil event candidates were observed during the run. The candidate events exhibit timing characteristics that are not consistent with the hypothesis of a uniform time distribution, and no evidence for a dark matter signal is claimed. These data provide the most sensitive direct detection constraints on WIMP-proton spin-dependent scattering to date, with significant sensitivity at low WIMP masses for spin-independent WIMP-nucleon scattering.

Melanoma metastatic to the bronchus: radiologic features in two patients.

Two patients with cutaneous melanoma metastatic to the bronchus are described. Chest radiographs revealed only indirect signs of bronchial obstruction. Computed tomography (CT) clearly demonstrated the intraluminal lesion. Magnetic resonance (MR) imaging signal characteristics were not specific for melanoma.

Distribution of joint effusion in patients with traumatic knee joint disorders: MRI assessment.

One hundred forty-five knee magnetic resonance imaging examinations with joint effusions were reviewed to clarify the usual distribution of joint fluids in patients with traumatic knee joint disorders. Almost all knees (99%) had effusions in the central portion, and most knees (76%) had effusions in the suprapatellar pouch. Effusions were rarely found in the posterior femoral recess (9%) or subpopliteal recess (2%). However, this difference was considered to be only a reflection of anatomic communications. Effusions were occasionally found around posterior cruciate ligaments (36%), but were less frequently seen around anterior cruciate ligaments (18%).

Use of biologic markers for toxic end-points in assessment of risks from exposure to chemicals.

Biologic markers are familiar tools for monitoring human absorption of, and reaction to, potentially toxic chemicals. The concept of applying biologic markers to the risk assessment process is a natural, but more recent, development and the principles remain to be fully elaborated. Biologic markers may be measurements of exposure, of effects, of genetic or induced sensitivity or of disease. The ideal biologic marker for risk assessment purposes is a quantitative measurement of a chemical, biochemical, functional or morphological change in the system that is initiated by a chemical and which results in pathologic change and overt toxicity. It follows that some understanding of the mechanism of toxicity and of dose-response relationships are pre-requisite for selection of suitable biologic markers for use in risk assessment. Where biologic markers for toxicity are common between mammalian species, extrapolation of data for quantitative risk assessment purposes becomes more reasonable. In the field of carcinogenesis, some DNA and protein adducts have been proposed as biologic markers for assessment of risk associated with exposure to genotoxic carcinogens. However, less progress is evident in relation to other toxic end-points including those for pulmonary, reproductive, immuno- and neuro-toxicity, despite intensive efforts.

Iron deposition in cranial bone marrow with sickle cell disease: MR assessment using a fat suppression technique.

Thirteen patients with sickle cell disease (SCD) undergoing transfusion therapy and 8 control patients were examined by magnetic resonance imaging to discriminate bone marrow change due to iron deposition from hematologic marrow hyperplasia. Using T1-weighted spin echo images, only two subjects showed extremely low signal intensity marrow compatible with iron deposition. However, using T2-weighted fast spin echo images with fat suppression, cranial bone marrow in SCD patients with transfusion therapy showed considerably lower signal than that of controls. The main cause of marrow signal decrease in SCD patients with transfusion therapy was considered to be iron deposition due to repeated transfusion therapy rather than red marrow hyperplasia.

Peripheral findings in MR using surface coil.

Incidental peripheral lesions found during neuroradiological MR examinations with surface coils are reviewed. These include intracranial metastases during orbital examinations, cerebellar and thyroid lesions during cervical spine examinations, and dissecting and saccular abdominal aneurysms, as well as renal and intrapelvic abnormalities during lumbar spine examinations. Because of the reduced field-of-view and rapid signal drop-off in deeper portions of the body when examinations are performed with surface coils, peripheral and deep regions also need careful attention during routine evaluation.

Leiomyosarcoma after retinoblastoma radiotherapy.

The CT and MR appearance of leiomyosarcoma in the left orbit in a 15-year-old girl is presented. This tumor developed after successful radiation therapy for bilateral retinoblastoma.