Temperature measurements of shocked silica aerogel foam.

We present recent results of equation-of-state (EOS) measurements of shocked silica (SiO_{2}) aerogel foam at the OMEGA laser facility. Silica aerogel is an important low-density pressure standard used in many high energy density experiments, including the novel technique of shock and release. Due to its many applications, it has been a heavily studied material and has a well-known Hugoniot curve. This work then complements the velocity and pressure measurements with additional temperature data providing the full EOS information within the warm dense matter regime for the temperature interval of 1-15 eV and shock velocities between 10 and 40 km/s corresponding to shock pressures of 0.3-2 Mbar. The experimental results were compared with hydrodynamic simulations and EOS models. We found that the measured temperature was systematically lower than suggested by theoretical calculations. Simulations provide a possible explanation that the emission measured by optical pyrometry comes from a radiative precursor rather than from the shock front, which could have important implications for such measurements.

Evaluation of MR angiographic technique in the assessment of thoracic outlet syndrome.

AIM: To evaluate two-dimensional time of flight (2D TOF) and three-dimensional contrast-enhanced magnetic resonance angiographic (3DCE MRA) techniques in the assessment of patients with suspected thoracic outlet syndrome (TOS) of vascular origin. MATERIALS AND METHODS: Fifty-five consecutive examinations, in 51 patients with suspected TOS of vascular origin, were examined using either a 1T or 1.5T Siemens magnetic resonance imaging (MRI) unit, using either 2D TOF (n=13) or 3DCE MRA (n=42). Examinations were performed with the arms abducted (n=27) or both abducted and adducted (n=28). The source images and MIPs were reviewed retrospectively and assessed for image quality and the presence of significant persistent stenosis or impingement (a >60% reduction in the diameter of the subclavian vessels at the thoracic outlet or evidence of post-stenotic dilatation). When significant impingement was identified, the images were reformatted with multiplanar reconstruction to determine the cause. RESULTS: Images were sub-optimal in 53% 2D TOF and 10% 3DCE MRA examinations. 3DCE MRA offered vessel coverage from the aortic arch to the distal axilliary arteries, whereas, 2D TOF sequences gave more limited coverage. Eight patients were found to have significant impingement (n=7) or stenosis (n=1) of the subclavian artery attributable to TOS. 3DCE MRA also demonstrated other relevant significant stenoses not attributable to TOS (n=5). All cases of impingement were either seen only, or more prominently, on sequences with the arms abducted. Reformatting the 3DCE MRA studies demonstrated the cause of impingement. CONCLUSIONS: Both 2D TOF and 3DCE MRA may demonstrate TOS with significant arterial impingement. In comparison with 2D TOF sequences, 3DCE MRA offers extensive vessel coverage, is less prone to artefact and frequently demonstrates the underlying cause of TOS when studies are reformatted. Evidence of impingement should be sought from sequences performed with the arms abducted and venous phase sequences may show corroborative venous impingement.

The UK national study of magnetic resonance imaging as a method of screening for breast cancer (MARIBS).

The UK national study of magnetic resonance imaging as a method of screening for breast cancer (MARIBS) is in progress. The study design, accrual to date, and related research projects are described. Revised accrual rates and expected recruitment are given. 15 cancers have been detected to date, from a total of 1236 screening measurements. This event rate and the tumour grades reported are compared with recent reports from other studies in women at high risk of breast cancer.

Post-radiation sarcomas: a review of the clinical and imaging features in 63 cases.

AIMS: The development of sarcomas is a recognized complication of radiation therapy. We set out to retrospectively review the clinical and therapeutic demographics, as well as the cross-sectional imaging findings in patients with post-radiation sarcomas. MATERIALS AND METHODS: Sixty-three patients with post-radiation sarcomas were identified at a single institution. Computed tomography and/or magnetic resonance imaging was available for all patients. The medical records were reviewed for the primary diagnoses, the radiation history, and the latency period to the development of the sarcoma. RESULTS: There were 43 women and 20 men with a mean age of 52.8 years. The mean radiation dose delivered was 50.1 Gy, with a mean latency period for the development of the sarcoma of 15.5 years. The most common primary diagnoses were breast cancer, lymphoma and head and neck cancer. The most common sarcoma histopathologies were osteosarcoma and malignant fibrous histiocytoma. The most common imaging findings were a soft tissue mass and bone destruction. CONCLUSIONS: Post-radiation sarcomas, while uncommon, are not rare. The imaging findings are not pathognomonic, but an appreciation of the expected latency period may help to suggest the diagnosis. Sheppard, D. G. and Libshitz, H. I. (2001). Clinical Radiology56, 22-29.

Blur identification from vector quantizer encoder distortion.

Blur identification is a crucial first step in many image restoration techniques. An approach for identifying image blur using vector quantizer encoder distortion is proposed. The blur in an image is identified by choosing from a finite set of candidate blur functions. The method requires a set of training images produced by each of the blur candidates. Each of these sets is used to train a vector quantizer codebook. Given an image degraded by unknown blur, it is first encoded with each of these codebooks. The blur in the image is then estimated by choosing from among the candidates, the one corresponding to the codebook that provides the lowest encoder distortion. Simulations are performed at various bit rates and with different levels of noise. Results show that the method performs well even at a signal-to-noise ratio (SNR) as low as 10 dB.

Tubular carcinoma of the breast: mammographic and sonographic features.

OBJECTIVE: The purpose of this study was to define specific mammographic and sonographic features of tubular carcinoma of the breast. MATERIALS AND METHODS: Seventeen pathologically confirmed cases of tubular carcinoma were characterized retrospectively by two radiologists. Mammograms and sonograms were available for all patients. RESULTS: Fifteen of the 17 tubular carcinomas appeared as irregularly shaped masses with spiculated margins on mammography. Sixteen of the 17 masses had central densities. Spicules longer than the diameter of the central lesion were noted in eight (53%) of 15 tubular carcinomas. Eight tubular carcinomas had associated calcifications, with calcifications suspected of being malignant in four cases. On sonography, 15 hypoechoic masses were seen. The margins of the masses on sonography were described as ill-defined in 14 (93%) of the 15 cases. Posterior acoustic shadowing was present in 14 of the 15 cases. CONCLUSION: Tubular carcinomas are usually seen on mammography as irregularly shaped masses with central densities and spiculated margins, and most tubular carcinomas can be identified on sonography as hypoechoic masses with ill-defined margins and posterior acoustic shadowing. Although the mammographic and sonographic features of tubular carcinoma are not sufficiently specific to differentiate tubular carcinomas from radial scars, sonography can be useful for guiding biopsies and evaluating for multifocal and multicentric disease.

Lapped nonlinear interpolative vector quantization and image super-resolution.

This correspondence presents an improved version of an algorithm designed to perform image restoration via nonlinear interpolative vector quantization (NLIVQ). The improvement results from using lapped blocks during the decoding process. The algorithm is trained on original and diffraction-limited image pairs. The discrete cosine transform is again used in the codebook design process to control complexity. Simulation results are presented which demonstrate improvements over the nonlapped algorithm in both observed image quality and peak signal-to-noise ratio. In addition, the nonlinearity of the algorithm is shown to produce super-resolution in the restored images.

Subtraction CT colonography: feasibility in an animal model.

AIM: To determine, in an in vitro animal model, the feasibility of subtracting residual faecal material, during virtual colonoscopy, by uniform mixing of the colonic contents with barium. MATERIALS AND METHODS: Segments of animal colon containing simulated soft-tissue polyps, measuring 3-10 mm, were filled with a faecal substitute consisting of a barium and peanut butter mix that had an attenuation value greater than 200 Hounsfield units. The colonic segments were then examined by CT using 3-10 mm beam collimations, and at pitch factors of 1 and 2. Using subtraction cut-off levels varying from 100-250 Hounsfield units, the barium and peanut butter mix was then subtracted to reveal the underlying polyps. RESULTS: Our optimal technical parameters required 3-mm beam collimation, a helical pitch factor of 2, reconstruction intervals of 3 mm, and a subtraction cut-off level of 150 Hounsfield units. The subtraction technique, in this animal model, had a sensitivity of 94% and a specificity of 80% for polyps measuring greater than 3 mm. CONCLUSION: In this limited animal model, the subtraction technique utilized was technically feasible and had an acceptable sensitivity.

Filling in of radiation therapy-induced bronchiectatic change: a reliable sign of locally recurrent lung cancer.

PURPOSE: To determine if filling in of radiation therapy-induced bronchiectatic change is a reliable computed tomographic (CT) sign of locally recurrent lung cancer. MATERIALS AND METHODS: The study included 28 patients who were free of disease and had stable radiation therapy-induced consolidation in ectatic bronchi at least 9 months after completion of radiation therapy for non-small cell lung cancer. Serial CT scans were retrospectively reviewed for evidence of local recurrence. RESULTS: Filling in of previously patent ectatic bronchi occurred in the 20 patients with recurrent disease. Filling in was the first sign of recurrence in six patients (30%), was seen concurrently with other evidence of local recurrence in 11 (55%), and was seen after the occurrence of other signs in three (15%). Eight patients with stable radiation-induced fibrosis and patent bronchi remained disease free. CONCLUSION: Filling in of radiation therapy-induced bronchiectatic change is a reliable CT sign of locally recurrent lung cancer.

Brachial plexus: demonstration at US.

Five healthy volunteers underwent ultrasonography (US) to determine the feasibility of visualizing the brachial plexus. The roots, trunks, and cords could be identified in the supraclavicular and infraclavicular regions. The roots within the neural foramina and the epidural space could not be evaluated. US may play a complementary role in the evaluation of patients with brachial plexopathy.

Imaging of the portal vein during transjugular intrahepatic portosystemic shunt procedures: a comparison of carbon dioxide and iodinated contrast.

We report our experience with wedged hepatic injections of carbon dioxide (CO2) in the imaging of the portal vein during transjugular intrahepatic portosystemic shunt (TIPS) procedures. In all patients CO2 allowed quick and effective visualization of the portal vein. The image quality and extent of visualization of the portal vein was considered superior to iodinated contrast media in all cases. We suggest that CO2 should be used more frequently during TIPS.

Giant-cell tumor of the tendon sheath arising from the posterior cruciate ligament of the knee: a case report and review of the literature.

The localized form of a giant-cell tumor of the tendon sheath is uncommon and rarely intraarticular. While the sonographic findings are nonspecific, the magnetic resonance (MR) findings can be diagnostic. Relatively homogeneous iso- or marginal hyperintensity on T2-weighted sequences, lack of susceptibility effects due to hemosiderin, the demonstration of a fibrous capsule and the absence of adjacent joint involvement may help to differentiate localized and diffuse forms of giant-cell tumors of tendon sheaths and pigmented villonodular synovitis.

A vector quantizer for image restoration.

This paper presents a novel technique for image restoration based on nonlinear interpolative vector quantization (NLIVQ). The algorithm performs nonlinear restoration of diffraction-limited images concurrently with quantization. It is trained on image pairs consisting of an original image and its diffraction-limited counterpart. The discrete cosine transform is used in the codebook design process to control complexity. Simulation results are presented that demonstrate improvements in visual quality and peak signal-to-noise ratio of the restored images.