[Using CT to Evaluate Cardiac Function]

A comprehensive evaluation of cardiac function includes information in relation to cardiac output and systemic venous return. The heart is composed of four chambers: two atria and two ventricles, each with its own unique mechanical function. These four cardiac chambers, their valves, and the pulmonary circulation system are inter-related as they preload or afterload on each other. Cardiac dysfunction is a failure of global cardiac function, resulting in typical clinical manifestations. To investigate the underlying cause of cardiac dysfunction, a step-by-step evaluation of cardiac blood flow tracks is necessary. In this context, imaging markers showing details of the cardiac structures have an important role in assessing cardiac function. An image-based evaluation allows for investigation of function in terms of individual cardiac components. Evaluation of cardiac function using cardiac CT has recently been validated. This review aimed to discuss cardiac CT-based imaging markers for comprehensive and detailed cardiac function assessment.

Left Atrial Diverticula Supplied by the Anomalistic Branch of the Right Coronary Artery

We have reported several cases of pulmonary vein thrombosis in elderly individuals with or without chest pain; pulmonary vein thrombosis is common in aged individuals and should be evaluated further. However, the properties and roles of pulmonary vein thrombi (PVTs) have not been determined. During infection, neutrophil extracellular traps (NETs) are produced to kill pathogens, and arterial thrombi (ATs) are produced in pulmonary veins to prevent pathogens from spreading to all organs. We reported that fine PVTs became larger PVTs and extended to the LA wall. PVTs can cause acute myocardial infarction (AMI) and ischemic stroke (IS) by releasing larger particles; therefore, the characteristics of PVTs need to be determined to prevent the occurrence of AMI and IS. PVTs can cause several diseases by releasing smaller particles, such as NETs, for which cumulative effects should be determined. PVTs and their effects on human health need to be studied to avoid missing the chances of treating patients with these diseases moderately. We reported that PVTs often extend to the left atrium (LA) and attach to the LA wall; however, the effects of attachment remain unclear. According to cardiac computed tomography (CT), left atrial diverticula (LADs) reportedly occur in 10%-50% of patients; however, the details of the LAD are unknown. Therefore, we examined the relationships among PVTs, LA thrombi, and LADs using cardiac CT and transesophageal echocardiography (TEE). The patient was a 65-year-old male with hypertension and severe palpitations. He had no history of AMI or IS. TEE revealed that the LA thrombi were attached to the anterior wall of the right lower pulmonary vein and that they were attached to the anterior wall of the LA. TEE revealed an LAD near the attachment area. Cardiac CT revealed an LAD without thrombi near the attachment area. Sagittal images from a cardiac CT scan revealed that a part of the attachment region in the LA was a dark line, where no blood flow was observed in the LA, and that there seemed to be the LAD on top of the dark line. The anomalistic branch of the right coronary artery (#1) connected around the top of the LAD.

Left Atrial Diverticula Present in the Right Lower Pulmonary Vein Thrombus Attachment Area

Left atrial diverticula (LADs) are thought to be associated with atrial fibrillation and an ischemic brain state. However, the mechanisms of LAD formation are unknown. Pulmonary vein thrombi (PVTs) can cause acute myocardial infarction (AMI) and ischemic stroke by releasing rather large particles. Additionally, PVTs can release much smaller particles, including neutrophil extracellular traps (NETs) and/or other components of NETs, such as DNA and histones. To treat these diseases, it may be crucial to know the specific traits of PVTs. However, these issues are not direct effects of PVTs on the left atrium (LA). It is unclear whether PVTs affect the LA directly. We checked the direct effects of PVTs on the LA using cardiac computed tomography (CT) and transesophageal echocardiography (TEE). The patient was a 73-year-old female with hypertension. TEE revealed extended LA thrombi from the right lower pulmonary vein, which were attached to the anterosuperior wall of the LA. Cardiac CT revealed the attaching area as a defect of enhancement and dimly revealed LAD with full thrombi on the attaching area. It was difficult to recognize the LAD at first; however, after one month of standard-dose heparin-warfarin treatment, the LAD was clearly detected using cardiac CT. LA thrombi could not be detected using cardiac CT.

Effect of papillary muscle and trabeculae on left ventricular function analysis via computed tomography: A cross-sectional study

Deciding whether to include or exclude the papillary muscles and trabeculae to blood pool is essential, because quantifications of left ventricular (LV) functional parameters and myocardial mass are significantly affected. As a result, such inclusion or exclusion might produce different indices for diagnosis and therapy. Using cardiac computed tomography (CT), we obtained standard values of the portion of papillary muscle and trabeculae in normal adults, and to find out how the inclusion or exclusion of papillary muscle and trabeculae affect LV functional parameters depending on the patient group. Excluding the papillary muscles from the LV mass results in easier automated contour detection using CT. The percentage portions of papillary muscle and trabeculae to LV end-diastolic volume (EDV) and LV mass (LVM) were 11.9 ± 5.6% and 20.2 ± 4.3%, respectively, significantly affecting disease diagnosis. Imaging should be consistent at follow-up and include or exclude the papillary muscles and trabeculae to avoid introducing significant differences between measurements.

Multidetector Computed Tomography (MDCT) Angiography Evaluation of Total Anomalous Pulmonary Venous Connection

Total anomalous pulmonary venous connection (TAPVC) is a rare congenital cardiovascular malformation in which all four pulmonary veins anomalously drain into the right atrium (RA) either directly or indirectly. There are four main types based on the site of connection. Any type of TAPVC may be associated with obstruction and presents early in the neonatal period with cyanosis, tachycardia, or respiratory distress. We present four cases of all types of TAPVC and its imaging findings in multidetector computed tomography (MDCT) angiography. Cardiac CT and magnetic resonance imaging (MRI) are very useful in delineating the anatomy and drainage pathway of anomalous pulmonary veins. MDCT angiography is noninvasive and easily available, and rapid image acquisition is possible with high spatial resolution. Since early diagnosis and surgical correction are necessary for the survival of these neonates, rapid image acquisition using MDCT angiography can be preferred over MRI.

Vieussens' ring coronary collateral circulation: a natural bypass history

"Vieussens' ring" or "arterial circle of Vieussens" is a crucial hetero-coronaric pathway, bridging proximal right coronary artery (RCA) and left anterior descending artery (LAD) when a hemodynamically stenosis is established in the either of the vessel. In detail such coronary collateral circulation is usually supplied by branches of the conus artery. We present a case of a 62-year-old man who was admitted to our emergency department complaining of chest pain. Coronary angiography showed LAD occlusion at the mid tract with delayed and slight opacification of its distal segment sustained by Vieussens' ring. Coronary computed tomography angiography (CCTA) was subsequently performed which confirmed the presence of such natural bypass and evaluated its relationship with adjacent structures. Imaging, particularly CCTAoffers a valid tool in assessing the hetero-coronaric collateral vessel. Due to its high spatial resolution it may provide many information about the coronary anatomy by delineating their origin, course and termination.

Myocardial Cut-off Sign is a Sensitive and Specific Cardiac Computed Tomography and Magnetic Resonance Imaging Sign to Distinguish Left Ventricular Pseudoaneurysms From True Aneurysms

PURPOSE

The purpose of this study was to describe the myocardial cut-off sign, assess its ability to distinguish left ventricular pseudoaneurysms (LV PSAs) from true aneurysms (LVAs), and compare its performance with other imaging findings and quantitative measurements used to differentiate LV PSAs from LVAs.

MATERIALS AND METHODS

This retrospective single-center study identified patients with preoperative cardiac computed tomography (CT) or magnetic resonance imaging (MRI) and surgically confirmed LVAs or LV PSAs over a 10-year period. Seventeen LV PSAs (11 MRI, 6 CT) and 18 LVAs (10 MRI, 8 CT) were included. The myocardial cut-off sign was objectively a >50% decrease in aneurysm sac wall thickness measured at 1 cm from the aneurysmal neck (measurements at 2 cm were also assessed) and subjectively an abrupt "cut-off" of myocardium for the aneurysm sac for PSA compared with a gradual tapering of sac wall thickness for LVA. Two radiologists independently evaluated images for the subjective presence of this sign.

RESULTS

The myocardial cut-off sign was 91% sensitive and 97% specific when measured 1 cm from the aneurysm neck. When measured at 2 cm from the neck, the sign was 100% sensitive and 69% specific. Subjective analysis of whether the myocardium appeared "cut-off" was 94% to 100% sensitive and 78% to 94% specific with excellent agreement for both PSA (κ=0.94) and LVA (κ=0.83).

CONCLUSIONS

The myocardial cut-off sign on cardiac CT and MRI is a sensitive and specific finding of LV PSA. Specificity is improved with objective measurements compared with subjective assessment (97% vs. 78% to 94%). This sign may help radiologists distinguish between LV PSAs and LVAs.

Coronary-Cameral Fistula, Thebesian Veins, and Anomalous Coronary Vein on Cardiac Computed Tomography

A 63-year-old female with a history of hypertension presented with progressively worsening shortness of breath. She underwent a cardiac catheterization and was found to have prominent Thebesian veins as well as anomalous connections between the proximal right coronary artery and the right ventricle. Cardiac computed tomography was ordered for further evaluation and showed a coronary fistula to the right ventricular outflow tract confirming the diagnosis of a coronary-cameral fistula (CCF). CCF are rare congenital anomalous communications that occur between coronary arteries and a cardiac chamber. They are usually an incidental finding and patients are rarely symptomatic. As the use of coronary computed tomography angiography is rapidly expanding, the detection of CCF will likely increase in the general population.

Coronary CT angiography: a guide to examination, interpretation, and clinical indications

INTRODUCTION

The introduction of Cardiac Computed Tomography (CCT) has changed the paradigm in the field of diagnostic cardiovascular medicine. CCT is the primary tool in the assessment of suspected Coronary Artery Disease (CAD) and should be followed by functional assessment when needed to stratify disease and to plan potential interventional or surgical therapy.

AREAS COVERED

We provided the current state of the knowledge on the main aspects of technique of examination, image interpretation and clinical indications. We have focused our attention on the basic routine applications and activities.

EXPERT OPINION

The primary role of CCT in suspected CAD will progressively become the standard approach. In general, any situation in which anatomy of the heart and thoracic vessels/structures is mandatory must be approached using CT first, whenever possible. The quantity and quality of information that can be provided by CCT is big and the operators should learn how to deal with this information. On the other hand, CCT is only apparently a straightforward and simple examination. It is actually the most complex diagnostic procedure that can be performed on CT and requires highly skilled operators and state-of-art-technology.

EDUCATIONAL SERIES IN CONGENITAL HEART DISEASE: Cardiovascular MRI and CT in congenital heart disease

Cardiovascular MRI and CT are useful imaging modalities complimentary to echocardiography. This review article describes the common indications and consideration for the use of MRI and CT in the management of congenital heart disease.

Rupture of Sinus of Valsalva Aneurysm into Interventricular Septum: Role of Cardiac CT

Sinus of Valsalva aneurysm dissecting and forming sinus tract into interventricular septum is an extremely rare complication of sinus of Valsalva aneurysm. Echocardiography and conventional angiography were used earlier to diagnose ruptured sinus of Valsalva aneurysm. Cardiac CT has emerged as a valuable non-invasive diagnostic tool for evaluation of complications of sinus of Valsalva aneurysm. In this article, we report two cases of ruptured sinus of Valsalva aneurysm arising from right and left coronary sinuses into the interventricular septum without aorto-cardiac shunt formation evaluated using 256 slice cardiac CT imaging. After diagnosis on cardiac CT, these findings were confirmed perioperatively and were repaired surgically.

The role of acquisition and quantification methods in myocardial blood flow estimability for myocardial perfusion imaging CT

In this work, we clarified the role of acquisition parameters and quantification methods in myocardial blood flow (MBF) estimability for myocardial perfusion imaging using CT (MPI-CT). We used a physiologic model with a CT simulator to generate time-attenuation curves across a range of imaging conditions, i.e. tube current-time product, imaging duration, and temporal sampling, and physiologic conditions, i.e. MBF and arterial input function width. We assessed MBF estimability by precision (interquartile range of MBF estimates) and bias (difference between median MBF estimate and reference MBF) for multiple quantification methods. Methods included: six existing model-based deconvolution models, such as the plug-flow tissue uptake model (PTU), Fermi function model, and single-compartment model (SCM); two proposed robust physiologic models (RPM1, RPM2); model-independent singular value decomposition with Tikhonov regularization determined by the L-curve criterion (LSVD); and maximum upslope (MUP). Simulations show that MBF estimability is most affected by changes in imaging duration for model-based methods and by changes in tube current-time product and sampling interval for model-independent methods. Models with three parameters, i.e. RPM1, RPM2, and SCM, gave least biased and most precise MBF estimates. The average relative bias (precision) for RPM1, RPM2, and SCM was  ⩽11% (⩽10%) and the models produced high-quality MBF maps in CT simulated phantom data as well as in a porcine model of coronary artery stenosis. In terms of precision, the methods ranked best-to-worst are: RPM1  >  RPM2  >  Fermi  >  SCM  >  LSVD  >  MUP [Formula: see text] other methods. In terms of bias, the models ranked best-to-worst are: SCM  >  RPM2  >  RPM1  >  PTU  >  LSVD [Formula: see text] other methods. Models with four or more parameters, particularly five-parameter models, had very poor precision (as much as 310% uncertainty) and/or significant bias (as much as 493%) and were sensitive to parameter initialization, thus suggesting the presence of multiple local minima. For improved estimates of MBF from MPI-CT, it is recommended to use reduced models that incorporate prior knowledge of physiology and contrast agent uptake, such as the proposed RPM1 and RPM2 models.

Quantitative myocardial perfusion from static cardiac and dynamic arterial CT

Quantitative myocardial blood flow (MBF) estimation by dynamic contrast enhanced cardiac computed tomography (CT) requires multi-frame acquisition of contrast transit through the blood pool and myocardium to inform the arterial input and tissue response functions. Both the input and the tissue response functions for the entire myocardium are sampled with each acquisition. However, the long breath holds and frequent sampling can result in significant motion artifacts and relatively high radiation dose. To address these limitations, we propose and evaluate a new static cardiac and dynamic arterial (SCDA) quantitative MBF approach where (1) the input function is well sampled using either prediction from pre-scan timing bolus data or measured from dynamic thin slice 'bolus tracking' acquisitions, and (2) the whole-heart tissue response data is limited to one contrast enhanced CT acquisition. A perfusion model uses the dynamic arterial input function to generate a family of possible myocardial contrast enhancement curves corresponding to a range of MBF values. Combined with the timing of the single whole-heart acquisition, these curves generate a lookup table relating myocardial contrast enhancement to quantitative MBF. We tested the SCDA approach in 28 patients that underwent a full dynamic CT protocol both at rest and vasodilator stress conditions. Using measured input function plus single (enhanced CT only) or plus double (enhanced and contrast free baseline CT's) myocardial acquisitions yielded MBF estimates with root mean square (RMS) error of 1.2 ml/min/g and 0.35 ml/min/g, and radiation dose reductions of 90% and 83%, respectively. The prediction of the input function based on timing bolus data and the static acquisition had an RMS error compared to the measured input function of 26.0% which led to MBF estimation errors greater than threefold higher than using the measured input function. SCDA presents a new, simplified approach for quantitative perfusion imaging with an acquisition strategy offering substantial radiation dose and computational complexity savings over dynamic CT.

Cardiac helical CT involving a low-radiation-dose protocol with a 100-kVp setting: Usefulness of hybrid iterative reconstruction and display preset optimization

To compare the radiation dose and image quality of retrospective electrocardiogram (ECG)-gated cardiac computed tomography (CT) between a 100-kVp protocol, hybrid iterative reconstruction (HIR), and display preset optimization and the 120-kVp protocol.We prospectively enrolled 100 patients with tachycardia or atrial fibrillation scanned retrospective ECG-gated cardiac CT. We randomly assigned 50 patients to the 120-kVp protocol and 50 patients to the 100-kVp protocol. We compared effective doses (EDs) between the two protocols. The 120-kVp images were post-processed using filtered back projection (FBP). The 100-kVp images were post-processed using FBP (100-kVp protocol) and HIR (i-100-kVp protocol). We compared attenuation of the ascending aorta, signal-to-noise ratio (SNR), and image noise between the 120-kVp, 100-kVp, and i-100-kVp protocols. We performed qualitative image analysis for the 120-kVp and i-100-kVp protocols.ED of the 100-kVp protocol (4.4 ± 0.4 mSv) was 76% lower than that of the 120-kVp protocol (18.4 ± 0.6 mSv). Attenuations of the 100-kVp (549.1 ± 73.8 HU) and i-100-kVp (550.5 ± 73.7 HU) protocols were higher than that of the120-kVp protocol (437.3 ± 55.7 HU). Image noise of the 100-kVp (53.6 ± 18.5 HU) and i-100-kVp (30.9 ± 8.6 HU) protocols were higher than that of the120-kVp protocol (23.8 ± 5.7 HU). There was no significant difference in SNR and the result of qualitative image analysis between the 120-kVp and i-100-kVp protocols.The 100-kVp protocol with HIR reduced the 76% radiation dose while preserving the image quality compared with the conventional 120-kVp protocol on retrospective ECG-gated cardiac CT.

Aged Garlic Extract Reduces Low Attenuation Plaque in Coronary Arteries of Patients with Metabolic Syndrome in a Prospective Randomized Double-Blind Study

BACKGROUND

Although several previous studies have demonstrated that aged garlic extract (AGE) inhibits the progression of coronary artery calcification, its effect on noncalcified plaque (NCP) has been unclear.

OBJECTIVE

This study investigated whether AGE reduces coronary plaque volume measured by cardiac computed tomography angiography (CCTA) in patients with metabolic syndrome (MetS).

METHODS

Fifty-five patients with MetS (mean ± SD age: 58.7 ± 6.7 y; 71% men) were prospectively assigned to consume 2400 mg AGE/d (27 patients) or placebo (28 patients) orally. Both groups underwent CCTA at baseline and follow-up 354 ± 41 d apart. Coronary plaque volume, including total plaque volume (TPV), dense calcium (DC), NCP, and low-attenuation plaque (LAP), were measured based upon predefined intensity cutoff values. Multivariable linear regression analysis, adjusted for age, gender, number of risk factors, hyperlipidemia medications, history of coronary artery disease, scan interval time, and baseline %TPV, was performed to examine whether AGE affected each plaque change.

RESULTS

The %LAP change was significantly reduced in the AGE group compared with the placebo group (-1.5% ± 2.3% compared with 0.2% ± 2.0%, P = 0.0049). In contrast, no difference was observed in %TPV change (0.3% ± 3.3% compared with 1.6% ± 3.0%, P = 0.13), %NCP change (0.2% ± 3.3% compared with 1.4% ± 2.9%, P = 0.14), and %DC change (0.2% ± 1.4%, compared with 0.2% ± 1.7%, P = 0.99). Multivariable linear regression analysis found a beneficial effect of AGE on %LAP regression (β: -1.61; 95% CI: -2.79, -0.43; P = 0.008).

CONCLUSIONS

This study indicates that the %LAP change was significantly greater in the AGE group than in the placebo group. Further studies are needed to evaluate whether AGE has the ability to stabilize vulnerable plaque and decrease adverse cardiovascular events. This trial was registered at clinicaltrials.gov as NCT01534910.

Increased regional epicardial fat volume associated with reversible myocardial ischemia in patients with suspected coronary artery disease

Epicardial adipose tissue is a source of pro-inflammatory cytokines and has been linked to the development of coronary artery disease. No study has systematically assessed the relationship between local epicardial fat volume (EFV) and myocardial perfusion defects. We analyzed EFV in patients undergoing SPECT myocardial perfusion imaging combined with computed tomography (CT) for attenuation correction. Low-dose CT without contrast was performed in 396 consecutive patients undergoing SPECT imaging for evaluation of coronary artery disease. Regional thickness, cross-sectional areas, and total EFV were assessed. 295 patients had normal myocardial perfusion scans and 101 had abnormal perfusion scans. Mean EFVs in normal, ischemic, and infarcted hearts were 99.8 ± 82.3 cm(3), 156.4 ± 121.9 cm(3), and 96.3 ± 102.1 cm(3), respectively (P < 0.001). Reversible perfusion defects were associated with increased local EFV compared to normal perfusion in the distribution of the right (69.2 ± 51.5 vs 46.6 ± 32.0 cm(3); P = 0.03) and left anterior descending coronary artery (87.1 ± 76.4 vs 46.7 ± 40.6 cm(3); P = 0.005). Our results demonstrate increased regional epicardial fat in patients with active myocardial ischemia compared to patients with myocardial scar or normal perfusion on nuclear perfusion scans. Our results suggest a potential role for cardiac CT to improve risk stratification in patients with suspected coronary artery disease.

Completeness map evaluation demonstrated with candidate next-generation cardiac CT architectures

PURPOSE

In this report, the authors introduce the general concept of the completeness map, as a means to evaluate the completeness of data acquired by a given CT system design (architecture and scan mode). They illustrate the utility of completeness map by applying the completeness map concept to a number of candidate CT system designs, as part of a study to advance the state-of-the-art in cardiac CT.

METHODS

In order to optimally reconstruct a point within a volume of interest (VOI), the Radon transform on all possible planes through that point should be measured. The authors quantified the extent to which this ideal condition is satisfied for the entire image volume. They first determined a Radon completeness number for each point in the VOI, as the percentage of possible planes that is actually measured. A completeness map is then defined as a 3D matrix of the completeness numbers for the entire VOI. The authors proposed algorithms to analyze the projection datasets in Radon space and compute the completeness number for a fixed point and apply these algorithms to various architectures and scan modes that they are evaluating. In this report, the authors consider four selected candidate architectures, operating with different scan modes, for a total of five system design alternatives. Each of these alternatives is evaluated using completeness map.

RESULTS

If the detector size and cone angle are large enough to cover the entire cardiac VOI, a single-source circular scan can have ≥99% completeness over the entire VOI. However, only the central z-slice can be exactly reconstructed, which corresponds to 100% completeness. For a typical single-source architecture, if the detector is limited to an axial dimension of 40 mm, a helical scan needs about five rotations to form an exact reconstruction region covering the cardiac VOI, while a triple-source helical scan only requires two rotations, leading to a 2.5x improvement in temporal resolution. If the source and detector of an inverse-geometry (IGCT) system have the same axial extent, and the spacing of source points in the axial and transaxial directions is sufficiently small, the IGCT can also form an exact reconstruction region for the cardiac VOI. If the VOI can be covered by the x-ray beam in any view, a composite-circling scan can generate an exact reconstruction region covering the VOI.

CONCLUSIONS

The completeness map evaluation provides useful information for selecting the next-generation cardiac CT system design. The proposed completeness map method provides a practical tool for analyzing complex scanning trajectories, where the theoretical image quality for some complex system designs is impossible to predict, without yet-undeveloped reconstruction algorithms.

Fast exact/quasi-exact FBP algorithms for triple-source helical cone-beam CT

Cardiac computed tomography (CT) has been improved over past years, but it still needs improvement for higher temporal resolution in the cases of high or irregular cardiac rates. Given successful applications of dual-source cardiac CT scanners, triple-source cone-beam CT seems a promising mode for cardiac CT. In this paper, we propose two filtered-backprojection algorithms for triple-source helical cone-beam CT. The first algorithm utilizes two families of filtering lines. These lines are parallel to the tangent of the scanning trajectory and the so-called L lines. The second algorithm utilizes two families of filtering lines tangent to the boundaries of the Zhao window and L lines, respectively, but it eliminates the filtering paths along the tangent of the scanning trajectory, thus reducing the required detector size greatly. The first algorithm is theoretically exact for r < 0.265R and quasi-exact for 0.265R <or= r < 0.495R, and the second algorithm is quasi-exact for r < 0.495R , where r and R denote the object radius and the trajectory radius, respectively. Both algorithms are computationally efficient. Numerical results are presented to verify and showcase the proposed algorithms.

Demonstration of dose and scatter reductions for interior computed tomography

With continuing developments in computed tomography (CT) technology and its increasing use of CT imaging, the ionizing radiation dose from CT is becoming a major public concern particularly for high-dose applications such as cardiac imaging. We recently proposed a novel interior tomography approach for x-ray dose reduction that is very different from all the previously proposed methods. Our method only uses the projection data for the rays passing through the desired region of interest. This method not only reduces x-ray dose but scatter as well. In this paper, we quantify the reduction in the amount of x-ray dose and scattered radiation that could be achieved using this method. Results indicate that interior tomography may reduce the x-ray dose by 18% to 58% and scatter to the detectors by 19% to 59% as the FOV is reduced from 50 to 8.6 cm.

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.