How do radiographic techniques affect image quality and patient doses in CT?

The effects of simulating a realistic eye model on the eye dose of an adult male undergoing head computed tomography

In head computed tomography, radiation upon the eye lens (as an organ with high radiosensitivity) may cause lenticular opacity and cataracts. Therefore, quantitative dose assessment due to exposure of the eye lens and surrounding tissue is a matter of concern. For this purpose, an accurate eye model with realistic geometry and shape, in which different eye substructures are considered, is needed. To calculate the absorbed radiation dose of visual organs during head computed tomography scans, in this study, an existing sophisticated eye model was inserted at the related location in the head of the reference adult male phantom recommended by the International Commission on Radiological Protection (ICRP). Then absorbed doses and distributions of energy deposition in different parts of this eye model were calculated and compared with those based on a previous simple eye model. All calculations were done using the Monte Carlo code MCNP4C for tube voltages of 80, 100, 120 and 140 kVp. In spite of the similarity of total dose to the eye lens for both eye models, the dose delivered to the sensitive zone, which plays an important role in the induction of cataracts, was on average 3% higher for the sophisticated model as compared to the simple model. By increasing the tube voltage, differences between the total dose to the eye lens between the two phantoms decrease to 1%. Due to this level of agreement, use of the sophisticated eye model for patient dosimetry is not necessary. However, it still helps for an estimation of doses received by different eye substructures separately.

Radiation intensity (CTDIvol) and visibility of anatomical structures in head CT examinations

The purpose of this study was to quantify how changing the amount of radiation used to perform routine head CT examinations (CTDIvol) affects visibility of key anatomical structures. Eight routine noncontrast head CT exams were selected from six CT scanners, each of which had a different CTDIvol setting (60 to 75 mGy). All exams were normal and two slices were selected for evaluation, one at the level of basal ganglia and the other at the fourth ventricle. Three experienced neuroradiologists evaluated the visibility of selected structures, including the putamen, caudate nucleus, thalamus, internal capsule, grey/white differentiation, and brainstem. Images were scored on a five‐point scoring scheme (1, unacceptable, 3, satisfactory, and 5, excellent). Reader scores, averaged over the cases obtained from each scanner, were plotted as a function of the corresponding CTDIvol. Average scores for the fourth ventricle were 3.06±0.83 and for the basal ganglia were 3.20±0.86. No image received a score of 1. Two readers showed no clear trend of an increasing score with increasing CTDIvol. One reader showed a slight trend of increasing score with increasing CTDIvol, but the increase in score from a 25% increase in CTDIvol was a fraction of the standard deviation associated average scores. Collectively, results indicated that there were no clear improvements in visualizing neuroanatomy when CTDIvol increased from 60 to 75 mGy in routine head CT examinations. Our study showed no apparent benefit of using more than 60 mGy when performing routine noncontrast head CT examinations.

PACS number(s): 87.57.C‐

A model-based approach of scatter dose contributions and efficiency of apron shielding for radiation protection in CT

Given the contribution of scattered radiations to patient dose in CT, apron shielding is often used for radiation protection. In this study the efficiency of apron was assessed with a model-based approach of the contributions of the four scatter sources in CT, i.e. external scattered radiations from the tube and table, internal scatter from the patient and backscatter from the shielding. For this purpose, CTDI phantoms filled with thermoluminescent dosimeters were scanned without apron, and then with an apron at 0, 2.5 and 5 cm from the primary field. Scatter from the tube was measured separately in air. The scatter contributions were separated and mathematically modelled. The protective efficiency of the apron was low, only 1.5% in scatter dose reduction on average. The apron at 0 cm from the beam lowered the dose by 7.5% at the phantom bottom but increased the dose by 2% at the top (backscatter) and did not affect the centre. When the apron was placed at 2.5 or 5 cm, the results were intermediate to the one obtained with the shielding at 0 cm and without shielding. The apron effectiveness is finally limited to the small fraction of external scattered radiation.

Real practice radiation dose and dosimetric impact of radiological staff training in body CT examinations

OBJECTIVES

To evaluate the radiation dose of the main body CT examinations performed routinely in four regional diagnostic centres, the specific contribution of radiologists and technologists in determining CT dose levels, and the role of radiological staff training in reducing radiation doses.

METHODS

We retrospectively evaluated the radiation dose in terms of dose-length product (DLP) values of 2,016 adult CT examinations (chest, abdomen-pelvis, and whole body) collected in four different centres in our region. DLP values for contrast-unenhanced and contrast-enhanced CT examinations performed at each centre were compared for each anatomical area. DLP values for CT examinations performed before and after radiological staff training were also compared.

RESULTS

DLP values for the same CT examinations varied among centres depending on radiologists' preferences, variable training of technologists, and diversified CT image acquisition protocols. A specific training programme designed for the radiological staff led to a significant overall reduction of DLP values, along with a significant reduction of DLP variability.

CONCLUSIONS

Training of both radiologists and technologists plays a key role in optimising CT acquisition procedures and lowering the radiation dose delivered to patients.

MAIN MESSAGES

• The effective dose for similar CT examinations varies significantly among radiological centres. • Staff training can significantly reduce and harmonise the radiation dose. • Training of radiologists and technologists is key to optimise CT acquisition protocols.

The effect of CT dose on glenohumeral joint congruency measurements using 3D reconstructed patient-specific bone models

The study of joint congruency at the glenohumeral joint of the shoulder using computed tomography (CT) and three-dimensional (3D) reconstructions of joint surfaces is an area of significant clinical interest. However, ionizing radiation delivered to patients during CT examinations is much higher than other types of radiological imaging. The shoulder represents a significant challenge for this modality as it is adjacent to the thyroid gland and breast tissue. The objective of this study was to determine the optimal CT scanning techniques that would minimize radiation dose while accurately quantifying joint congruency of the shoulder. The results suggest that only one-tenth of the standard applied total current (mA) and a pitch ratio of 1.375:1 was necessary to produce joint congruency values consistent with that of the higher dose scans. Using the CT scanning techniques examined in this study, the effective dose applied to the shoulder to quantify joint congruency was reduced by 88.9% compared to standard clinical CT imaging techniques.

Comparison of radiation doses using weight-based protocol and dose modulation techniques for patients undergoing biphasic abdominal computed tomography examinations

Computed tomography (CT) of the abdomen contributes a substantial amount of man-made radiation dose to patients and use of this modality is on the increase. This study intends to compare radiation dose and image quality using dose modulation techniques and weight- based protocol exposure parameters for biphasic abdominal CT. Using a six-slice CT scanner, a prospective study of 426 patients who underwent abdominal CT examinations was performed. Constant tube potentials of 90 kV and 120 kV were used for all arterial and portal venous phase respectively. The tube current-time product for weight-based protocol was optimized according to patient's body weight; this was automatically selected in dose modulations. The effective dose using weight-based protocol, angular and z-axis dose modulation was 11.3 mSv, 9.5 mSv and 8.2 mSv respectively for the patient's body weight ranging from 40 to 60 kg. For patients of body weights ranging 60 to 80 kg, the effective doses were 13.2 mSv, 11.2 mSv and 10.6 mSv respectively. The use of dose modulation technique resulted in a reduction of 16 to 28% in radiation dose with acceptable diagnostic accuracy in comparison to the use of weight-based protocol settings.

Radiation dose at cardiac computed tomography: facts and fiction

Cardiac computed tomography (CT) dosimetry makes use of two radiation parameters: a volume CT dose index (CTDI) and a dose length product (DLP). The volume CTDI quantifies the intensity of the radiation used to perform CT examinations, whereas DLP quantifies the amount of radiation used. CTDI metrics can be converted into patient dose metrics by using dose/CTDI conversion factors. In cardiac CT imaging, these need to take into account the x-ray tube voltage, scan length, and scan region, as well as patient size. Organ doses to patients in cardiac CT can be converted into cancer risks when patient demographic factors are taken into account. A risk analysis of patients undergoing cardiac CT angiography at our institution showed that a majority (62%) were males, with a median age of approximately 60 years and a median weight of approximately 90 kg. The median DLP was approximately 1100 mGy cm, corresponding to an effective dose of approximately 29 mSv in normal-sized patients. The average patient lifetime risk for a radiation-induced cancer was estimated to be 0.12%, with 85% of it attributed to lung cancer. Patients with an age and weight at the 10th percentile, who also received a DLP at the 90th percentile, would have cancer risk estimates approximately double the average value. Radiation risks are required to determine whether examinations are indicated, defined as examinations in which individual patient benefit exceeds corresponding patient risk. Understanding radiation risks in cardiac CT encourages operators to use the least amount of radiation to achieve satisfactory diagnostic performance.

Relationship between radiographic techniques (kilovolt and milliampere-second) and CTDI(VOL)

To investigate the relationship between radiographic techniques (i.e. kilovolt and milliampere-second) and the corresponding volume computed tomography dose index (CTDI(vol)). Data were obtained for CTDI(vol) for head and body phantoms from the ImPACT CT patient dosimetry calculator for 43 scanners from four major vendors of medical imaging equipment (i.e. GE, Philips, Siemens and Toshiba). CTDI(vol) were obtained with the largest X-ray beam width, and using a CT pitch of unity. For each scanner, relative values of CTDI(vol) were also computed as a function of X-ray tube voltage, normalised to unity at 120 kV. The average CTDI(vol) for 43 commercial scanners was 167 + or - 44 microGy (mA s)(-1) for the head phantom and 78 + or - 22 microGy (mA s)(-1) for the body phantom. The 90th percentile CTDI(vol) values are approximately twice the corresponding 10th percentile values for both head and body phantoms. Over the last 20 y, the head phantom CTDI(vol) has increased approximately 50 % and the body phantom CTDI(vol) has increased approximately 90 %. For both, the head phantom and the body phantom, CTDI(vol) is proportional to kilovolt(2.6). CT output must be specified using CTDI(vol) because for a fixed kilovolt and milliampere-second, CT scanner outputs (CTDI(vol)) differ by about a factor of 2. Increasing the X-ray tube voltage from 80 to 140 kV increases CTDI(vol) by about a factor of 4.

In defense of body CT

OBJECTIVE

Rapid technical developments and an expanding list of applications that have supplanted less accurate or more invasive diagnostic tests have led to a dramatic increase in the use of body CT in medical practice since its introduction in 1975. Our purpose here is to discuss medical justification of the small potential risk associated with the ionizing radiation used in CT and to provide perspectives on practice-specific decisions that can maximize overall patient benefit. In addition, we review available dose management and optimization techniques.

CONCLUSION

Dose reduction strategies described in this article must be well understood and properly used, but also require broad-based practice strategies that extend beyond the CT scanner console and default, generic manufacturer settings. In the final analysis, physicians must request the imaging examination that best addresses the specific medical question without allowing worries about radiation to dissuade them or their patients from obtaining needed CT examinations. Ongoing efforts to ensure that CT examinations are both medically justified and optimally performed must continue, and education must be provided to the medical community and general public that put both the potential risks--and benefits--of CT examinations into proper perspective.

Recurrent CT, cumulative radiation exposure, and associated radiation-induced cancer risks from CT of adults

PURPOSE

To estimate cumulative radiation exposure and lifetime attributable risk (LAR) of radiation-induced cancer from computed tomographic (CT) scanning of adult patients at a tertiary care academic medical center.

MATERIALS AND METHODS

This HIPAA-compliant study was approved by the institutional review board with waiver of informed consent. The cohort comprised 31,462 patients who underwent diagnostic CT in 2007 and had undergone 190,712 CT examinations over the prior 22 years. Each patient's cumulative CT radiation exposure was estimated by summing typical CT effective doses, and the Biological Effects of Ionizing Radiation (BEIR) VII methodology was used to estimate LAR on the basis of sex and age at each exposure. Billing ICD9 codes and electronic order entry information were used to stratify patients with LAR greater than 1%.

RESULTS

Thirty-three percent of patients underwent five or more lifetime CT examinations, and 5% underwent between 22 and 132 examinations. Fifteen percent received estimated cumulative effective doses of more than 100 mSv, and 4% received between 250 and 1375 mSv. Associated LAR had mean and maximum values of 0.3% and 12% for cancer incidence and 0.2% and 6.8% for cancer mortality, respectively. CT exposures were estimated to produce 0.7% of total expected baseline cancer incidence and 1% of total cancer mortality. Seven percent of the cohort had estimated LAR greater than 1%, of which 40% had either no malignancy history or a cancer history without evidence of residual disease.

CONCLUSION

Cumulative CT radiation exposure added incrementally to baseline cancer risk in the cohort. While most patients accrue low radiation-induced cancer risks, a subgroup is potentially at higher risk due to recurrent CT imaging.

Strategies for reducing radiation dose in CT

In recent years, the media has focused on the potential danger of radiation exposure from CT, even though the potential benefit of a medically indicated CT far outweighs the potential risks. This attention has reminded the radiology community that doses must be as low as reasonably achievable (ALARA) while maintaining diagnostic image quality. To satisfy the ALARA principle, the dose reduction strategies described in this article must be well understood and properly used. The use of CT must also be justified for the specific diagnostic task.

Horseshoe lung associated with rare bilateral variant of scimitar syndrome: demonstration by 64-slice MDCT angiography

Scimitar syndrome with bilateral abnormal venous drainage and horseshoe lung is extremely rare. These rare complex anomalies were diagnosed in a 5-year-old boy by 64-slice multidetector CT (MDCT). This technique provides high-quality visualization of vascular, bronchial and parenchymal structures in a single session, such that no further invasive techniques are required. One obvious disadvantage of MDCT is the radiation exposure, especially in paediatric patients. The use of a single phase of contrast material administration reduces radiation exposure. The workstation platforms of MDCT systems allow multiplanar 2-D and 3-D postprocessing. As a result, various complex pathologies, such as that discussed here, can be diagnosed following a single imaging session with a certain precision.

Computing effective doses to pediatric patients undergoing body CT examinations

BACKGROUND

The computation of patient effective doses to children is of particular interest given the relatively high doses received from this imaging modality, as well as the increased utilization of CT in all areas of medicine. Current methods for computing effective doses to children are relatively complex, and it would be useful to develop a simple method of computing pediatric effective doses for clinical purposes that could be used by radiologists and technologists.

OBJECTIVE

To obtain pediatric effective doses for body CT examinations by the use of adult effective doses obtained from effective dose (E) per unit dose length product (DLP) coefficients, and energy imparted to a child relative to an adult.

MATERIALS AND METHODS

Adult E/DLP coefficients were obtained at 120 kV using the ImPACT CT dosimetry spreadsheet. Patients were modeled as cylinders of water, and values of energy imparted to cylinders of varying radii were generated using Monte Carlo modeling. The amounts of energy imparted to the chest and abdomen of children relative to adults (R(en)) were obtained. Pediatric effective doses were obtained using scaling factors that accounted for scan length, mAs, patient weight, and relative energy imparted (R(en)).

RESULTS

E/DLP values were about 16 microSv/mGy cm for males and about 19 microSv/mGy cm for females. R(en) at 120 kV for newborns was 0.35 for the chest and 0.49 for the abdomen. At constant mAs, the effective dose to 6-month-old patients undergoing chest CT examinations was found to be about 50% higher than that to adults, and for abdominal examinations about 100% higher.

CONCLUSION

Adult effective doses can be obtained using DLP data and can be scaled to provide corresponding pediatric effective doses from body examinations on the same CT scanner.

Multi-detector row computed tomography angiography of peripheral arterial disease

With the introduction of multi-detector row computed tomography (MDCT), scan speed and image quality has improved considerably. Since the longitudinal coverage is no longer a limitation, multi-detector row computed tomography angiography (MDCTA) is increasingly used to depict the peripheral arterial runoff. Hence, it is important to know the advantages and limitations of this new non-invasive alternative for the reference test, digital subtraction angiography. Optimization of the acquisition parameters and the contrast delivery is important to achieve a reliable enhancement of the entire arterial runoff in patients with peripheral arterial disease (PAD) using fast CT scanners. The purpose of this review is to discuss the different scanning and injection protocols using 4-, 16-, and 64-detector row CT scanners, to propose effective methods to evaluate and to present large data sets, to discuss its clinical value and major limitations, and to review the literature on the validity, reliability, and cost-effectiveness of multi-detector row CT in the evaluation of PAD.

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.

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.

CT Angiography of Pulmonary Arteries to Detect Pulmonary Embolism: Improvement of Vascular Enhancement with Low Kilovoltage Settings

PURPOSE

To retrospectively compare a low kilovoltage scanning protocol with a reduced radiation dose with a standard high kilovoltage, moderate-dose protocol for the depiction of central and peripheral pulmonary arteries at single-detector spiral computed tomography (CT).

MATERIALS AND METHODS

This retrospective study had institutional review board approval; informed consent was waived. A 100-kVp protocol (volume CT dose index [CTDI(vol)], 3.4 mGy) was compared with a standard 140-kVp protocol (CTDI(vol), 10.4 mGy) in two groups that were each composed of 35 consecutive patients who were suspected of having pulmonary embolism (PE) and scanned with otherwise identical acquisition parameters and contrast material injection protocols. Mean main pulmonary artery enhancement and maximum enhancement in peripheral pulmonary arteries were compared. In a blinded evaluation, the percentages of segmental and subsegmental arteries that were considered analyzable for assessment of PE were determined. Overall image quality and delineation of various anatomic areas were subjectively assessed. Comparison of percentages of analyzable segmental and subsegmental arteries and subjective grading of image quality between the two different protocols were performed with the Mann-Whitney U test.

RESULTS

There were 38 male and 24 female patients (mean age, 61 years; range, 17-86 years) in the final evaluation. There was a significantly higher average CT number in the main pulmonary artery (379 HU +/- 95) for the 100-kVp protocol than for the 140-kVp protocol (268 HU +/- 63, P < .001, two-sided t test). Maximum CT numbers in peripheral pulmonary arteries at the level of the aortic arch and lung bases, respectively, were 290 HU +/- 91 and 279 HU +/- 100 for 100 kVp and 185 HU +/- 65 and 144 HU +/- 63 for 140 kVp (P < .001). Mean percentage of subsegmental arteries considered analyzable per patient was higher for 100 kVp than for 140 kVp (segmental arteries, 92% vs 88%, P = .13; subsegmental arteries, 71% vs 55%, P < .001). Subjective grading of overall image quality and of the delineation of structures in the lungs, mediastinum, and upper abdomen did not significantly differ between protocols.

CONCLUSION

At reduced radiation exposure, low kilovoltage scanning increases the percentage of central and peripheral pulmonary arteries that can be evaluated with CT angiography without a substantial decrease in image quality.

The effect of skull volume and density on differentiating gray and white matter on routine computed tomography scans of the head

Increased volume and density of the skull makes computed tomography differentiation of gray and white matter (GM and WM, respectively) more difficult. The purpose of this investigation was to study the effects of skull volume and bone density on GM and WM differentiation. A total of 21 patients with thick skulls and 22 controls were included in this study. Three consecutive slices from the computed tomography scan were analyzed. The basal ganglia had to be visualized on at least 1 slice. Calvarial volume measurement, mean pixel value in each slice, and Hounsfield unit difference between WM and GM, were compared between the thick-skulled and control groups. The mean bone volume of each slice in the thick-skulled group was 55.7, 54.3, and 56 mL, whereas the mean volume of each slice in the normal group was 39.3, 38.5, and 39.9 mL (P < 0.001). In our series, patients with thick skulls had 41% more bone volume than the normal group. The mean skull pixel value in each slice was 935.9 in patients with thick skulls and 987 in patients in the normal group. There was no difference between right and left sides of the same group of patients. Patients with larger volumes of skull have significant decrease in the Hounsfield unit of the GM and WM compared with the control group. As a result, diagnosing any low-contrast brain abnormality including early/subtle infarction in subjects with a thicker calvarium may be more difficult.

Patient-circumference-adapted dose regulation in body computed tomography. A practical and flexible formula

PURPOSE

To illustrate that the attenuation formula based on monochromatic radiation in homogeneous objects may be used for dose regulation in body computed tomography (CT) based on patient circumference and using a simple cloth measuring tape.

MATERIAL AND METHODS

Based on the attenuation formula for monochromatic radiation the following Microsoft Excel equation was derived: mAs(x) = mAs(n)*EXP((0.693/ HVT)*(O(x)-O(n))/PI()), where mAs(x) (milliampere second) in a patient with circumference O(x) is calculated based on the nominal mAs(n) set for a reference patient with the circumference O(n) with regard to indication, scan protocol, and available CT scanner. The HVT = half-value thickness (object thickness change in cm affecting mAs setting by a factor of 2) resulting in the least mAs difference compared with published studies investigating the mAs needed for constant image noise in abdominal CT phantoms at 80-140 kVp was evaluated. Clinically recommended HVT values were applied to 20 patients undergoing abdominal CT using 130 effective mAs and 94 cm circumference as nominal settings, and an HVT of 9 cm.

RESULTS

The object-sized dependent mAs for constant image noise at 80-140 kVp in 10-47 cm diameter abdominal phantoms (31-148 cm in circumference) differed, with few exceptions, by no more than 10% from those obtained with our formula using an HVT of 3.2-3.8 cm. An HVT of 9 cm in the patient study resulted in the same image noise-patient circumference relation as a phantom study using a "clinically adapted mAs" resulting in an acceptable noise according to diagnostic requirements. Clinical experiences recommend an HVT of about 8 cm for abdominal CT and 12 cm in thoracic CT. Changing the kVp from 120 to 80, 100, or 140 requires a mAs change roughly by factors of 4, 2, and 0.6, respectively, for constant image noise.

CONCLUSION

Until fully automatic automatic exposure control systems have been introduced, applying the formula in a computer program provides the radiologist with an easy, quick, flexible, and practical instrument for reasonably good patient-sized adjusted exposure levels in clinical practice.

Novel Developments in Cardiac Computed Tomography

Recent advances in computed tomography have the potential to change the way imaging is performed in the detection of coronary artery disease. The current generation of scanners offers the ability to rapidly acquire thin sections in conjunction with the electrocardiogram, allowing for both anatomic and physiologic data to be obtained. These advancements hold the promise for a noninvasive means of directly evaluating the coronary arteries that can be applied in every day practice. This article reviews the advances in technology and their implications for imaging the heart.

Aorto-iliac multidetector-row CT angiography with low kV settings: improved vessel enhancement and simultaneous reduction of radiation dose

The aim of the study was to implement an abdominal CT angiography protocol using 100 kVp and to compare SNR and CNR, as well as subjective image quality, to a standard CT angiography protocol using 120 kVp on a 16 detector-row CT scanner. Forty-eight patients were referred for routine abdominal CT angiography on a 16 detector-row CT scanner. Patients were scanned using either 120 or 100 kVp at constant mAs settings. Vessel opacification was provided by automated contrast injection using similar injection protocols. Density measurements were performed along the aorto-iliac axis with SNR and CNR calculation. In addition, the estimated effective patient radiation dose was calculated. Results of both protocols were compared. The 100-kVp protocol (432+/-80 HU) showed a significantly higher vessel density than the 120-kVp (333+/-90 HU; P<0.001) protocol, corresponding to an average increase in signal intensity of 30.7%. SNR (36.0 vs 37.0) and CNR (31.1 vs 31.7) for the 100-kV protocol were not significantly lower that those for the standard protocol (P=0.79 and P=0.87), whilst the average estimated dose was significantly lower using the 100-kVp protocol (6.7+/-0.4 vs 10.1+/-1.2 mSv; P<0.0001). Tube kVp reduction from 120 to 100 kVp allows for significant reduction of patient dose in abdominal CT angiography, without significant change in SNR,CNR and image quality.

Contrast-enhanced ultrasound for extrahepatic lesions: preliminary experience

Ultrasound imaging (US) is a convenient, inexpensive and non-invasive investigation. Its use is limited by low sensitivity in the detection of a number of parenchymal lesions, especially those produced by trauma, such as infarctions. Contrast enhancement with SonoVue improves the sensitivity of ultrasound in the detection and characterization of focal liver lesions to such an extent, that it may replace computed tomography (CT) and magnetic resonance imaging (MRI). Preliminary experience suggests that SonoVue-enhanced sonography may be useful in the detection of lesions in which blood flow is severely reduced as compared to surrounding parenchyma, such as infarctions, lacerations, hematomas, necrotic tissue and non-vascular cysts, especially in the spleen, kidney and pancreas. This technique can also rule out occlusion of the superior mesenteric, splenic and portal veins, and dilation of the biliary tree. Clinical trials comparing contrast-enhanced sonography with contrast-enhanced computed tomography are warranted to establish the role of this inexpensive and non-invasive technique in the routine work-up of patients with abdominal trauma or presenting with sudden flank pain.

Multidetector-row CT angiography of the aorta and visceral arteries

Within recent years, technical developments of multidetector-row CT (MDCT) have dramatically changed the application of CT angiography in the assessment of abdominal vascular pathologies. The simultaneous acquisition of multiple thin collimated slices in combination with enhanced gantry rotation speed offers thin slice coverage of extended volumes without any loss in spatial resolution. Using 4 detector-row CT scanners, the scan volume still has to be restricted and focused on dedicated abdominal vessel territories in order to provide high spatial resolution (1-2 mm), while 16 detector-row technology now enables full abdominal coverage from the diaphragm to the groin with full spatial resolution. Therefore, comprehensive CT angiography of the abdomen can be performed without the necessity of focusing on any vascular territory. This technique enables the evaluation of the whole arterial visceral vasculature (e.g., hepatic vessels, mesenteric vessels, renal arteries) and the aortic-iliac axis in a single data acquisition.

Radiation exposure from chest CT: issues and strategies

Concerns have been raised over alleged overuse of CT scanning and inappropriate selection of scanning methods, all of which expose patients to unnecessary radiation. Thus, it is important to identify clinical situations in which techniques with lower radiation dose such as plain radiography or no radiation such as MRI and occasionally ultrasonography can be chosen over CT scanning. This article proposes the arguments for radiation dose reduction in CT scanning of the chest and discusses recommended practices and studies that address means of reducing radiation exposure associated with CT scanning of the chest.

3T MR for Clinical Use: Update

Clinical experience with 3-tesla MRI for body applications has only a short history; to date, it has no proven practical advantage over 1.5-tesla or less powerful systems. However, the theoretical advantage of higher field strength-which includes a higher signal-to-noise ratio with identical scan parameters, higher special resolution available within clinically acceptable scan time, and better spectral resolution-can contribute to the clinical outcome. This paper seeks to demonstrate some of the clinical advantages of the 3-tesla system through preliminary experiences as well as the potential advantages of a 3-tesla system when combined with much of the hardware and software that is clinically accepted in the 1.5-tesla world.