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Technical Aspects of Multidetector Computed Tomography
Published in Paul Schoenhagen, Frank Dong, Cardiac CT Made Easy, 2023
Currently available contrast media are quickly diluted in the blood and distributed into the extracellular space, providing only a short time window for enhanced imaging. The transit time from the standard injection site (antecubital vein) to the heart is patient-dependent, and can vary between 20 and 40 s depending on the contrast flow rate and the patient's cardiac output. Therefore, determination of the scan delay (time between start of contrast agent injection and start of the scan) is critical to ensure optimal enhancement of the desired cardiovascular structures. This can be achieved with a small ‘timing bolus' or by monitoring the diagnostic bolus (‘bolus tracking’). With the use of a timing bolus, approximately 20 mL of contrast agent is injected, and a single image slice (typically at a level ∼2 cm below the carina for imaging of the coronaries) is repeatedly imaged. The transit time of contrast agent to the region of interest (ROI) is determined from a time enhancement curve (Figure 3.6) and used for timing of the diagnostic bolus (Figure 3.7). Alternatively, with bolus tracking techniques, the entire diagnostic bolus is injected, and contrast enhancement is monitored in the ROI by repeated imaging at a single level. Once a certain enhancement threshold is achieved, breath-hold instructions are given, and scanning is started.
Principles behind Magnetic Resonance Imaging (MRI)
Published in Michael Ljungberg, Handbook of Nuclear Medicine and Molecular Imaging for Physicists, 2022
The most established MRI technique for assessment of cerebral blood flow (CBF) is dynamic susceptibility contrast MRI (DSC-MRI). A Gd-based contrast agent is injected intravenously, and the signal time course is monitored by rapid T2*-weighted EPI (approximately 1 image/second for 1–2 minutes) during the first passage of the contrast agent bolus in the brain. The contrast agent concentration is quantified, as a function of time, in the tissue (pixel by pixel) as well as in a brain-feeding artery (providing the arterial input function, AIF). Perfusion-related parameters such as cerebral blood volume (CBV), CBF (Figure 32.22b), and mean transit time (MTT) can be calculated using kinetic theory for intravascular tracers, most commonly by using deconvolution of the tissue concentration time curve with the AIF to obtain CBF and MTT. The basic concept is often referred to as ‘bolus tracking’ (applicable also to, for example, computed tomography). Quantification in absolute terms has, so far, been problematic due to difficulties in obtaining accurate AIFs and uncertainties concerning the transverse relaxivities in tissue and blood.
Cardiovascular system
Published in A Stewart Whitley, Jan Dodgeon, Angela Meadows, Jane Cullingworth, Ken Holmes, Marcus Jackson, Graham Hoadley, Randeep Kumar Kulshrestha, Clark’s Procedures in Diagnostic Imaging: A System-Based Approach, 2020
A Stewart Whitley, Jan Dodgeon, Angela Meadows, Jane Cullingworth, Ken Holmes, Marcus Jackson, Graham Hoadley, Randeep Kumar Kulshrestha
The bolus chase technique involves performing baseline, non-contrast, overlapping X-rays down the legs at pre-set positions for the mask images. A single, large volume contrast injection (100 ml at 6–8 ml/s) is then injected and angiograms are performed with the table moving sequentially to the pre-set positions. The table movement to the next pre-set position is triggered by the radiographer in order to ‘chase’ the contrast bolus down the leg. The advantage of bolus tracking is that it is potentially quicker and uses a smaller volume of contrast than the stepping table technique. In reality however, additional angiograms are often required if there is differential passage of contrast down each leg or if there has been movement of the limb between the single mask image and subsequent contrast images. Thus, in most departments the stepping table technique is preferred.
Coronary CT angiography: a guide to examination, interpretation, and clinical indications
Published in Expert Review of Cardiovascular Therapy, 2021
Filippo Cademartiri, Giancarlo Casolo, Alberto Clemente, Sara Seitun, Cesare Mantini, Eduardo Bossone, Luca Saba, Nicola Sverzellati, Stefano Nistri, Bruna Punzo, Carlo Cavaliere, Ludovico La Grutta, Giovanni Gentile, Erica Maffei
The modality of administration of contrast material in CCT is a key factor that have to be optimized and combined with the choice of the other parameters in order to obtain a proper intravascular enhancement [4]. The general rule is to obtain an acquisition of the heart while the bolus of iodinated contrast material transits the first time through the left chambers and the coronary arteries (i.e. arterial first pass). The synchronization can be obtained using test bolus or real time bolus tracking methods. The best scenario is characterized by the minimum amount of contrast material that allows the highest intravascular attenuation. This is important because the quality and confidence of image assessment and the speed and actual capabilities of segmentation and quantification tools is very much depending on the proper enhancement (differential attenuation) of the lumen of vessels and cardiac chambers with respect to neighboring structures.
Optimization of radiation settings for angiography using 3D fluoroscopy for imaging of intracranial aneurysms
Published in Computer Assisted Surgery, 2021
Thomas Linsenmann, Alexander März, Vera Dufner, Christian Stetter, Judith Weiland, Thomas Westermaier
It should be emphasized that radiation settings do not alone determine the quality of vascular imaging. The flooding of the contrast agent is likely to play an equally important For CTA, this was extensively examined in the past. Maintaining stable blood pressure is certainly a prerequisite for good-quality contrast imaging but not in a proportional function [16]. To date, there is still no clear algorithm for the timing of contrast agents in CTA. For that reason, manufacturers added bolus tracking in the field of CTA [17]. In 3D-rotational fluoroscopy, this issue may be even more challenging because the arteriogram is – at least in peripheral vessels – hard to distinguish from the venogram. The latter, however, is not useful for the purpose of imaging cerebral imaging and may worsen image quality.
Oxytocin selectively reduces blood flow in uterine fibroids without an effect on myometrial blood flow: a dynamic contrast enhanced MRI evaluation
Published in International Journal of Hyperthermia, 2020
Saara Otonkoski, Teija Sainio, Gaber Komar, Visa Suomi, Jani Saunavaara, Roberto Blanco Sequeiros, Antti Perheentupa, Kirsi Joronen
MRI protocol included a dynamic contrast-enhanced (DCE) T1-weighted sequence, the parameters of which are shown in Table 1. A single dose (0.2 ml/kg) of contrast agent (Dotarem, Guebert, Roissy, France) was manually injected at a constant rate followed by 10 ml saline flush after the acquisition of the first five time frames of the dynamic scans. The DCE-MRI data were analyzed with NordicICE software v. 4.1.1 (NordicNeuroLab AS, Bergen, Norway). The arterial input function was determined from the iliac artery by placing a circular region of interest (ROI) onto the artery lumen. Blood flow values were calculated by standard model-independent deconvolution technique by means of contrast bolus tracking [17]. Parametric blood flow values were obtained by T1 perfusion deconvolution arithmetic with the first pass of an AIF curve. Averaged blood flow values were obtained for the fibroids, myometrium and muscle. The fibroid ROIs were drawn within three middle slices of the fibroid to include most of the fibroid. The myometrium ROIs were drawn on the negative side of the fibroid in the three most representative slices of the myometrium and the muscle ROI’s were drawn on the abdominal muscle within the three middle slices as the fibroid ROIs.