A linear array silicon pixel detector: images of a mammographic test object and evaluation of delivered doses.

We present images of a mammographic test object obtained using a linear array silicon pixel detector capable of single-photon counting. The detector pixel size was 200 x 300 microns2 and images were acquired by scanning the test object between the laminar detector and the x-ray source with a scanning step of 100 microns. A molybdenum anode tube was used with two different filtrations: 2 mm aluminium and 25 microns molybdenum. Conventional film-screen images were also obtained in order to compare spatial and contrast resolution. In our digital images it is possible to recognize low-contrast details having dimensions smaller than or equal to the dimensions of details visible by means of a clinical mammographic unit. The detection of microcalcifications smaller than 150 microns was possible only when using the Mo filtration. However a copper wire of 50 microns diameter was detectable when embedded in a simulated tissue. We discuss in detail the mean glandular doses (MGDs) delivered during the image acquisition. The MGDs necessary to obtain good-quality images are always smaller than at a conventional mammographic unit. Since MGDs depend on the x-ray spectrum, the dose reduction becomes larger when the applied spectrum is harder than in film-screen acquisition (Al filtration and 35 kVp).

Diagnostic imaging and interventional therapy of hepatocellular carcinoma.

Diagnostic imaging has many important roles in the management of patients with hepatocellular carcinoma (HCC). In diagnosis, lipiodol CT (LCT) has been shown to be the most sensitive imaging modality (90-97%) for all sizes of lesions; all other modalities have high sensitivities for lesions 1-3 cm but low sensitivities for lesions < 1 cm (ultrasound 33-37%, conventional CT 20-42% and digital subtraction angiography 40-55%). All imaging modalities understage HCC. Once again LCT is the most accurate method of evaluating the extent of tumour, but even this method does not identify all satellite nodules. Ultrasound has been proposed as a screening method, but this cannot be justified on the basis of its results or cost benefit analysis. Both CT and dynamic MRI play useful roles in evaluating the efficacy and follow-up of patients undergoing chemoembolization (TACE) and percutaneous ethanol injection (PEI). Although surgery remains the best treatment of HCC, it is unsuitable in most of the cases which would be better treated with interventional therapy. This article presents a review of the literature regarding the use of TACE, PEI or a combination of both procedures in the treatment of HCC. A multicentric study has shown that patients with monofocal lesions less than 5 cm in diameter are better treated with PEI, which is therefore a good alternative to the surgical treatment; patients with multifocal lesions (maximum of three lesions) show a better survival with TACE. Combined treatment with TACE and PEI proves to be effective in patients with large HCC.

Abdominal contrast tomography in the evaluation of the gall-bladder and biliary tract (with emphasis upon jaundiced patients).

Tomography of the right upper quadrant after the rapid intravenous infusion of a high dose of contrast medium is a valuable method of investigation of hepato-biliary disease. Gall-bladder wall opacification may be normal, but if the wall is thicker than 2 mm and if irregular, it indicates inflammatory or calculous disease. Gall-bladder area greater than 35 cm2 indicates bile duct obstruction. This also causes the ducts to appear as lucent bands within the opacified liver parenchyma. Secondary deposits in the liver may also become visible. Various patterns of these findings are described which suggest specific biliary abnormalities.

Effects of a dimeric vs a monomeric nonionic contrast medium on renal function in patients with mild to moderate renal insufficiency: a double-blind, randomized clinical trial.

The efficacy and safety of nonionic dimeric contrast media in subjects with impaired renal function is largely unknown. The present study was aimed at determining the risk of tubular nephrotoxicity in patients with mild to moderate renal insufficiency who underwent intravenous urography (IVU) with the nonionic dimeric contrast agent iodixanol (Visipaque, Nycomed Imaging, Oslo, Norway). In a double-blind protocol 64 patients (55 males; mean age 68.3 years) with serum creatinine between 135 and 265 micromol/l who were to undergo IVU were randomized to receive iodixanol (a nonionic dimer) or iopromide (a nonionic monomer), 600 mg I/kg b. w. Renal function was evaluated before and 1 h, 6 h, 24 h, 48 h and 7 days after IVU with analysis of serum creatinine, urinary enzymes alanylaminopeptidase and N-acetyl-beta-glucosaminidase, and urinary microproteins alpha-1-microglobulin and albumin. Renal function remained stable in both contrast medium groups during the follow-up period. No statistically significant differences were observed between the monomer and the dimer in terms of urinary enzyme and microprotein excretion or serum creatinine. Transient radiocontrast-induced nephropathy developed in 1 patient who had received iodixanol. The administration of the nonionic dimeric contrast medium iodixanol, or of the nonionic monomer iopromide, entailed a low nephrotoxic potential in patients with mild to moderate renal insufficiency undergoing excretory urography.

Mammography with synchrotron radiation: phase-detection techniques.

The authors evaluated the effect on mammographic examinations of the use of synchrotron radiation to detect phase-perturbation effects, which are higher than absorption effects for soft tissue in the energy range of 15-25 keV. Detection of phase-perturbation effects was possible because of the high degree of coherence of synchrotron radiation sources. Synchrotron radiation images were obtained of a mammographic phantom and in vitro breast tissue specimens and compared with conventional mammographic studies. On the basis of grades assigned by three reviewers, image quality of the former was considerably higher, and the delivered dose was fully compatible.