Daniela Münzel

Initial performance characterization of a clinical noise-suppressing reconstruction algorithm for MDCT.

OBJECTIVE The number of CT examinations is increasing relatively dramatically, hence the radiation dose of the associated population. Thus, there is a need for efficient reconstruction methods with dose reduction potential that also maintain the image quality. In this article, we present the initial performance evaluation of such a reconstruction algorithm (iDose, Philips Healthcare). MATERIALS AND METHODS iDose is a hybrid iterative reconstruction algorithm that provides enhanced image quality while reducing the radiation dose compared with the current clinical standard reconstruction. To quantify the advantages of this algorithm in image quality and dose reduction, we compared iDose with the conventional filtered back projection algorithm. Furthermore, we describe the performance of iDose with respect to several image quality metrics. RESULTS The HU values remain stable while employing iDose. With iDose, the noise is significantly reduced. This is reflected by an improvement in the contrast-to-noise ratio and in the noise power spectrum compared with a standard reconstruction. The measurements of the modulation transfer function confirm that, with iDose, there is no decline in spatial resolution. CONCLUSION We conclude that iDose is an important tool in the reduction of radiation dose in CT. However, continuous efforts to reduce radiation dose should be pursued.

Bisphosphonate related osteonecrosis of the jaw: A minipig large animal model☆

Bisphosphonate related osteonecrosis of the jaw (BRONJ) is rare but potentially severe, and the etiopathology and risk factors are poorly defined. To date, it has not been possible to induce BRONJ in a large animal model, a shortfall this study aims to redress. Ten two-year-old adult Göttingen minipigs were split into two groups. Five pigs (group 1) were administered intravenously a weekly dose of a bisphosphonate (zoledonate 0.05mg/kg body weight, approximating the oncologic dose in humans) and five pigs (group 2) served as controls. After 6 weeks, tooth extractions were performed in the upper and lower jaw (both groups) and the bisphosphonate administration continued for a further 10 weeks (group 1 only). Clinical and blood parameters were monitored throughout the entire experiment; thereafter, the jaw-bones were subjected to macroscopic, radiological (CT) and histological investigations. Whilst the extraction sites in the control group healed within two weeks, all animals in the bisphosphonate group exhibited exposed bone and impaired wound healing, indicators that are synonymous of macroscopically advanced osteonecrosis. Radiological and in particular histological investigations confirmed the presence of BRONJ in the animals from group 1. This paper demonstrates that the administration of bisphosphonates, in combination with tooth extractions, induces BRONJ in a minipig model. The ability to study BRONJ in miniature pigs, animals with a bone structure not dissimilar to humans, may improve our knowledgebase regarding the etiopathology, the prophylaxis and potentially uncover new therapies of BRONJ.

Does iterative reconstruction lower CT radiation dose: evaluation of 15,000 examinations.

Purpose Evaluation of 15,000 computed tomography (CT) examinations to investigate if iterative reconstruction (IR) reduces sustainably radiation exposure. Method and Materials Information from 15,000 CT examinations was collected, including all aspects of the exams such as scan parameter, patient information, and reconstruction instructions. The examinations were acquired between January 2010 and December 2012, while after 15 months a first generation IR algorithm was installed. To collect the necessary information from PACS, RIS, MPPS and structured reports a Dose Monitoring System was developed. To harvest all possible information an optical character recognition system was integrated, for example to collect information from the screenshot CT-dose report. The tool transfers all data to a database for further processing such as the calculation of effective dose and organ doses. To evaluate if IR provides a sustainable dose reduction, the effective dose values were statistically analyzed with respect to protocol type, diagnostic indication, and patient population. Results IR has the potential to reduce radiation dose significantly. Before clinical introduction of IR the average effective dose was 10.1±7.8mSv and with IR 8.9±7.1mSv (p*=0.01). Especially in CTA, with the possibility to use kV reduction protocols, such as in aortic CTAs (before IR: average14.2±7.8mSv; median11.4mSv /with IR:average9.9±7.4mSv; median7.4mSv), or pulmonary CTAs (before IR: average9.7±6.2mSV; median7.7mSv /with IR: average6.4±4.7mSv; median4.8mSv) the dose reduction effect is significant(p*=0.01). On the contrary for unenhanced low-dose scans of the cranial (for example sinuses) the reduction is not significant (before IR:average6.6±5.8mSv; median3.9mSv/with IR:average6.0±3.1mSV; median3.2mSv). Conclusion The dose aspect remains a priority in CT research. Iterative reconstruction algorithms reduce sustainably and significantly radiation dose in the clinical routine. Our results illustrate that not only in studies with a limited number of patients but also in the clinical routine, IRs provide long-term dose saving.

Ultra-low-dose CT pulmonary angiography with iterative reconstruction

Objective Evaluation of a new iterative reconstruction algorithm (IMR) for detection/rule-out of pulmonary embolism (PE) in ultra-low dose computed tomography pulmonary angiography (CTPA). Methods Lower dose CT data sets were simulated based on CTPA examinations of 16 patients with pulmonary embolism (PE) with dose levels (DL) of 50%, 25%, 12.5%, 6.3% or 3.1% of the original tube current setting. Original CT data sets and simulated low-dose data sets were reconstructed with three reconstruction algorithms: the standard reconstruction algorithm “filtered back projection” (FBP), the first generation iterative reconstruction algorithm iDose and the next generation iterative reconstruction algorithm “Iterative Model Reconstruction” (IMR). In total, 288 CTPA data sets (16 patients, 6 tube current levels, 3 different algorithms) were evaluated by two blinded radiologists regarding image quality, diagnostic confidence, detectability of PE and contrast-to-noise ratio (CNR). Results iDose and IMR showed better detectability of PE than FBP. With IMR, sensitivity for detection of PE was 100% down to a dose level of 12.5%. iDose and IMR showed superiority to FBP regarding all characteristics of subjective (diagnostic confidence in detection of PE, image quality, image noise, artefacts) and objective image quality. The minimum DL providing acceptable diagnostic performance was 12.5% (= 0.45 mSv) for IMR, 25% (= 0.89 mSv) for iDose and 100% (= 3.57 mSv) for FBP. CNR was significantly (p < 0.001) improved by IMR compared to FBP and iDose at all dose levels. Conclusion By using IMR for detection of PE, dose reduction for CTPA of up to 75% is possible while maintaining full diagnostic confidence. This would result in a mean effective dose of approximately 0.9 mSv for CTPA.

Evaluation of an iterative model-based reconstruction algorithm for low-tube-voltage (80 kVp) computed tomography angiography.

Abstract. The objective of this study was to investigate the improvement in diagnostic quality of an iterative model–based reconstruction (IMBR) algorithm for low-tube-voltage (80-kVp) and low-tube-current in abdominal computed tomography angiography (CTA). A total of 11 patients were imaged on a 256-slice multidetector computed tomography for visualization of the aorta. For all patients, three different reconstructions from the low-tube-voltage data are generated: filtered backprojection (FBP), IMBR, and a mixture of both IMBR+FBP. To determine the diagnostic value of IMBR-based reconstructions, the image quality was assessed. With IMBR-based reconstructions, image noise could be significantly reduced, which was confirmed by a highly improved contrast-to-noise ratio. In the image quality assessment, radiologists were able to reliably detect more third-order and higher aortic branches in the IMBR reconstructions compared to FBP reconstructions. The effective dose level was, on average, 3.0 mSv for 80-kVp acquisitions. Low-tube-voltage CTAs significantly improve vascular contrast as presented by others; however, this effect in combination with IMBR enabled yet another substantial improvement of diagnostic quality. For IMBR, a significant improvement of image quality and a decreased radiation dose at low-tube-voltage can be reported.

Is multidetector CT-based bone mineral density and quantitative bone microstructure assessment at the spine still feasible using ultra-low tube current and sparse sampling?

ObjectiveOsteoporosis diagnosis using multidetector CT (MDCT) is limited to relatively high radiation exposure. We investigated the effect of simulated ultra-low-dose protocols on in-vivo bone mineral density (BMD) and quantitative trabecular bone assessment.Materials and methodsInstitutional review board approval was obtained. Twelve subjects with osteoporotic vertebral fractures and 12 age- and gender-matched controls undergoing routine thoracic and abdominal MDCT were included (average effective dose: 10 mSv). Ultra-low radiation examinations were achieved by simulating lower tube currents and sparse samplings at 50%, 25% and 10% of the original dose. BMD and trabecular bone parameters were extracted in T10–L5.ResultsExcept for BMD measurements in sparse sampling data, absolute values of all parameters derived from ultra-low-dose data were significantly different from those derived from original dose images (p<0.05). BMD, apparent bone fraction and trabecular thickness were still consistently lower in subjects with than in those without fractures (p<0.05).ConclusionIn ultra-low-dose scans, BMD and microstructure parameters were able to differentiate subjects with and without vertebral fractures, suggesting osteoporosis diagnosis is feasible. However, absolute values differed from original values. BMD from sparse sampling appeared to be more robust. This dose-dependency of parameters should be considered for future clinical use.Key Points• BMD and quantitative bone parameters are assessable in ultra-low-dose in vivo MDCT scans.• Bone mineral density does not change significantly when sparse sampling is applied.• Quantitative trabecular bone microstructure measurements are sensitive to dose reduction.• Osteoporosis subjects could be differentiated even at 10% of original dose.• Radiation exposure should be considered when comparing quantitative bone parameters.

Simulated Cystic Renal Lesions: Quantitative X-ray Phase-Contrast CT—An in Vitro Phantom Study

PURPOSE To determine if grating-based x-ray phase-contrast computed tomography (CT) can allow differentiation of simulated simple, protein-rich, hemorrhagic, and enhancing cystic renal lesions in an in vitro phantom. MATERIALS AND METHODS An in vitro phantom specifically designed to simulate simple, protein-rich, hemorrhagic, and enhancing renal cysts was scanned with an experimental grating-based phase-contrast CT setup consisting of a Talbot-Lau interferometer with a rotating anode x-ray tube and a single photon counting detector. Various combinations of serum and saline (100% and 0% to 0% and 100%), blood and saline, blood and serum (100% and 0% to 6.25% and 93.75% for both), and an iodinated contrast agent and saline (7.6-1.6 mg per milliliter of saline) were used to reproduce the chemical composition of the different types of cysts. A thickened solution of an iodinated contrast agent calibrated with a clinical multidetector CT scanner served as contrast agent-enhanced renal parenchyma (195 HU at 80 kVp, 400 mAs and 98 HU at 140 kVp, 200 mAs). Standard attenuation- and phase-contrast images were reconstructed from the raw projection data. Quantitative values for attenuation and phase contrast and image noise were determined. Contrast-to-noise ratios were calculated. Simulated lesions were assessed for visual differentiability by means of pairwise comparison of the attenuation- and phase-contrast images and both images simultaneously. RESULTS Attenuation-contrast imaging showed large differences in Hounsfield units with increasing concentrations of iodine (118.9 HU for 1.6 mg/mL vs 331.4 HU for 7.6 mg/mL). Values for phase-contrast imaging were substantially distinguishable for saline, serum, and blood (7.9, 23.7, and 52.8 HU, respectively). Both imaging modalities combined allowed differentiation of all four types of simulated cysts (100% saline, 100% serum, 100% blood, and 1.6-7.6 mg of iodine per milliliter of saline) with one imaging acquisition. CONCLUSION Grating-based phase-contrast CT allows differentiation of simulated simple, protein-rich, hemorrhagic, and enhancing renal cysts in an in vitro phantom through simultaneous assessment of their distinct attenuation- and phase-contrast signal.

Accuracy of iodine quantification in dual-layer spectral CT: Influence of iterative reconstruction, patient habitus and tube parameters

PURPOSE Evaluation of the influence of iterative reconstruction, tube settings and patient habitus on the accuracy of iodine quantification with dual-layer spectral CT (DL-CT). MATERIAL AND METHODS A CT abdomen phantom with different extension rings and four iodine inserts (1, 2, 5 and 10 mg/ml) was scanned on a DL-CT. The phantom was scanned with tube-voltages of 120 and 140 kVp and CTDIvol of 2.5, 5, 10 and 20 mGy. Reconstructions were performed for eight levels of iterative reconstruction (i0-i7). Diagnostic dose levels are classified depending on patient-size and radiation dose. RESULTS Measurements of iodine concentration showed accurate and reliable results. Taking all CTDIvol-levels into account, the mean absolute percentage difference (MAPD) showed less accuracy for low CTDIvol-levels (2.5 mGy: 34.72%) than for high CTDIvol-levels (20 mGy: 5.89%). At diagnostic dose levels, accurate quantification of iodine was possible (MAPD 3.38%). Level of iterative reconstruction did not significantly influence iodine measurements. Iodine quantification worked more accurately at a tube voltage of 140 kVp. Phantom size had a considerable effect only at low-dose-levels; at diagnostic dose levels the effect of phantom size decreased (MAPD <5% for all phantom sizes). CONCLUSION With DL-CT, even low iodine concentrations can be accurately quantified. Accuracies are higher when diagnostic radiation doses are employed.

Evaluation of a method for improving the detection of hepatocellular carcinoma

ObjectiveTo improve the detection of liver lesions in patients with hepatocellular carcinoma (HCC) via an iodine contrast enhancement tool.MethodsThirty-two patients with clinically proven HCCs underwent imaging with a three-phase protocol on a 256-slice MDCT. The contrast enhancement in the reconstructed slices was improved via a post-processing tool. Mean image noise was measured in four different regions: liver lesion, healthy liver, subcutaneous fat and bone. For each image set the image noise and contrast-to-noise ratio (CNR) were assessed. For subjective image assessment, four experienced radiologists evaluated the diagnostic quality.ResultsWhile employing the post-processing algorithm, CNR between the liver lesion and healthy liver tissue improves significantly by a factor of 1.78 (CNRwithout vC = 2.30 ± 1.92/CNRwith vC = 4.11 ± 3.05) (P* = 0.01). All results could be achieved without a strengthening of artefacts; mean HU values of subcutaneous fat and bone did not significantly change. Subjective image analysis illustrated a significant improvement when employing post-processing for clinically relevant criteria such as diagnostic confidence.ConclusionWith post-processing we see a significantly improved detection of arterial uptake in hepatic lesions compared with non-processed data. The improvement in CNR was confirmed by subjective image assessment for small lesions and for lesions with limited uptake.Key Points• Enhancement with iodine-based contrast agents is an essential part of CT.• A new post-processing tool significantly improves the diagnostics of hepatocellular carcinoma.• It also improves detection of small lesions with limited iodine uptake.

Joint Statistical Iterative Material Image Reconstruction for Spectral Computed Tomography Using a Semi-Empirical Forward Model

By acquiring tomographic measurements with several distinct photon energy spectra, spectral computed tomography (spectral CT) is able to provide additional material-specific information compared with conventional CT. This information enables the generation of material selective images, which have found various applications in medical imaging. However, material decomposition typically leads to noise amplification and a degradation of the signal-to-noise ratio. This is still a fundamental problem of spectral CT, especially for low-dose medical applications. Inspired by the success for low-dose conventional CT, several statistical iterative reconstruction algorithms for spectral CT have been developed. These algorithms typically rely on detailed knowledge about the spectrum and the detector response. Obtaining this knowledge is often difficult in practice, especially if photon counting detectors are used to acquire the energy specific information. In this paper, a new algorithm for joint statistical iterative material image reconstruction is presented. It relies on a semi-empirical forward model which is tuned by calibration measurements. This strategy allows to model spatially varying properties of the imaging system without requiring detailed prior knowledge of the system parameters. We employ an efficient optimization algorithm based on separable surrogate functions to accelerate convergence and reduce the reconstruction time. Numerical as well as real experiments show that our new algorithm leads to reduced statistical bias and improved image quality compared with projection-based material decomposition followed by analytical or iterative image reconstruction.