Optimizing radiation dose parameters in MDCT arthrography of the shoulder: illustration of basic concepts in a cadaveric study.

OBJECTIVE: To determine in a cadaveric study the lowest achievable radiation dose and optimal tube potential generating diagnostic image quality in multidetector computed tomography (MDCT) arthrography of the shoulder. MATERIALS AND METHODS: Six shoulders from three human cadavers were scanned using a 256-MDCT system after intra-articular injection of diluted iodinated contrast material. Using six decreasing radiation dose levels (CTDIvol: 20, 15, 10, 8, 6, and 4 mGy) and for each dose level, four decreasing tube potentials (140, 120, 100, and 80 kVp), image noise and contrast-to-noise ratio (CNR) were measured. Two independent and blinded observers assessed the overall diagnostic image quality, subjective amount of noise, and severity of artifacts according to a four-point scale. Influence of those MDCT data acquisition parameters on objective and subjective image quality was analyzed using the Kruskal-Wallis and Wilcoxon signed-rank tests, and pairwise comparisons were performed. RESULTS: Multidetector CT protocols with radiation doses of 15 mGy or higher, combined with tube potentials of 100 kVp or higher, were equivalent in CNR to the reference 20 mGy-140 kVp protocol (all p ≥ 0.054). Above a CTDIvol of 10 mGy and a tube potential of 120 kVp, all protocols generated diagnostic image quality and subjective noise equivalent to the 20 mGy-140 kVp protocol (all p ≥ 0.22). CONCLUSIONS: Diagnostic image quality in MDCT arthrography of the shoulder can be obtained with a radiation dose of 10 mGy at an optimal tube potential of 120 kVp, corresponding to a reduction of up to 50% compared with standard-dose protocols, and as high as 500% compared with reported protocols in the literature.

Could new reconstruction CT techniques challenge MRI for the detection of brain metastases in the context of initial lung cancer staging?

OBJECTIVES: To evaluate the diagnostic performance of brain CT images reconstructed with a model-based iterative algorithm performed at usual and reduced dose. METHODS: 115 patients with histologically proven lung cancer were prospectively included over 15 months. Patients underwent two CT acquisitions at the initial staging, performed on a 256-slice MDCT, at standard (CTDIvol: 41.4 mGy) and half dose (CTDIvol: 20.7 mGy). Both image datasets were reconstructed with filtered back projection (FBP) and iterative model-based reconstruction (IMR) algorithms. Brain MRI was considered as the reference. Two blinded independent readers analysed the images. RESULTS: Ninety-three patients underwent all examinations. At the standard dose, eight patients presented 17 and 15 lesions on IMR and FBP CT images, respectively. At half-dose, seven patients presented 15 and 13 lesions on IMR and FBP CT images, respectively. The test could not highlight any significant difference between the standard dose IMR and the half-dose FBP techniques (p-value = 0.12). MRI showed 46 metastases on 11 patients. Specificity, negative and positive predictive values were calculated (98.9-100 %, 93.6-94.6 %, 75-100 %, respectively, for all CT techniques). CONCLUSION: No significant difference could be demonstrated between the two CT reconstruction techniques. KEY POINTS: • No significant difference between IMR100 and FBP50 was shown. • Compared to FBP, IMR increased the image quality without diagnostic impairment. • A 50 % dose reduction combined with IMR reconstructions could be achieved. • Brain MRI remains the best tool in lung cancer staging.

Low contrast detectability and spatial resolution with model-based Iterative reconstructions of MDCT images: a phantom and cadaveric study.

OBJECTIVES: To compare image quality [low contrast (LC) detectability, noise, contrast-to-noise (CNR) and spatial resolution (SR)] of MDCT images reconstructed with an iterative reconstruction (IR) algorithm and a filtered back projection (FBP) algorithm. METHODS: The experimental study was performed on a 256-slice MDCT. LC detectability, noise, CNR and SR were measured on a Catphan phantom scanned with decreasing doses (48.8 down to 0.7 mGy) and parameters typical of a chest CT examination. Images were reconstructed with FBP and a model-based IR algorithm. Additionally, human chest cadavers were scanned and reconstructed using the same technical parameters. Images were analyzed to illustrate the phantom results. RESULTS: LC detectability and noise were statistically significantly different between the techniques, supporting model-based IR algorithm (p < 0.0001). At low doses, the noise in FBP images only enabled SR measurements of high contrast objects. The superior CNR of model-based IR algorithm enabled lower dose measurements, which showed that SR was dose and contrast dependent. Cadaver images reconstructed with model-based IR illustrated that visibility and delineation of anatomical structure edges could be deteriorated at low doses. CONCLUSION: Model-based IR improved LC detectability and enabled dose reduction. At low dose, SR became dose and contrast dependent. KEY POINTS: • Model- based Iterative Reconstruction improves detectability of low contrast object. • With model- based Iterative Reconstruction, spatial resolution is dose and contrast dependent. • Model-based Iterative Reconstruction algorithms enable improved IQ combined with dose-reduction possibilities. • Improvement of SR and LC detectability on the same IMR data set would reduce reconstructions.

Right ventricle function assessment by MDCT.

OBJECTIVE: The right ventricle is often overlooked on chest and even cardiac MDCT studies. This article will review the normal anatomy of the right ventricle on MDCT and the signs of its functional alterations. CONCLUSION: MDCT signs of right ventricular dysfunction should be known and checked in relevant cases, such as pulmonary embolism in particular, and in any disease that affects both the structure and function of the lungs in general.

Is the lung scan alive and well? Facts and controversies in defining the role of lung scintigraphy for the diagnosis of pulmonary embolism in the era of MDCT.

PURPOSE: The last decade has seen a changing pattern of utilization of multidetector CT (MDCT) versus lung perfusion scintigraphy in the investigation of pulmonary venous thromboembolism (VTE). In response to this the International Atomic Energy Agency (IAEA) determined that the subject required an overview. METHOD: The IAEA has invited a group of five specialists in the relevant fields to review the current status and optimum role of scintigraphy, to explore some of the facts and controversies surrounding the use of both modalities and to make recommendations about the continued role of nuclear medicine for the investigation of pulmonary embolism. This paper identifies the relative merits of each technique, highlights benefits, focuses on complementary roles and seeks a nonadversarial symbiosis. CONCLUSION: The consultants reached a consensus that the continued use of scintigraphy for diagnosis of thromboembolic disease is recommended, particularly in scenarios where scintigraphy confers specific benefits and is complementary to MDCT.