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Recently, machine learning has outperformed established tools for automated segmentation in medical imaging. However, segmentation of cardiac chambers still proves challenging due to the variety of contrast agent injection protocols used in clinical practice, inducing disparities of contrast between cavities. Hence, training a generalist network requires large training datasets representative of these protocols. Furthermore, segmentation on unenhanced CT scans is further hindered by the challenge of obtaining ground truths from these images. Newly available spectral CT scanners allow innovative image reconstructions such as virtual non-contrast (VNC) imaging, mimicking non-contrasted conventional CT studies from a contrasted scan. Recent publications have demonstrated that networks can be trained using VNC to segment contrasted and unenhanced conventional CT scans to reduce annotated data requirements and the need for annotations on unenhanced scans. We propose an extensive evaluation of this statement. We undertake multiple trainings of a 3D multi-label heart segmentation network with (HU-VNC) and without (HUonly) VNC as augmentation, using decreasing training dataset sizes (114, 76, 57, 38, 29, 19 patients). At each step, both networks are tested on a multi-vendor, multi-centric dataset of 122 patients, including different protocols: pulmonary embolism (PE), chest-abdomen-pelvis (CAP), heart CT angiography (CTA) and true non-contrast scans (TNC). An in-depth comparison of resulting Dice coefficients and distance metrics is performed for the networks trained on the largest dataset. HU-VNC-trained on 57 patients significantly outperforms HUonly trained on 114 regarding CAP and TNC scans (mean Dice coefficients of 0.881/0.835 and 0.882/0.416, respectively). When trained on the largest dataset, significant improvements in all labels are noted for TNC and CAP scans (mean Dice coefficient of 0.882/0.416 and 0.891/0.835, respectively). Adding VNC images as training augmentation allows the network to perform on unenhanced scans and improves segmentations on other imaging protocols, while using a reduced training dataset.

The very high cycle fatigue (VHCF) behavior of an additively manufactured aluminum alloy, AlSi10Mg-T6, has been studied to better understand the role of process-related defects on fatigue life and, in particular, initiation and small crack propagation behavior. Ultrasonic fatigue methodologies were used for the determination of an operative fatigue strength for lifetimes in the range of 108-109 cycles. Fatigue crack growth rates were determined for small fatigue cracks that initiated and grew from artificially produced (FIB) surface defects in specimens subjected to ultrasonic fatigue. X-ray computed tomography (CT) was used in an effort to detect possible crack initiation and growth in specimens cycled for fractions of the nominal VHCF fatigue strength. From the baseline fatigue experiments using fully reversed loading (R = − 1), a nominal fatigue strength of 90 MPa was established for lifetimes in the 108-109 range, and this maximum stress value was used in subsequent crack growth and CT studies. Using ultrasonic fatigue allowed very slow average crack growth rates on the order of 10−11 m/cycle at a °ΔK of 1.5 Mpa m1/2. Small crack growth from FIB-produced micronotches appeared to be transgranular and non-crystallographic. While modest increase in size of some features identified by x-ray CT for interrupted fatigue tests, particularly at defects characterized as flat or oblate spheroids, no definitive evidence of the emergence of a fatal crack from a single defect was observed. This contrasts with the fatigue behavior of as-built AM AlSi10Mg alloy, where porosity-dominated fatigue crack initiation and the size and type of defects can be correlated with fatigue lifetimes.

Highly permeable asphalt mixtures are prone to moisture damage leading to reduction in pavement service life. This study correlates dense-graded asphalt mixture’s air voids with its permeability. As permeability initiates due to significant interconnectivity of air voids, the relation between total air voids (TAVs) and connected air voids (CAVs) requires a critical review. Permeability of laboratory-compacted asphalt specimens was measured in the laboratory using four different permeameters. Conventional and Baily methods were utilized to develop aggregate gradations for asphalt mixtures. Different testing techniques were also used to ascertain the amount of CAVs, as aggregate gradation affects the airvoids significantly. An equation, based upon Darcy’s law, while assuming equilibrium of inflow/outflow of water to and from asphalt sample was proposed to determine the CAVs in the asphalt mix. The digital images of asphalt specimens were captured, and digital computed tomography (CT) technique was employed using ImageJ software for validation of the CAVs estimated from the relationship. It was observed that air voids, especially CAVs, and type of aggregate gradation have significant effects on permeability of asphalt mixture. The Baily modified mixes exhibited lower permeability. The permeability also increased with an increase in nominal maximum aggregate size. The interconnected pores, determined with the help of digital CT technique, validate the values of air voids estimated from the proposed relationship.

For 99mTc-sestamibi parathyroid single photon emission computed tomography/computed tomography (SPECT/CT), the traditional full-arc 360° acquisition technique has been suggested but not the theoretically low tissue-attenuated anterior 180° method. We aimed to compare the diagnostic performances and target-to-background ratios of anterior 180° and 360° SPECT/CT imaging. Ninety-nine patients who underwent 99mTc-sestamibi scintigraphy and received a surgical–pathological diagnosis of parathyroid adenoma or hyperplasia were enrolled. The SPECT/CT reconstructed images with anterior 180° and full-arc 360° data were interpreted by two physicians using a scoring scale, and the lesions were semi-quantified using target-to-background ratios for both image sets. In total, 113 abnormal parathyroid lesions were identified on the SPECT/CT images. The agreements of interpretation between the two image sets and readers were very good (κ value: 0.83–1.00). The accuracies of summative interpretation for the anterior 180° and full-arc 360° SPECT/CT were 83.04% and 82.46%, respectively. The target-to-background ratios were significantly higher for the anterior 180° than the full-arc 360° images (P

Variation of visual selective attention through the day has been demonstrated in several arenas of human performance, including radiology. It is uncertain whether this variation translates to an identifiable diurnal pattern of error rates for radiology interpretation. The purpose of this study was to attempt to identify particular days of the week and times of the day when radiologists might be most prone to error. Abdomen/pelvis CT studies containing at least one major error were collected from a 10-year period from the quality assurance (QA) database at our institution. A major error was defined as a missed finding that had altered management in a way potentially detrimental to the patient. The identified studies were categorized by the day of the week and hour of the day that the study was interpreted. Study volume data over this same period was also obtained by day of the week and time of day, so to normalize the data based on case volume. Standard errors of the volume-adjusted error rates were obtained based on the binomial distribution. The null hypothesis of constant error rates over time was tested using a weighted logistic regression model with linear time as predictor. A total of 252 major errors were identified. More errors were made on Monday than on any other day of the week (n = 58). Major error rates increased through the mid to late morning (9 am to 12 pm), and then decreased progressively through the afternoon until 4 pm, when a rise in the error rate was seen. This pattern persisted when error rates were normalized by study volume within each hour. Overall tests of time-constancy of error rates by day and hour were statistically significant (both p-values

We aimed to determine at what size melanoma metastases become detectable by PET/CT. We reviewed a total of 293 whole-body PET/CT studies performed on 212 patients for staging of melanoma where there was an MRI within a month of the PET/CT. MR and PET/CT were reviewed independently by separate readers. PET/CT revealed an overall incidental true-positive rate of 1% on a per-patient basis, consistent with other studies, with ‘hot’ lesions (more avid than brain parenchyma) visible at smaller sizes than ‘cold’ lesions. PET/CT can detect metastatic melanoma lesions over about 2 cm in size, with hot lesions generally visible at smaller sizes.

Introduction: Adequate suppression of physiologic myocardial glucose uptake is important to ensure the interpretability and diagnostic reliability of [18F]fluorodeoxyglucose (FDG) PET/CT studies performed in the context of cardiac inflammation and infection. This study describes our experience with 4 preparatory protocols used in our institution. Methods: FDG PET/CT scans were performed according to 4 preparatory protocols (716 scans total), i.e. 6-h fast (group 1), low-carbohydrate diet plus 12-h fast (group 2), low-carbohydrate diet plus 12-h fast plus intravenous heparin pre-administration (15 IU/kg) (group 3), and low-carbohydrate diet plus 12-h fast plus intravenous heparin pre-administration (50 IU/kg) (group 4). Consecutive scans were retrospectively included from time frames during which the particular protocol was used. FDG uptake in normal myocardium was scored on a scale ranging from 0 (uptake less than that in the left ventricular blood pool) to 4 (diffuse uptake greater than that in the liver). Complete suppression was defined as uptake less than or equal to the blood pool (scores 0–1). Results: Complete suppression was accomplished in 27% in group 1, 68% in group 2, 69% in group 3 and 81% in group 4. Complete suppression was significantly lower in group 1 compared with all other groups (P < 0.0001 for all comparisons) and significantly higher in group 4 compared with group 2 (P = 0.005) and group 3 (P = 0.007). Groups 2 and 3 did not differ significantly (P = 0.92). Conclusion: A total of 50 IU/kg single-dose heparin administration before FDG PET/CT in addition to a low-carbohydrate diet and prolonged fast significantly outperformed protocols with no or lower dose (15 IU/kg) heparin in completely suppressing myocardial glucose metabolism.

Within medical age assessment practice, the indicator "medial clavicular ossification" constitutes crucial evidence capable of excluding age minority "beyond reasonable doubt" concerning age-disputed individuals doubtfully claiming children's rights during legal procedures. Yet, one of its characteristics affects the morphological variability including a fair amount of downright peculiar appearances. As a result, inexperienced examiners are tempted to classify actually not-assessable formations according to the two established developmental typologies of Schmeling et al. and Kellinghaus et al. being at the same time the most frequent systemic error of age-related clavicular taxation. Since a respective overview appears missing, the study extracts not-assessable shape variants of the medial collar bone from a large sample of 2820 male borderline-adults as seen from thin-slice, sternoclavicular computed tomography. The two already highlighted configurations "more than one, medial, secondary ossification centres" and "medial metaphyseal concavity" are found as the most commonly encountered features impeding reliable delineation of staging criteria. In accordance with previous literature, it is emphasized that "qualified" rating of extremitas sternalis claviculae within age assessment practice presupposes "knowledge about the diversity of [its] anatomic shape variants."

Background The SwiftScan solution (General Electric Healthcare) combines a new low-energy high-resolution sensitivity collimator and a tomographic step-and-shoot continuous (SSC) mode acquisition. The purpose of this study is to determine whether SSC mode can be used in clinical practice with shorter examination times, while preserving image quality and ensuring accurate semi-quantification. Twenty bone scan and 10 lung scan studies were randomly selected over a period of 2 months. Three sets of image datasets were produced: step-and-shoot (SS) acquisition, simulated 25% count reduction using the Poisson resampling method (SimSS), and SimSS continuous acquisition (SimSSC), where SimSS was summed with counts acquired during detector head rotation. Visual assessment (5-point Likert scale, 2 readers) and semi-quantitative evaluation (50 focal uptake from 10 bone studies), assessed by SUVmean, coefficient of variation (COV), and contrast-to-noise ratio (CNR), were performed using t test and Bland-Altman analysis. Results Intra-reader agreement was substantial for reader 1 (k = 0.71) and for reader 2 (k = 0.61). Inter-reader agreement was substantial for SS set (k = 0.93) and moderate for SimSSC (k = 0.52). Bland-Altman analysis showed a good interchangeability of SS and SimSSC SUV values. The mean CNR between SS and SimSSC was not significantly different: 42.9 ± 43.7 [23.7–62.1] vs. 43.1 ± 46 [22.9–63.3] (p = 0.46), respectively. COV values, assessing noise level, did not deviate significantly between SS and SimSSC: 0.20 ± 0.08 [0.18–0.23] vs. 0.21 ± 0.08, [0.18–0.23] (p = 0.15), respectively, whereas a significant difference was demonstrated between SS and SimSS: 0.20 ± 0.08 [0.18–0.23] vs. 0.23 ± 0.09 [0.20–0.25] (p < 0.0001), respectively. Conclusions SSC mode acquisition decreases examination time by approximately 25% in bone and lung SPECT/CT studies compared to SS mode (~ 2 min per single-bed SPECT), without compromising image quality and signal quantification. This SPECT sensitivity improvement also offers the prospect of more comfortable exams, with less motion artifacts, especially in painful or dyspneic patients.

Background COVID-19 is a pandemic disease and is important to know the nature of the disease during follow-up. We aimed to study different imaging signs and changes that occurred during the initial scan, follow-up, and complications. Moreover, to study the CT severity score and its relation to the patients’ clinical condition using oxygen saturation as a parameter. This was a retrospective study conducted on 125 patients, including 293 CT studies, from March till the end of August 2020. The mean age was 47.4 ± 15.7 years and 64.8% of the patients were males. All patients proved to have COVID-19 by the RT-PCR test. The CT studies of the patients were divided into four stages according to the timing after the onset of symptoms. The incidence of different CT features, patterns, complications, CT severity score, and oxygen saturation were recorded in different stages. Results During follow-up studies, GGOs were the most constant and common CT features. Consolidation and crazy paving showed gradual progression to reach the peak at the 3rd stage. Mixed attenuation pattern was the commonest pattern at the 3rd stage while a pure GGO pattern was the commonest feature in other stages. The complications occurred mostly in the 3rd stage. Nevertheless, the CT severity score showed an inverse relation with oxygen saturation. Conclusion Radiological evaluation of COVID-19 pneumonia showed gradual progression till the peak critical stage at 8-14 days from the onset of symptoms. Consolidation and mixed attenuation pattern can be considered as CT signs of disease severity.

Aim and objectives The aim of this study was to assess the role of 18-F FDG-PET/CT in evaluating the peripheral malignant neuronal affection as well as perineural tumoral spread that occurs in patients with cancers. Methodology 50 patients with clinical symptoms of neurological deficits (34 male and 16 female) were included, their ages ranged from 17 to 74 with a mean of 45 years. PET/CT was done for all patients followed by clinical correlation after anti-inflammatory drugs and chemotherapy. Results Interpretation of the PET/CT studies and clinical correlation revealed 10 true positive cases with malignant neuronal involvement, 4 false positive cases diagnosed clinically as radiotherapy-induced neuropathy, 34 true negative cases and 2 false negative cases with negative PET/CT study and clinical evidence of nerve affection with sensitivity 83.33%, specificity 89.47%, PPV 71.43%, NPV 94.44% and diagnostic accuracy 88%. P-value > 0.05 was considered statistically significant. Conclusion PET/CT has a significant role in detection of neuronal involvement by malignancy in cancer patients. Correlation between PET/CT and clinical outcome after chemotherapy improves the accuracy of diagnosis.

Objectives To benchmark CT-dose data for standard adult CT studies to regional and national reference levels using a dose-tracking system. Methods Data from five CT systems from three hospitals were collected over a 1- to 2.5-year period (2012–2014), using the same type of dose management system. Inclusion criteria were adult patients and standard CT-head, CT-abdomen-pelvis, CT-thorax, CT-lumbar spine, CT-pulmonary embolism, CT-cervical spine and CT-thorax-abdomen studies, with one helical scan. Volumetric CT-dose index (CTDIvol), dose length product (DLP) and scan length from 31,709 scans were analysed statistically. Results After dose optimisation CTDIvol and DLP values were below the national diagnostic reference levels (DRLs) for all CT studies and for all systems investigated. Mostly no significant differences were found between CTDIvol and DLP levels (p values ≥ 0.01) of CT studies performed on different scanners within the same hospital. Significant dose differences (p values < 0.01) were instead observed among hospitals for comparable CT studies. Dose level range and scan length differences for similar CT studies were revealed. Conclusions Dose-tracking systems help to reduce CT-dose levels below national DRLs. However, dose and protocol data comparison between and within hospitals has the potential to further reduce variability in dose data of standard adult CT studies. Key Points • Retrospective three-centre study on dose levels of standard adult CT procedures. • Dose-tracking systems help hospitals to stay below national dose reference levels. • Dose-tracking systems help to align CT dose levels between scanners within hospitals. • Benchmarking shows CT dose level variability for similar examinations in different hospitals. • Differences in dose level range/scan length for similar CT studies are revealed. Electronic supplementary material The online version of this article (10.1007/s13244-017-0570-5) contains supplementary material, which is available to authorized users.

To determine if focal increased uptake at the rotator interval (RI) and/or inferior capsule (IC) on18F-FDG PET/CT (“positive PET”) predicts the presence of adhesive capsulitis (AC). Three populations were retrospectively examined. Group 1 included 1,137 consecutive 18F-FDG PET/CT studies and was used to determine the prevalence of focal uptake at the RI or IC. Group 2 included 361 cases from a 10-year period with 18F-FDG PET/CT and MRI of shoulder performed within 45 days of each other and was used to enrich the study group. Group 3 included 109 randomly selected patients from the same time frame as groups 1 and 2 and was used to generate the control group. The study group consisted of 15 cases from the three groups, which had positive PET findings. PET/CT images were assessed in consensus by two musculoskeletal radiologists. The reference standard for a diagnosis of AC was clinical and was made by review of the medical record by a pain medicine physician. The prevalence of focal activity at either the RI or IC (“positive PET”) was 0.53%. Nine patients had a clinical diagnosis of AC and 15 patients had a positive PET. The sensitivity and specificity of PET for detection of AC was 56% and 87%, respectively. PET/CT had a positive likelihood ratio for AC of 6.3 (95% CI: 2.8–14.6). Increased uptake at the RI or IC on PET/CT confers a moderate increase in the likelihood of AC.

The acoustic-emission (AE) nondestructive monitoring method was used to investigate the deformation–failure of Longmaxi marine shale samples from the Sichuan Basin in uniaxial compression tests. Millions of AE ring counts were recorded by six sensors that were mounted on the surface of cylindrical specimens. The AE ring counts rate and energy rate were applied to study crack development during fracturing. AE locations at different stress stages during the loading process were obtained to study the fracture spatial distribution and the crack-propagation tendency. An X-ray computed tomography (CT) system was used to scan samples after damage. CT images were reconstructed to acquire three-dimensional pictures that show the internal invisible-fault system. The combination of AE method and CT technique helps explain temporal and spatial crack evolution. Variable damage evolution was determined by the number of AE ring counts, which demonstrates the degradation behavior of shale.

The authors are trying to develop an ultrasonic CT technique for concrete structures. As the first step of its development, we study how the ultrasonic waves propagate in concrete structures and pose a problem to develop ultrasonic CT, applying which we give a non-destructive inspection technique for concrete cover by application of the idea of the ultrasonic CT. The authors claim that this study gives the foundation of the theory of ultrasonic CT for concrete structures.

Objectives The purpose of this study was to verify whether application of a quantitative computed tomography (QCT) technique was helpful for quantitative measurement of bone density using dental cone-beam CT (CBCT).

In modern oncology, disease progression and response to treatment are routinely evaluated with a series of volumetric scans. The number of tumors and their volume (mass) over time provides a quantitative measure for the evaluation. Thus, many of the scans are follow-up scans. We present a new, fully automatic algorithm for lung tumors segmentation in follow-up CT studies that takes advantage of the baseline delineation. The inputs are a baseline CT scan and a delineation of the tumors in it and a follow-up scan; the output is the tumor delineations in the follow-up CT scan; the output is the tumor delineations in the follow-up CT scan. The algorithm consists of four steps: (1) deformable registration of the baseline scan and tumor’s delineations to the follow-up CT scan; (2) segmentation of these tumors in the follow-up CT scan with the baseline CT and the tumor’s delineations as priors; (3) detection and correction of follow-up tumors segmentation leaks based on the geometry of both the foreground and the background; and (4) tumor boundary regularization to account for the partial volume effects. Our experimental results on 80 pairs of CT scans from 40 patients with ground-truth segmentations by a radiologist yield an average DICE overlap error of 14.5 % ( $$\hbox {std}=5.6$$ ), a significant improvement from the 30 % ( $$\hbox {std}=13.3$$ ) result of stand-alone level-set segmentation. The key advantage of our method is that it automatically builds a patient-specific prior to the tumor. Using this prior in the segmentation process, we developed an algorithm that increases segmentation accuracy and robustness and reduces observer variability.

The purpose of this retrospective investigation is to characterize and illustrate the appearances of celiomesenteric trunk (CMT) and hepatosplenomesenteric trunk (HSMT) using CT with three-dimensional volume-rendering with attention to the proximal branching patterns. We also correlate our results with an embryologic model and assess the accuracy of radiologists in recognizing these entities. CT studies on 36 adult subjects with CMT and 10 with HSMT were analyzed to determine the proximal branching patterns and lengths of the common vascular trunks. The official reports in appropriately selected cases were reviewed to ascertain if the interpreting radiologists recognized the anomalies. Two types of CMT were found. In 29 of 36 cases (81%), the CMT bifurcated into the celiac trunk and superior mesenteric artery (Type A CMT), while in 7 cases the left gastric artery (LGA) arose from the CMT proximal to the hepatosplenic trunk and superior mesenteric artery (Type B CMT). Type A trunks (mean length = 10.4 mm) were significantly shorter (p = 0.007) than Type B trunks (mean length = 17.8 mm). Short common trunks (less than 1.0 cm) were only seen with Type A CMT. Branching patterns in all 10 cases of HSMT were identical with no short common trunks. The CMT was not mentioned in the radiology reports in 88% of the cases assessed. The location of the LGA origin distinguishes the two variants of CMT and differentiates CMT from HSMT. These anomalies are easily overlooked during evaluation of routine clinical cases.

To investigate the potential of virtual non-contrast CT (VNCT) from dual-energy CT to replace true nonenhanced CT (TNCT) for the detection of enlarged cervical lymph nodes.Thirty-nine patients with 94 histopathologically proven cervical lymph nodes were imaged with the dual-energy CT technique. VNCT images from the arterial [VNCT-A] and venous phases [VNCT-V] were obtained with the liver VNC application. The mean CT number and signal-to-noise ratio (SNR) were compared. Image quality was evaluated with a score scale of 1-5. Effective dose (ED) was calculated and compared.Mean CT numbers of cervical lymph nodes were higher on VNCT than on TNCT (P = 0.034). There was no difference in the SNR among three sets of non-enhanced CT images, but the CNR of VNCT images was higher than that of TNCT images (P0.001). Image quality of VNCT from two phases was comparable to that of TNCT (P = 0.070). There was no difference in image quality of three sets of non-enhanced CT images (P0.05). ED from dual-phase dual-energy CT was lower than that from tri-phase CT scans (P0.001).VNCT images from dual-energy CT of the neck had diagnostic image quality; they have the potential to replace TNCT, thus reducing the radiation dose.

To assess the frequency of clinically significant incidental CT findings on PET/CT. Reports of 345 cases of baseline standard skull base to thighs PET/CT exams done over the course of a 6 month period at an outpatient facility affiliated with a large tertiary care level 1 trauma medical center were retrospectively reviewed. Incidental CT findings were assigned a level of clinical significance on a scale of 1–5, from doubtful significance to very significant. CT findings already known from prior CT reports were not included. CT findings corresponding to PET findings were also excluded. A score of 3 or greater was considered significant and reportable. Out of 345 cases, 171 (50%) had a least one CT finding rated at or above a score of 3 on our scale of significance, while 96 (28%) were found to have at least one CT finding with score at or above 4, and 25 cases (7%) showed at least one CT finding rated 5. A substantial percentage of baseline PET/CT studies contain previously undiagnosed, significant incidental findings on the CT images.

Computed Tomography (CT) is extensively used as a medical diagnostic tool, and increasingly adopted for scientific and industrial research. In the wood industry, there is a growing interest in using the CT technique to assess the quality of logs entering a sawmill to enable the material to be appropriately processed into maximum value products. Internal features of interest include knots, heartwood/sapwood boundary, rot and splits. Most commercially available CT scanning systems are modeled on medical designs and provide high spatial and density resolution. They are very complex and delicate devices with correspondingly high cost. However, log scanning has its own distinctive characteristics: specific overall and feature geometries and relatively coarse scanning resolution requirement. To fit these characteristics, the novel geometry-based coarse-resolution CT scanning approach described here has been developed and implemented. The models, algorithms, scanner design and result validation are presented in detail. The resulting CT reconstructions for an example log using the proposed geometry-based coarse-resolution approach compare well with CT reconstructions for same log using the same data with conventional filtered back projection inversion. The good comparison gives confidence in the usefulness and applicability of the proposed CT method for industrial use in sawmills for log quality assessment.

A method for calibration of LiF: Mg, Ti thermoluminescent dosimeters is presented. The calibrated dosimeters are used in various CT studies involving anthropomorphic phantoms of the human body for estimating the reference levels of effective patient dose. It is shown that application of the method in some cases improves the accuracy of dose estimates by 80% versus conventional calibration in air using standard radiation sources.

Simultaneous positron emission tomography/magnetic resonance was released few years ago and there is a (non-official) perspective of almost 100 scanners worldwide being installed until 2016. Despite the enormous marketing success for such an expensive and fine hybrid imaging tool, PET/MR is still seen primarily as a research tool. Currently this clinical validation process is more than necessary to justify the additional expenses in a world with increasing difficulties regarding health system reimbursement. The current PET/MR feasibility has been demonstrated with the published data so far in almost every body region, with great potential applications. The main fields of research in PET/MR are oncologic and neurologic, basically for two reasons: (1) because almost 90 % of PET/CT studies come from oncology; (2) and also because of the recent development of new medications and treatments for dementia, making PET/MR an important character in this new scenario. Inflammation has become the newest potential application, and will also be discussed further on. In this article such potential clinical PET/MR applications are compiled and updated and will be thoroughly discussed.

We describe a case report of dorsal radiocarpal dislocation with fracture of the radial styloid process. A 21-year-old right-handed male was injured in a fall while snowboarding. Plain radiographic findings revealed dorsal dislocation of radiocarpal joint with fracture of the radial styloid process; we performed CT studies to examine the radius fracture in greater detail. These findings revealed a radial styloid fracture with avulsion fracture of dorsal articular margin of the distal part of the radius. Surgical treatment was performed 4 days after the injury. However, it was impossible to reduce the dorsal dislocation of radiocarpal joint only after the fixation of the radial styloid process. The dorsal radiocarpal ligaments and articular capsule had ruptured transversely on the radiocarpal joint with avulsion fracture of dorsal articular margin of the distal part of the radius. To repair the torn ligaments and capsule, we inserted three mini suture anchors into the dorsal edge of the radius and fixed these tissues on the radius. At present, 1 year after surgery, he has no pain with activity or at rest, and satisfactory results have been obtained.

Greater than 10% of diagnostic imaging studies performed in developed countries are CT examinations. In the United States, as many as 60 million CT studies are performed each year, up to 7 million of which are performed in pediatric patients. In the spirit of the ALARA principle, both adult and pediatric radiologists should strive to decrease pediatric radiation exposure whenever possible. This can be achieved by utilizing imaging studies that do not require the use of ionizing radiation, thus decreasing the number of CT studies performed. If a CT study is indicated, the delivered dose should be optimized to use the lowest possible dose level while still answering the clinical question.

The peroral pneumocolon represents a time-honored but somewhat forgotten and underutilized technique for improved ileocecal evaluation at small bowel fluoroscopy. The peroral pneumocolon entails fluoroscopically guided gaseous insufflation per rectum following the arrival of barium at the cecum at conventional small bowel follow-through examination. In most cases, high-quality double contrast evaluation of the terminal ileum can be achieved, often superior to enteroclysis examination for this critical location. The peroral pneumocolon improves diagnostic confidence, including assessment of disease activity, and may result in a reversal of the diagnostic impression. This simple procedure will be discussed and a spectrum of fluoroscopic findings with CT and endoscopic correlation will be provided to demonstrate the added yield of this technique in the evaluation of known or suspected Crohn's disease. Application of the pneumocolon technique to CT for combined small and large bowel evaluation ("CT coloenterography") will also be discussed, which represents an attractive new option for investigating inflammatory bowel disease and other bowel-related conditions. Through the use of automated low-pressure carbon dioxide delivery per rectum, supplemented by IV glucagon for relaxation of the ileocecal valve, a CT-based pneumocolon examination may prove to be a useful hybrid technique for bowel evaluation in the future.

The aim of this study was to evaluate the accuracy and interobserver variability of dynamic computed tomography (CT) for diagnosis of small bowel obstruction. A total of 115 patients with a CT diagnosis of small bowel obstruction were included. Two radiologists and two residents performed blinded, independent, retrospective reviews of CT studies. Attention was focused on the presence of reduced early enhancement of the bowel wall and closed loop obstruction. Results were correlated with surgical findings in 15 cases and clinical follow-up in 100 cases. Sensitivity and specificity were calculated, and kappa statistics were used to analyze interobserver agreement. In all, 13 cases were surgically confirmed small bowel ischemia. Sensitivity, specificity, positive predictive value, and negative predictive value for the diagnosis of ischemia were 85%, 96%–97%, 73%–79%, and 97%–98%, respectively, for radiologists and 69%–93%, 93%–95%, 63%–64%, and 96%–99%, respectively, for residents. For agreement in the interpretations of reduced early enhancement of bowel wall, closed loop obstruction, and presence of bowel ischemia, the values were 0.62, 0.71, and 0.80, respectively, between radiologists and 0.57–0.70, 0.63–0.74, and 0.56–0.68, respectively, between radiologists and residents. There was moderate or substantial agreement for the diagnosis of small bowel ischemia between radiologists and residents. However, there was substantial agreement for the presence of closed loop obstruction.

F-18 fluorodeoxyglucose (FDG) PET/CT that simultaneously offers anatomic and metabolic information is widely used and has become an effective modality in many clinical fields, especially oncology. For accurate interpretation, it is necessary to understand false-positive findings in the F-18 FDG PET image, such as physiologic conditions, findings related to patients' medical and surgical histories, normal variants, and artificial conditions. We report three cases of incidental focal F-18 FDG accumulation in lung parenchyma without abnormal CT findings in the PET/CT images. In the primary PET/CT studies, two cases showed single and one case showed multiple FDG foci in the lung without any CT abnormalities. All FDG accumulations disappeared in PET/CT studies repeated 1-3 days after the primary scannings. These artifacts are probably related to microembolisms attributable to the intravenous injection of F-18 FDG. Therefore, a cautious interpretation of the correspondence between anatomic and metabolic images is required and repeated PET/CT is helpful.

One of the most significant advances in imaging evaluation of paediatric cardiovascular disorders has been multidetector CT angiography (MDCTA). While MDCTA remains a supplemental problem solving technology for both echocardiography and catheter angiography, the technique has also emerged as a first line diagnostic modality, especially as the diminished role of radiography is recognized [1]. At the same time, MDCTA can impart high radiation doses, and this must be understood when considering CTA in children. Proper technique is fundamental since errors can substantially impact diagnostic benefit. The objectives of the following material are to discuss the role of MDCTA, and to describe technical guidelines, being mindful of what is currently understood about radiation dose from this technology. Applications will be summarized, and will also serve to illustrate technical principles.

With the widespread application of cardiac CT has come increasing concern over the effects of radiation dose associated with this exam. Dual source CT provides a number of methods for dose reduction in helical ECG-gated cardiac CT studies. This article discusses several of these methods, with a particular emphasis on low kVp scanning, which can be applied in a large percentage of patients.

Given the well-recognized association of radiation and thyroid cancer, the objective of this study was to assess the frequency of radiation overlap at the level of the thyroid gland as part of standard protocols for computed tomography (CT) assessment of trauma, incorporating both cervical spine and chest images. A survey was sent to physician members of the American Society of Emergency Radiology. Among other questions, the respondents were asked to indicate their CT protocol with respect to the lower boundary of their cervical spine series and the upper boundary of their chest CT series. Forty-one surveys were returned. Of these, 83% reported overlap of the contiguous margins of the two CT studies resulting in partial or total double radiation deposition to the thyroid gland, which typically extends from vertebral levels C5 to T1. Sixty-one percent reported overlapping at T1 only, 15% at C7 to T1, 4.9% at C6 to T1, and 2.4% at C5 to T1. These data reveal that the predominant practice among the respondents is to include the thyroid gland in coincident CT studies of the cervical spine and chest in trauma protocols.

Noninvasive visualization of the heart by CT is highly accurate and useful, but its association with ionizing radiation and the potential risk of cancer induction has raised concerns. Dose-saving algorithms, new CT scanners, and scanning techniques have been developed to effectively reduce the amount of radiation exposure without deterioration of image quality. Furthermore, additional strategies for dose reduction can be pursued in daily practice following the ALARA (as low as reasonably achievable) principle. However, there still is a high additional dose-saving potential in a consequent application of dose reduction measures, and we recommend individually adapted scan protocols to obtain cardiac CT studies with optimal diagnostic image quality and lowest possible radiation dose.

The purpose of the study was to evaluate trends in the utilization of different imaging modalities and review how imaging utilization practices affect hospital charges for patients with intestinal obstruction. All patients discharged with a primary diagnosis of intestinal obstruction during 6 fiscal years (1999-2004) were retrospectively studied. We obtained data on patients' demographics, procedures, outcomes, imaging services utilization, and hospital and imaging charges from our institution's transition system (a clinical and financial decision support software system). The institutional review board approved this study. Surgery was performed in 26% of patients in 1999 and in 40% in 2004 (p = 0.01) with the mortality rate significantly (p < 0.01) dropping from 3.8% to 0.4%. A total of 5,292 abdominal imaging studies were obtained; 93% of those were either abdominal radiographs or abdomino-pelvic computed tomography (CT) scans. CT studies per patient increased from 0.5 in 1999 to 1 in 2004 (p < 0.01), while abdominal radiographs (mean = 2.4) did not significantly change over the entire study period (p = 0.6). Average imaging charges doubled during the study period ($1,572 to $3,012, p < 0.01). Average hospital charges increased from $18,138 in 1999 to $32,808 in 2004 (p < 0.01). The fraction of hospital charges attributed to imaging varied between 8.7% and 9.2%. CT utilization for intestinal obstruction increased from 1999 to 2004 without modality substitution. While hospital and imaging charges have significantly increased, the fraction represented by imaging has remained constant, suggesting that imaging is an unlikely cause for the increase in hospital charges.

The purpose of this study was to report case studies of iatrogenic splenic injuries on computed tomography (CT) in symptomatic postsurgical patients. The medical records and CT studies of all patients with injury to the spleen after abdominal surgery were reviewed. CT was performed in the postoperative period, urgently in all patients. Unsuspected splenic injuries were found on CT performed in the early postoperative period in seven symptomatic patients (five women and two men, age range 21-81 years) after various abdominal surgical procedures. Injuries as detected on CT included splenic infarct in five, subcapsular hematoma in two, and laceration of the spleen in one. These findings were the only abnormal abdominal findings in four of the patients and were probably the source of the postoperative abdominal pain and fever. Splenic injury is a rare complication of abdominal surgery. It is often the radiologist who diagnoses the injury, and awareness of this possible complication can obviate further investigations.

To prevent possible seismic catastrophe, naturally, its assessment is deeply concerned over in China as a series of arch dams of about 300 m high will be constructed in the severe seismic regions. In this paper the major obstacles to the seismic catastrophe assessment of high arch dams which focused on clearly defining the Maximum Credible Earthquake (MCE) and reasonably selecting its site-specific seismic input parameters as well as quantitatively evaluating the limit state of dam-breach for designers are emphasized. Some breakthrough progress with pending problems is presented, such as to adopt more reasonable seismic input parameters based on seismic hazard evaluation of dam site; to develop model and method more fit in with the reality for non-linear seismic analysis of dam-foundation-reservoir system. The ideals of further improvement both in evaluating the MCE and defining the quantitative index of its performance objective are discussed, including how to use semi-empirical method of simulating strong ground motion near fault, how to solve the long-standing problem of stress singularity at dam heel, and how to investigate dynamic behaviors of fully-graded dam concrete through dynamic tests and 3-dimensional meso-mechanics analysis checked by CT technique.

The purpose of the present study was to determine the diagnostic accuracy of non-enhanced CT and contrast-enhanced CT in integrated PET/CT studies for preoperative nodal staging of rectal cancer.Retrospective analysis was performed in 53 patients with pathologically proven rectal cancer who had been referred for preoperative staging. All patients underwent integrated PET/CT consisting of non-enhanced and contrast-enhanced CT followed by whole-body fluorine-18-fluorodeoxyglucose ([(18)F]FDG) PET. Both non-enhanced and contrast-enhanced PET/CT images were evaluated separately by two observers in consensus. The reference standard was histopathologic results. For nodal staging of rectal cancer, we compared diagnostic accuracy on a per-patient basis between the two modalities.Nodal staging was correctly determined with non-enhanced studies in 37 patients (70%) and with contrast-enhanced studies in 42 patients (79%). On a per-patient basis, sensitivity, specificity, positive predictive value, negative predictive value, and accuracy of regional lymph node staging were 85%, 68%, 83%, 72%, and 79%, respectively, with contrast-enhanced studies, and 85%, 42%, 73%, 62%, and 70%, respectively, with non-enhanced studies. The difference in the accuracy of nodal staging between the two modalities was not significant (p = 0.063). Compared with non-enhanced studies, contrast-enhanced studies determined more correctly the status of pararectal lymph nodes (p = 0.002), internal iliac lymph nodes (p = 0.004), and obturator lymph nodes (p0.0001).Contrast-enhanced PET/CT is superior to non-enhanced PET/CT for precise definition of regional nodal status in rectal cancer.

To assess 18F-fluorodeoxyglucose (FDG) uptake in bone metastases in patients with and without previous treatment, and compare positive positron emission tomography (PET) with osteolytic or osteoblastic changes on computed tomography (CT). One hundred and thirty-one FDG-PET/CT studies were reviewed for bone metastases. A total of 294 lesions were found in 76 patients, 81 in untreated patients and 213 in previously treated patients. PET was assessed for abnormal FDG uptake localised by PET/CT to the skeleton. CT was evaluated for bone metastases and for blastic or lytic pattern. The relationship between the presence and pattern of bone metastases on PET and CT, and prior treatment was statistically analysed using the chi-square test. PET identified 174 (59%) metastases, while CT detected 280 (95%). FDG-avid metastases included 74/81 (91%) untreated and 100/213 (47%) treated lesions (p

The aim of this study was to retrospectively compare the value of integrated PET/CT and separate PET plus morphological imaging studies for lesion localisation in cancer patients. Two different series of consecutive patients who had previously been treated for neoplastic disease were considered. One series consisted of 105 patients who had undergone [(18)F]fluorodeoxyglucose (FDG) PET/CT ( n=70) or [(11)C]choline PET/CT ( n=35) studies (PET/CT group). The other series comprised 105 patients who had undergone FDG PET scan ( n=70) or [(11)C]choline PET scan ( n=35) alone; in this series, PET findings were correlated with the results of morphological imaging (MI) studies, i.e. CT ( n=92) or MR imaging ( n=13) (PET+MI group). Regions of abnormal tracer uptake at PET scanning were classified as ambiguous or unambiguous depending on their precise anatomical localisation. A total of 207 and 196 lesions were found in the PET/CT and PET+MI groups, respectively. The difference in terms of number of lesions per patient detected with the two imaging protocols was not statistically significant ( P=0.718). When analysis of lesion localisation was performed, there were 7/207 (3.4%) and 30/196 (15.3%) ambiguous lesions in the PET/CT and PET+MI groups, respectively. The number of ambiguous lesions was significantly higher in the PET+MI group than in the PET/CT group (chi(2)=15.768, P

The purpose of the study was to determine the feasibility of international teleradiology, utilizing day-night time differences, for online interpretation of overnight computed tomography (CT) studies. One hundred and two consecutive Emergency Room patients who underwent CT examinations between the hours of 11 pm and 7 am were enrolled. All age groups and study types were included. CT studies were transmitted from the in-hospital PACS system (Kodak, Fremont, Calif.) to a web-based server (Medweb, San Francisco, Calif.). A radiologist in Bangalore, India, working an 8 amto 4 pm day shift, downloaded and reviewed the studies on a desktop PC using a 128-kbps internet connection at 10-20:1 wavelet compression and generated a report. The report was then uploaded to the server, noting the time at upload. Each study report was compared with the official in-house diagnostic report and concordance assessed on a three-point scale. Mean download time was 8.14 s per image. For head CT reports ( n=47), the mean turnaround time for a final transcribed report was 39.5 min. For abdomen/pelvis CT reports ( n=48) the mean turnaround time was 84.4 min. Out of 106 cases, there was discordance between the clinical diagnostic report and the study report in 20 (19%); however, on subsequent review the teleradiology report was found to be correct in 13 of these. Day-night time differences across the globe can be utilized to provide overnight emergency radiology coverage using web-based teleradiology. Scan download and report upload times are within acceptable limits.

Background: Perfusion CT is a technology which allows functional evaluation of tissue vascularity. Due to this potential, it is finding increasing utility in oncology. Although since its introduction continuous advances have interested CT technique, some issues have to be still defined, concerning both clinical and technical aspects. In this study, we dealt with the comparison of two widely employed mathematical models (dual input one compartment model - DOCM - and maximum slope - SM -) analyzing their robustness to the noise. Methods. We carried out a computer simulation process to quantify effect of noise on the evaluation of an important perfusion parameter (Arterial Blood Flow - BFa) in liver tumours. A total of 4500 liver TAC, corresponding to 3 fixed BFa values, were simulated using different arterial and portal TAC (computed from 5 real CT images) at 10 values of signal to noise ratio (SNR). BFa values were calculated by applying four different algorithms, specifically developed, to these noisy simulated curves. Three algorithms were developed to implement SM (one semiautomatic, one automatic and one automatic with filtering) and the last for the DOCM method. Results: In all the simulations, DOCM provided the best results, i.e., those with the lowest percentage error compared to the reference value of BFa. Concerning SM, the results are variable. Results obtained with the automatic algorithm with filtering are close to the reference value, but only if SNR is higher than 50. Vice versa, results obtained by means of the semiautomatic algorithm gave, in all simulations, the lowest results with the lowest standard deviation of the percentage error. Conclusions: Since the use of DOCM is limited by the necessity that portal vein is visible in CT scans, significant restriction for patients' follow-up, we concluded that SM can be reliably employed. However, a proper software has to be used and an estimation of SNR would be carried out.

A new method for the coverage prediction of Cellular Mobile Radio (CMR) system is developed and its basic principle is presented. Unlike the Statistical Prediction Model (SPM) that estimates propagation loss by empirical formulas or the Deterministic Prediction Model (DPM) that reckons propagation loss with analytical expressions, the Radio Computerized Tomography (RCT) method does not seek to express the propagation loss explicitly. The 2-D distribution of propagation loss factor is computed using CT technique, based on measured data collected through drive test under appropriate geometric constraint. The total propagation loss can be obtained by integral of propagation loss factor along the equivalent, ray path. The advantages and limitations of the technique, as well as its implementation are discussed.

The CT technique was first applied to observing the nasal cavity of Ikechosaurus sunailinae. The results indicate that the nasal cavity is very complex, and it was divided into two parts: the posterior-upper part and the anterior-lower one. These control olfaction and thermoregulation respectively. The partial loss of pineal systems suggests that this animal may have been evolving toward endothermy. Therefore, Ikechosaurus may have had a strong ability to thermoregulate, thus keeping a high level of activity. But it still did not maintain constant temperature, as the birds and mammals do.

Patienten mit Orbitafrakturen sind haufig schwer verletzt. Eine direkte, konventionelle koronale Computertomographie (CT) ist aufgrund der dafur notigen Positionierung in Bauchlage mit uberstreckten Nacken in der Regel nicht moglich. Die Diagnostik beruht demnach nur auf konventionellen axialen Schichten, da koronal rekonstruierte Bilder eine stark eingeschrankte Bildqualitat besitzen. In einer Pilotstudie an sechs Patienten verglichen wir anhand von Orbitafrakturen die konventionelle Computertomographie in axialen und koronalen Schnittrichtungen mit der Spiral-CT in axialer Schnittebene und koronaler, aus dem Datensatz rekonstruierter Schnitte. Bildqualitat und Beurteilbarkeit von Orbitafrakturen wurden von zwei Untersuchern anhand eines Scores konsensuell bewertet. Die axialen Schnitte in konventioneller und Spiral-CT-Technik zeigten keine wesentlichen Unterschiede bezuglich Bildqualitat. Bei den koronalen Schichten aus Spiral-CT Datensatzen zeigten sich geringe Nachteile in der Beurteilbarkeit des Orbitabodens, jedoch eine deutlich verbesserte Beurteilbarkeit dieser, sowie auch horizontaler Strukturen bezuglich axialer Daten. Bei verletzten Patienten sollte die Untersuchung der Orbita in Spiral-CT-Technik erfolgen, da koronal rekonstruierte Bilder eine deutlich verbesserte Diagnostik gegenuber herkommlichen axialen Schnitten ermoglichen und fast an die Bildqualitat primar koronaler Schichten heranreichen. Patients with orbital fractures frequently suffer from concomitant severe trauma which makes the positioning needed (prone with hyperextended neck) for direct coronal computed tomography (CT) impossible. In this situation just axial scans are acquired directly with the possibility of reconstruction of coronal images from the axially acquired data. However, these reconstructed images show severe shortcomings of image quality making misdiagnosis more likely. In a pilot study with six patients we compared image quality and the ability to assess orbital bone fractures on axial and coronal scans of conventional- and spiral-CT. Evaluation criterion was a modified score which was used consensually by two reviewers to judge the hardcopies. Scores of image quality between spiral-CT and conventional CT were comparable on axial scans. In addition, spiral-CT generates coronal scans of diagnostic quality through multiplanar reconstruction. We recommend the use of spiral — CT technique for severely traumatized patients since reconstructed coronal images improve diagnostic accuracy significantly compared to axial images alone and come close to image quality of direct coronal scans.

We report our 11/2-year experience with 24-hour consulting teleradiology coverage between a rural hospital and a tertiary care center. During this period, 215 studies were transmitted over a T-1 telephone line from Barnesville Hospital to Ohio State Hospital Medical Center. We interpreted 116 computed tomographic studies, of which 64 were head, 31 abdominal, 6 chest, 3 spinal, and 12 miscellaneous CT studies. We also interpreted 26 chest x-rays, 12 cervical spine series, 43 skeletal radiographs, 9 ultrasound studies, 7\(\dot V/\dot Q\) scans, and 2 venograms. Comparison of digital to film interpretations demonstrated agreement in 211 of 215 cases, for a ratio of 98.1%.

Purpose: When a computed tomography (CT) scan on a patient from the emergency department is completed at University of Medicine and Dentistry of New Jersey (UMDNJ)-University Hospital, a non-picture archiving and communication system (PACS) environment, formal diagnostic review cannot begin until the images are printed and transported to the on-call radiology resident. The time to reach a final diagnosis has been significantly reduced by the introduction of a single workstation in the on-call reading room.Materials and Methods: Five radiology residents were studied. Each read 10 CT studies on film and 10 on a workstation. After a training period to familiarize the residents with the workstation, measurements were taken of the time required to read the examination and the time required for printing and transporting or networking the images.Results: The average time required to transmit the images was reduced from approximately 40 minutes to 16 minutes. Interpretation times between the workstation and film were comparable.Conclusion: The addition of a single workstation significantly reduces the time required to reach a final diagnosis by obviating the need to print and transport the images to the on-call radiology resident. Such time savings can have a significant impact on the care of trauma patients.

Objective: To describe the long-term changes in the traumatized spleen following conservative man- agement in pediatric patients. Methods: Between 1991 and 1997, 92 children were imaged with splenic trauma. The study population includes the 25 boys and 11 girls with follow-up computed tomography (CT) imaging at our institution. The follow-up CT studies were evalu- ated to determine the evolution of splenic injury. Re- sults: On initial CT there were 6 grade I, 12 grade II, 9 grade III, and 9 grade IV-V splenic injuries. In follow- up 11 spleens were normal (30 %), including at least one in each grade of severity of injury. Splenic abnor- malities were identified on follow-up in 25 children. These findings comprised clefts in 8 children, small cysts in 4, and devascularized segments involving less than 1c m 3 in 6, 1-2 cm 3 in 2, and 2-4 cm 3 in 5 children. Con- clusions: All grades of splenic injury can resolve com- pletely on subsequent CT imaging. In this series 30 % of patients had a normal follow-up CT. The most com- mon persistent abnormalities included clefts and devas- cularized areas less than 4 cm 3 .

As neuro-imaging techniques have improved, variations of the Dandy-Walker malformation are being reported. In order to succeed in the therapy and avoid or minimize the complications, the fluid dynamics have to be evaluated by contrast CT studies. We are reporting three different types of this malformation and discuss the therapeutic possibilities.

Sir,We appreciate Dr. Sinzig’s interest in our report of theimaging findings of a rapidly involuting congenital heman-gioma [1]. Dr. Sinzig’s questions raise several interestingpoints about the role of the pediatric radiologist in the clinicalcare of patients, the understanding of the risks of ionizingradiation and the influence of hindsight bias on scientificanalysis.The initial evaluation with CT in this case was performedbecause CT provides the best evaluation of the effect of thetumor on the adjacent osseous structures, as well as the highestresolution of vascular features short of catheter angiography.Subsequent CT studies were performed in response to whatwere perceived to be potentially ominous clinical findings;these exams were performed as emergency studies. None oftheCTstudieswasperformedtodocumentexpectedinvolutionof the lesion. Indeed, there was considerable debate regardingthe diagnosis of RICH until the involution became apparent toall. All subsequent evaluations have been with MR imaging.ForallbutthefirstCT,apediatricradiologistwasnotconsultedabout what modality should or should not be used to urgentlyevaluatethischildwithaknownhemorrhagicintracranialmass.Dr. Sinzig’s questions reflect the perspective of one whois aware of the eventual benign evolution of this lesion. Thisis a classic demonstration of hindsight bias [2], in whichhaving knowledge of future events (the eventual benign out-come) shapes one’s perspective of past decision-making. Theclinicians who ordered the exams in this case were not at allconfident of the eventual involution ofthis large hemorrhagictumor in this small child’s brain. Any criticism of their deci-sions needs to recognize this fact.Finally, Dr. Sinzig refers to the “continuously better-known side effects of ionizing radiation, especially ininfants and children” in her letter, citing recent publications[3, 4] that document the estimated risk of radiation exposureon populations. It is important that we all recognize thedifference between estimated risk as it applies to popula-tions, and known side effects as they apply to individuals.Increased incidence of cancer in populations is not a sideeffect of performing CTin any one individual. Rather, it is atheoretical concern based upon what we know of the ioniz-ing effects of radiation exposure. It is our responsibility torecognize this concern and do what we can to minimize thetheoretical risk. We also have a responsibility to educateourselves and our patients and their families as to the relativerisks of performing or not performing diagnostic studies, sothat our decisions can be seen as justifiable and in the bestinterests of our patients, even in retrospect.References