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Digital chest phantoms continue to play a significant role in optimizing imaging parameters for chest X-ray examinations. The purpose of this study was to develop a digital chest phantom for studies on energy subtraction techniques under ideal conditions without image noise. Computed tomography (CT) images from the LIDC (Lung Image Database Consortium) were employed to develop a digital chest phantom. The method consisted of the following four steps: 1) segmentation of the lung and bone regions on CT images; 2) creation of simulated nodules; 3) transformation to attenuation coefficient maps from the segmented images; and 4) projection from attenuation coefficient maps. To evaluate the usefulness of digital chest phantoms, we determined the contrast of the simulated nodules in projection images of the digital chest phantom using high and low X-ray energies, soft tissue images obtained by energy subtraction, and "gold standard" images of the soft tissues. Using our method, the lung and bone regions were segmented on the original CT images. The contrast of simulated nodules in soft tissue images obtained by energy subtraction closely matched that obtained using the gold standard images. We thus conclude that it is possible to carry out simulation studies based on energy subtraction techniques using the created digital chest phantoms. Our method is potentially useful for performing simulation studies for optimizing the imaging parameters in chest X-ray examinations.

Using TOSHIBA Digiformer X, digital subtraction angiography (DSA) was performed in 286 patients, in whom 229 patients of cerebro-spinal vascular disease was included. The authors emphasize the usefulness of DSA in cerebro-spinal vascular disease in relation to conventional angiography. DSA taken by single small dose injection of contrast medium into the ascending aorta clearly demonstrates not only aortic arch and thoracic major vessels, but also cervical vessels and all intracranial vessels. Therefore, we could rapidly understand gross dynamics of the circulation and obtain useful informations prior to catheterization to the selective artery. This advantage of DSA was particularly useful for occlusive vascular diseases. Gradual injection of small dose of contrast medium obviously reduced recoiling of the catheter tip, which enabled the selective angiography with setting of the tip of the catheter at the entrance of cervical major vessels without its sufficient insertion into the selective vessels. This advantage is particularly beneficial for the patients with severe arteriosclerosis who was found to be difficult for selective catheterization. In our experience, demonstration of a presence of aneurysm by DSA was possible in almost all cases of subarachnoid hemorrhage, although spatial resolution of DSA is said to be inferior to the conventional angiography. Real time display of DSA decreased the time required for examination and enabled repeated angiography. This advantage of DSA is especially useful for the patients with spinal arterio-venous malformation and thoracic outlet syndrome.

A new simplified cerebral digital subtraction angiography (DSA) has been performed using a fine subcutaneous needle (21G-23G) and minimal volume (1.5 2 ml) contrast medium in 33 cases. Representative angiograms have been presented in 3 cases (one of occlusive cerebrovascular disease, cerebral aneurysm, and superior sagittal sinus thrombosis respectively). Advantages of this method are simple procedure, easy puncture with little carotid injury and almost none of patient's complaints accompanied by dye-injection. Therefore, this technique is very useful in emergency cases, as a screening test in an outpatient clinic, and also in senile cases. Periarterial injection of contrast media was experienced in 5 cases which would be overcome by using a little larger needle like 21G in the future.