Photon-counting detectors in computed tomography: from quantum physics to clinical practice.

Over the last decade, a fundamentally new type of computed tomography (CT) detectors has proved its superior capabilities in both physical and preclinical evaluations and is now approaching the stage of clinical practice. These detectors are able to discriminate single photons and quantify their energy and are hence called photon-counting detectors. Among the promising benefits of this technology are improved radiation dose efficiency, increased contrast-to-noise ratio, reduced metal artifacts, improved spatial resolution, simultaneous multi-energy acquisitions, and the prospect of multi-phase imaging within a single acquisition using multiple contrast agents. Taking the conventional energy-integrating detectors as a reference, the authors demonstrate the technical principles of this new technology and provide phantom and patient images acquired by a whole-body photon-counting CT. These images serve as a basis for discussing the potential future of clinical CT.

[Safety aspects of ultrasound diagnostics]. / Sicherheitsaspekte der Ultraschalldiagnostik.

Ultrasonography is free of ionizing radiation but during the examination it is accompanied by energy deposition in the tissue. Therefore, users should be familiar with the mechanisms of action and possible risks. Thermal and non-thermal (e.g. cavitation) effects are related to the intensity and sound pressure of ultrasound waves and are therefore also dependent on the ultrasound modality used, e.g., B­mode, color Doppler and/or pulsed wave (pw) Doppler. With B­mode ultrasound no dangerous thermal effects are to be expected. In embryos and foetuses as well as febrile patients caution should be exercised. The pw Doppler mode can cause temperature spikes and the risks increase with the duration of use. Ultrasound contrast media are pathogenic for cavitation and should be avoided during the 24 h prior to shock wave lithotripsy. In ultrasound modalities with high local energy deposition, the values for the thermal index (TI) and mechanical index (MI) displayed on the screen should be observed and as with ionizing radiation, the ALARA (as low as reasonably achievable) principle should be adhered to.

[Imaging of medullary thyroid carcinoma]. / Bildgebung beim medullären Schilddrüsenkarzinom.

BACKGROUND: About 10% of thyroid cancers are medullary thyroid carcinoma (MTC) and can occur sporadically, familially and in the context of type II multiple endocrine neoplasia (MEN). Imaging plays a pivotal role in screening family members and in diagnosis. DIAGNOSTIC METHODS: Diagnosis is based on ultrasound (US), thyroid scintigraphy, serum calcitonin and carcinoembryonic antigen (CEA) as well as fine needle biopsy. High-resolution US is the most important imaging method for locoregional staging, combined with computed tomography (CT) of the mediastinum. Positron emission tomography (PET-CT) using 18-F-DOPA is particularly suited for suspected occult metastases in case of rising tumor markers in serum. FINDINGS AND COURSE OF DISEASE: Diagnosis is made based on cytologic findings in a hypoechoic, cold thyroid nodule, combined with an elevation of serum calcitonin and CEA. US is the most important imaging modality during routine follow-up. CT is indicated for suspected mediastinal, lung, or liver metastases. CT should be replaced by MRI as early as possible to prevent significant cumulative radiation doses over time. RECENT CLINICAL DEVELOPMENTS: Although MTC is curable by surgery only, owing to its radio- and chemoresistance, the disease will often progress only slowly, and even patients with metastases will frequently survive 10 years or longer. For more aggressive variants and late symptomatic stages, targeted drugs that have the potential to indicate stabilization or even a partial remission of the disease are under clinical investigation or already approved.

[Quantitative methods in sonography]. / Quantitative Verfahren in der Sonographie.

B­mode and color Doppler ultrasound are standard radiological methods to quantify tissue echo texture and tissue perfusion. Microstructure and composition of tissue influence echo texture parameters and acoustic parameters, such as speed of sound, attenuation and backscatter and quantitative color Doppler image parameters are influenced by the hemodynamics in depictable vessels. Dynamic contrast-enhanced ultrasound enables quantification of tissue perfusion and ultrasound elastography assists in assessing tissue stiffness. B­mode texture analysis, analysis of high-frequency echo signals and quantitative color Doppler image analysis are able to contribute to the assessment of tissue microstructure but have so far not been implemented clinically due to their complexity. Dynamic contrast-enhanced ultrasound and ultrasound elastography have proven to be robust under clinical conditions.

Percutaneous treatment of late complications of the Bentall procedure.

Aortic pseudo-aneurysm following the Bentall procedure is a rare but potentially severe complication. Surgical reintervention represents a high risk. We report on two cases with different pseudo-aneurysm types which were successfully treated using two different percutaneous techniques. © 2017 Wiley Periodicals, Inc.

[Target volume concepts in radiotherapy and their implications for imaging]. / Zielvolumenkonzepte in der Strahlentherapie und ihre Bedeutung für die Bildgebung.

CLINICAL ISSUE: Successful radiotherapy requires precise localization of the tumor and requires high-quality imaging for developing a treatment plan. STANDARD TREATMENT: Irradiation of the tumor region, including a safety margin. TREATMENT INNOVATIONS: The target volume consists of the gross tumor volume (GTV) containing visible parts of the tumor, the clinical target volume (CTV) covering the GTV plus invisible tumor extensions, and the planning target volume (PTV) to account for uncertainties. The non-GTV parts of the CTV are based on historical patient data. The PTV margins are based on a calculation of possible uncertainties during planning, setup, or treatment. Normal tissue deserves the identical care in contouring, since its tolerance may limit the tumor dose, taking into account the contours of organs at risk. Serial risk organs benefit from defining a planning organ of risk volume (PRV) to better limit the dose delivered to them. DIAGNOSTIC WORK-UP: The better the imaging, the more reliable the definition of the GTV and treatment success will be. Multiple imaging sequences are desirable to support the delineation of the tumor. They may result in different CTVs that, depending on their tumor burden, may require different doses. PERFORMANCE: The definition of standardized target volumes according to the ICRU reports 50, 62, and 83 forms the basis for an individualized radiation treatment planning according to unified criteria on a high-quality level. ACHIEVEMENTS: Radio-oncology is by nature interdisciplinary, the diagnostic radiologist being an indispensable team partner. A regular dialogue between the disciplines is pivotal for target volume definition and treatment success. PRACTICAL RECOMMENDATIONS: Imaging for target volume definition requires highest quality imaging, the use of functional imaging methods and close cooperation with a diagnostic radiologist experienced in this field.

Diffusion-weighted breast imaging.

Magnetic resonance imaging (MRI) of the breast represents one of the most sensitive imaging modalities in breast cancer detection. Diffusion-weighted imaging (DWI) is a sequence variation introduced as a complementary MRI technique that relies on mapping the diffusion process of water molecules thereby providing additional information about the underlying tissue. Since water diffusion is more restricted in most malignant tumors than in benign ones owing to the higher cellularity of the rapidly proliferating neoplasia, DWI has the potential to contribute to the identification and characterization of suspicious breast lesions. Thus, DWI might increase the diagnostic accuracy of breast MRI and its clinical value. Future applications including optimized DWI sequences, technical developments in MR devices, and the application of radiomics/artificial intelligence algorithms may expand the potential of DWI in breast imaging beyond its current supplementary role.

Maximum intensity breast diffusion MRI for BI-RADS 4 lesions detected on X-ray mammography.

AIM: To investigate an abbreviated, contrast-agent free diffusion-weighted (DW) breast magnetic resonance imaging (MRI) protocol that provides a single image for the radiologist to read in order to non-invasively examine Breast Imaging-Reporting and Data System (BI-RADS) 4 lesions detected using breast cancer screening X-ray mammography. MATERIALS AND METHODS: This retrospective evaluation within a institutional review board-approved, prospective study included 115 women (mean 57 years, range 50-69 years) with BI-RADS 4 findings on X-ray mammography and indication for biopsy over a period of 15 months. Full diagnostic breast MRI (FDP) was performed prior to biopsy (1.5 T). Maximum intensity breast diffusion (MIBD) images were generated from DW images (b = 1,500 mm/s2, 3 mm section thickness) of the breast. MIBD and T2-weighted (T2W) images were read by two radiologists and compared to the diagnostic accuracy of an expert reading of the FDP with histopathology as the reference standard. The acquisition time of MIBD and T2W MRI was about 7 minutes. RESULTS: MIBD MRI provided a diagnostic accuracy of 87.93% (95% confidence interval [CI]: 80.58-93.24%) for R1 and 89.66% (95% CI: 82.63-94.54%) for R2. Expert reading of the FDP revealed a similar accuracy of 86.2% (95% CI: 78.67-91.43%). The positive predictive value (PPV) could be increased from 36.2% (95% CI: 28.02-45.28; X-ray mammography alone) to a mean PPV of 80.89% (R1 79.17%, R2 82.16%) using MIBD MRI. Mean reading time was 30 seconds (25%/75 percentile 24.5-41.25). CONCLUSIONS: MIBD MRI might be of supplemental value if added to the work-up of BI-RADS 4 X-ray mammography screening findings. MIBD MRI might help reduce the false-positive rate prior to biopsy for reference lesions at only limited expense of measurement and reading time.

[Prerequisites for a successful lung cancer screening program]. / Voraussetzungen für ein erfolgreiches Lungenkrebsscreeningprogramm.

The American national lung cancer screening trial (NLST) has provided the first confirmation of a reduction in lung cancer mortality by using low-dose multislice computed tomography (MSCT). Preliminary evaluations of smaller European trials could not confirm such a reduction. The final evaluation of the larger Dutch-Belgian NELSON trial and five other European trials are expected within the next 1-2 years. The results of the completed rounds of screening in all these studies indicate that the margin between a positive and a negative benefit-to-harm balance will be narrow. In such a scenario it will be crucial to optimize the definition of the target population for screening as a high-risk group for lung cancer, the quality of screening in terms of high sensitivity and specificity as well as high quality treatment and an effective ongoing control of program quality. Not all healthcare systems are suitable to fulfill these prerequisites.

[Retention of contrast media in the history of radiology : Sequelae of the former use of thorotrast and new challenges]. / Kontrastmittelretention in der Geschichte der Radiologie : Folgen der früheren Thorotrastanwendungen und neue Herausforderungen.

Detection of gadolinium deposits in patients who have repeatedly been administered intravenous gadolinium chelates have given rise to concern regarding the long-term safety of magnetic resonance imaging (MRI) contrast media. Nevertheless, negative long-term clinical effects have not yet been observed. In some publications parallels have been drawn to the sequelae of thorotrast that was formerly used for arterial angiography. In this article the history of thorotrast use is briefly described and in particular why, despite warnings, this substance was used frequently and worldwide. A brief summary of the results of the German Thorotrast Study revealed that high excess rates were only observed for primary malignant liver tumors after a 15-year or longer latency period and to a lesser degree of leukemias, as well as for severe local complications due to paravascular injections, particularly in the neck region. Based on this historical review, we will venture to take stock of the outcome from the "success story" of this contrast agent.

The application of Gadopentate-Dimeneglumin has no impact on progression free and overall survival as well as renal function in patients with monoclonal plasma cell disorders if general precautions are taken.

OBJECTIVES: The current analysis investigated the prognostic significance of gadopentetate dimeglumine on survival and renal function in patients with monoclonal plasma cell disorders. METHODS: In this study 263 patients who had received gadopentetate dimeglumine within a prospective trial investigating dynamic contrast-enhanced magnetic resonance imaging (MRI) were compared with 335 patients who had undergone routine, unenhanced MRI. RESULTS: We found no significant prognostic impact of the application of contrast agent on progression-free survival in patients with either monoclonal gammopathy of undetermined significance, smouldering or symptomatic myeloma and no significant prognostic impact on overall survival in patients with symptomatic myeloma. Since renal impairment is a frequent complication of myeloma, and decreased renal function is associated with a higher risk of complications in patients receiving contrast agents, we evaluated the impact of contrast agent on renal function after 1 year. In the present analysis the only significant adverse impact on kidney function occurred in symptomatic myeloma patients who already had impaired renal parameters at baseline. Here, the renal function did not recover during therapy, whereas it did so in patients with normal or only slightly impaired renal function. CONCLUSION: If general recommendations are adhered to, gadopentetate dimeglumine can be safely applied in patients with monoclonal plasma cell disease.

[Principles of Doppler sonography]. / Verfahren der Dopplersonographie.

The techniques of medical Doppler are spectral Doppler (contiuous-wave (CW) and pulse-wave (PW) Doppler) and color flow imaging (Color Doppler and Power Doppler). All are based on the fact that the frequency of an echo from a moving reflecting particle will be altered by a characteristic frequency shift determined by its velocity in relation to the source/detector. The CW Doppler will only detect flow within a pre-defined depth and will not be guided by an image, whereas the PW Doppler is carried out with B-mode guidance (Duplex doppler). The so derived curves permit to assess the temporal distribution of flow velocities and directions and flow disturbances as well. In the case of color flow imaging, a part of the interrogated tissue section is mapped for Doppler signals and then color-coded, resulting in a dynamic color map of flow, where the colors encode characteristic flow parameters (e. g. mean flow velocity plus direction). This article describes the technical and physical basics of medical Doppler techniques.