@phdthesis{Schmid2021,
  author    = {Schmid, Andrea},
  title     = {Diagnostische Genauigkeit der Dual-Energy Computertomographie Angiographie bei Patienten mit peripherer arterieller Verschlusskrankheit},
  doi       = {10.25972/OPUS-25113},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-251137},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2021},
  abstract  = {Es wurde die diagnostische Genauigkeit f{\"u}nf verschiedener Rekonstruktionsalgorithmen der DE-CTA der Becken-Bein-Gef{\"a}ße von Patienten mit pAVK an einem Dual-Source CT mit dem diagnostischen Goldstandard der DSA verglichen. Die DE-CTA zeigte eine exzellente Sensitivit{\"a}t an Becken- und Beingef{\"a}ßen hinsichtlich einer korrekten Stenosegraduierung, unabh{\"a}ngig von der Rekonstruktion. Die Standard MPR zeigte insgesamt die besten Ergebnisse und ist deshalb vor allem in nicht eindeutigen F{\"a}llen die Methode der Wahl. Die Auswertung von DE-CS MPRs, DE-CS MIPs, gekr{\"u}mmten MPRs oder die semi-automatische quantitative Stenosegradauswertung bringt keinen Zugewinn an diagnostischer Performance im Vergleich zur visuellen Auswertung der Standard MPR. Das Ausmaß der Gef{\"a}ßwandverkalkungen und die intraluminale Kontrastierung hatten keinen signifikanten Effekt auf die Sensitivit{\"a}t zur Erkennung signifikanter Stenosen an den Becken- und Beingef{\"a}ßen. Jedoch verschlechterten sich die Spezifit{\"a}t und die Genauigkeit der Rekonstruktionen, welche auf der DE-Knochen- und DE-Plaqueentfernung basieren, signifikant in stark verkalkten oder nur schwach kontrastierten Gef{\"a}ßsegmenten. Beim Auswerten von DE-CS Rekonstruktionen ist infolgedessen vor allem in schlecht kontrastierten oder stark verkalkten Gef{\"a}ßen eine weitere Verifizierung des Befundes n{\"o}tig, um unn{\"o}tige invasive DSAs als Folge von falsch positiven CTA-Befunden zu reduzieren.},
  subject      = {Dual-Source-Computertomographie},
  language  = {de}
}
@phdthesis{Portmann2023,
  author    = {Portmann, Johannes},
  title     = {Accelerated inversion recovery MRI of the myocardium using spiral acquisition},
  doi       = {10.25972/OPUS-30282},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-302822},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2023},
  abstract  = {This work deals with the acceleration of cardiovascular MRI for the assessment of functional information in steady-state contrast and for viability assessment during the inversion recovery of the magnetization. Two approaches are introduced and discussed in detail. MOCO-MAP uses an exponential model to recover dynamic image data, IR-CRISPI, with its low-rank plus sparse reconstruction, is related to compressed sensing. MOCO-MAP is a successor to model-based acceleration of parametermapping (MAP) for the application in the myocardial region. To this end, it was augmented with a motion correction (MOCO) step to allow exponential fitting the signal of a still object in temporal direction. Iteratively, this introduction of prior physical knowledge together with the enforcement of consistency with the measured data can be used to reconstruct an image series from distinctly shorter sampling time than the standard exam (< 3 s opposed to about 10 s). Results show feasibility of the method as well as detectability of delayed enhancement in the myocardium, but also significant discrepancies when imaging cardiac function and artifacts caused already by minor inaccuracy of the motion correction. IR-CRISPI was developed from CRISPI, which is a real-time protocol specifically designed for functional evaluation of image data in steady-state contrast. With a reconstruction based on the separate calculation of low-rank and sparse part, it employs a softer constraint than the strict exponential model, which was possible due to sufficient temporal sampling density via spiral acquisition. The low-rank plus sparse reconstruction is fit for the use on dynamic and on inversion recovery data. Thus, motion correction is rendered unnecessary with it. IR-CRISPI was equipped with noise suppression via spatial wavelet filtering. A study comprising 10 patients with cardiac disease show medical applicability. A comparison with performed traditional reference exams offer insight into diagnostic benefits. Especially regarding patients with difficulty to hold their breath, the real-time manner of the IR-CRISPI acquisition provides a valuable alternative and an increase in robustness. In conclusion, especially with IR-CRISPI in free breathing, a major acceleration of the cardiovascular MR exam could be realized. In an acquisition of less than 100 s, it not only includes the information of two traditional protocols (cine and LGE), which take up more than 9.6 min, but also allows adjustment of TI in retrospect and yields lower artifact level with similar image quality.},
  subject      = {Kernspintomografie},
  language  = {en}
}
@phdthesis{Richter2021,
  author    = {Richter, Julian Alexander J{\"u}rgen},
  title     = {Wave-CAIPI for Accelerated Dynamic MRI of the Thorax},
  doi       = {10.25972/OPUS-23207},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-232071},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2021},
  abstract  = {In summary, the wave-CAIPI k-space trajectory presents an efficient sampling strategy for accelerated MR acquisitions. Using wave-CAIPI in parallel imaging reconstructions leads to a reduced noise level in the reconstructed images, compared to the Cartesian standard trajectory. This effect could be quantified by means of noise and SNR calculations. An SNR gain can be traded for a reduced scan time, i.e., additional undersampling, or for an enhanced image quality, keeping scan time constant. Acceleration of MR imaging is especially important in dynamic applications, since these examinations are inherently time-consuming. The impact of wave-CAIPI sampling on image quality and its potential for scan time reduction was investigated for two dynamic applications: self-gated dynamic 3D lung MRI during free breathing and cardiac 4D flow MRI. Dynamic 3D Lung MRI By employing wave-CAIPI sampling in self-gated, free-breathing dynamic 3D lung MRI for the purpose of radiotherapy treatment planning, the image quality of accelerated scans could be enhanced. Volunteer examinations were used to quantify image quality by means of similarity between accelerated and reference images. To this end, the normalized mutual information and the root-mean-square error were chosen as quantitative image similarity measures. The wave-CAIPI sampling was shown to exhibit superior quality, especially for short scan times. The values of the normalized mutual information were (10.2 +- 7.3)\% higher in the wave-CAIPI case -- the root-mean-square error was (18.9 +- 13.2)\% lower on average. SNR calculations suggest an average SNR benefit of around 14\% for the wave-CAIPI, compared to Cartesian sampling. Resolution of the lung in 8 breathing states can be achieved in only 2 minutes. By using the wave-CAIPI k-space trajectory, precise tumor delineation and assessment of respiration-induced displacement is facilitated. Cardiac 4D Flow MRI In 4D flow MRI, acceleration of the image acquisition is essential to incorporate the corresponding scan protocols into clinical routine. In this work, a retrospective 6-fold acceleration of the image acquisition was realized. Cartesian and wave-CAIPI 4D flow examinations of healthy volunteers were used to quantify uncertainties in flow parameters for the respective sampling schemes. By employing wave-CAIPI sampling, the estimated errors in flow parameters in 6-fold accelerated scans could be reduced by up to 55\%. Noise calculations showed that the noise level in 6-fold accelerated 4D flow acquisitions with wave-CAIPI is 43\% lower, compared to Cartesian sampling. Comparisons between Cartesian and wave-CAIPI 4D flow examinations with a prospective acceleration factor R=2 revealed small, but partly statistically significant discrepancies. Differences between 2-fold and 6-fold accelerated wave-CAIPI scans are comparable to the differences between Cartesian and wave-CAIPI examinations at R=2. Wave-CAIPI 4D flow acquisitions of the aorta could be performed with an average, simulated scan time of under 4 minutes, with reduced uncertainties in flow parameters. Important visualizations of hemodynamic flow patterns in the aorta were only slightly affected by undersampling in the wave-CAIPI case, whereas for Cartesian sampling, considerable discrepancies were observed.},
  subject      = {Magnetresonanztomographie},
  language  = {en}
}
@phdthesis{Pannenbecker2024,
  author    = {Pannenbecker, Pauline Luisa},
  title     = {Vergleich von Dual- und Single-Source Dual-Energy CT in der Diagnostik der akuten Lungenarterienembolie hinsichtlich Bildqualit{\"a}t und Strahlendosis},
  doi       = {10.25972/OPUS-35206},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-352064},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2024},
  abstract  = {Hintergrund: Die CT-Pulmonalisangiographie (CTPA) ist diagnostischer Goldstandard der Diagnostik der Lungenarterienembolie (LAE). Durch Dual-Energy CT (DECT) k{\"o}nnen mithilfe von Joddistributionskarten LAEs auf Segment- und Subsegmentebene besser detektiert werden. Neben der etablierten Dual-Source-Technik erm{\"o}glicht ein Split-Filter eine DECT-Akquisition mit Single-Source-Scannern. Ein solcher SF-DECT-Scanner sollte hinsichtlich der Bildqualit{\"a}t sowie der Strahlendosis mit einem etabliertem DS-DECT-Ger{\"a}t verglichen werden. Material und Methoden: Insgesamt wurden 135 Patienten eingeschlossen, die eine CTPA erhielten: 68 erhielten einen DS-DECT-Scan mit 90/Sn150 kV und 67 einen SF-DECT-Scan mit Au/Sn120 kV. F{\"u}r beide Protokolle wurden farbkodierte Joddistributionskarten erstellt. Die objektive (CT-Abschw{\"a}chung in relevanten Gef{\"a}ßen in HU, Signal-Rausch-Verh{\"a}ltnis (SNR), Kontrast-Rausch-Verh{\"a}ltnis (CNR), perfused blood volume (PBV)) und subjektive Bildqualit{\"a}t (2 Befunder (B), 5-Punkte-Likert-Skala) sowie Dosisparameter wurden erhoben und verglichen. Ergebnisse: Alle CTPAs waren von diagnostischer Qualit{\"a}t. Ihre subjektive Bildqualit{\"a}t wurde in 80,9/82,4\% (B1/B2) der DS-DECT und in 77,6/76,1\% der SF-DECT als exzellent oder gut bewertet. Die subjektive Bildqualit{\"a}t der Joddistributionskarten der SF-DECT wurde von beiden Befundern als schlechter beurteilt. Die HU-Werte der relevanten Gef{\"a}ße unterschieden sich nicht signifikant (p>0.05), SNR und CNR der SF-Gruppe waren in zentralen Gef{\"a}ßen jedoch h{\"o}her (p<0.05); die PBV-Werte der SF-Gruppe waren teils h{\"o}her (p<0.05). Alle erhobenen Dosisparameter waren in der SF-Gruppe h{\"o}her (p<0,05). Konklusion: In der diagnostischen Abkl{\"a}rung eines V.a. eine akute LAE erm{\"o}glicht der Einsatz eines Split-Filters an einem Single-Source-CT-Scanner eine Dual-Energy-Untersuchung. Dies geht im Vergleich zu etablierten DS-Scannern jedoch mit einer schlechteren Qualit{\"a}t der Joddistributionskarten und einer h{\"o}heren Strahlendosis einher.},
  subject      = {Lungenembolie},
  language  = {de}
}