Improved vascular opacification in cerebral computed tomography angiography with 80 kVp.

PURPOSE: We sought to intraindividually compare computed tomography angiographies (CTAs) acquired at 80 kVp and 120 kVp with respect to vessel contrast, noise level, and radiation dose. MATERIAL AND METHODS: CTA was performed on a single-slice CT scanner using tube voltages of 80 kVp and 120 kVp in 29 patients with arteriovenous malformations. Mean Hounsfield Units (HU) were evaluated for different vessels and brain parenchyma. To determine contrast-to-noise ratios (CNRs), noise levels were estimated from phantom measurements. RESULTS: The calculated effective dose to male/female patients was 0.4/0.5 mSv for 80 kVp and 0.7/0.8 mSv for 120 kVp. CT density in blood vessels was between 297 and 458 HU for 80 kVp and 152 and 229 HU for 120 kVp (P<0.0001). Despite an increased noise level in the low-voltage images, the CNR was 26-59% higher at 80 kVp than at 120 kVp (P<0.05). CONCLUSION: The use of a reduced tube potential leads to improved CNR in CTA of the cerebral vasculature and a markedly reduced radiation exposure to patients.

Assessment of focal liver reaction by multiphasic CT after stereotactic single-dose radiotherapy of liver tumors.

PURPOSE: To characterize and quantitatively assess focal radiation reactions in the liver after stereotactic single-dose radiotherapy for liver malignancies. METHODS AND MATERIALS: A total of 131 multiphasic CT scans were performed in 36 patients before and after stereotactic radiotherapy for liver tumors. The examination protocol included a nonenhanced scan and contrast-enhanced scans at different times after contrast injection. The volume of the reaction was determined in each scan and the threshold dose calculated using the dose-volume histogram of the treatment plan. RESULTS: Every patient showed a focal radiation reaction on at least one follow-up examination. In 74% of the posttherapeutic scans, a sharply demarcated hypodense area surrounded the treated tumor in the nonenhanced scans. The reaction occurred at a median of 1.8 months (range 1.2-4.6) after radiotherapy. The median threshold dose was 13.7 Gy (range 8.9-19.2). The threshold dose strongly correlated with the time of detection after therapy (r = 0.7). Radiologically, three reaction types were found on the enhanced scans: type 1, portal-venous phase: hypodense and late phase: isodense; type 2, portal-venous phase: hypodense and late phase: hyperdense; and type 3, portal-venous phase: isodense/hyperdense and late phase: hyperdense. Type 1 or 2 reactions were observed significantly earlier than type 3 (p <0.05). The median threshold dose for type 1 or 2 reactions was significantly lower than for type 3 (p <0.05). The reaction volume decreased with longer follow-up (2-4 months: median 40% of initial volume). The reaction types shifted with follow-up: 58% were of type 1 at the initial manifestation and 58% were of type 3 at the next examination thereafter. CONCLUSION: A focal radiation reaction occurs after stereotactic single-dose therapy in the liver. The volume of the reaction decreases and changes its radiologic appearance during follow-up. This reaction has to be differentiated from recurrent tumor.

Detection of rheumatoid arthritis by evaluation of normalized variances of fluorescence time correlation functions.

Fluorescence imaging using the dye indocyanine green as a contrast agent was investigated in a prospective clinical study for the detection of rheumatoid arthritis. Normalized variances of correlated time series of fluorescence intensities describing the bolus kinetics of the contrast agent in certain regions of interest were analyzed to differentiate healthy from inflamed finger joints. These values are determined using a robust, parameter-free algorithm. We found that the normalized variance of correlation functions improves the differentiation between healthy joints of volunteers and joints with rheumatoid arthritis of patients by about 10% compared to, e.g., ratios of areas under the curves of raw data.

Ventricular oversensing: a study of 101 patients implanted with dual chamber defibrillators and two different lead systems.

UNLABELLED: Modern dual chamber ICD systems are able to overcome various sensing problems. However, improvement of their performance is still required. The aim of this study was to assess the sensing function in 101 consecutive patients (84 men, 17 women; mean age 63 +/- 12 years; mean follow-up 24 +/- 4 months) implanted with dual chamber defibrillators and integrated (IB) or dedicated bipolar (DB) lead systems. Follow-up data were analyzed for the presence of ventricular oversensing. Oversensing occurred in 25 (25%) patients, significantly more frequent in patients implanted with IB compared to DB lead systems (21/52 vs 4/49, P = 0.0002). Patients with cardiomyopathies (CMs) were more prone to sensing malfunctions than patients with no CM (12/30 vs 13/71, P = 0.04). T wave oversensing (n = 14), respirophasic ventricular oversensing (n = 4), and P wave oversensing (n = 6) were the most common pitfalls of ventricular sensing. P wave oversensing was unique to the IB lead system. CT scans performed in these patients disclosed the position of the RV coil to be proximal to the tricuspid area. Four patients received inappropriate ICD shocks due to oversensing. In all but two patients who received lead revision, oversensing was resolved by noninvasive means. IN CONCLUSION: (1) ventricular oversensing is a common problem occurring in up to 25% of patients with dual chamber ICDs; (2) P wave oversensing is a ventricular sensing problem affecting function of 11% of dual chamber devices with IB lead systems; (3) IB leads are significantly more susceptible to T wave and P wave oversensing than DB leads; and (4) patients with cardiomyopathies are more prone to oversensing than patients with other heart diseases.