Xe CT Research Articles

小児もやもや病でのstable xenon enhanced CTを用いた脳血流量測定における実効線量軽減

Measurement of cerebral blood flow (CBF) is necessary for the management of childhood moyamoya disease. Computed tomography (stable Xe CT) enhanced by three minutes of inhalation of stable xenon is an established method for measurement of CBF. In this retrospective study, we evaluated a decrease in serial scan times in stable Xe CT in childhood moyamoya disease in order to lessen the effective dose. CBF values obtained by usually performed stable Xe CT were evaluated in 12 patients with childhood moyamoya disease. Clinically, nine serial scans were performed as usual. In this retrospective study, CBF was calculated based on nine serial scans (S9), based on seven serial scans out of the obtained nine serial scans (S7), and based on five scans out of the obtained nine serial scans (S5). Both S7 and S5 had a significantly simple linear correlation with S9 as follows: S9=1.642+1.031×S7, S9=2.726+0.983×S5. CBF maps obtained by S9, S7, and S5 were almost identical. In childhood moyamoya disease, measurement of CBF using stable Xe CT with performance of five serial scans in each slice can be used to lessen the effective dose.

Usefulness of 99mTc-Technegas and 133Xe dynamic SPECT in ventilatory impairment

To assess the usefulness of SPECT images using (99m)Tc-Technegas (Technegas) and (133)Xe dynamic single photon emission computed tomography (SPECT) (Xe gas) and high-resolution computed tomography (HRCT), as compared with pathological assessment in the detection of small-airway disease including pulmonary emphysema. Seventeen patients with lung cancer were studied. All patients who had undergone both Technegas and Xe gas and CT prior to surgery were examined. SPECT and HRCT results were compared with the results of pathological findings. Histopathological analysis was performed in an area distant from cancer in lobectomy specimens obtained at surgery. Pathological analysis was performed in relation to bronchitis, bronchiolitis, fibrosis of the alveoli and disruption in walls of the alveoli. Pathological abnormality (mild-to-moderate abnormal change) was seen in all 17 cases. Three patients showed low attenuation areas on CT, and abnormal patterns in SPECT images. In 11 of 14 patients who showed normal findings on CT, SPECT imaging depicted abnormal findings. The remaining three patients had no abnormal findings on CT and both SPECT imaging. Technegas and (133)Xe SPECT imaging is useful for evaluating small-airway disease including pulmonary emphysema. Furthermore, SPECT imaging is more useful than morphological HRCT imaging in the evaluation of small-airway disease including pulmonary emphysema.

Investigation of cerebral blood volume measurement

Cerebral blood blow (ml/100g/min) (CBF) and cerebral blood volume (%) (CBV) were determined in 102 patients (68 men and 34 women; average age, 55.6 years) with diagnostic cerebral blood flow accident. CBF was obtained by xenon inhalation computed tomography (Xe CT) and transit time (TT) by perfusion CT. CBV was calculated under the expression CBV=CBF x TT. The patients were divided into three categories: mild (outpatient), moderate (inpatient), and serious (dead), and CBF and CBV were compared between categories. On regions of interest (ROI) in the thalamus, the value for mild cases was 58.8+/-10.4 ml/100g/min (CBF) and that for moderate cases was 40.2+/-19.4, a significant difference. In serious cases, CBV was decreased in the thalamus, but there was no difference in CBF between mild and moderate cases. CBV was useful for determining prognosis in severe cases of diagnostic cerebral blood flow accident.

Xenon CT cerebral blood flow in patients with head injury: influence of pulmonary trauma on the input function.

The noninvasive xenon-enhanced CT (Xe CT) cerebral blood flow (CBF) method has been used in patients with severe traumatic brain injury (TBI) to identify the blood-flow thresholds for the development of irreversible ischaemia or infarction following severe TBI. Quantitative regional CBF (rCBF) estimates are based on the assumption of identity between the end-tidal xenon concentration curve, used as the input function, and the arterial xenon concentration curve, being the true input function to the brain. Accordingly, rCBF data addressing the issue of ischaemia should be viewed in relation to possible deviations between the end-tidal and arterial xenon concentration curves. To evaluate this possible source of error, we studied five patients with severe TBI (Glasgow coma score < or =7) who also had pulmonary trauma. CBF was studied with the Xe CT CBF method and flow rates were determined by fitting the Kety equation to each CT voxel using either the end-tidal or the arterial xenon curve as input function. In all patients rCBF estimates were lower using the end-tidal xenon curve than with the arterial xenon curve; the mean underestimation was 20.3% in gray metter and 17.3 % in white matter. The deviation between the end-tidal and arterial xenon concentration curves should be considered as a source of error when defining critical flow values according to the flow thresholds of tissue viability.

The pharmacokinetics of hyperpolarized xenon: implications for cerebral MRI.

In this work, a compartmental model to predict the concentration of hyperpolarized xenon (Xe) in the brain is developed based on the well established kinetics of Xe and estimated T1 values for the compartments. For the gaseous compartments, T1 was set to 12 seconds. For the tissue compartments, T1 was set to 6 seconds. Three gas delivery techniques were modeled: hyperventilation followed by breath-hold, continual breathing, and hyperventilation followed by continual breathing. Based on Xe CT, it is estimated that the maximum concentration of Xe that could be breathed is 80%. Based on this value and the estimated maximum polarization of 50%, the peak gray matter concentration of hyperpolarized Xe is calculated to be .036 mM. This leads to an estimated signal-to-noise ratio (SNR), at 2 T, for hyperpolarized Xe that is a factor of 50 lower than the SNR for proton MRI. The peak concentration of hyperpolarized Xe was also calculated over a wide range of gas and tissue T1 values. This model also predicts that the arterial blood will have a concentration of hyperpolarized Xe that is 10 times greater than the concentration in gray matter. An interactive version of the model can be found on the World Wide Web at http:(/)/ric.uthscsa.edu/staff /charlesmartinphd.html.

Current status and controversies in the inhalation protocols for the Xenon CT CBF method.

The historical background and current status of the inhalation protocols for the xenon CT CBF method are reviewed. A wash-in method has been established and widely accepted as a standard protocol. A wash-in/washout method is a useful alternative for a practical CBF study. The effect of flow activation with xenon gas can be minimized by shortening the inhalation time. Xe CT CBF method remains to be an indispensable technology for the clinical decision-making in various brain disorders.

Middle cerebral artery endarterectomy: Experience with two cases

Atherosclerotic stenosis of the middle cerebral artery (MCA) is uncommon and long-term prognosis is not well defined. Methods of treating stenosis of the MCA range from the administration of anticoagulants to endarterectomy. We present two cases of patients with focal symptomatic stenosis of the MCA with evidence of focally decreased cerebral blood flow and compromise of cerebral blood flow reserves on xenon-enhanced computed tomography (Xe CT) scanning. Endarterectomies were performed after unsuccessful anticoagulation therapy. Both patients underwent successful endarterectomies of the MCA. Improvement in cerebral blood flow postoperatively was documented for both patients. At last follow-up neither patient had demonstrated any additional ischemic episodes. Atherosclerotic stenosis of the MCA may be responsible for distal emboli and compromised hemodynamics, and endarterectomy of this vessel may provide definitive therapy.

Reversibility of cerebral ischaemia. Dynamic and xenon computed tomography study on ischaemic cerebrovascular disease.

Flow studies using dynamic CT and xenon (Xe) CT were carried out in 25 patients with ischaemic stroke in the territory of the middle cerebral artery to define the clinical characteristics of cerebral ischaemia at a chronic stage. The parameter of peak height/mean transit time (PH/MTT) obtained from dynamic CT can provide an accurate index for blood circulation in the cerebral vascular bed. Xe CT measurements revealed various kinds of ischaemia around the infarction even in the chronic stages. In mild ischaemia of more than 30 ml/100 g/min, reduction of cerebral blood flow (CBF) was well correlated to the PH/MTT. However, in severe ischaemia between 20 and 30 ml/100 g/min, changes of CBF were no longer correlated with the PH/MTT. There were cases showing severe reduction of CBF but which showed sufficient blood circulation (moderate value of PH/MTT). Mild reductions of CBF in parallel with decreased blood supply were often found in the peri-infarct area of infarctions in the centrum semiovale. On the other hand, infarctions in the cortico-subcortical region showed severe ischaemia, in even where blood circulation was relatively well sustained.

Regional cerebral perfusion measurements: a comparative study of xenon-enhanced CT and C15O2 build-up using dynamic PET

Regional cerebral perfusion can be determined by monitoring the uptake of a diffusable tracer concurrently in cerebral tissue and arterial blood. Two techniques based on this methodology are xenon-enhanced computed tomography (Xe CT) and C15O2 build-up using dynamic positron emission tomography (C15O2 PET). Serial images are used by both Xe CT and C15O2 PET to characterize the uptake of the tracer in cerebral tissue. The noise present in these images will reduce the precision of the perfusion measurements obtained by either technique. Using Monte Carlo type computer simulations, the precision of the two techniques as a function of image noise has been examined. It is concluded that the precision of the Xe CT technique is comparable to the precision of C15O2 PET when realistic clinical protocols are employed for both.

Mapping of rCBF and cerebrovascular reserve capacity by stable xenon CT in cerebrovascular disease: Pathophysiological aspects and effects of operative therapy

In 65 patients with extracranial occlusive vascular disease treated by operation, the rCBF was investigated by Xe CT before and after microsurgical operation