SUMMARY Regional brain blood flow was determined in 23 awake, unparalyzed gerbils with a simplified indicator-fractionation technique. The use of intravenous "C-butanol, an indicator that is freely diffusible into the brain, eliminated the need for repetitive sampling of arterial and cerebral venous blood and reduced the period of indicator circulation to 10 seconds. Gerbils spontaneously breathing room air (Paco 2 = 32 ± I (SE) mm Hg) had blood flows in whole cerebrum, cerebellum, and brainstem of 102 ± 4, 93 ± 5, and 114 ± 6 ml/lOOgm/min respectively. Cerebral blood flow increased linearly with elevations in Paco, (r = 0.969) and averaged 3.14 ± 0.17 ml/lOOgm/min per mm Hg increase in Paco 2 . Interpolated cerebral blood flow at a Paco, of 40 mm Hg was 127 ± 2 ml/lOOgm/min. This technique is easy and convenient to use, involves no intracrania! surgery, requires steady state conditions for only 10 seconds, and minimizes blood loss in small animals. In more discrete brain regions a less volatile indicator is needed.

Purpose:To assess the effect of using computer-aided detection (CAD) in second-read mode on readers' accuracy in interpreting computed tomographic (CT) colonographic images. Materials and Methods:The contributing institutions performed the examinations under approval of their local institutional review board, with waiver of informed consent, for this HIPAA-compliant study. A cohort of 100 colonoscopy-proved cases was used: In 52 patients with fi ndings positive for polyps, 74 polyps of 6 mm or larger were observed in 65 colonic segments; in 48 patients with fi ndings negative for polyps, no polyps were found. Nineteen blinded readers interpreted each case at two different times, with and without the assistance of a commercial CAD system. The effect of CAD was assessed in segment-level and patient-level receiver operating characteristic (ROC) curve analyses. Results:Thirteen (68%) of 19 readers demonstrated higher accuracy with CAD, as measured with the segment-level area under the ROC curve (AUC). The readers' average segment-level AUC with CAD (0.758) was signifi cantly greater ( P = .015) than the average AUC in the unassisted read (0.737). Readers' per-segment, per-patient, and per-polyp sensitivity for all polyps of 6 mm or larger was higher ( P , .011, .007, .005, respectively) for readings with CAD compared with unassisted readings (0.517 versus 0.465, 0.521 versus 0.466, and 0.477 versus 0.422, respectively). Sensitivity for patients with at least one large polyp of 10 mm or larger was also higher ( P , .047) with CAD than without (0.777 versus 0.743). Average reader sensitivity also improved with CAD by more than 0.08 for small adenomas. Use of CAD reduced specifi city of readers by 0.025 ( P = .05). Conclusion:Use of CAD resulted in a signifi cant improvement in overall reader performance. CAD improves reader sensitivity when measured per segment, per patient, and per polyp for small polyps and adenomas and also reduces specifi city by a small amount.q RSNA, 2010 Supplemental material: http://radiology.rsna.org/lookup /suppl

One-hundred-forty patients with atrial fibrillation (AF) due to non-rheumatic, non-valvular heart disease (NVHD) who suffered a cerebral infarct were identified. Fifty-three (38%) died of the initial stroke. The surviving patients were followed up to 9 years without anticoagulant therapy. In the 59 patients available for follow-up, the risk of recurrent cerebral ischemia remained at approximately 20% per year throughout the 9 year observation period. The recurrence rate was the same regardless of age, sex, previous myocardial infarction, or whether chronic AF or intermittent AF were present. Only 7 (12%) died from a second stroke, however. The high annual rate of recurrence and lack of controlled therapeutic trials in this population of patients warrant a prospective study to define the benefits and relative risks of anticoagulant therapy in AF due to NVHD.

Cerebral blood flow (CBF) was assessed with radioactive butanol and antipyrine during and after 1 hour of unilateral carotid artery occlusion in gerbils. Animals with clinical evidence of stroke demonstrated a marked fall in ipsilateral CBF during occlusion "no-reflow" phenomenon did not develop; instead, blood flow returned to normal 5 minutes after the termination of carotid occlusion. Flow subsequently fell to half the control value, however, and remained depressed for several hours despite local metabolic demands. This delayed imbalance in energy supply and demand creates a potential for additional brain damage that might be prevented by appropriate therapeutic intervention.

The uptake of compounds by the brain depends upon cerebral blood flow. To determine the normal blood flow-cerebral extraction relationship, a method for rapid, simultaneous measurement of cerebral blood flow and brain extraction was developed and applied to blood-brain leucine transfer. Awake rats were injected intravenously with a mixture of n-[(14)C]butanol and [(3)H]leucine. The quantities of indicators accumulated over the following 5-12 s in brain and in a sample of arterial blood withdrawn at a know rate were used to determine the flux of butanol and leucine into brain. Butanol extraction was assessed independently by measuring arterial and cerebral venous concentrations of the indicator after a bolus injection. Cerebral blood flow was equal to the ratio of butanol flux into brain to butanol extraction by brain; leucine extraction was then calculated as the ratio of leucine influx to cerebral blood flow. Leucine extraction by brain and cerebral blood flow were shown to be related exponentially. The maximum velocity of active leucine transport was virtually the same at flows of 150 and 400 ml/100 g/min. The present method is theoretically applicable to the measurement of the extraction of any compound from blood by brain. By measuring the normal blood flow-extraction relationship, one can differentiate changes in extraction secondary to altered flow from changes intrinsic to pathologic conditions with inconstant cerebral blood flow.