National conference on dose reduction in CT, with an emphasis on pediatric patients

CT dose optimization when changing to CT multi-detector row technology

The purpose of this article was to review the strategies to control patient dose in adult and pediatric computed tomography (CT), taking into account the change of technology from single-detector row CT to multi-detector row CT. First the relationships between computed tomography dose index, dose length product, and effective dose in adult and pediatric CT are revised, along with the diagnostic reference level concept. Then the effect of image noise as a function of volume computed tomography dose index, reconstructed slice thickness, and the size of the patient are described. Finally, the potential of tube current modulation CT is discussed.

Informing parents about CT radiation exposure in children: it's OK to tell them

OBJECTIVE

The purpose of our study was to determine how parents' understanding of and willingness to allow their children to undergo CT change after receiving information regarding radiation dose and risk.

MATERIALS AND METHODS

One hundred parents of children undergoing nonemergent CT studies at a tertiary-care children's hospital were surveyed before and after reading an informational handout describing radiation risk. Parental knowledge of whether CT uses radiation or increases lifetime risk of cancer was assessed, as was willingness to permit their child to undergo both a CT examination that their child's doctor recommended and one for which their doctor thought observation might be equally effective.

RESULTS

Of the 100 parents who were surveyed, 66% believed CT uses radiation before reading the handout, versus 99% afterward (p < 0.01). Before reading the handout, 13% believed CT increases the lifetime risk of cancer, versus 86% afterward (p < 0.01). After reading the handout, parents became less willing to have their child undergo CT given a hypothetic situation in which their doctor believed that either CT or observation would be equally effective (p < 0.01), but their willingness to have their child undergo CT recommended by their doctor did not significantly change. After reading the handout, 62% of parents reported no change in level of concern. No parent refused or requested to defer CT after reading the handout.

CONCLUSION

A brief informational handout can improve parental understanding of the potential increased risk of cancer related to pediatric CT without causing parents to refuse studies recommended by the referring physician.

Pregnancy screening of adolescents and women before radiologic testing: does radiology need a national guideline?

Ionizing radiation has known teratogenic and cancer risks to fetuses. Policies for radiation exposure of pregnant patients during imaging tests in radiology departments vary widely and may or may not be in fully written form. No national guideline exists for how individual radiologists or radiology departments should protect fetuses from ionizing radiation exposure. With the rapid increase in the use of radiologic testing in general, particularly computed tomography, more adolescents and women undergo computed tomographic imaging and may unintentionally expose their fetuses. A national discussion within radiology organizations is needed to understand the advantages and disadvantages in the development of a national guideline for screening women of childbearing age for pregnancy before any procedures using ionizing radiation are performed. Given the increased public concern and increased use of radiologic testing, such a national guideline would improve consumer satisfaction and safety.

The evolving role of radiologists within the health care system

The traditional view of radiologists as physicians who add value to the health care system solely by generating and interpreting diagnostic images is outdated. Radiologists' roles have expanded to encompass economic gatekeeping, political advocacy, public health delivery, patient safety, quality-of-care improvement, and information technology. It is through these roles that radiologists will continue to find new ways to add value to the health care system.

Radiation risk to children from computed tomography

Imaging studies that use ionizing radiation are an essential tool for the evaluation of many disorders of childhood. Ionizing radiation is used in radiography, fluoroscopy, angiography, and computed tomography scanning. Computed tomography is of particular interest because of its relatively high radiation dose and wide use. Consensus statements on radiation risk suggest that it is reasonable to act on the assumption that low-level radiation may have a small risk of causing cancer. The medical community should seek ways to decrease radiation exposure by using radiation doses as low as reasonably achievable and by performing these studies only when necessary. There is wide agreement that the benefits of an indicated computed tomography scan far outweigh the risks. Pediatric health care professionals' roles in the use of computed tomography on children include deciding when a computed tomography scan is necessary and discussing the risk with patients and families. Radiologists should be a source of consultation when forming imaging strategies and should create specific protocols with scanning techniques optimized for pediatric patients. Families and patients should be encouraged to ask questions about the risks and benefits of computed tomography scanning. The information in this report is provided to aid in decision-making and discussions with the health care team, patients, and families.

Computed tomography and radiation: understanding the issues

We are currently seeing increasing opportunities to improve patient care with computed tomography (CT). At the same time, we are challenged to use this technology wisely. In particular, we are being asked to balance the benefits against the risks, chiefly those of ionizing radiation. To do this, we must have a foundation from which to determine the relative risks. This foundation necessarily must be composed of several components. First, it is important to understand the patterns of use and increasing application of CT, particularly multidetector CT. In addition, it is helpful to be familiar with measures of radiation pertinent to CT and the doses provided by this modality. This foundation then provides a context in which to discuss the issue of low-dose radiation and cancer risk as well as potential changes in CT practice guidelines and regulation. It is with an understanding of these issues that radiologists and other radiology personnel can participate in an informed discussion with referring physicians and patients and continue to optimize the practice of CT.

Facts and controversies about radiation exposure, part 1: controlling unnecessary radiation exposures

In this 2-part article, the authors address the need to put in perspective the risks of radiation exposure in the rapidly changing field of radiology, considering the current state of knowledge of effects at low levels. The article is based on the content of the refresher course RC 516 presented at the Radiological Society of North America's 2005 annual meeting. After a brief review of epidemiologic studies, part 1 contains a discussion of typical radiation doses experienced in medicine, by both patients and professionals, and it concludes with a description of practical approaches to reduce unnecessary exposures. Part 2 of the article addresses a special concern for the unborn and discusses advisory and regulatory cancer risk estimates based mainly on epidemiologic studies. The limitations of epidemiologic studies at low-level exposures and recent new findings in radiobiology, some of which are summarized, challenge the notion that any amount of radiation causes adverse effects.

Radiation exposure and pregnancy: when should we be concerned?

The potential biological effects of in utero radiation exposure of a developing fetus include prenatal death, intrauterine growth restriction, small head size, mental retardation, organ malformation, and childhood cancer. The risk of each effect depends on the gestational age at the time of exposure, fetal cellular repair mechanisms, and the absorbed radiation dose level. A comparison between the dose levels associated with each of these risks and the estimated fetal doses from typical radiologic examinations lends support to the conclusion that fetal risks are minimal and, therefore, that radiologic and nuclear medicine examinations that may provide significant diagnostic information should not be withheld from pregnant women. The latter position is advocated by the International Commission on Radiological Protection, National Council on Radiation Protection, American College of Radiology, and American College of Obstetrics and Gynecology. However, although the risks are small, it is important to ensure that radiation doses are kept as low as reasonably achievable.

Peer assessment of pediatric surgeons for potential risks of radiation exposure from computed tomography scans

PURPOSE

Radiology literature reports potential cancer risk from radiation exposure from computed tomography (CT). We hypothesized that pediatric surgeons' knowledge of potential risks of radiation exposure from CT scan is limited.

METHODS

We used an anonymous, Internet-based peer assessment survey for members of the American Pediatric Surgical Association (APSA). The survey assessed surgeon's knowledge based on potential risks of radiation exposure from CT as well as current practice patterns for use of CT. The chi2 test of significance was used to detect any differences in responses based on years in training.

RESULTS

Twenty percent (147/753) of the American Pediatric Surgical Association members completed the survey. About one half (54%) of surgeons believe that the lifetime risk of cancer was increased because of radiation from one abdominal/pelvic CT scan, although more than 75% of respondents underestimated the radiation dose from a CT scan compared to a chest radiograph. Most surgeons generally did not discuss the potential risks of CT scan with their patients. Surgeons demonstrated a range of responses for use of CT for select clinical scenarios.

CONCLUSIONS

Pediatric surgeon's knowledge of potential risks of radiation exposure from CT scan is limited. As the radiology literature indicates an increasing awareness for potential cancer risks from radiation exposure from CT, there is also a need for education of subspecialties outside of radiology.

Imaging strategies to reduce the risk of radiation in CT studies, including selective substitution with MRI

"When one admits that nothing is certain one must, I think, also admit that some things are much more nearly certain than others." Bertrand Russell (1872-1970) Computed tomography (CT) is one of the largest contributors to man-made radiation doses in medical populations. CT currently accounts for over 60 million examinations in the United States, and its use continues to grow rapidly. The principal concern regarding radiation exposure is that the subject may develop malignancies. For this systematic review we searched journal publications in MEDLINE (1966-2006) using the terms "CT," "ionizing radiation," "cancer risks," "MRI," and "patient safety." We also searched major reports issued from governmental U.S. and world health-related agencies. Many studies have shown that organ doses associated with routine diagnostic CT scans are similar to the low-dose range of radiation received by atomic-bomb survivors. The FDA estimates that a CT examination with an effective dose of 10 mSv may be associated with an increased chance of developing fatal cancer for approximately one patient in 2000, whereas the BEIR VII lifetime risk model predicts that with the same low-dose radiation, approximately one individual in 1000 will develop cancer. There are uncertainties in the current radiation risk estimates, especially at the lower dose levels encountered in CT. To address what should be done to ensure patient safety, in this review we discuss the "as low as reasonably achievable" (ALARA) principle, and the use of MRI as an alternative to CT.

Automatic exposure control in multichannel CT with tube current modulation to achieve a constant level of image noise: Experimental assessment on pediatric phantoms

Automatic exposure control (AEC) systems have been developed by computed tomography (CT) manufacturers to improve the consistency of image quality among patients and to control the absorbed dose. Since a multichannel helical CT scan may easily increase individual radiation doses, this technical improvement is of special interest in children who are particularly sensitive to ionizing radiation, but little information is currently available regarding the precise performance of these systems on small patients. Our objective was to assess an AEC system on pediatric dose phantoms by studying the impact of phantom transmission and acquisition parameters on tube current modulation, on the resulting absorbed dose and on image quality. We used a four-channel CT scan working with a patient-size and z-axis-based AEC system designed to achieve a constant noise within the reconstructed images by automatically adjusting the tube current during acquisition. The study was performed with six cylindrical poly(methylmethacrylate) (PMMA) phantoms of variable diameters (10-32 cm) and one 5 years of age equivalent pediatric anthropomorphic phantom. After a single scan projection radiograph (SPR), helical acquisitions were performed and images were reconstructed with a standard convolution kernel. Tube current modulation was studied with variable SPR settings (tube angle, mA, kVp) and helical parameters (6-20 HU noise indices, 80-140 kVp tube potential, 0.8-4 s. tube rotation time, 5-20 mm x-ray beam thickness, 0.75-1.5 pitch, 1.25-10 mm image thickness, variable acquisition, and reconstruction fields of view). CT dose indices (CTDIvol) were measured, and the image quality criterion used was the standard deviation of the CT number measured in reconstructed images of PMMA material. Observed tube current levels were compared to the expected values from Brooks and Di Chiro's [R.A. Brooks and G.D. Chiro, Med. Phys. 3, 237-240 (1976)] model and calculated values (product of a reference value multiplied by a dose ratio measured with thermoluminescent dosimeters). Our study demonstrates that this AEC system accurately modulates the tube current according to phantom size and transmission to achieve a stable image noise. The system accurately controls the tube current when changing tube rotation time, tube potential, or image thickness, with minimal variations of the resulting noise. Nevertheless, CT users should be aware of possible changes of tube current and resulting dose and quality according to several parameters: the tube angle and tube potential used for SPR, the x-ray beam thickness (tube current decreases and image noise increases when doubling x-ray beam thickness), the pitch value (a pitch decrease leads to a higher dose but also to a higher noise), and the acquisition field of view (FOV) (tube current is lower when using the small acquisition FOV compared to the large one, but the use of small acquisition FOV at 120 kVp leads to a peculiar increase of tube current and CTDIvol).

Clinical importance of precursor lesions in the pancreas

Three distinct noninvasive precursor lesions to invasive ductal adenocarcinoma of the pancreas have been described. These include the mucinous cystic neoplasm, intraductal papillary mucinous neoplasm, and pancreatic intraepithelial neoplasia. The early detection and treatment of these lesions can interrupt the progression of a curable noninvasive precursor to an almost uniformly deadly invasive cancer.

Increasing utilization of computed tomography in the pediatric emergency department, 2000–2006

The objective of this study is to characterize changes in computed tomography (CT) utilization in the pediatric emergency department (ED) over a 6-year period. CT scans ordered on pediatric (ages 0 to 17 years) ED patients from July 2000 to July 2006 were analyzed in five groups: head, cervical spine, chest, abdomen, and miscellaneous. Pediatric ED patient volume and triage acuity scores were determined. There were 6,073 CT scans performed on 4,138 pediatric patients in the ED during the study period. During this same period, 78,932 pediatric patients were evaluated in the ED. From 2000 to 2006, pediatric ED patient volume increased by 2%, while triage acuity remained stable. During this same period, head CT increased by 23%, cervical spine CT by 366%, chest CT by 435%, abdominal CT by 49%, and miscellaneous CT by 96%. Increases in CT utilization were most pronounced in adolescents ages 13 to 17 years. Increases in CT utilization in this age group met or exceeded increases seen in the adult population. In children less than 13 years of age, increases were substantially smaller. Pediatric ED CT utilization particularly in the adolescent population has increased at a rate far exceeding the growth in ED patient volume, mimicking the adult trend. This increase has occurred despite considerable discussion in the medical literature about the radiation risks of CT in the pediatric population and may reflect increased availability of CT, improvements in CT diagnostic capabilities, and increased desire on the part of physicians and patients for diagnostic certainty. Whether this increased utilization results in improved patient outcomes is uncertain and deserves further study.

Review of radiation risks from computed tomography: essentials for the pediatric surgeon

BACKGROUND/PURPOSE

Over the past several years, increasing attention has been focused on the potential for radiation exposure from computed tomography (CT) for inducing the development of cancers. An understanding of these issues is important for the practice of pediatric surgery.

METHODS

Medline based clinical review of current medical literature of the risks for the induction of cancers by CT. Data includes estimates of cancer risk from computer models, epidemiologic data from survivors of atomic bomb radiation exposure, and consensus opinions from expert panels.

RESULTS

Review of scientific evidence demonstrates varied opinions, but consensus suggests there may be a potential for an increased risk of cancer from low level radiation exposure such as from CT. These calculations suggest that there may be as high as 1 fatal cancer for every 1000 CT scans performed in a young child.

CONCLUSIONS

Pediatric surgeons should be aware of the potential risks of CT. Minimizing the radiation risks of CT is a complex endeavor, and will require investments from pediatric surgeons as well as pediatric radiologists.

Dose reduction in paediatric MDCT: general principles

The number of multi-detector array computed tomography (MDCT) examinations performed per annum continues to increase in both the adult and paediatric populations. Estimates from 2003 suggested that CT contributed 17% of a radiology department's workload, yet was responsible for up to 75% of the collective population dose from medical radiation. The effective doses for some CT examinations today overlap with those argued to have an increased risk of cancer. This is especially pertinent for paediatric CT, as children are more radiosensitive than adults (and girls more radiosensitive than boys). In addition, children have a longer life ahead of them, in which radiation induced cancers may become manifest. Radiologists must be aware of these facts and practise the ALARA (as low as is reasonably achievable) principle, when it comes to deciding CT protocols and parameters.

Patient Radiation Doses from Adult and Pediatric CT

OBJECTIVE

The purpose of our study was to determine typical organ doses, and the corresponding effective doses, to adult and pediatric patients undergoing a single CT examination.

MATERIALS AND METHODS

Heads, chests, and abdomens of patients ranging from neonates to oversized adults (120 kg) were modeled as uniform cylinders of water. Monte Carlo dosimetry data were used to obtain average doses in the directly irradiated region. Dosimetry data were used to compute the total energy imparted, which was converted into the corresponding effective dose using patient-size-dependent effective-dose-per-unit-energy-imparted coefficients. Representative patient doses were obtained for scanning protocols that take into account the size of the patient being scanned by typical MDCT scanners.

RESULTS

Relative to CT scanners from the early 1990s, present-day MDCT scanners result in doses that are approximately 1.5 and approximately 1.7 higher per unit mAs in head and body phantoms, respectively. Organ absorbed doses in head CT scans increase from approximately 30 mGy in newborns to approximately 40 mGy in adults. Patients weighing less than approximately 20 kg receive body organ absorbed doses of approximately 7 mGy, which is a factor of 2 less than for normal-sized (70-kg) adults. Adult head CT effective doses are approximately 0.9 mSv, four times less than those for the neonate. Effective doses for neonates undergoing body CT are approximately 2.5 mSv, whereas those for normal-sized adults are approximately 3.5 mSv.

CONCLUSION

Representative organ absorbed doses in CT are substantially lower than threshold doses for the induction of deterministic effects, and effective doses are comparable to annual doses from natural background radiation.

Relationship between noise, dose, and pitch in cardiac multi-detector row CT

In spiral computed tomography (CT), dose is always inversely proportional to pitch. However, the relationship between noise and pitch (and hence noise and dose) depends on the scanner type (single vs multi-detector row) and reconstruction mode (cardiac vs noncardiac). In single detector row spiral CT, noise is independent of pitch. Conversely, in noncardiac multi-detector row CT, noise depends on pitch because the spiral interpolation algorithm makes use of redundant data from different detector rows to decrease noise for pitch values less than 1 (and increase noise for pitch values > 1). However, in cardiac spiral CT, redundant data cannot be used because such data averaging would degrade the temporal resolution. Therefore, the behavior of noise versus pitch returns to the single detector row paradigm, with noise being independent of pitch. Consequently, since faster rotation times require lower pitch values in cardiac multi-detector row CT, dose is increased without a commensurate decrease in noise. Thus, the use of faster rotation times will improve temporal resolution, not alter noise, and increase dose. For a particular application, the higher dose resulting from faster rotation speeds should be justified by the clinical benefits of the improved temporal resolution.

3-Dimensional Adaptive Raw-Data Filter

OBJECTIVES

To evaluate a 3-dimensional adaptive raw-data filter in reducing streak artifacts in low dose chest computed tomographic (CT) images.

METHODS

Fourteen adult patients who underwent low dose chest CT examination (parameters: 25 or 50 mAs, 120 kV) on 64-detector CTscanner were included in this study. We prepared 2 sets of contiguous 5-mm thick images by reconstruction with and without 3-dimensional adaptive raw-data filter (filter-processed and unprocessed images). Streak artifacts and visualization of peripheral vessels in both filter-processed and unprocessed images were evaluated using a 5-point scale. Upper, middle, and lower thorax were evaluated separately.

RESULTS

The difference in artifact severity was statistically significant in upper and lower thorax (P = 0.002 and 0.03, respectively), whereas it was not significant in middle thorax (P = 0.13). The difference in the visibility of peripheral pulmonary vessels was not statistically significant in all anatomical regions.

CONCLUSIONS

The 3-dimensional adaptive raw-data filter reduced streak artifacts in low dose chest CT in upper and lower thorax.

Is there a role for CT in the neonate?

Choice of imaging modalities should be based on scientific proof and best practice guidelines. However, in the neonatal age group there is a paucity of medical evidence, and imaging is often guided by local experience, availability of equipment and expertise, and by logistical factors. This paper discusses possible indications for CT in the neonate, the associated radiation protection issues, common CT findings and potential pitfalls in technique and image interpretation. Due to the particular range of abnormalities in this age group, imaging must be tailored to the individual, and should in most cases be done in specialist units.

CT dose reduction and dose management tools: overview of available options

In the past decade, the tremendous advances in computed tomography (CT) technology and applications have increased the clinical utilization of CT, creating concerns about individual and population doses of ionizing radiation. Scanner manufacturers have subsequently implemented several options to appropriately manage or reduce the radiation dose from CT. Modulation of the x-ray tube current during scanning is one effective method of managing the dose. However, the distinctions between the various tube current modulation products are not clear from the product names or descriptions. Depending on the scanner model, the tube current may be modulated according to patient attenuation or a sinusoidal-type function. The modulation may be fully preprogrammed, implemented in near-real time by using a feedback mechanism, or achieved with both preprogramming and a feedback loop. The dose modulation may occur angularly around the patient, along the long axis of the patient, or both. Finally, the system may allow use of one of several algorithms to automatically adjust the current to achieve the desired image quality. Modulation both angularly around the patient and along the z-axis is optimal, but the tube current must be appropriately adapted to patient size for diagnostic image quality to be achieved.

Role of 18F-FDG PET/CT in staging and follow-up of lymphoma in pediatric and young adult patients

OBJECTIVE

To assess the role of 18F-Fluorodeoxyglucose (18F-FDG) PET/CT in pediatric patients with Hodgkin disease (HD) and non-Hodgkin lymphoma (NHL).

MATERIALS AND METHODS

31 patients, mean age 12.9 +/- 5.1, HD (n = 24), and NHL (n = 7) underwent 18F-FDG PET/CT at diagnosis (n = 31 studies) and later in the course of the disease (n = 75 studies). The findings of PET/CT were correlated with diagnostic CT and clinical follow-up.

RESULTS

PET/CT findings resulted in a change of disease staging in 10 patients (32.3%), upstaging in 7 (22.6%) and downstaging in 3 (9.6%). On a lesion analysis, 164 disease sites were detected by PET/CT of which 38 were overlooked by DCT. At mid-treatment, PET was negative in 28 out of 31 patients (90%) with negative predictive value of 96% as all latter patients except for 1, were disease free (mean 15.4 +/- 8.8 months). The positive predictive value of persistent increased 18F-FDG uptake was 100% as 3 patients with latter findings had active disease. On the CT part, 76 residual masses were identified in 22 patients. Increased 18F-FDG uptake was detected in 11 masses in 4 patients who had active disease. Remaining 65 PET negative masses were false positive findings. The positive predictive value of residual CT mass was 14%.

CONCLUSIONS

PET/CT is associated with change in staging in approximately 1 out of 3 pediatric patients with HD and NHL. When used for monitoring response to treatment, a negative study is associated with disease-free period, even when residual mass is detected. A positive PET study indicates residual malignant disease.

Periampullary and pancreatic incidentaloma: a single institution's experience with an increasingly common diagnosis

BACKGROUND

While incidental masses in certain organs have received particular attention, periampullary and pancreatic incidentalomas (PIs) remain poorly characterized.

METHODS

We reviewed 1944 consecutive pancreaticoduodenectomies (PD) over an 8-year period (April 1997 to October 2005). A total of 118 patients (6% of all PDs) presented with an incidental finding of a periampullary or pancreatic mass. The PI patients were analyzed and compared with the rest of the cohort (NI, nonincidentaloma group, n = 1826).

RESULTS

Thirty-one percent of the PI patients (n = 37) had malignant disease (versus 76% of the NI patients, P < 0.001), 47% (n = 55) had premalignant disease, and the remaining 22% (n = 26) had little or no risk for malignant progression. The 3 most common diagnoses in the PI group were IPMN without invasive cancer (30%), cystadenoma (17%), and pancreatic ductal adenocarcinoma (10%). The PI group had a higher overall complication rate (55% versus 43%, P = 0.02), due in part to a significantly increased rate of pancreatic fistulas (18.4% PI versus 8.5% NI, P < 0.001). Patients in the PI group with malignant disease had a superior long-term survival (median, 30 months, P = 0.01) compared with patients in the NI group with malignant disease (median, 21 months).

CONCLUSIONS

Incidentally discovered periampullary and pancreatic masses comprise a substantial proportion of patients undergoing PD. Roughly three fourths of these lesions are malignant or premalignant, and amenable to curative resection. Resected malignant PIs have favorable pathologic features as compared with resected malignant NIs, and resection of these early lesions in asymptomatic individuals is associated with improved survival, compared with patients with symptomatic disease.

The utilization of pediatric computed tomography in a large Israeli Health Maintenance Organization

BACKGROUND

Concern has been raised about the potential risks related to radiation exposure from CT scans, particularly among children. However, to date, there are few data available describing the magnitude of pediatric CT utilization.

OBJECTIVE

The aim of the study was to explore patterns of CT use in pediatric patients, with respect to time, use of multiple scans, body regions imaged, and medical diagnoses.

MATERIALS AND METHODS

Records of 22,223 scans performed on 18,075 people aged < or =18 years over the period 1999-2003, including diagnoses recorded within 21 days after the examination, were obtained from a large Israeli Health Maintenance Organization (1,600,000 members).

RESULTS

The highest annual CT examination rate (per 1,000) was recorded in 2001 (10.1) compared to 7.0 and 6.3 in 1999 and 2003, respectively. The lowest rate (three scans per 1,000) was found for 3-year-old children, with increasing rates with age. The head was the most frequently scanned region, both in young children (78%) and adolescents (39%). Symptoms of ill-defined conditions and injuries were documented in 22% and 10% of all scans, respectively.

CONCLUSIONS

Although the results suggest that children comprise only 3% of all patients undergoing CT, this important modality must be carefully used because of their increased radiosensitivity, higher effective radiation doses, and longer life expectancy.

Incidence of Pulmonary Embolism in Younger Versus Older Patients Using CT

OBJECTIVE

The aim of this study is to compare the incidence of pulmonary embolism (PE) on computed tomography (CT) studies between younger and older patients to determine if there is an age-related bias for overutilization of CT pulmonary angiography (CTPA) in younger patients.

MATERIAL AND METHODS

Six hundred thirty-one consecutive CTPA cases for suspected acute PE between 11/10/2003 and 3/19/2004 were retrospectively studied. Of these 631 cases, 59 patients were found to have clots in the pulmonary arteries (ranging from central to subsegmental PA). CTPA was performed using multidetector CT at 1.25-mm collimation, 120 kVp, 320 mA. Patients were categorized by gender and age: A, less than 20 (n = 11); B, 20 to 29 (n = 44); C, 30 to 39 (n = 59); D, 40 to 49 (n = 90); E, 50 to 59 (n = 120); F, 60 to 69 (n = 114); G, 70 to 79 (n = 104); H, 80 to 89 (n = 72); I, 90 or more (n = 21). The incidences of PE were calculated in each gender and age group. To compare the incidence of PE between younger and older groups, they were divided into 2 groups at the ages of 40 (<39 and > or = 40), 50 (<49 and > or = 50), and 60 (<59 and > or = 60). Statistical analysis was performed using the chi test.

RESULTS

The incidences of PE were 11.9% in males (A, 0%; B, 17.6%; C, 10%; D, 8.3%; E, 13.3%; F, 6.9%; G, 17.5%; H, 23.5%; I, 0%), 7.7% in females (A, 0%; B, 7.4%; C, 5.1%; D, 12.5%; E, 4.2%; F, 14.5%; G, 7.8%; H, 5.5%; I, 0%), and 9.4% in total patients (A, 0%; B, 11.1%; C, 6.8%; D, 11.1%; E, 7.5%; F, 10.5%; G, 11.5%; H, 9.7%; I, 0%). No significant differences in the incidences of PE were observed when patients were divided at the age of 40 (male, female, total; P=1.0, 0.6252, 0.7220), at the age of 50 (male, female, total; P = 0.6748, 0.6879, 1.0), or at the age of 60 (male, female, total; P = 0.8458, 0.7046, 0.6820).

CONCLUSION

No statistically significant difference in the incidence of PE was observed between younger and older patients. Our findings suggest that there is no age-related bias for overutilization of CT angiography (CTA) in younger patients.

Tube current reduction in pediatric non-ECG-gated heart CT by combined tube current modulation

BACKGROUND

Dose reduction by combined tube current modulation has not been evaluated in pediatric low-dose CT.

OBJECTIVE

This study was performed to evaluate tube current reduction in non-ECG-gated heart CT angiography in children by combined tube current modulation, and to assess the effects of body weight, age, sex, and scan direction on tube current reduction.

MATERIALS AND METHODS

From September 2004 to January 2005, non-ECG-gated heart CT examinations were performed with combined tube current modulation in 50 children (median age 1 year, range 1 month to 16 years; M/F 29/21) with congenital heart disease. Sixteen-slice spiral CT studies were obtained using a weight-based low-dose protocol (80 kVp, 50-160 effective mA). CT scans were obtained in the craniocaudal direction when leg veins (n=36) were used for IV injection of contrast agent and in the caudocranial direction when arm veins (n=13) were used. In one child who underwent a Fontan operation, both arm and leg veins were used. We calculated tube current reduction by combined tube current modulation and evaluated the effects of body weight, age, sex, and scan technique on tube current reduction. The quality of CT angiography images was visually evaluated by an experienced pediatric radiologist.

RESULTS

Overall tube current reduction by combined tube current modulation was 15.8+/-11.1%. The reduction was variable among five body weight groups (9.3+/-7.9% for <4.9 kg, 14.3+/-9.3% for 5.0-9.9 kg, 16.4+/-12.5% for 10.0-19.9 kg, 25.8+/-9.8% for 20.0-39.9 kg, 15.9+/-12.7% for 40.0-59.9 kg) and was significantly different among the five groups (P=0.017). When eight children in the 40.0-59.9-kg group were excluded, age showed a significant positive correlation with tube current reduction (gamma=0.4, P=0.003). There was no significant difference in tube current reduction between boys and girls. Tube current reduction was significantly greater for the caudocranial scan (21.2+/-9.2%) than for the craniocaudal scan (14.2+/-11.3%) (P=0.049). All CT angiography images were of diagnostic quality.

CONCLUSIONS

Combined tube current modulation reduced tube current in pediatric non-ECG-gated heart CT by 15.8% without degradation of image quality. With our CT protocol, for body weights up to 39.9 kg, age showed a significant positive correlation with tube current reduction, but there was a lower dose-saving effect in children heavier than 40 kg. Tube current reduction was not affected by sex, but was affected by scan direction.

Multidetector CT of musculoskeletal disease in the pediatric patient: principles, techniques, and clinical applications

Computed tomography (CT) plays an important role in the evaluation of musculoskeletal disease in the pediatric patient. With the advent of high-performance 16-section multidetector CT, images can be produced with subsecond gantry rotation times and with submillimeter acquisition, which yields true isotropic high-resolution volume data sets; these features are not attainable with older spiral CT technology. Such capabilities are particularly helpful in the evaluation of pediatric patients by virtually eliminating the need for sedation and minimizing dependence on patient cooperation. The role of three-dimensional (3D) volume imaging in the evaluation of pediatric musculoskeletal disease continues to evolve, with this technique becoming increasingly important in detection and characterization of lesions as well as in decisions about patient care. Specific designs and protocols for multidetector CT studies can be selected to minimize radiation dose to the patient. Principal clinical applications of 3D CT in evaluation of the pediatric musculoskeletal system include developmental abnormalities, trauma, neoplasms, and postoperative imaging.

CT in children with abdominal cancer: should we routinely include the pelvis?

BACKGROUND

It has been suggested that the pelvis should not be habitually included on abdominal CT examinations, but the potential benefit of such a practice in childhood abdominal malignancies is unknown.

OBJECTIVE

To estimate the yield and potential diagnostic benefit of abnormal findings on CT of the pelvis in children with malignant primary tumours in the upper abdomen.

MATERIALS AND METHODS

From a paediatric tertiary referral hospital we retrospectively included patients having abdominal CT for primary upper abdominal tumours (1997-2004), the scan range routinely including the pelvis. We reviewed and tabulated any pelvic abnormality, and calculated group proportions with 95% confidence intervals.

RESULTS

We identified 230 children (2 days to 17 years old, median 2.9 years). Six (2.6%; 95% CI 0.5-4.7%) had abnormalities in the pelvis that would not have affected clinical management. Four (1.7%; 95% CI 0.1-3.4%) had findings that might have influenced staging, but only one was not detected by other modalities within 1 week of the CT.

CONCLUSIONS

Our data suggest that diagnostically significant findings in the pelvis are rare; consequently, the habitual inclusion of the pelvis on abdominal CT for primary malignant tumours in the abdomen is not justified.

Pediatric Superior Vena Cava Syndrome: Assessment at Low Radiation Dose 64-slice CT Angiography

We report a case of an 8-year-old boy with a history of aortopexy for aortic compression and multiple venous thrombosis. A 64-slice multidetector-row computed tomography examination was performed to evaluate the cause of esophageal varices and the extent of previously reported thrombi. Despite extremely low radiation dose settings, the 64-slice computed tomography angiography was fully diagnostic and showed discontinuity of the superior vena cava and brachiocephalic veins. In addition, the azygous system and large collateral vessels across the anterior, medial, and posterior mediastinum and chest wall were observed. This case shows that in pediatric patients complicated vascular pathology can reliably be assessed and radiation exposure can be safely minimized.

Simulation of Liver Lesions for Pediatric CT

PURPOSE

To develop and validate a technique based on characteristics of real lesions for simulating realistic small liver lesions on pediatric computed tomographic (CT) images.

MATERIALS AND METHODS

The institutional review board provided exempt status for this study, determined that it was not subject to HIPAA compliance, and did not require informed consent. Patient identification information was removed from clinical images from contrast material-enhanced multi-detector row CT examinations performed in 10 children. Patients were infants or children up to 18 years old. Information about sex was not available. Children had one or more liver lesions of 2-6 mm in maximum transverse diameter. Images with more than one lesion were rendered multiple times, and each time, all but one of the lesions were digitally removed in sequence. This process provided images (n = 19) with a single real lesion. For consistency, the same image backgrounds (images with all real lesions removed) were used to create an identical number of images (n = 19), each with a single simulated lesion. Subsequently, three radiologists independently assessed images of real and simulated lesions that were presented in random order with a score on a continuous scale of 0 (definitely simulated) to 100 (definitely real). Mixed-model analysis of variance was used to test the null hypothesis that the difference in population mean scores between the two lesion types was zero.

RESULTS

The observer study did not reveal a significant difference in the ability of any radiologist to discriminate between real and simulated lesions (P > .31). The differences in mean scores for discrimination between real and simulated lesions for the three observers were -6, 9, and -7, respectively. The estimated overall difference was -1.

CONCLUSION

Mathematic simulation of liver lesions is a feasible technique for creating realistic lesions for image quality or dose reduction studies in pediatric CT.

Dose reduction for CT in children with cystic fibrosis: is it feasible to reduce the number of images per scan?

BACKGROUND

Reducing the dose for each CT scan is important for children with cystic fibrosis (CF).

OBJECTIVE

To determine whether the number of CT images and therefore the dose per CT scan could be reduced without any significant loss of information in children with CF.

MATERIALS AND METHODS

A cohort of children with CF was followed with biennial surveillance CT scans, obtained in inspiration after a voluntary breath-hold as 1-mm thick images at 10-mm intervals from lung apex to base. A random set of 20 baseline CT scans and 10 follow-up CT scans were blinded. Sets of every image (10-mm intervals), every second image (20-mm intervals), every third image (30-mm intervals) and a selection of three and five images were scored randomly using a published CT scoring system by one experienced observer.

RESULTS

The 20 subjects were 10 years of age with a range of 3.7-17.6 years at baseline. Fewer CT images resulted in a significantly lower (less abnormal) CT score and the number of patients positive for abnormalities decreased subsequently. At intervals greater than 20 mm no significant change in CT score over 2 years could be detected, while the CT scores at 10-mm (P=0.02) and 20-mm (P=0.02) intervals worsened significantly.

CONCLUSIONS

A reduction in the number of inspiratory CT images by increasing the interval between images to greater than 10 mm is not a valid option for radiation dose reduction in children with CF.

Use of an Automatic Exposure Control Mechanism for Dose Optimization in Multi–Detector Row CT Examinations: Clinical Evaluation

PURPOSE

To prospectively compare dose reduction and image quality achieved with an automatic exposure control system that is based on both angular (x-y axis) and z-axis tube current modulation with dose reduction and image quality achieved with an angular modulation system for multi-detector row computed tomography (CT).

MATERIALS AND METHODS

The study protocol was approved by the institutional review board, and oral informed consent was obtained. In two groups of 200 patients, five anatomic regions (ie, the thorax, abdomen-pelvis, abdomen-liver, lumbar spine, and cervical spine) were examined with this modulation system and a six-section multi-detector row CT scanner. Data from these patients were compared with data from 200 patients who were examined with an angular modulation system. Dose reduction by means of reduction of the mean effective tube current in 600 examinations, image noise in 200 examinations performed with each modulation system, and subjective image quality scores in 100 examinations per-formed with each modulation system were compared with Wilcoxon signed rank tests.

RESULTS

Mean dose reduction for the angular and z-axis tube current modulation system and for the angular modulation system was as follows: thorax, 20% and 14%, respectively; abdomen-liver, 38% and 18%, respectively; abdomen-pelvis, 32% and 26%, respectively; lumbar spine, 37% and 10%, respectively; and cervical spine, 68% and 16%, respectively. These differences were statistically significant (P < .05). There was no significant difference in image noise and mean image quality scores between modulation systems, with the exception of cervical spinal examinations (P < .001 for both), where the examinations with angular modulation resulted in better scores. There is good correlation between the mean effective tube current level and the body mass index of patients with the new modulation system. Correlation was as follows: thorax, 0.77; abdomen-pelvis, 0.83; abdomen-liver, 0.84; lumbar spine, 0.8; and cervical spine, 0.6. This correlation was not observed with the angular modulation system.

CONCLUSION

An automatic exposure control mechanism that is based on real-time anatomy-dependent tube current modulation delivers good image quality with a significantly reduced radiation dose.

[Radiation exposure of patients from diagnostic and interventional X-ray procedures. Facts, assessment and trends]

Man-made radiation exposure to the German population predominantly results from the medical use of ionizing radiation. According to the most recent evaluation, the mean effective dose per inhabitant and year from X-ray procedures increased from 1.6 to 1.8 mSv between 1996 and 2001. This rise is mainly caused by the expanding use of CT and reflects the growing importance of this imaging modality. Besides actual data on the frequency and dose of various types of X-ray examinations, patient-specific factors will be highlighted which have to be considered in the assessment of the associated individual and collective radiation risk. Moreover, different concepts to reduce radiation exposure of patients will be discussed as well as some current trends in health service that may affect radiation hygiene -- such as diagnosis-related groups for inpatients and CT screening.

Comparison of effective doses for low-dose MDCT and radiographic examination of sinuses in children

OBJECTIVE

Our objective was to show that in low-dose MDCT of the sinuses in children the effective dose can be lowered to a level comparable to that used for standard radiographic images, with resultant CT scans that are still of diagnostic image quality.

MATERIALS AND METHODS

In standard radiographic examinations of sinuses (anteroposterior and lateral views) with 75 kV, 20 mAs, and 3-mm aluminum filtration in 69 children (mean age, 4.2 years), the dose-area-product (DAP; mGy x cm2) was measured and converted to effective dose (mSv) according to coefficients published by the British National Radiological Protection Board. Another group of 125 children (mean age, 6.8 years) underwent low-dose MDCT of the sinuses with 6- or 16-MDCT in two phases and with different scanning protocols. An effective dose for MDCT was calculated from conversion of the dose-length-product (DLP, mGy xm) according to age.

RESULTS

The mean effective dose (E) for standard radiography was 0.0528 mSv. The mean E value for low-dose MDCT was 0.096 mSv in the first phase of the study but could be lowered in the second phase to 0.0531 mSv by a combination of higher pitch and faster scan rotation time in our scan protocols, which results in diagnostic image quality at a very low dose. Statistical analysis showed no significant differences in effective dose between radiography and MDCT of the second phase.

CONCLUSION

With modern MDCT technology, low-dose CT of the sinuses in children can yield diagnostic image quality using an effective dose comparable to that used for standard radiography.

Radiation Cost of Helical High-Resolution Chest CT

OBJECTIVE

In our department, most high-resolution CT (HRCT) scans of the lungs are performed in conjunction with a standard helical examination to assess the entire chest. This requires scanning the patient twice. The goal of this study was to determine if the radiation dose could be decreased by performing a single combination helical scan of the chest from which both 5-mm standard and 1.25-mm HRCT images could be obtained.

CONCLUSION

Because the total measured radiation dose is 32% greater from a single combination helical HRCT scan of the chest versus separate standard helical plus axial HRCT scans, helical HRCT is not a clinically advisable technique.

Patient dose in multislice CT: why is it increasing and does it matter?

A brief review is presented of the reasons why multislice spiral/helical CT is associated with a higher radiation dose burden to the patient even than incremental CT. These include both intrinsic technological and geometric factors as well as simply a growing use of CT in an increasing number of applications. The typical magnitude of this dose burden is indicated and the basis for the anxiety that underpins it, namely the linear no-threshold (LNT) hypothesis, is discussed, together with the countervailing hypothesis that there is indeed a threshold for radiation harm in man and that the radiation doses associated with CT may lie below this threshold and may even be beneficial (radiation hormesis). There are as yet no certainties in this important area but it is argued that it is not a given that the doses associated with CT are harmful.

Review of radiation issues for computed tomography

Over the past three decades, computed tomography (CT) has proven to be central in imaging evaluation. Multidetector technology continues to drive practice patterns by combining fast scanning with high quality data sets. This has resulted in new applications as well as improved use in traditional applications. With this recognition has also come the realization that there are potential costs of CT. One major cost is the radiation dose. Therefore, in order to begin to assess benefits (which are relatively familiar to radiologists) versus costs (which are less familiar), the issues related to CT radiation need to be addressed. Familiarity with measures of CT radiation and the actual doses delivered by CT are important issues as they provide a basis for understanding the potential cancer risks from CT radiation. Moreover, these justify development of strategies to minimize radiation dose. Strategies include obtaining only necessary CT examinations and adjusting the examinations based on scan indication, region examined, and patient size. These strategies must also be combined with efforts by manufacturers in development and implementation of technology aimed at radiation dose management, as well as efforts in research, education, and CT standards and regulation. This article reviews the subject of radiation dose with multidetector CT technology, including measures of CT radiation, the dose that can result from CT examinations, the risks of this amount of radiation, and strategies for minimizing CT radiation dose.

Medical perspective on ways to improve radiation protection standards

Radiation has been used in medical practice for over a century. While hazards were recognized very early, radiation protection in medicine evolved over many subsequent decades. Current issues and problems of radiation protection in medicine are mainly the result of rapidly changing technology and lack of education. With the widespread application of computed tomography and digital radiography, use of high dose radiological equipment by nonradiologists, and continuing accidental exposures in radiation therapy there are problems not envisioned before. Radiation protection in medicine is not likely to be improved significantly simply with the addition of more standards, but it will require a combined approach with the medical and educational communities.

Appendiceal abscess drainage

Appendicitis is the most common abdominal inflammatory process in children, and the most frequent indication for abdominal drainage encountered in pediatric interventional radiology. Imaging in the diagnosis of appendicitis is evolving with CT becoming more common, although the incidence of perforation is not definitely improving. Tailored CT techniques for the diagnosis of acute appendicitis are designed to expedite care, but are not optimal in the diagnosis or characterization of abscesses. In the appropriate clinical setting the CT study needs to be altered for appropriate therapeutic planning. Drainage of appendiceal abscesses utilizes multiple techniques, some of which are more useful in children than adults. Image-guided drainage can facilitate a more limited surgery and can avoid repeat surgery from postoperative abscesses. Radiation doses must be minimized due to the increased risk in children. This article will discuss imaging in children with suspected appendiceal abscesses and drainage techniques.

Radiation Exposure and Projected Risks With Multidetector-Row Computed Tomography Scanning

A substantial increase in computed tomography (CT) scanning with availability of state-of-the-art multidetector-row CT scanners has generated debate about its safety and considerable interest in formulating clinical and technologic strategies to reduce radiation exposure. This review describes the magnitude of radiation exposure associated with CT scanning and projected radiation risks as well as clinical strategies and major technologic innovations for reducing radiation dose to patients undergoing CT scanning.

The use of sonography versus computed tomography in the triage of blunt abdominal trauma: the European perspective

The management of the trauma-emergency patient has become an important political and economic issue and one of the major challenges of the industrialized countries. In Europe ultrasonography is always part of the basic work-up, following physical examination, whereas computed tomography (CT) remains a second-line investigation. Injury prevalence, radiation dose exposure, practicability, and costs are relevant considerations in our emergency departments, where we have a growing number of patients seeking medical attention. The radiologist's task is to decide which imaging modality is most appropriate after the clinical context has been taken into consideration. The clinical value of CT is unquestioned; what is questionable is only its systematic use. With the growing demand for trauma care, screening ultrasonography can lower the number of inappropriate CT examinations.

Diagnostic CT scans: assessment of patient, physician, and radiologist awareness of radiation dose and possible risks

PURPOSE

To determine the awareness level concerning radiation dose and possible risks associated with computed tomographic (CT) scans among patients, emergency department (ED) physicians, and radiologists.

MATERIALS AND METHODS

Adult patients seen in the ED of a U.S. academic medical center during a 2-week period with mild to moderate abdominopelvic or flank pain and who underwent CT were surveyed after acquisition of the CT scan. Patients were asked whether or not they were informed about the risks, benefits, and radiation dose of the CT scan and if they believed that the scan increased their lifetime cancer risk. Patients were also asked to estimate the radiation dose for the CT scan compared with that for one chest radiograph. ED physicians who requested CT scans and radiologists who reviewed the CT scans were surveyed with similar questions and an additional question regarding the number of years in practice. The chi(2) test of independence was used to compare the three respondent groups regarding perceived increased cancer risk from one abdominopelvic CT scan.

RESULTS

Seven percent (five of 76) of patients reported that they were told about risks and benefits of their CT scan, while 22% (10 of 45) of ED physicians reported that they had provided such information. Forty-seven percent (18 of 38) of radiologists believed that there was increased cancer risk, whereas only 9% (four of 45) of ED physicians and 3% (two of 76) of patients believed that there was increased risk (chi(2)(2) = 41.45, P <.001). All patients and most ED physicians and radiologists were unable to accurately estimate the dose for one CT scan compared with that for one chest radiograph.

CONCLUSION

Patients are not given information about the risks, benefits, and radiation dose for a CT scan. Patients, ED physicians, and radiologists alike are unable to provide accurate estimates of CT doses regardless of their experience level.

Computed tomography and radiation risks: what pediatric health care providers should know

Computed tomography (CT) is an extremely valuable diagnostic tool. Recent advances, particularly multidetector technology, have provided increased and more diverse applications. However, there is also the potential for inappropriate use and unnecessary radiation dose. Because some data indicate that low-dose radiation (such as that in CT) may have a significant risk of cancer, especially in young children, it is important to limit CT radiation by following the ALARA (as low as reasonably achievable) principle. There is a variety of strategies to limit radiation dose, including performing only necessary examinations, limiting the region of coverage, and adjusting individual CT settings based on indication, region imaged, and size of the child. The pediatric health care provider has a pivotal role in the performance of CT and may be the only individual who discusses these important CT radiation issues with the child and family. For this reason, this article will summarize the issues with CT patterns of use and radiation risk, and provide dose reduction strategies pertinent to pediatric health care providers.