A difference list theta on a finite group G is called compressed if is an integer, and it is called compressible if theta+a.G is compressed for some integer a. We discuss the compressibility property, mostly for difference lists on cyclic groups.

Fifty patients were studied prospectively. The extracranial portions of the carotid arteries were examined by duplex sonography and IA-DSA in order to demonstrate haemodynamically significant stenoses or plaques which might give rise to emboli and the findings compared with the pathologic specimens. The results indicate high sensitivity (up to 90%) for more than 75% detection of stenoses. On the other hand ulceration was diagnosed sonographically with an accuracy of 66% and plaque hemorrhage with an accuracy of 56%.

I I Die hochauflösende 1 0 MHz-ß-ßild-SonoI graphie wurde bei 27 Hypertonikern. 24 Diabetikern, 39 hypertonen Diabetikern und 23 gesunden Probanden präventivdiagnostisch zum Nachweis asymptomatischer arteriosklerotischer Läsionen der extrakraniellen .4. carotis eingesetzt. Im Vergleich zum Kontrollkollektiv wiesen Diabetiker und Hypertoniker eirie erhöhte Gefäßwanddicke, jedoch nur die Hypertoniker auch cin gehäuftes Auftreten von Plaques und relevanten KarotisStenosen auf. Die linke A. carotis war bevorzugt betroffen. Es empfiehlt sich nach den vorliegenden Ergebnissen, den präventivdiagnostiscl~en Einsatz der Karotis-BScan-Sonographie aris der Sicht von Nutzen, Aufwand und der Häufigkeit zu erwartender Karotisstenosen auf die Risikopopiilation der Hypertoniker zu beschränken.

High-resolution 10 Mhz sonography was performed on 27 hypertensive patients, 24 diabetics, 39 hypertensive diabetics and 23 normal people in order to demonstrate asymptomatic arteriosclerotic lesions of the extra-cranial carotid artery. Compared with normal controls, diabetics and hypertensives showed increased vessel wall thickness, but only patients with hypertension showed a higher frequency of plaques and relevant carotid stenoses. The left carotid artery is involved more often. On the basis of these results, it appears that the use of B-scan sonography as a preventive measure should be limited to the high-risk hypertensive population.

One hundred and five carotid stenoses were examined by B-scan sonography (10 MHz) and the results compared with the macroscopic and histological appearances. The most important sonographic findings depended on surface structure, echo amplitude and the presence of acoustic shadows. From the therapeutic point of view, B-scan sonography is complementary to angiography by evaluating the morphology of the plaques, particularly if the indications for surgery are ill-defined.

Isolated aneurysms of the iliac arteries are rare. They must be considered as a disease pattern of their own as against aneurysms of the abdominal aorta because of the specific anatomical conditions in the pelvis. The clinical symptomatology is determined by their localisation and topographical relationships within the pelvis; this can give rise to problems in differential diagnosis primary urological, neurological or gastrointestinal diseases. The prognosis is decisively determined by early and correct diagnosis because of the danger of rupture. Sonography, computed tomography and angiography are indispensable aids in preoperative planning.

Following rectal irrigation, it is possible to demonstrate the ileo-caecal valve sonographically, using a right para-inguinal approach. The shape, position and motility of the valve can be evaluated. The normal valve is two to three mm. thick, similar to the colonic wall, but its lips are thickened. Two distinct mechanisms are responsible for opening the valve, the ileocolic pressure gradient and relaxation of the circular muscle round the valve. The resulting intraluminal flow can be quantified by duplex sonography. The information may be of diagnostic and therapeutic significance, particularly during childhood.

Contrast administration through the superior mesenteric or splenic arteries provided additional information in 22 out of 31 patients, when compared with intravenous contrast bolus for CT of the liver. In 11 patients, the demonstration of a tumour lead to a change in treatment. False positive findings occurred in four of the 31 patients. In 2 patients intrahepatic lesions were overlooked, but were found during angiography carried out at the same examination. The diagnosis of intrahepatic space-occupying lesions is discussed as well as the CT appearances of portal-venous liver perfusion.

Contrast administration through the superior mesenteric or splenic arteries provided additional information in 22 out of 31 patients, when compared with intravenous contrast bolus for CT of the liver. In 11 patients, the demonstration of a tumour lead to a change in treatment. False positive findings occurred in four of the 31 patients. In 2 patients intrahepatic lesions were overlooked, but were found during angiography carried out at the same examination. The diagnosis of intrahepatic space-occupying lesions is discussed as well as the CT appearances of portal-venous liver perfusion.

This is a report on an intra-abdominally fixed T-drain. Surgical removal was avoided without complications by detaching it with a ring stripper.

Following rectal irrigation, it is possible to demonstrate the ileo-caecal valve sonographically, using a right para-inguinal approach. The shape, position and motility of the valve can be evaluated. The normal valve is two to three mm. thick, similar to the colonic wall, but its lips are thickened. Two distinct mechanisms are responsible for opening the valve, the ileocolic pressure gradient and relaxation of the circular muscle round the valve. The resulting intraluminal flow can be quantified by duplex sonography. The information may be of diagnostic and therapeutic significance, particularly during childhood.

Fifty-one patients, on whom a total of 64 carotid thromboendarterectomies had been performed, were followed up by duplex sonography. Five asymptomatic occlusions of the internal carotid artery (8%) and one occlusion of the common carotid artery were found. Two patients (3%) developed a restenosis of more than 50% and another two patients a restenosis of less than 50%. Changes in the vessel wall not producing significant luminal change were observed in another 18 cases (28%). Thirty-six of the operated vessels (56%) showed no change.