Current Issue : July - September Volume : 2013 Issue Number : 3 Articles : 6 Articles
Background: Aggressive dose reduction strategies for cardiac CT require the prospective selection of limited\r\ncardiac phases. At lower heart rates, the period of mid-diastole is typically selected for image acquisition. We aimed\r\nto identify the effect of heart rate on the optimal CT acquisition phase within the period of mid-diastole.\r\nMethods: We utilized high temporal resolution tissue Doppler to precisely measure coronary motion within diastole.\r\nTissue-Doppler waveforms of the myocardium corresponding to the location of the circumflex artery (100 patients) and\r\nmid-right coronary arteries (50 patients) and the duration and timing of coronary motion were measured. Using\r\nregression analysis an equation was derived for the timing of the period of minimal coronary motion within the RR\r\ninterval. In a validation set of 50 clinical cardiac CT examinations, we assessed coronary motion artifact and the effect of\r\nusing a mid-diastolic imaging target that was adjusted according to heart rate vs a fixed 75% phase target.\r\nResults: Tissue Doppler analysis shows the period of minimal cardiac motion suitable for CT imaging decreases almost\r\nlinearly as the RR interval decreases, becoming extinguished at an average heart rate of 91 bpm for the circumflex\r\n(LCX) and 78 bpm for the right coronary artery (RCA). The optimal imaging phase has a strong linear relationship with\r\nRR duration (R2 = 0.92 LCX, 0.89 RCA). The optimal phase predicted by regression analysis of the tissue-Doppler\r\nwaveforms increases from 74% at a heart rate of 55 bpm to 77% at 75 bpm. In the clinical CT validation set, the optimal\r\nCT acquisition phase similarly occurred later with increasing heart rate. When the selected cardiac phase was adjusted\r\naccording to heart rate the result was closer to the optimal phase than using a fixed 75% phase. While this effect was\r\nstatistically significant (p < 0.01 RCA/LCx), the mean effect of heart-rate adjustment was minor relative to typical\r\nbeat-to-beat variability and available precision of clinical phase selection.\r\nConclusion: High temporal resolution imaging of coronary motion can be used to predict the optimal acquisition\r\nphase in cardiac CT. The optimal phase for cardiac CT imaging within mid-diastole increases with increasing heart rate\r\nalthough the magnitude of change is small....
Background: Bias with regard to participation in epidemiological studies can have a large impact on the\r\ngeneralizability of results. Our aim was to investigate the direction and magnitude of potential bias by comparing\r\nhealth-related factors among participants and non-participants in a MRI-study based on HUNT, a large Norwegian\r\nhealth survey.\r\nMethods: Of 14,033 individuals aged 50ââ?¬â??65, who had participated in all three large public health surveys within the\r\nNorwegian county of Nord-TrÃ?¸ndelag (HUNT 1, 2 and 3), 1,560 who lived within 45 minutes of travel from the city\r\nof Levanger were invited to a MRI study (MRI-HUNT). The sample of participants in MRI-HUNT (n = 1,006) were\r\ncompared with those who were invited but did not participate (n = 554) and with those who were eligible but not\r\ninvited (n = 12,473), using univariate analyses and logistic regression analyses adjusting for age and education level.\r\nResults: Self-reported health did not differ between the three groups, but participants had a higher education level\r\nand were somewhat younger than the two other groups. In the adjusted multivariate analyses, obesity was\r\nconsistently less prevalent among participants. Significant differences in blood pressure and cholesterol were also\r\nfound.\r\nConclusion: This is the first large population-based study comparing participants and non-participants in an MRI\r\nstudy with regard to general health. The groups were not widely different, but participants had a higher level of\r\neducation, and were less likely to be obese and have hypertension, and were slightly younger than nonparticipants.\r\nThe observed differences between participants and non-invited individuals are probably partly\r\nexplained by the inclusion criterion that participants had to live within 45 minutes of transport to where the MRI\r\nexamination took place. One will expect that the participants have somewhat less brain morphological changes\r\nrelated to cardiovascular risk factors than the general population. Such consequences underline the crucial\r\nimportance of evaluation of non-participants in MRI studies....
Background: The purpose of this study was to evaluate the utility of a noninvasive ultrasound-based method,\r\nvibro-acoustography (VA), for thyroid imaging and determine the feasibility and challenges of VA in detecting\r\nnodules in thyroid.\r\nMethods: Our study included two parts. First, in an in vitro study, experiments were conducted on a number of\r\nexcised thyroid specimens randomly taken from autopsy. Three types of images were acquired from most of the\r\nspecimens: X-ray, B-mode ultrasound, and vibro-acoustography. The second and main part of the study includes\r\nresults from performing VA and B-mode ultrasound imaging on 24 human subjects with thyroid nodules. The\r\nresults were evaluated and compared qualitatively.\r\nResults: In vitro vibro-acoustography images displayed soft tissue structures, microcalcifications, cysts and nodules\r\nwith high contrast and no speckle. In this group, all of US proven nodules and all of X-ray proven calcifications of\r\nthyroid tissues were detected by VA. In vivo results showed 100% of US proven calcifications and 91% of the US\r\ndetected nodules were identified by VA, however, some artifacts were present in some cases.\r\nConclusions: In vitro and in vivo VA images show promising results for delineating the detailed structure of the\r\nthyroid, finding nodules and in particular calcifications with greater clarity compare to US. Our findings suggest\r\nthat, with further development, VA may be a suitable imaging modality for clinical thyroid imaging....
Background: Circle contact lenses, also known as color contact lenses and big eye contact lenses, are a type of\r\ncosmetic contact lens. It is not generally known that a circle contact lens usually contains iron oxide and other\r\nmetals, which means their use during magnetic resonance imaging (MRI) is a potential hazard.\r\nCase presentation: We present a rare case of incidental discovery of circle contact lenses by MRI and MRI images\r\nof circle lenses in vitro.\r\nConclusions: Circle contact lenses usually contain iron oxide, which is a known source of susceptibility artifact on\r\nMRI. Not only radiologists and radiographers but also referring physicians should be familiar with the imaging\r\nfindings and potential risk of scanning circle contact lenses by MRI....
Background: To evaluate the contrast agent performance of Gd-EOB-DTPA and Gd-BOPTA for detection and\r\nassessment of extrahepatic findings, semi-quantitatively and qualitatively.\r\nMethods: 13 patients with 19 extrahepatic lesions underwent liver MRI with Gd-EOB-DTPA and Gd-BOPTA.\r\nQuantitative and relative SNR measurements were performed in each dataset in the arterial and portalvenous phase\r\nwithin the extrahepatic lesion, aorta, inferior vena cava, portal vein, spleen, pancreas and renal cortex. Further,\r\nrelative CNR measurements were performed. Three readers assessed contrast quality using a five-point scale and\r\nchoosing the preferred image dataset. Statistical analysis consisted of a Student�s t-test with p < 0.05 deemed\r\nsignificant, a weighted kappa statistic for assessment of interobserver variability and an ROC analysis.\r\nResults: Mean SNR after injection of Gd-BOPTA was significantly higher compared with Gd-EOB-DTPA for all\r\nmeasurements (p < 0.05). Mean relative SNR was also higher for Gd-BOPTA, but without being statistically\r\nsignificant. There was no significant difference in relative CNR. Interobserver agreement for selection of image\r\npreference was moderate (mean weighted kappa 0.485). The area under the curve for the ROC-analysis regarding\r\ncontrast agent performance was 0.464.\r\nConclusion: Even though mean SNR is significantly higher after injection of Gd-BOPTA compared with Gd-EOB\r\n-DTPA, there is no significant difference in relative CNR with extrahepatic lesions being assessed equally well. Visual\r\nimpression may differ after injection of Gd-EOB-DTPA, but does not influence image interpretation. Extrahepatic\r\nfindings can be assessed similarly to MRI after injection of Gd-BOPTA....
Background: Diffusion tensor imaging (DTI) is increasingly used in various diseases as a clinical tool for assessing\r\nthe integrity of the brainââ?¬â?¢s white matter. Reduced fractional anisotropy (FA) and an increased apparent diffusion\r\ncoefficient (ADC) are nonspecific findings in most pathological processes affecting the brainââ?¬â?¢s parenchyma.\r\nAt present, there is no gold standard for validating diffusion measures, which are dependent on the scanning\r\nprotocols, methods of the softwares and observers. Therefore, the normal variation and repeatability effects on\r\ncommonly-derived measures should be carefully examined.\r\nMethods: Thirty healthy volunteers (mean age 37.8 years, SD 11.4) underwent DTI of the brain with 3T MRI.\r\nRegion-of-interest (ROI) -based measurements were calculated at eleven anatomical locations in the pyramidal\r\ntracts, corpus callosum and frontobasal area. Two ROI-based methods, the circular method (CM) and the freehand\r\nmethod (FM), were compared. Both methods were also compared by performing measurements on a DTI\r\nphantom. The intra- and inter-observer variability (coefficient of variation, or CV%) and repeatability (intra-class\r\ncorrelation coefficient, or ICC) were assessed for FA and ADC values obtained using both ROI methods.\r\nResults: The mean FA values for all of the regions were 0.663 with the CM and 0.621 with the FM. For both\r\nmethods, the FA was highest in the splenium of the corpus callosum. The mean ADC value was 0.727 Ã?â??10-3 mm2/s\r\nwith the CM and 0.747 Ã?â??10-3 mm2/s with the FM, and both methods found the ADC to be lowest in the corona\r\nradiata. The CV percentages of the derived measures were < 13% with the CM and < 10% with the FM. In most of\r\nthe regions, the ICCs were excellent or moderate for both methods. With the CM, the highest ICC for FA was in the\r\nposterior limb of the internal capsule (0.90), and with the FM, it was in the corona radiata (0.86). For ADC, the\r\nhighest ICC was found in the genu of the corpus callosum (0.93) with the CM and in the uncinate fasciculus (0.92)\r\nwith FM.\r\nConclusions: With both ROI-based methods variability was low and repeatability was moderate. The circular\r\nmethod gave higher repeatability, but variation was slightly lower using the freehand method. The circular method\r\ncan be recommended for the posterior limb of the internal capsule and splenium of the corpus callosum, and the\r\nfreehand method for the corona radiata....
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