Purpose-To investigate the effect on radiation dose and image quality of the use of additional spectral filtration for dual-energy CT (DECT) imaging using dual-source CT (DSCT).Materials and Methods-A commercial DSCT scanner was modified by adding tin filtration to the high-kV tube, and radiation output and noise measured in water phantoms. Dose values for equivalent image noise were compared among DE-modes with and without tin filtration and singleenergy (SE) mode. To evaluate DECT material discrimination, the material-specific DE ratio for calcium and iodine were determined using images of anthropomorphic phantoms. Data were additionally acquired in 38 and 87 kg pigs, and noise for the linearly mixed and virtual non-contrast (VNC) images compared between DE-modes. Finally, abdominal DECT images from two patients of similar sizes undergoing clinically-indicated CT were compared.Results-Adding tin filtration to the high-kV tube improved the DE contrast between iodine and calcium as much as 290%. Pig data showed that the tin filtration had no effect on noise in the DECT mixed images, but decreased noise by as much as 30% in the VNC images. Patient VNC-images acquired using 100/140 kV with added tin filtration had improved image quality compared to those generated with 80/140 kV without tin filtration.Conclusion-Tin filtration of the high-kV tube of a DSCT scanner increases the ability of DECT to discriminate between calcium and iodine, without increasing dose relative to SECT. Furthermore, use of 100/140 kV tube potentials allows improved DECT imaging of large patients.

These quantitative findings about the relationships among scan acquisition parameters, radiation dose, and image quality have practical implications for using ECG pulsing to reduce radiation doses in MDCT coronary angiography.

SynopsisAs a result of the changes in utilization of imaging procedures that rely on ionizing radiation, the collective dose has increased by over 700% and the annual per-capita dose, by almost 600% over recent years. It is certainly possible that this growing use may have significant effects on public health. Although there are uncertainties related to the accuracy of calculated radiation exposure and the estimated biologic risk, there are measures that can be taken to reduce any potential risks while maintaining diagnostic accuracy. This article will review the existing data regarding biological hazards of radiation exposure associated to medical diagnostic testing, the methodology used to estimate radiation exposure and the measures that can be taken to effectively reduce it. IntroductionIn recent years, reports on radiation exposure resulting from medical imaging have unfailingly attracted intense attention by the media, whose reporting typically emphasizes the risks of such exposure. It is certainly possible that the growing use of imaging procedures that rely on ionizing radiation may have significant effects on public health. However, the potential health risks of ionizing radiation at the levels used in medical imaging are rarely portrayed in a balanced fashion that would highlight the patterns of use of medical imaging, the uncertainties about the magnitude of risk of cancer, or the undeniable benefits of medical imaging in specific scenarios. The purpose of this review is to provide an understanding of 1. the strengths and shortcomings of epidemiologic evaluations of radiation exposure to the general population, 2. the uncertainties related to radiation dosimetry and estimating the biologic risk (including carcinogenesis) resulting from exposure to ionizing radiation, and 3. the measures that can be taken to maximize our opportunities to perform the right study in the right patient with a radiation dose that is as low as reasonably achievable. In keeping with the main theme of the current issue of Cardiology Clinics, our review will focus on cardiac CT imaging in adults.Address for Correspondence: Thomas C Gerber, M.D., Ph.D., Associate Professor of Medicine and Radiology, Division of Cardiovascular Diseases, Mayo Clinic, 4500 San Pablo Road, Jacksonville, Florida 32224, gerber.thomas@mayo.edu. Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. Taken together, the estimated 67 million CT (computed tomography) and 19 million nuclear medicine studies performed in 2006 accounted for 22% of imaging procedures that used ionizing radiation but 75% of the collective E (ex...

Despite numerous animal trials reporting that cell therapy promotes collateral flow, clinical trials have not convincingly shown benefit. Patient-related risk factors are often used to explain these discrepancies. However, during the course of our own angiogenesis studies using mice, we noted large anatomical variability in collateral vessels. The purpose of the present investigation was to define how important this factor might be in determining intervention outcomes. Hindlimb ischemia was induced in BALB/c mice by ligating the superficial femoral artery. After 24 h, animals were treated by injecting the adductor muscle with either control media or cultured mesenchymal stem cells (MSCs). Blood flow recovery was measured using laser-Doppler [laser-Doppler perfusion imaging (LDPI) ratio]. In a second experiment, mice were stratified 24 h after arterial ligation before treatment by using a simple clinical score of the ligated leg: 1, able to flex, mild discoloration; 2, no flexion, mild discoloration; 3, severe discoloration; and 4, any necrosis. Without stratification, blood flow recovery significantly increased in the MSC-treated group ( P < 0.05, n = 6 MSC group, n = 7 media group). In the experiment employing stratification, all differences between the groups disappeared ( n = 11 MSC group, n = 10 media group; P = 0.3). Furthermore, we found a striking inverse correlation between clinical score on day 1 and the LDPI ratio on day 28 ( P < 0.0001; n = 79). Anatomical confirmation of the disparity in preexisting collaterals was found in two different mouse strains using microscopic computed tomography. In conclusion, there is substantial interanimal variability in preexisting collateral flow, and this variability can importantly influence outcome. To overcome this, either animals must be stratified before treatment, the number of animals must be increased substantially, or, preferably, both.

Objective-Vibroacoustography allows imaging of objects on the basis of their acoustic signal emitted during low-frequency (kHz) vibrations produced by 2 intersecting ultrasound beams at slightly different frequencies. This study tested the feasibility of using vibroacoustography to distinguish between normal and calcified femoral arteries in a pig model. Materials and Methods-Thirteen normal porcine femoral arteries, 7 with experimentally induced arterial calcifications, and 1 control artery injected with saline only were scanned in vivo. Images were obtained at 45 kHz using a 3 MHz confocal transducer. The acoustic emission signal was detected with a hydrophone placed on the animal's limb. Images were reconstructed on the basis of the amplitude of the acoustic emission signal. Vessel patency, vessel dimensions, and the extent of calcified plaques were confirmed in vivo by angiography and conventional ultrasound. Excised arteries were reexamined with vibroacoustography, X-ray radiography, and histology.Results-In vivo, vibroacoustography produced high-resolution, speckle-free images with a high level of anatomic detail. Measurements of femoral artery diameter were similar by vibroacoustography and conventional ultrasound (mean difference ± SD, 0.1 ± 0.4 mm). Calcified plaque area measured by different methods was comparable (vibroacoustography, in vivo: 1.0 ± 0.9 cm 2 ; vibroacoustography in vitro: 1.1 ± 0.6 cm 2 ; X-ray radiography: 0.9 ± 0.6 cm 2 ). The reproducibility of measurements was high. Sensitivity and specificity for detecting calcifications were 100% and 86%, respectively, and positive and negative predictive values were 77% and 100%, respectively. Computed tomography (CT) is currently the most widely used noninvasive imaging modality for the quantitative assessment of total calcium burden on the cardiovascular system. However, there are concerns regarding the reproducibility of CT 11 and the X-ray exposure of sequential scanning, for example, to follow the effects of therapeutic interventions. 12-15 Conclusions-VibroacoustographyVibroacoustography is a new ultrasound-based method to detect vascular calcifications. 16-18 This technique uses acoustic radiation pressure produced by 2 intersecting ultrasound beams at slightly different frequencies to induce a vibration (kHz range) of the object from a distance. The image of the object is obtained on the basis of the vibration-induced acoustic emission signal. This signal depends on the stiffness as well as the acoustic properties of the object. 17, 19Vibroacoustography can easily detect calcified deposits in excised tissue specimens scanned in a water bath. The resulting images faithfully resemble X-ray images of specimens. 16-22 However, in vivo, numerous factors could distort the ultrasound and acoustic emission signals.To our knowledge, this is the first in vivo study to test the ability of vibroacoustography to image normal femoral arteries and to detect calcified plaques in femoral arteries of anesthetized swine, an animal model that allows...