Low radiation dose in computed tomography: the role of iodine.

Recent approaches to reducing radiation exposure during CT examinations typically utilize automated dose modulation strategies on the basis of lower tube voltage combined with iterative reconstruction and other dose-saving techniques. Less clearly appreciated is the potentially substantial role that iodinated contrast media (CM) can play in low-radiation-dose CT examinations. Herein we discuss the role of iodinated CM in low-radiation-dose examinations and describe approaches for the optimization of CM administration protocols to further reduce radiation dose and/or CM dose while maintaining image quality for accurate diagnosis. Similar to the higher iodine attenuation obtained at low-tube-voltage settings, high-iodine-signal protocols may permit radiation dose reduction by permitting a lowering of mAs while maintaining the signal-to-noise ratio. This is particularly feasible in first pass examinations where high iodine signal can be achieved by injecting iodine more rapidly. The combination of low kV and IR can also be used to reduce the iodine dose. Here, in optimum contrast injection protocols, the volume of CM administered rather than the iodine concentration should be reduced, since with high-iodine-concentration CM further reductions of iodine dose are achievable for modern first pass examinations. Moreover, higher concentrations of CM more readily allow reductions of both flow rate and volume, thereby improving the tolerability of contrast administration.

Comparison of inversion recovery and contrast-enhanced T1-weighted fat-suppressed sequences for the staging of cervical lymphoma.

In a retrospective analysis with two readers blinded to the clinical information, coronal short tau inversion recovery (STIR) images were compared to contrast-enhanced fat-saturated T1-weighted imaging (T1 CEfs) in 51 cases of cervical lymphoma. Interrater reliability was good to excellent. Although sensitivity and subjective quality of the STIR sequence were higher than those of the T1 CEfs sequence (sensitivity 85%/72%, respectively), specificity (82%/95%) as well as positive likelihood ratio (4.65/15.93) was much lower. Therefore, contrast-enhanced sequences should be included in the primary staging of lymphoma.

Small bowel imaging with MRI.

Magnetic resonance imaging (MRI) has evolved as a powerful tool for the assessment of the small bowel. Strengths of MRI include the superb soft-tissue contrast, lack of radiation exposure, and the implementation of fast scanning techniques. Clinically relevant findings such as inflammation and tumor disease can be well-depicted. We describe in this article current techniques of small bowel MRI including its implementation and clinical outcome in comparison to other radiological and endoscopic procedures.

Coronary MR imaging: navigator echo biofeedback increases navigator efficiency--initial experience.

RATIONALE AND OBJECTIVES: The aim of this study was to investigate whether a respiratory biofeedback system could increase navigator efficiency and maintain image quality compared to conventional respiratory-gated magnetic resonance coronary angiography (MRCA). MATERIALS AND METHODS: Eighteen healthy volunteers underwent MRCA using three different respiratory-gating protocols. A conventional expiratory free-breathing (FB) sequence was compared to two approaches using navigator echo biofeedback (NEB), a midinspiratory approach (NEBin) and an expiratory approach (NEBex). Navigator data reflecting the position of the diaphragm relative to a 3-mm gating window were made available to the subject using a video projector in combination with a Plexiglas screen and mirror goggles. Image quality was graded by two radiologists in consensus using a visual score ranging from 1 (not visible) to 4 (excellent vessel depiction). RESULTS: The NEB approaches improved navigator efficiency (71.1% with NEBex and 68.0% with NEBin vs 42.2% with FB), thus reducing total imaging time. This difference was statistically significant (P(NEBin)=.007; P(NEBex)=.001). Image quality in the NEBex group was comparable to that in the FB group (median score, 2.44 vs 2.52), but it proved to be significantly lower (median score, 1.94 vs 2.52) for the right coronary artery and the left anterior descending coronary artery in the NEBin group. CONCLUSION: NEB maintains image quality and significantly increases navigator efficiency, thereby decreasing total imaging time by about 40% compared to a conventional FB acquisition strategy.

Aortic wall thickness assessed by multidetector computed tomography as a predictor of coronary atherosclerosis.

Purpose of this study was the evaluation of the thoracic aortic wall thickness as a potential identifier of patients at increased risk for future cardiac events. Thoracic aortic wall thickness was measured with MDCT in 160 patients. The CT-scans were implemented as non-invasive coronary angiography studies. Relationships between aortic wall thickness, sex, age, major risk factors and atherosclerotic plaque burden of the coronary arteries were explored. Higher values of maximum aortic wall thickness of the descending aorta (women P = 0.02, men P = 0.01) were found in patients with coronary atherosclerosis, compared to patients with same gender but excluded atherosclerosis. Aortic wall thickness of the mid-portion of the descending aorta of 3.0 mm is associated with coronary artery disease (CAD) with a specificity of 96.6% (sensitivity 27.5%) and a positive predictive value (PPV) of 93.3%. For patients with two or more major risk factors and a maximum wall thickness of equal or more than 2.6 mm we found a PPV of 100%. We conclude that measurements of maximum wall thickness of the descending aorta are a potential tool for detecting patients with coronary atherosclerosis. The potential effect of combining measurements of aortic wall thickness at routine chest CT studies with a possible cardiovascular screening is substantial and merits further study.

The cisterna chyli: prevalence, characteristics and predisposing factors.

The purpose of this study was to determine the prevalence and characteristics of the cisterna chyli (CC) in a large 3,000-patient cohort and to identify potential predisposing factors for the development of a CC. Three thousand consecutive contrast-enhanced CT examinations (1,261 women, 1,739 men, mean age 61.0 years) of the chest and/or abdomen were included in this retrospective study. Imaging characteristics of the CC (size, attenuation, location) were documented as well as clinical information (malignant disease, pattern of metastasis). A CC was found in 16.1% of the patients with an average volume of 302 microl. The mean attenuation was 4.8 Hounsfield units (HU). Twenty percent of the CC showed CT densities of 15 HU and higher. Patients with malignancies showed a significantly (p < 0.001) higher prevalence of CC (340/1,757, 19.4%) than patients with benign conditions (144/1,243, 11.6%). Especially the finding of a large CC (>1,000 microl) represents an elevated relative risk for malignancy of 1.7 (p = 0.0017). We found a significant association between malignant disease and the presence and size of a cisterna chyli. Identifying the continuity between the CC and the thoracic duct is a safer method to distinguish a CC from retrocrural lymph nodes than near-water CT attenuation alone.

Electronic colon-cleansing for CT colonography: diagnostic performance.

BACKGROUND: The purpose of this study was to evaluate whether an electronic-colonic-cleansing (ECC) algorithm is beneficial for the diagnostic performance compared to a CT colonography (CTC) evaluation without electronic cleansing in tagged datasets. METHODS: Two blinded readers evaluated CTC datasets from 79 patients with 153 colorectal polyps confirmed by optical colonoscopy. Cases were read in a randomized order with and without the use of electronic colon-cleansing software. Per-polyp sensitivity, per-polyp/per-patient specificity and reading times (with and without ECC) have been calculated and reported. RESULTS: Per-polyp sensitivity for polyps >6 mm without using ECC was 60.4% (Reader 1: 59.7%, Reader 2: 61.1%), while polyps >10 mm were detected with a sensitivity of 58.3% (Reader 1: 66.7%, Reader 2: 50%). On electronically cleansed datasets, the sensitivity was 73.6% (Reader 1: 76.4%; Reader 2: 70.8%) for polyps >6 mm and 83.3% (Reader 1: 83.3%; Reader 2: 83.3%), respectively. Per-patient specificity was 75% without using cleansing (Reader 1: 68%, Reader 2: 82%) and 81.5% using ECC (Reader 1: 86%, Reader 2: 77%). CONCLUSION: Reading CTC cases using ECC software improves sensitivity in detecting clinically relevant colorectal polyps.

MRI-based separation of congenital and acquired vertebrobasilar artery anomalies in ischemic stroke of the posterior circulation.

BACKGROUND AND PURPOSE: Stroke MRI protocols provide useful information about underlying vessel pathologies in the anterior circulation by means of intracranial time-of-flight angiography. However, these protocols mostly fail in the posterior circulation to differentiate between congenital variants and secondary thrombosis. Therefore, a high-resolution anatomic True Fast Imaging in Steady State Precession sequence, added to a commonly used stroke imaging protocol, was evaluated. METHODS: MRIs of all emergency admissions to the stroke unit over 2 months were analyzed. Variations in the posterior circulation as displayed by time-of-flight and by the True Fast Imaging in Steady State Precession sequence, respectively, were graded by 2 readers blinded to the diagnosis. RESULTS: In the time-of-flight angiography, 50% of patients presented with distinctive vertebrobasilar alterations. Half of these were judged as high-grade anomalies, of which the True Fast Imaging in Steady State Precession sequence identified 25% as hypoplasia. In 40% of all patients with posterior ischemia, the True Fast Imaging in Steady State Precession sequence confirmed an acquired occlusion of the vertebrobasilar arteries. CONCLUSIONS: The addition of an anatomic (True Fast Imaging in Steady State Precession) to a functional sequence (time-of-flight) in stroke MRI protocols enables the differentiation between artery occlusions and hypoplastic variants of the vertebral arteries.

Comparison of manual and automated size measurements of lung metastases on MDCT images: potential influence on therapeutic decisions.

PURPOSE: The goal of this study was to evaluate the influence of automated measurement of diameter, area, and volume from chest CT scans on therapeutic decisions of lung nodules as compared to manual 2-D measurements. PATIENTS AND METHOD: The retrospective study involved 25 patients with 75 lung metastases. Contrast enhanced CT scans (16 row) of the lung were performed three times during chemotherapy with a mean time interval of 67.9 days between scans. In each patient, three metastases were evaluated (n=225). Automatic measurements were compared to manual assessment for the following parameters: diameter, area, and density. The influence on the therapeutic decisions was evaluated using the RECIST criteria. RESULTS: The maximum diameter measured by the automatic application was on an average 27% (S.D. 39; CI: 0.22-0.32; p<0.0001) higher than the maximum diameter with manual assessment, and the differences depended on metastases size. Based on diameter calculation, manual and automated assessment disagreed in up to 32% of therapeutic decisions. Volumetric assessment tended towards more changes in therapy as compared to diameter calculation. The calculation of mean transversal area of metastases was 36% (S.D. 0.305; CI: -0.40 to -0.32; p<0.0001) less with automated measurement. Therapeutic strategy would be changed in up to 25.7% of nodules using automated area calculation. Automated assessment of nodules' area and volume could influence the therapeutic decisions in up to 51.4% of all nodules. Density of the nodules was not validated to determine the influence on therapeutic decisions. CONCLUSION: There is a discrepancy between the manual and automated size measurement of lung metastases which could be significant.

CT colonography: an update.

Computed tomographic (CT) colonography (CTC)--also known as "virtual colonoscopy"--was first described more than a decade ago. As advancements in scanner technology and three-dimensional (3D) postprocessing helped develop this method to mature into a potential option in screening for colorectal cancer, the fundamentals of the examination remained the same. It is a minimally invasive, CT-based procedure that simulates conventional colonoscopy using 2D and 3D computerized reconstructions. The primary aim of CTC is the detection of colorectal polyps and carcinomas. However, studies reveal a wide performance variety in regard to polyp detection, especially for smaller polyps. This article reviews the available literature, discusses established indications as well as open issues and highlights potential future developments of CTC.

Objective evaluation of vessel attenuation in multidetector-row computed tomographic pulmonary angiography using high-density contrast material for the detection of pulmonary embolism.

OBJECTIVE: The purpose of this study was to analyze the pulmonary vessel enhancement obtainable using high-density contrast material and saline flushing with automated bolus tracking for multidetector-row computed tomographic (MDCT) pulmonary angiography in a routine clinical setting. METHODS: Attenuation values of pulmonary vessels were retrospectively measured in 51 CT scans performed on a 40-channel MDCT for unselected emergency patients with clinically suspected pulmonary embolism. RESULTS: Mean vascular attenuation measured 326.7 +/- 104 Hounsfield units (HU) in the pulmonary trunk and 299.1 +/- 102 HU in the left distal lower lobe artery. Mean vascular attenuation values in the distal lower lobe artery were equal or higher than 150 HU for 94.1% (48/51) of patients. CONCLUSIONS: In conclusion, the combination of high-density contrast media and saline flushing with automated bolus tracking on a fast CT scanner reliably results in a homogenously high attenuation of pulmonary vessels, allowing precise delineation of clots down to the subsegmental level in MDCT pulmonary angiography.

Computer-aided detection in computer tomography colonography: a review.

BACKGROUND: Colorectal cancer is one of the most common causes of death from cancer. Computer tomography colonography (CTC) - also known as 'virtual colonoscopy' - is a minimally invasive, CT-based procedure that can simulate conventional colonoscopy using three-dimensional computerized reconstructions. In an attempt to improve the method further, a lot of research emphasis has been put on computer-aided detection (CAD) to overcome potential limitations of this examination. OBJECTIVE: This review recapitulates basic principles of CTC and CAD and highlights the importance of this method as a tool for screening for colorectal cancer. METHODS: This article reviews the current literature on CAD used with CT colonography. RESULTS/CONCLUSION: CAD potentially helps to improve the detection rate for adenomas, decrease interobserver variability and data set interpretation time.

Multiple gastrointestinal stromal tumors and bilateral pheochromocytoma in neurofibromatosis.

The coincidence of a gastrointestinal stromal tumor (GIST) and a neuroendocrine tumor (NET) in neurofibromatosis type 1 (NF1) is described only five times within the literature. We report on a 63 year old Caucasian female with the rare condition of neurofibromatosis type 1 coinciding with recurrent gastrointestinal stromal tumor plus bilateral pheochromocytoma (PCC). After a history of palpitations and dizziness that lasted for years, a left adrenal mass was detected by CT. Laparotomy revealed a pheochromocytoma of the left adrenal gland while an ileoterminal GIST was found incidentally intraoperatively. After six months contralateral PCC and multiple recurrent GIST were resected again. After four years the patient is doing well without any signs of further recurrent tumors. Discussion includes review of the literature.

MR neurography with multiplanar reconstruction of 3D MRI datasets: an anatomical study and clinical applications.

INTRODUCTION: Extracranial MR neurography has so far mainly been used with 2D datasets. We investigated the use of 3D datasets for peripheral neurography of the sciatic nerve. METHODS: A total of 40 thighs (20 healthy volunteers) were examined with a coronally oriented magnetization-prepared rapid acquisition gradient echo sequence with isotropic voxels of 1 x 1 x 1 mm and a field of view of 500 mm. Anatomical landmarks were palpated and marked with MRI markers. After MR scanning, the sciatic nerve was identified by two readers independently in the resulting 3D dataset. RESULTS: In every volunteer, the sciatic nerve could be identified bilaterally over the whole length of the thigh, even in areas of close contact to isointense muscles. The landmark of the greater trochanter was falsely palpated by 2.2 cm, and the knee joint by 1 cm. The mean distance between the bifurcation of the sciatic nerve and the knee-joint gap was 6 cm (+/-1.8 cm). The mean results of the two readers differed by 1-6%. CONCLUSION: With the described method of MR neurography, the sciatic nerve was depicted reliably and objectively in great anatomical detail over the whole length of the thigh. Important anatomical information can be obtained. The clinical applications of MR neurography for the brachial plexus and lumbosacral plexus/sciatic nerve are discussed.

Bowel preparation for CT-colonography: comparison of two different cleansing protocols.

OBJECTIVE: Comparison of cleansing effects and colonic distension observed with two polyethyleneglycol-solution (PEG) containing bowel preparation techniques prior to CT-colonography (CTC). MATERIALS AND METHODS: One hundred and three patients that received CTC in our institution were retrospectively evaluated. Fifty-one patients received preparation 1 (BP1; based on a GoLytely formulation+bisacodyl), 52 preparation 2 (BP2; based on a NuLytely formulation+bisacodyl). On multi-planar-reformatted (MPR) images, fluid residuals and colon distension were assessed in five colonic segments, from the ascending colon to the rectum. RESULTS: On average, significantly (p<0.001) lower fluid residuals were assesses when using BP2 regardless of the patient position. In prone position, a significantly lower fluid level was observed in the sigmoid using bowel preparation 2. The average maximum diameter measured for the whole colon was 5.2+/-0.6 cm in prone position and 4.8+/-0.6 cm in the supine position in BP1 (p<0.01). In BP2 the average maximum diameter measured for the whole colon was 5.3+/-0.6 cm in prone position and 4.7+/-0.5 cm in supine position, respectively (p<0.001). CONCLUSION: Overall, lower fluid residuals were scored using BP2. In both preparation groups we achieved better colonic distension in prone position. We were not able to distend the sigmoid better when insufflating air during patient repositioning.

Spectral coronary multidetector computed tomography angiography: dual benefit by facilitating plaque characterization and enhancing lumen depiction.

OBJECTIVE: To assess ex vivo specimens of atherosclerotic coronary arteries by dual energy (DE) multidetector computed tomography (MDCT) imaging, and to correlate depicted vessel lumen morphology and detected tissue characteristics with histopathologic analysis. METHODS: Coronary arteries were imaged on a 16-slice MDCT using a DE protocol consisting of a 90- and 140-kV scan. Coronary arteries were perfused with iodine- and gadolinium-based contrast agents. The DE K-edge subtractions were performed. Regions-of-interest were placed on histopathologically/radiographically-matched vascular lumen and wall, fibromuscular and calcified plaque, and fat tissues. Vascular/tissue contrast-to-noise ratios (CNR) were calculated, and their dependence on tissue type and contrast agent type was statistically evaluated. RESULTS: Tissue CNR analysis confirmed that all tissue types were successfully distinguished. Vascular wall and fibromuscular plaque achieved a significant increase in CNR ratios when DE techniques were used compared with 140 kV protocols. CONCLUSIONS: Spectral DE MDCT imaging of ex vivo atherosclerotic coronary arteries allows successful tissue characterization and enhances depiction of coronary lumen.

MDCT angiography of the spinal vasculature and the artery of Adamkiewicz.

OBJECTIVE: The purpose of our study was to prospectively assess 40-MDCT technology in combination with adapted brain reconstruction algorithms to visualize the spinal vasculature, in particular the artery of Adamkiewicz and its anatomic variants. SUBJECTS AND METHODS: One hundred patients underwent contrast-enhanced MDCT of the thoracolumbar junction with collimation of 40 x 0.625 mm. The adapted brain algorithm reconstructed the spinal canal with a field of view of 90 mm at 0.6-mm slice thickness. Curved multiplanar reformations identified the artery of Adamkiewicz as a continuous vascular tract extending from the aortic orifices of the intercostal or lumbar arteries via the anterior radiculomedullary artery to the anterior spinal artery. Segment of origin and length were noted. Diameter and contrast-to-noise ratio (CNR) were evaluated along the posterior branch, the radiculomedullary artery, the artery of Adamkiewicz, and the anterior spinal artery. Univariate general linear model analysis with Bonferroni post hoc corrections evaluated whether laterality, segment of origin, and length of the artery of Adamkiewicz showed a sex-specific propensity. Multivariate general linear model analysis assessed whether spinal vascular diameters and intraluminal CNR showed correlations with sex, laterality, and segment of origin. Finally, the luminal diameters of the feeding posterior branches were statistically compared with those of the ipsilateral and contralateral adjacent posterior branches. RESULTS: Successful depiction of the artery of Adamkiewicz was achieved in all patients; longitudinally the artery measured 40.1 +/- 13.51 mm. In 63% of patients it originated from the left side of the body, and in 74% it originated from the level of the 10th-12th thoracic vertebrae. Duplications were found in 5% of patients. Segmental distribution, laterality, and length did not show significant sex-specific differences (p > 0.05). The vascular diameter and luminal contrast did not show significant differences caused by sex, laterality, or segment of origin (p > 0.05). The diameter of the posterior branches (2.8 +/- 0.71 mm) arising in the segments of origin showed a significantly wider lumen than any of the other posterior branches (contralateral, 1.9 +/- 0.32 mm; upper ipsilateral, 2.0 +/- 0.47 mm; lower ipsilateral, 1.9 +/- 0.39 mm) (p < 0.0001). CONCLUSION: Contrast-enhanced 40-MDCT technology, in combination with an adapted brain reconstruction algorithm, can depict the artery of Adamkiewicz and its anatomic variants.

Synergy of MDCT and cine MRI for the evaluation of cardiac motility.

OBJECTIVE: The objective of our study was to validate the feasibility of the synergistic use of cardiac MR and CT data sets for ventricular motility analysis and to correlate measurement variability with underlying heart rate. SUBJECTS AND METHODS: Twenty patients underwent concurrent ECG-gated MDCT and MRI for evaluation of ventricular motility, expressed as ventricular wall thickening and motion. Initially, individual measurement repetition series were analyzed by determining intraobserver variability and detecting intraobserver bias related to heart rates. Subsequently, absolute measurement differences of CT or MR data were statistically evaluated. Finally, absolute measurement differences were correlated with underlying heart rates by curve estimation regression. RESULTS: Analysis of measurement reproducibility proved that data variability was dependent on only the anatomic localization of the analyzed ventricular segment, not on the imaging technique used or underlying heart rate, in normofrequent patients. Comparing MR and CT image data sets, no statistically significant differences were identified when ventricular motility was evaluated based on data sets of either imaging technique in normofrequent patients. Tachycardic frequencies, above 100 beats per minute, led to exponential error propagation due to insufficient temporal resolution of the current CT technology. CONCLUSION: This study proved that cardiac motility assessment based on ECG-gated CT and MR data sets resulted in comparable ventricular function results for normofrequent patients; however, the high spatial resolution of cardiac MDCT cannot compensate for the lack of temporal resolution in patients with tachycardia, thus emphasizing the necessity of reporting ventricular motility analysis results in combination with heart rate to allow consideration of this possible cause for measurement variation.

CT colonography: comparison of a colon dissection display versus 3D endoluminal view for the detection of polyps.

The purpose of this study was to compare sensitivity, specificity, and postprocessing time of a colon dissection approach to regular 3D-endoluminal workup of computed tomography (CT) colonography for the detection of polypoid lesions. Twenty-one patients who had received conventional colonoscopy after CT colonography were selected; 18 patients had either colon polyps or colon cancer and three had no findings. CT colonography was performed using a 4-channel multi-detector-row (MDR) CT in ten cases and a 16-channel MDR-CT in 11 cases. A blinded reader retrospectively evaluated all colonographies using both viewing methods in a randomized order. Thirty-seven polyps were identified by optical colonoscopy. An overall per-lesion sensitivity of 47.1% for lesions smaller than 5 mm, 56.3% for lesions between 5 mm and 10 mm, and 75.0% for lesion larger than 10 mm was calculated using the colon dissection approach. This compared to an overall per-lesion sensitivity of 35.3% (<5 mm), 81.5% (5-10 mm), and 100.0% (>10 mm) using the endoluminal view. The average time consumption for CT colonography evaluation with the colon dissection software was 10 min versus 38 min using the endoluminal view. A colon dissection approach may provide a significant time advantage for evaluation of CT colonography while obtaining a high sensitivity. It is especially superior in the detection of lesions smaller than 5 mm.

Automatic determination of minimal cardiac motion phases for computed tomography imaging: initial experience.

Low motion phases for cardiac computed tomography reconstructions are currently detected manually in a user-dependent selection process which is often time consuming and suboptimal. The concept of motion maps was recently introduced to achieve automatic phase selection. This pilot study compared the accuracy of motion-map phase selection to that with manual iterative selection. The study included 20 patients, consisting of one group with low and one with high heart rate. The technique automatically derives a motion strength function between multiple low-resolution reconstructions through the cardiac cycle, with periods of lowest difference between neighboring phases indicating minimal cardiac motion. A high level of agreement was found for phase selection achieved with the motion map approach compared with the manual iterative selection process. The motion maps allowed automated quiescent phase detection of the cardiac cycle in 85% of cases, with best results at low heart rates and for the left coronary artery. They can also provide additional information such as the presence of breathing artifacts. Motion maps show promise as a rapid off-line tool to automatically detect quiescent cardiac phases in a variety of patients.