Image Quality Required for the Diagnosis of Skull Fractures Using Head CT: A Comparison of Conventional and Improved Reconstruction Kernels

BACKGROUND AND PURPOSE:Although skull fractures are generally assessed on bone images obtained by using head CT, the combined multikernel technique that enables evaluation of both brain and bone through a change in the window settings of an image set has been reported. The purpose of this retrospective study was to determine the image quality required for the accurate assessment of skull fractures by using head CT.MATERIALS AND METHODS:A random sample of 50 patients (25 nonfracture and 25 simple nondisplaced skull fractures) was selected, and sets of conventional brain and bone images and improved combined multikernel images were reconstructed (4614 images). Three radiologists indicated their confidence levels regarding the presence of skull fractures by marking on a continuous scale for each image set. The mean area under the receiver operating characteristic curve was calculated for each kernel, and the statistical significance of differences was tested by using the Dorfman-Berbaum-Metz method.RESULTS:Although a difference in the diagnostic performance of the 3 radiologists was suggested, the mean area under the curve value showed no significant differences among the 3 reconstruction kernels (P = .95 [bone versus combined]), P = .91 [bone versus brain]), and P = .88 [brain versus combined]). However, the quality of brain images was distinctly poorer than the quality of the other 2 images.CONCLUSIONS:There was no significant difference in the diagnostic performance of brain, bone, and combined multikernel images for skull fractures. Skull fracture diagnosis is made possible by brain image assessments. Combined multikernel images offer the advantage of high-quality brain and bone images.

The quality of CT images reconstructed with conventional filtered back-projection depends on the type of reconstruction kernel used. In head CT, low-pass filter kernels that decrease higher spatial frequencies and noise are generally used to reconstruct brain images, whereas high-pass filter kernels that preserve higher spatial frequencies and increase noise are generally used to reconstruct bone images.^1,2 In all cases, the reconstruction of brain images is required. In contrast, according to the policy of each institution, bone images are reconstructed either in all cases or only for patients with clinically suspected bone disease. Because assessment of bone tissue is not required for all cases, worthless images increase if there is reconstruction for all cases. However, when bone images are reconstructed only in case of clinical suspicion, additional reconstruction is required if the need for bone images is determined after examination (in the situation of assessing brain images) or if the radiology technician forgets to reconstruct before sending the images (despite reconstruction of bone image being ordered in advance). Furthermore, bone image reconstruction is not possible once the raw data are deleted from the CT device. Although observers have to assess the bone tissue on brain images reconstructed by low-pass filter kernels in such cases, to our knowledge, the diagnostic performance for bone lesions has not been reported.To resolve this issue, the usefulness of a combined multikernel technique that enables the evaluation of both brain and bone through a change in the window settings of an image set for the assessment of skull fractures has been reported.^3,4 The use of this technique not only decreases the number of stored images and simplifies head CT examinations, but also enables the assessment of bone tissue in all cases. However, the diagnostic performance of this technique has not been sufficiently investigated.The purpose of this study was to determine the CT image quality required for the assessment of skull fractures by using receiver operating characteristic (ROC) analysis of different reconstruction kernels and to evaluate the diagnostic performance of the combined multikernel technique for skull fractures.     

Bayesian image reconstruction for emission tomography based on median root prior

The aim of the present study was to investigate a new type of Bayesian one-step late reconstruction method which utilizes a median root prior (MRP). The method favours images which have locally monotonous radioactivity concentrations. The new reconstruction algorithm was applied to ideal simulated data, phantom data and some patient examinations with PET. The same projection data were reconstructed with filtered back-projection (FBP) and maximum likelihood-expectation maximization (ML-EM) methods for comparison. The MRP method provided good-quality images with a similar resolution to the FBP method with a ramp filter, and at the same time the noise properties were as good as with Hann-filtered FBP images. The typical artefacts seen in FBP reconstructed images outside of the object were completely removed, as was the grainy noise inside the object. Quantitatively, the resulting average regional radioactivity concentrations in a large region of interest in images produced by the MRP method corresponded to the FBP and ML-EM results but at the pixel by pixel level the MRP method proved to be the most accurate of the tested methods. In contrast to other iterative reconstruction methods, e.g. ML-EM, the MRP method was not sensitive to the number of iterations nor to the adjustment of reconstruction parameters. Only the Bayesian parameter had to be set. The proposed MRP method is much more simple to calculate than the methods described previously, both with regard to the parameter settings and in terms of general use. The new MRP reconstruction method was shown to produce high-quality quantitative emission images with only one parameter setting in addition to the number of iterations.     

Image quality of multiplanar reconstruction of pulmonary CT scans using adaptive statistical iterative reconstruction

Objective

We investigated the image quality of multiplanar reconstruction (MPR) using adaptive statistical iterative reconstruction (ASIR).

Methods

Inflated and fixed lungs were scanned with a garnet detector CT in high-resolution mode (HR mode) or non-high-resolution (HR) mode, and MPR images were then reconstructed. Observers compared 15 MPR images of ASIR (40%) and ASIR (80%) with those of ASIR (0%), and assessed image quality using a visual five-point scale (1, definitely inferior; 5, definitely superior), with particular emphasis on normal pulmonary structures, artefacts, noise and overall image quality.

Results

The mean overall image quality scores in HR mode were 3.67 with ASIR (40%) and 4.97 with ASIR (80%). Those in non-HR mode were 3.27 with ASIR (40%) and 3.90 with ASIR (80%). The mean artefact scores in HR mode were 3.13 with ASIR (40%) and 3.63 with ASIR (80%), but those in non-HR mode were 2.87 with ASIR (40%) and 2.53 with ASIR (80%). The mean scores of the other parameters were greater than 3, whereas those in HR mode were higher than those in non-HR mode. There were significant differences between ASIR (40%) and ASIR (80%) in overall image quality (p<0.01). Contrast medium in the injection syringe was scanned to analyse image quality; ASIR did not suppress the severe artefacts of contrast medium.

Conclusion

In general, MPR image quality with ASIR (80%) was superior to that with ASIR (40%). However, there was an increased incidence of artefacts by ASIR when CT images were obtained in non-HR mode.Multiplanar reconstruction (MPR) of CT images plays an important role in the interpretation of the three-dimensional anatomical location or extent of disease, and is an essential technique in daily clinical practice. Multidetector row CT (MDCT) is widely used, and advances in MDCT technology have facilitated better images with thinner slice thickness and extended coverage, which has allowed more MPR images to be evaluated in greater detail. Coronal MPR images produced by MDCT supply good image quality for lung assessment and show similar image quality to axial high-resolution (HR) CT images [1^,2].To further enhance CT image quality, improvements in temporal resolution and/or spatial resolution are needed. MDCT equipped with more rapid gantry rotation or more detector arrays has already evolved for the improvement of temporal resolution. GE Healthcare (Milwaukee, WI) recently produced an MDCT unit containing a new detector composed of garnet, which has a faster response than the previous detector material. This apparatus can provide improved spatial resolution by acquiring more data.Reconstruction algorithms are also important for improved image quality. Although the filtered back-projection algorithm has traditionally been used for image reconstruction, new reconstruction algorithms are being developed. The iterative reconstruction algorithm has already been used for image reconstruction of positron emission tomography (PET) or single photon emission CT (SPECT), resulting in improved image quality [3-6]. Iterative reconstruction was also used in early CT systems and is currently used by many manufacturers of clinical CT systems. Adaptive statistical iterative reconstruction (ASIR), recently developed for CT by GE Healthcare, is expected to improve low-contrast detectability by reducing noise when using the same radiation dose as would be used with filtered back-projection. It is also expected to reduce the radiation dose for a similar noise level compared with filtered back-projection. Until now, the quality of CT images from multiplanar reconstruction using ASIR had not been analysed. The purpose of this study was to evaluate the image quality of MPR using ASIR.     

A quantitative comparison of the TERA modeling and DFT magnetic resonance image reconstruction techniques

The resolution of magnetic resonance images reconstructed using the discrete Fourier transform (DFT) algorithm is limited by the effective window generated by the finite data length. The transient error reconstruction approach (TERA) is an alternative reconstruction method based on autoregressive moving average (ARMA) modeling techniques. Quantitative measurements comparing the truncation artifacts present during DFT and TERA image reconstruction show that the modeling method substantially reduces these artifacts on "full" (256 X 256), "truncated" (256 X 192), and "severely truncated" (256 X 128) data sets without introducing the global amplitude distortion found in other modeling techniques. Two global measures for determining the success of modeling are suggested. Problem areas for one-dimensional modeling are examined and reasons for considering two-dimensional modeling discussed. Analysis of both medical and phantom data reconstructions are presented.     

Proposal of a conversion and processing system of digital images

The digital format of diagnostic images is gradually replacing the analogic one, as expected, thanks to its diagnostic, gestional, and economic advantages. Digital radiology is expanding, crossing the borders of conventional radiology: the spread of photostimulable plates will cancel all differences, offering a "digital dimension" to conventional examinations, that will produce numeric images using the conventional method. Off-line systems are a most useful approach to numeric format, because they offer diagnostic and gestional advantages at a low price. Moreover, they allow analogic images to be put into the "digital flow" of radiological departments, thus making a format standardization possible between different types of images. The system proposed has advanced characteristics, such as acquisition, reconstruction and visualization of digital images with a 2560 x 2048 x 8 bit matrix. The use of two scanning systems (CCD and laser scanner) has proved to be the most effective way to acquire images with different resolution, while the use of a 2k x 2k monitor makes both observation and reporting at the workstation more reliable.     

Iterative reconstruction reduces abdominal CT dose

Objective

In medical imaging, lowering radiation dose from computed tomography scanning, without reducing diagnostic performance is a desired achievement. Iterative image reconstruction may be one tool to achieve dose reduction. This study reports the diagnostic performance using a blending of 50% statistical iterative reconstruction (ASIR) and filtered back projection reconstruction (FBP) compared to standard FBP image reconstruction at different dose levels for liver phantom examinations.

Methods

An anthropomorphic liver phantom was scanned at 250, 185, 155, 140, 120 and 100 mA s, on a 64-slice GE Lightspeed VCT scanner. All scans were reconstructed with ASIR and FBP. Four readers evaluated independently on a 5-point scale 21 images, each containing 32 test sectors. In total 672 areas were assessed. ROC analysis was used to evaluate the differences.

Results

There was a difference in AUC between the 250 mA s FBP images and the 120 and 100 mA s FBP images. ASIR reconstruction gave a significantly higher diagnostic performance compared to standard reconstruction at 100 mA s.

Conclusion

A blending of 50–90% ASIR and FBP may improve image quality of low dose CT examinations of the liver, and thus give a potential for reducing radiation dose.     

Natural linewidth chemical shift imaging (NL-CSI).

The discrete Fourier transform (FT) is a conventional method for spatial reconstruction of chemical shifting imaging (CSI) data. Due to point spread function (PSF) effects, FT reconstruction leads to intervoxel signal leakage (Gibbs ringing). Spectral localization by imaging (SLIM) reconstruction was previously proposed to overcome this intervoxel signal contamination. However, the existence of magnetic field inhomogeneities creates an additional source of intervoxel signal leakage. It is demonstrated herein that even small field inhomogeneities substantially amplify intervoxel signal leakage in both FT and SLIM reconstruction approaches. A new CSI data acquisition strategy and reconstruction algorithm (natural linewidth (NL) CSI) is presented that eliminates effects of magnetic field inhomogeneity-induced intervoxel signal leakage and intravoxel phase dispersion on acquired data. The approach is based on acquired CSI data, high-resolution images, and magnetic field maps. The data are reconstructed based on the imaged object structure (as in the SLIM approach) and a reconstruction matrix that takes into account the inhomogeneous field distribution inside anatomically homogeneous compartments. Phantom and in vivo results show that the new method allows field inhomogeneity effects from the acquired MR signal to be removed so that the signal decay is determined only by the "natural" R2 relaxation rate constant (hence the term "natural linewidth" CSI).     

The removal of a "cupping" artefact from brain images produced by the EMI 7070 CT scanner

Brain images produced on the EMI 7070 scanner exhibit a "cupping" artefact due to a combination of beam hardening and scatter effects. The magnitude of the artefact is assessed by statistically analysing a series of concentric regions of interest in the final image. Once the magnitude has been determined it can be subtracted from the image. While the result of the technique does not modify the clinical analysis of images it does increase the observer's appreciation of the image. Both the technique and clinical results are presented, and the implications of this type of reconstruction artefact removal discussed.     

Functional imaging of neuronal brain activities: overlay of distributed neuromagnetic current density images and morphological MR images

Neuromagnetic imaging is a relatively new diagnostic tool for examination of electrical activities in the nervous system. It is based on the non-invasive detection of extremely weak magnetic fields around the human body with superconducting quantum interference device (SQUID) detectors. Often the equivalent current dipole model is used to describe the centre of the electrical activity. New current density reconstruction methods enable the imaging of the spatial extent and structure of neuronal activities. For practical use in medical diagnosis a combination of the abstract neuromagnetic images with MR or CT images is required in order to match the functional activity with anatomy and morphology. The neuromagnetic images can be overlaid onto three-dimensional morphological images with spatially arbitrarily selectable slices. The matching of both imaging modalities is discussed. On the basis of the detection of auditory evoked magnetic fields, neuromagnetic images are reconstructed with linear estimation theory algorithms. The MR images are used as a priori information of the volume conductor geometry and allow an attachment of functional and morphological properties. Correspondence to: M. Fuchs     

Display and visualization of three-dimensional reconstructed anatomic morphology: experience with the thorax, heart, and coronary vasculature of dogs.

A new method, termed reprojection, is used to visualize anatomic morphology contained within three-dimensional reconstructions made up of images of multiple parallel cross sections. This method involves the projection, either orthographically into a plane or radially onto a cylinder, of the volume picture elements (voxels) of the reconstruction. Orthographic reprojection images, formed by mathematically summing the magnitudes of the voxels along selected parallel paths through the reconstructed volume, are analagous to conventional radiographs formed by the passage of an X-ray beam through the volume. The reprojection image is a two-dimensional array of picture elements that is displayed on a television monitor using a digital-to-video scan converter. Also described are the techniques of noninvasive selective tissue dissolution and numerical dissection, whereby obscuring portions of the reconstructed volume are either partially "dissolved" or totally eliminated before reprojection. Utilizing these methods, anatomic information present in a three-dimensional reconstruction but not clearly seen in a reprojection image is rendered visible after removal of superposed structures. The usefulness of these methods is demonstrated utilizing three-dimensional reconstructions of the thorax, heart, and coronary arteries of dogs.     

Gesichtsweichteilrekonstruktion mithilfe einer Open-Source-Software

Background

The identification of an unknown deceased person is an important task in forensic anthropology. There are various methods for identification, such as fingerprinting, odontostomatology and genetic fingerprinting, which presuppose the existence of reference material of the missing person; however, if there is no evidence of a person’s identity the only possibility is often the use of forensic facial soft tissue reconstruction. This method is based on the high recognition level of a human face on the basis of bony structures of the skull and its anatomical features.

Aim

The aim of this study was the design and application of a novel process for a computer-aided 3D facial soft tissue reconstruction on the basis of digital photographs of a skull.

Material and methods

The facial soft tissue reconstruction was carried out on a selected forensic case and based on open source software.

Results

A complete facial soft tissue reconstruction of the deceased person was created based on 76 photographs of the skull taken with a Nikon D7100 SLR digital camera. The results show that for actual comparison images similar reconstruction results can be achieved. In addition, a model library for facial features was created.

Conclusion

The presented workflow of a computer-aided 3D facial soft tissue reconstruction based on open source software is a cost-effective and flexible alternative to conventional reconstruction methods. It could be demonstrated that comparable reconstruction results can be achieved. Whether the reconstruction result actually leads to the recognition of the person depends on many other factors.

     

Congenital bronchial abnormalities revisited.

Bronchial anatomy is adequately demonstrated with the appropriate spiral computed tomographic technique on cross-sectional images, multiplanar reconstruction images, and three-dimensional reconstruction images. Contrary to the numerous variations of lobar or segmental bronchial subdivisions, abnormal bronchi originating from the trachea or main bronchi are rare. Major bronchial abnormalities include accessory cardiac bronchus (ACB) and "tracheal" bronchus. An ACB is a supernumerary bronchus from the inner wall of the right main bronchus or intermediate bronchus that progresses toward the pericardium. Fourteen ACBs were found in 17,500 consecutive patients (frequency, 0.08%). The term tracheal bronchus encompasses a variety of bronchial anomalies originating from the trachea or main bronchus and directed to the upper lobe. In a series of 35 tracheal bronchi, only eight originated from the trachea, three originated from the carina, and 24 originated from the bronchi. Displaced tracheal bronchi (27 of 35) are more frequent than supernumerary tracheal bronchi (eight of 35). Minor bronchial abnormalities include variants of tracheal bronchus, displaced segmental bronchi, and bronchial agenesis. The main embryogenic hypotheses for congenital bronchial abnormalities are the reduction, migration, and selection theories. Knowledge and understanding of congenital bronchial abnormalities may have important implications for diagnosis, bronchoscopy, surgery, brachytherapy, and intubation.     

Artifacts in spiral CT protocols: The importance of the spatial reconstruction

Purpose

This study recorded and analysed streak and motion artifacts in spiral CT examinations and evaluated the elimination and minimization of them by the use of segmental reconstruction with and without alterations of the initial examination protocol.

Materials and methods

One hundred CT scans of the chest and 300 CT scans of the brain have been included in this study. All studies were performed by a helical CT scanner (Philips 5000 SR) with the standard protocol and were randomly selected due to the presence of either streak or motion artifacts. Segmental reconstruction was applied in all cases by the same experienced radiographer. Image evaluation was performed by two experienced radiologists using a scoring system for each artifact and a grading system for classifying post-processing images.

Results

Among series of images that were evaluated after the application of segmental reconstruction, brain examinations demonstrated the following results: 10.9% of the cases showed no artifact improvement, 19.6% showed slight artifact improvement 31.5% showed moderate improvement and 38% showed significant improvement. The results of chest examinations were as follows: 27% of the cases showed no artifact improvement, 23% showed slight artifact improvement, 26% showed moderate improvement and 24% of showed significant improvement. Spatial reconstruction was useless in brain CT images when a patient moved during the entire scan and in chest CT images when streak and motion artifacts co-existed.

Conclusions

Spatial reconstruction may improve the image quality in brain and chest CT examinations and thus may contribute to more diagnostic images. Elimination of motion artifacts is also suggested due to the limitation of intravenous contrast medium that can be administered per patient per day and in cases of non-cooperative patients.     

Evaluation of a simple method for reconstructing asymmetrically sampled echo data.

A simple method for reconstructing echo data with a large degree of sampling asymmetry was investigated. The method is based on the application of an optimized data sampling window before standard Fourier transform magnitude reconstruction. The performance of this "windowed direct" reconstruction was evaluated with theoretical simulations and experimental measurements and compared with that of the half-Fourier method. With the proper selection of data sampling window parameters, highly asymmetric echo data reconstructed with standard Fourier transform magnitude algorithms produced images similar in quality to those reconstructed with the half-Fourier method. Windowed direct reconstruction provides a simple and computationally fast alternative to more sophisticated algorithms and may be particularly applicable for specialized or developmental applications.     

Common SENSE (sensitivity encoding using hardware common to all MR scanners): a new method for single-shot segmented echo planar imaging.

A new method is presented that enables image acquisition to be segmented into two readouts. This is achieved using a new pulse sequence that creates two components of magnetization with different spatial profiles. Each component of the magnetization is measured in one of the readouts. This produces two images with complimentary "sensitivity profiles" and near identical contrast. The images can be acquired with a reduced data matrix that corresponds to shorter periods of data acquisition. The reduced matrix images are then combined to produce a full matrix image using reconstruction methods previously applied to images from multiple RF coils in the sensitivity encoding (SENSE) technique.The most promising application for this technique is in improving the performance of echo planar imaging (EPI) at high field. In this application, common SENSE obtains two segments of data in a single excitation of the magnetization (i.e., two readouts are performed per shot). The combination of these segments in image space avoids the difficulties normally associated with segmented EPI methods, namely, increased ghosting from discontinuities in the k-space data. The main advantages are a reduction in distortion and blurring. Common SENSE is compatible with parallel imaging and partial Fourier methods.     

Studies on circular isocentric cone-beam trajectories for 3D image reconstructions using FDK algorithm

Image reconstruction from X-ray cone-beam projections collected along a single-circular source trajectory is commonly done using the Feldkamp (FDK) algorithm which performs well only with a small cone-angle. Although this method does not provide an "exact" reconstruction, the approximation is considered adequate for many purposes. In FDK reconstruction the degree of inaccuracy is highly object-dependent, and the largest errors are to be expected for planes parallel to and remote from the midplane. In this study we investigated the possibility to accurately reconstruct these regions by applying FDK algorithm along three-orthogonal to each other circular scanning trajectories. After appropriate weighting, based on the expected errors for each individual reconstruction, the final 3D volume contains the most precisely recovered values. By comparing the quality of 3D reconstructed images using FDK algorithm on projections acquired along classical single-circular and two- and three-orthogonal circular trajectories, we show that using three-orthogonal circular isocentric orbits with an error-based weighted averaging, image quality of reconstructed slices significantly improves, reconstruction error due to circular scanning is reduced and becomes almost independent of the slice position even for relatively large cone-angles.     

EPI image reconstruction with correction of distortion and signal losses

PURPOSE: To derive and implement a method for correcting geometric distortions and recovering magnetic resonance imaging (MRI) signal losses caused by susceptibility-induced magnetic field gradients (SFGs) in regions with large static field inhomogeneities in echo-planar imaging (EPI). MATERIALS AND METHODS: Factors to account for field inhomogeneities and SFGs were added in a traditional EPI equation that was a simple Fourier transform (FT) for expressing the actual k-space data of an EPI scan. The inverse calculation of this "distorted EPI" equation was used as a kernel to correct geometric distortions and reductions in intensity during reconstruction. A step-by-step EPI reconstruction method was developed to prevent complicated phase unwrapping problems. Some EPI images of phantom and human brains were reconstructed from standard EPI k-spaces. RESULTS: All images were reconstructed using the proposed multistep method. Geometric distortions were corrected and SFG-induced MRI signal losses were recovered. CONCLUSION: Results suggest that applying our method for reconstructing EPI images to reduce distortions and MRI signal losses is feasible.     

Experimental measurement of impulse response and noise for an emission computed tomography system

Experimental studies have been made of the impulse response and noise characteristics of a tomographic system using a gamma camera. Fourier transform, deconvolution and iterative methods have been used with a CDC 6600 computer to reconstruct images from data obtained for various experimental arrangements of sources in a cylindrical phantom. It is shown that with an appropriate attenuation correction the impulse response in the reconstruction is substantially constant, independent of the position of the source in the phantom and that the reconstruction technique used is of secondary importance.The resolution obtained for the impulse response and the relative noise level throughout the non image part of the reconstructions is shown for different experimental situations.The measured variance in the reconstruction of an extended uniform activity source was found to be somewhat below the theoretical value except at high count densities (above 1,000 counts per image element) where the limit of accuracy of the reconstruction is shown to be imposed by the variation in the camera sensitivity over the field of view.     

MRS imaging using anatomically based K-space sampling and extrapolation

A comprehensive strategy for the acquisition, reconstruction, and postprocessing of MR spectroscopic images is presented. The reconstruction algorithm is the most critical component of this strategy. It is assumes that the desired image is spatially bounded, meaning that the desired image contains an object that is surrounded by a background of zeros. The reconstruction algorithm relies on prior knowledge of the background zeros for k-space extrapolation. This algorithm is a good candidate for proton MR spectroscopic image reconstruction because these images are often spatially bounded and prior knowledge of the zeros is easily obtained from a rapidly acquired high resolution conventional MRI. Although the reconstruction algorithm can be used with the standard 3DFT k-space distribution, a distribution that relies on anatomical features that are likely to occur in the spectroscopic image can produce better results. Prior knowledge of these anatomical features is also obtained from a conventional MRI. Finally, the postprocessing component of this strategy is valuable for reducing subcutaneous lipid contamination. Overall, the comprehensive approach presented here produces images that are better resolved than standard approaches without increasing acquisition time or reducing SNR. Examples using NAA data are provided.     

Periradicular infiltration of the lumbar spine: is iterative reconstruction software necessary to establish ultra-low-dose protocols? A quantitative and qualitative approach

Purpose

Computed tomography (CT)-guided periradicular infiltration therapy has emerged as an effective treatment option for patients with low back pain. Concern about radiation exposure requires approaches allowing significant dose reduction. The purpose of this study is to evaluate the need for iterative reconstruction software in CT-guided periradicular infiltration therapy with an ultra-low-dose protocol.

Materials and methods

One hundred patients underwent CT-guided periradicular infiltration therapy of the lumbar spine using an ultra-low-dose protocol with adaptive iterative dose reduction 3D (AIDR 3D) for image reconstruction. In addition, images were reconstructed with filtered back-projection (FBP). Four experienced raters evaluated both reconstruction types for conspicuity of anatomical and instrumental features important for ensuring safe patient treatment. Image noise was measured as a quantitative marker of image quality.

Results

Interrater agreement was good for both AIDR 3D (Kendall’s W?=?0.83) and FBP (0.78) reconstructions. Readers assigned the same scores for all features and both reconstruction algorithms in 81.3% of cases. Image noise was significantly lower (average SD of 60.07 vs. 99.54, p?<?0.05) for AIDR 3D-reconstructed images.

Conclusion

Although it significantly lowers image noise, iterative reconstruction software is not mandatory to achieve adequate image quality with an ultra-low-dose CT protocol for guiding periradicular infiltration therapy of the lumbar spine.