Validation of clinical brain imaging methods
Fast MRI
In the last ten years there has been an increased attention to significantly reduce examination times at MRI. At Karolinska University Hospital, MRI physicists together with Stefan Skare have developed methods for ultrafast MRI of the brain. Preliminary results from clinical application of the method indicate high diagnostic potential for the method to identify and characterize diseases of the brain. New and motion-insensitive multicontrast MR sequences at Karolinska Hospital, where the brain can be examined in 1-3 minutes, are expected to provide the same information as a 30-minute examination. Included sequences can demonstrate bleeding, edema, contrast enhancement, structural defects, ischemia, etc. This is done in a regular MRI machine. To clinically validate these new techniques, a comparison with regular clinical MR contrasts in the same patient is required. MRI of the brain in children is especially important to perform instead of the ionizing method computed tomography when pathology is suspected. However, children have difficulty both understanding and enduring an MRI examination due to discomfort and anxiety. Because of this, children are examined under sedation or under general anesthesia. Due to the child's sedated state, the examinations are also long in terms of time, as you do not want to miss anything once the patient is lying there sedated and you do not have an easy chance to add to the examination afterwards. Access to pediatric anesthesia is also very limited, which contributes to the waiting time for children for MRI of the brain up to several months. Our research aims to validate methods that, while maintaining diagnostic accuracy, still can reduce the need for long examination times and/or reduce the use of anesthesia in under MR examinations.
PETMR
PET (Positron Emission Tomography) is a diagnostic tool that involves the intravenous administration of chemical substances labeled with radioactive molecules. The distribution of these tracers confirms the presence of tumor/metastases and determines the effect of oncological therapy. In neuro-oncology, PET helps distinguish radionecrosis from tumor recurrence in an unclear lesion after radio/surgical treatment. PET-MRI combines positron emission tomography (PET) and magnetic resonance imaging (MRI) within an imaging system, morphological-MRI with functional information from PET. By doing so, the diagnosis becomes more accurate, which leads faster to the correct treatment. The PET-MR system offers an unprecedented opportunity to combine simultaneous measurements of brain structure, metabolism, neurochemistry, perfusion and neuronal activity. It enables imaging that combines a wide range of PET tracers for metabolism, receptors, proteins, amino acids, etc. with several different simultaneous MR-based measurements. As a result, PET-MR exposes patients to a lower radiation dose than PET-CT, enables simultaneous data collection and better distinguishes between radionecrosis and tumor recurrence. Our project aims to address the challenges that still exist in PET-MR image acquisition and to evaluate new PET-MR applications of future clinical relevance to increase diagnostic certainty in clinical PET-MR.
Flat panel detector
Several investigative methods are used together to diagnose and guide treatment of patients who present with symptoms consistent with acute stroke, such as focal disabling neurologic symptoms or loss of consciousness. A reliable diagnosis is essential to determine the most beneficial treatment strategy for the patient and is usually performed with the help of DT. Endovascular recanalization is performed under x-ray guidance in an interventional suite equipped with a flat detector C-arm system. A flat detector is primarily used for 2D image guidance during interventional procedures. However, it can also be used for diagnostic 3D imaging by rotating the detector around the patient and reconstructing the resulting 3D volume. This imaging technique is known as Cone Beam CT (CBCT) and enables important diagnostic information, usually in the context of an interventional procedure. Most often, CBCT is used for anatomical assessment such as bone morphology and characterization of iodine contrast-enhanced blood vessels, peri- and post-procedural information such as stent/graft placement, and detection of important procedure-related complications such as bleeding. Due to detector limitations, flat detector systems currently lack the capability for detailed low-contrast tissue discrimination, such as soft tissue and brain tissue characterization. Photon energy-separating imaging techniques (spectral imaging) have emerged and gained much attention in the last decade due to major technological advances and an increasing number of clinical applications. There are several spectral techniques and even more promising ones are under development. Spectral CT/DECT can add significant value to a diagnostic investigation, for example by offering the potential for improved tissue characterization through virtual monoenergetic image (VMI) reconstruction as well as material separation and iodine quantification. Today, DECT is widely used in neuroradiology, for example to separate blood from iodine contrast leakage after an interventional procedure. Recent studies show promising results using DECT for acute stroke imaging, indicating a possibility of higher diagnostic sensitivity and specificity for detecting early ischemic changes. So far, photon energy separation is most often used in CT scanners to improve image quality and extract additional image information.
Applying this concept to flat detectors situated in interventional suites would theoretically provide CBCT images with improved tissue and anatomical characterization, as well as an increased detectability of iodine. This technique has been called Spectral CBCT or Dual Energy CBCT (DE-CBCT). A technically sophisticated approach to enable energy separation is to superimpose detector layers on top of each other. With this technique, the top detector layer captures low energy photons and the bottom detector layer captures higher energy photons. This enables a separation of the photon energy spectra, which is used to enhance the image information content. Improved detector characteristics could also make it possible to lower the required radiation dose to the patient and healthcare professionals involved in a wide range of interventional procedures. Preclinical studies have provided insights into the possibilities of energy-separating flat detectors, and our research aims to evaluate this technology in a diagnostic application.