Martin Weibrecht

Fluoroscopic x-ray imaging with amorphous silicon thin-film arrays

The dream of an all-solid state large area x-ray image sensor with digital readout and full dynamic performance will most probably find a first realization in 2D thin-film amorphous silicon arrays. In this paper we address in particular the evaluation of the limits of the signal/noise ratio in this concept. Using small prototype detectors measurements of MTF and noise power spectra have been made as a function of x-ray dose. The results are given in terms of the detective quantum efficiency as a function of dose and spatial frequency. We further present an analysis of the different noise sources and their dependence on the detector parameters, and we provide estimates on the maximum signals that may be achieved per unit dose. The intrinsic lag of the amorphous silicon photodiodes causes a second problem area with this type of x-ray detectors. Especially in radiography/fluoroscopy mixed applications, memory effects may not be negligible.

Intensity-modulated radiotherapy for prostate cancer implementing molecular imaging with 18F-choline PET-CT to define a simultaneous integrated boost.

Purpose:To report the own experience with 66 patients who received 18F-choline PET-CT (positron emission tomography-computed tomography) for treatment planning.Patients and Methods:Image acquisition followed 1 h after injection of 178–355 MBq 18F-choline. An intraprostatic lesion (GTVPET [gross tumor volume]) was defined by a tumor-to-background SUV (standard uptake value) ratio > 2. A dose of 76 Gy was prescribed to the prostate in 2-Gy fractions, with a simultaneous integrated boost up to 80 Gy.Results:A boost volume could not be defined for a single patient. One, two and three or more lesions were found for 36 (55%), 22 (33%) and seven patients (11%). The lobe(s) with a positive biopsy correlated with a GTVPET in the same lobe in 63 cases (97%). GTVPET was additionally defined in 33 of 41 prostate lobes (80%) with only negative biopsies. GTVPET, SUVmean and SUVmax were found to be dependent on well-known prognostic risk factors, particularly T-stage and Gleason Score. In multivariate analysis, Gleason Score > 7 resulted as an independent factor for GTVPET > 8 cm3 (hazard ratio 5.5; p = 0.02) and SUVmax > 5 (hazard ratio 4.4; p = 0.04). Neoadjuvant hormonal treatment (NHT) did not affect SUV levels. The mean EUDs (equivalent uniform doses) to the rectum and bladder (55.9 Gy and 54.8 Gy) were comparable to patients (n = 18) who were treated in the same period without a boost (54.3 Gy and 55.6 Gy).Conclusion:Treatment planning with 18F-choline PET-CT allows the definition of an integrated boost in nearly all prostate cancer patients – including patients after NHT – without considerably affecting EUDs for the organs at risk. GTVPET and SUV levels were found to be dependent on prognostic risk factors, particularly Gleason Score.ZusammenfassungZiel:Erfahrungsbericht mit 66 Patienten nach 18F-Cholin-PET-CT (Positronenemissionstompgraphie-Computertomographie) zur Bestrahlungsplanung.Patienten und Methodik:Die Bildakquisition erfolgte 1 h nach Injektion von 178–355 MBq 18F-Cholin. Ein intraprostatischer Herd (GTVPET [makroskopisches Tumorvolumen]) wurde ab einem Tumor-zu-Hintergrund-SUV-(„standard uptake value“-)Quotienten > 2 definiert. Die Verschreibungsdosis für die Prostata betrug 76 Gy in 2-Gy-Einzeldosen mit simultanem integrierten Boost bis 80 Gy.Ergebnisse:Ein Boostvolumen konnte bei einem Patienten nicht definiert werden. Ein, zwei und drei oder mehr Herde wurden bei 36 (55 %), 22 (33 %) und sieben Patienten (11 %) gefunden. Der/die Lappen mit positiver Biopsie korrelierte/n in 63 Fallen (97 %)mit dem GTVPET im gleichen Lappen. Zusätzlich wurde ein GTVPET in 33 von 41 Lappen (80 %) mit nur negativen Biopsien definiert. GTVPET, SUVmean und SUVmax zeigten eine Abhängigkeit von bekannten Risikofaktoren, insbesondere T-Stadium und Gleason-Score. In multivariater Analyse resultierte ein Gleason-Score > 7 als ein unabhängiger Faktor für GTVPET > 8 cm3 (relatives Risiko 5,5; p = 0,02) und SUVmax > 5 (relatives Risiko 4,4; p = 0,04). Eine neoadjuvante Hormontherapie (NHT) war ohne Einfluss auf SUV-Werte. Die mittleren EUDs („equivalent uniform doses“) für Rektum und Blase (55,9 Gy und 54,8 Gy) waren vergleichbar zu Patienten (n = 18), die in der gleichen Periode ohne Boost bestrahlt wurden (54,3 Gy und 55,6 Gy).Schlussfolgerung:Die Bestrahlungsplanung nach 18F-Cholin-PET-CT ermöglicht die Definition eines integrierten Boostvolumens bei nahezu allen Patienten mit Prostatakarzinom – einschließlich Patienten nach NHT – ohne einen relevanten Einfluss auf die EUDs für die Risikoorgane. GTVPET- und SUV-Werte zeigten eine Abhängigkeit von prognostischen Risikofaktoren, insbesondere dem Gleason-Score.

Dynamic X-ray imaging system based on an amorphous silicon thin-film array

In this paper we address design concepts and performance characterization with our laboratory x-ray detector system. Key component is a 1k2 pixel TFT switched photodiode array with a pixel pitch of 200 micrometer. It is built of a-Si:H with a CsI:Tl scintillator layer. The detector system can be used for radiography and fluoroscopy applications with up to 30 images/s. It shows a S/N-ratio better than 23dB at a dose of 10nGy/frame and reaches a value for DQE of more than 60% at low spatial frequencies. We have developed a new evaporation process for CsI:Tl deposition directly on the array. It yields an x-ray sensitivity close to the theoretical limit and a spatial resolution on a sufficiently high level. An optimized plate design in combination with a dedicated charge sensitive readout amplifier chip lead to a very low level of electronic noise. In particular sources and properties of electronic noise and signal crosstalk have shown to be crucial for the clinical use of the new technology. The visual impression of the remaining noise in the images from our system is isotropic. This means especially that synchronous noise has been reduced to the edge of visibility.

Diffusion-weighted MRI does not reflect kidney fibrosis in a rat model of fibrosis.

To assess the apparent diffusion coefficient (ADC) derived from diffusion‐weighted (DW) magnetic resonance imaging (MRI) as a specific marker of renal fibrosis in rats with unilateral ureteral obstruction (UUO).

Intraindividual quantitative and qualitative comparison of gadopentetate dimeglumine and gadobutrol in time-resolved contrast-enhanced 4-dimensional magnetic resonance angiography in minipigs.

ObjectivesThe concentration and relaxivities of contrast agents affect quantitative and qualitative image quality in contrast-enhanced time-resolved 4-dimensional magnetic resonance angiography (4D-MRA). Gadobutrol has a high relaxivity and is the only gadolinium (Gd)-based contrast agent approved for clinical use at a 1 M concentration. This promises to confer superior bolus characteristics by generating a steeper and shorter bolus with a higher peak Gd concentration. The purpose of this study was to quantitatively examine bolus characteristics of 1 M gadobutrol compared with 0.5 M gadopentetate dimeglumine and to evaluate image quality in thoracoabdominal 4D-MRA. Materials and MethodsA total of 7 Goettingen minipigs received dynamic computed tomography (CT) on a clinical 64-slice CT (transverse slices, 80 kV, 20 seconds, 0.3 s/dynamic frame) and 4D-MRA (time-resolved imaging with stochastic trajectories; 1. transverse slices, 30 seconds, 0.49 s/frame; 2. coronal slices, 70 seconds, 1.3 s/frame) on a 1.5-T clinical whole-body magnetic resonance imaging under general anesthesia using gadopentetate dimeglumine and gadobutrol in an intraindividual comparative study. Computed tomography attenuations were converted into Gd concentrations on the basis of previous phantom experiments. Quantitative analysis included measurements of the full width at half maximum, time-to-peak intervals, and peak of each bolus in dynamic CT and transverse 4D-MRA. These studies were carried out at equivalent contrast agent flow rates of 1 mL/s. Quantitative analysis (7 arteries and veins) and qualitative image analysis were performed on coronal thoracoabdominal 4D-MRA studies carried out at flow rates of 1 mL/s and, in the case of gadopentetate dimeglumine, also at molarity-adjusted flow rates of 2 mL/s. ResultsThe bolus in both transverse 4D-MRA and dynamic CT was significantly narrower (full width at half maximum), earlier (time to peak), and higher (signal intensity enhancement in 4D-MRA, Gd concentration in dynamic CT) when using gadobutrol instead of gadopentetate dimeglumine at a flow rate of 1.0 mL/s (P = 0.008−< 0.0001). In thoracoabdominal 4D-MRA, the signal intensity level and overall image quality were highest in examinations with gadobutrol, followed by examinations with gadopentetate dimeglumine at flow rates of 2 mL/s, and lowest in examinations with gadopentetate dimeglumine at flow rates of 1 mL/s. ConclusionsA more compact bolus shape was observed after administration of gadobutrol compared with gadopentetate dimeglumine in minipigs. This was demonstrated both in 4D-MRA, where Gd concentration, relaxivity, and the image-acquisition technique play a role, and in CT, where the signal intensity depends only on the Gd concentration. The overall image quality was rated higher in examinations with 1.0 M gadobutrol than with 0.5 M gadopentetate dimeglumine.

Image quality assessment of monochrome monitors for medical soft copy display

Soft-copy presentation of medical images is becoming part of the medical routine as more and more health care facilities are converted to digital filmless hospital and radiological information management. To provide optimal image quality, display systems must be incorporated when assessing the overall system image quality. We developed a method to accomplish this. The proper working of the method is demonstrated with the analysis of four different monochrome monitors. We determined display functions and veiling glare with a high-performance photometer. Structure mottle of the CRT screens, point spread functions and images of stochastic structures were acquired by a scientific CCD camera. The images were analyzed with respect to signal transfer characteristics and noise power spectra. We determined the influence of the monitors on the detective quantum efficiency of a simulated digital x-ray imaging system. The method follows a physical approach; nevertheless, the results of the analysis are in good agreement with the subjective impression of human observers.

Variation of Kinetic Model Parameters Due to Input Peak Distortions and Noise in Simulated 82Rb PET Perfusion Studies

Cardiac 82Rubidium dynamic PET studies allow quantifying myocardial perfusion by using tracer kinetic modelling. The accuracy of the derived perfusion parameter K1 is limited e.g. by noise, which impacts the measurement of both the myocardium time activity curve (TAC) and the input function. Measuring the input function peak is particularly challenging for the sharp injection bolus. By simulation studies with a two-compartment model, we quantified the impact of both input peak distortions and data noise on K1. The input function was a generic analytical function. Modifying a function parameter, peak distortions were introduced. Gaussian noise was added to the simulated myocardium TAC and the model was fitted using the distorted input function. We analysed various sets of functions and model parameters covering a physiologically relevant range. We show that up to 20% noise in the tissue data, even moderate errors in the input peak (e.g. 10%) can dominate the error of the K1 estimate. Generally, the bias due to the peak distortion and the variance due to the tissue noise can easily lead to more than 30% error in K1. These data highlight the importance of optimizing the clinical acquisition protocols and data processing, especially with regard to a correct input peak estimation. An analysis similar to the one suggested here can help in this optimization, and can furthermore provide confidence limits on the perfusion parameters presented to the clinician.

New high-brightness monochrome monitor based on color CRT technology

With increasing availability of medical image communication infrastructures, medical images are more and more displayed as soft-copies rather than as hard-copies. Often however, the image viewing environment is characterized by high ambient light, such as in surgery rooms or offices illuminated by daylight. We are describing a very-high- brightness cathode-ray-tube (CRT) monitor which accommodates these viewing conditions without the typical deterioration in resolution due to electron focal spot blooming. The three guns of a standard color CRT are used to create a high brightness monochrome monitor. The CRT has no shadow-mask, and a homogeneous P45 phosphor layer has been deposited instead of the structured red-green-blue color phosphor screen. The electron spots of the three guns are dynamically matched by applying appropriate waveforms to four additional multiple magnetic fields around the gun assembly. We evaluated the image quality of the triple-gun CRT monitor concerning parameters which are especially relevant for medical imaging applications. We have measured characteristic curves, dynamic range, veiling glare, resolution, spot profiles, and screen noise. The monitor can provide a high luminance of more than 200 fL. Due to nearly perfect matching of the three spots, the resolution is mainly determined by the beam profile of a single gun and is remarkably high even at these high luminance values. The P45 phosphor shows very little structure noise, which is an advantage for medical desktop applications. Since all relevant monitor parameters are digitally controlled, the status of the monitor can be fully characterized at any time. This feature particularly facilitates the reproduction of brightness and contrast values and hence allows easy implementation of a display function standard or to return to a desired display function that has been found useful for a given application in the past.

Contrast Media in Time-Resolved MRA at 3T: A Systematic Quantitative and Qualitative Analysis of Concentration and Dose Effects on Image Parameters in Minipigs

PURPOSE Quantitative and qualitative analysis of gadopentetate dimeglumine (GD) versus standard-dose (sGb) and half-dose (hGb) gadobutrol in thoracoabdominal time-resolved contrast-enhanced magnetic resonance angiography (4D-MRA) with dynamic computed tomography (dCT) as the quantitative reference in minipigs. MATERIALS AND METHODS 7 anesthetized Goettingen minipigs received thoracoabdominal dCT (0.37 s rotation time) and transverse 4D-MRA (0.3 s/dynamic frame;) using sGb and hGb. 8 other minipigs received coronal 4D-MRA (1.3 s/dynamic frame; sGb, hGb, SGD). dCT attenuation levels were converted into absolute gadolinium concentrations and compared to 4D-MRA peak signal intensities (SI). Bolus lengths were quantified by full width at half maximum (FWHM) measurements. After this comparison of dose effects on SI in transverse 4D-MRA, coronal 4D-MRAs were analyzed regarding both quantitative and qualitative parameters. RESULTS In dCT (transverse 4D-MRA) hGb showed 39.0 % (14.5 %) lower arterial peak gadolinium concentrations (peak SIs) and 20.6 % (33.8 %) shorter FWHM compared to sGb. The difference was due to peak plateaus or reversals in 4D-MRA in 5/7 animals. While sGb led to the highest peak SIs, image quality ratings of arteries were rated similarly high with all contrast agent protocols despite a slightly higher SI with sGb. In contrast, venous peak SIs and image quality ratings were significantly higher when using sGb. CONCLUSION Peak Gd concentrations and 4D-MRA peak SIs are highest with sGB. These differences are most evident in the venous phase leading to superior image quality in multi-phase 4D-MRA. KEY POINTS · Standard-dose gadobutrol offers high vascular gadolinium concentrations and 4D-MRA peak signals.. · Absolute vascular gadolinium concentrations and 4D-MRA peak signal intensities at 3 T diverge.. · Peak plateaus or reversals cause decreased arterial 4D-MRA peak signals at 3 T.. · Arterial image quality is rated similarly high using different contrast agent protocols.. · Venous vessel visibility in 4D-MRA is significantly better using standard dose gadobutrol.. CITATION FORMAT · Hadizadeh DR, Keil VC, Jost G et al. Contrast Media in Time-Resolved MRA at 3T: A Systematic Quantitative and Qualitative Analysis of Concentration and Dose Effects on Image Parameters in Minipigs. Fortschr Röntgenstr 2018; 190: 747 - 757.

A High‐Resolution 2k Monochrome Monitor based on the Triple‐Gun Principle

We have studied a 2048 lines 2k high-resolution monochrome monitor concept operating with the three guns of a modified color CRT and a standard graphics controller. The major application for the monitor system is medical image presentation. The attainable performance has been analyzed and proven with the help of a prototype system. Major advantages over the standard single-gun monitor architectures are the reduced bandwidth and the attractive system price.