(BLISS) BLISS is a magnetic resonance imaging technique that provides the measurement of two bilateral volumes in a single acquisition. Localized shimming for each volume improves the fat suppression. BLISS is an imaging sequence for sagittal breast MRI studies with high spatial resolution and short scan time.

(BOLD) In MRI the changes in blood oxygenation level are visible. Oxyhaemoglobin (the principal haemoglobin in arterial blood) has no substantial magnetic properties, but deoxyhaemoglobin (present in the draining veins after the oxygen has been unloaded in the tissues) is strongly paramagnetic. It can thus serve as an intrinsic paramagnetic contrast agent in appropriately performed brain MRI. The concentration and relaxation properties of deoxyhaemoglobin make it a susceptibility , e.g. T2 relaxation effective contrast agent with little effect on T1 relaxation.
During activation of the brain, the oxygen consumption of the local tissue increase by approximately 5% with that the oxygen tension will decrease. As a consequence, after a short period of time vasodilatation occurs, resulting in a local increase of blood volume and flow by 20 - 40%. The incommensurate change in local blood flow and oxygen extraction increases the local oxygen level.
By using T2 weighted gradient echo EPI sequences, which are highly susceptibility sensitive and fast enough to capture the three-dimensional nature of activated brain areas will show an increase in signal intensity as oxyhaemoglobin is diamagnetic and deoxyhaemoglobin is paramagnetic. Other MR pulse sequences, such as spoiled gradient echo pulse sequences are also used.
As the effects are subtle and of the order of 2% in 1.5 T MR imaging, sophisticated methodology, paradigms and data analysis techniques have to be used to consistently demonstrate the effect.
As the BOLD effect is due to the deoxygenated blood in the draining veins, the spatial localization of the region where there is increased blood flow resulting in decreased oxygen extraction is not as precisely defined as the morphological features in MRI. Rather there is a physiological blurring, and is estimated that the linear dimensions of the physiological spatial resolution of the BOLD phenomenon are around 3 mm at best.

Blood pool agents (intravascular contrast agents) remain in the blood for a prolonged time compared with conventional contrast agents, which diffuse quickly into the interstitial space. Magnetic resonance angiography (MRA), cardiovascular imaging, or contrast enhanced MRIs are possible over an hour or more. This advantage over conventional MRI contrast media allows also higher resolution MRA of several territories using respiratory or cardiac gating techniques with a single contrast bolus.
Different types of blood pool contrast agents:
Blood pool MRI contrast agents with their longer intravascular circulation can be designed to be targeted to necrotic myocardium, to assess myocardial viability, or tumor directed to provide better diagnostic information for various tumors. A disadvantage of the use of blood pool agents for MRA is that the separation of arteries and veins is more difficult because they are present in both and the overlapping of those vessels is disturbing. This can be solved by e.g. different MIP segmentation algorithms.

See also Necrosis Avid Contrast Agent, Tumor Specific Agents, Feruglose, Gadofosveset Trisodium (Vasovist), Ultrasmall Superparamagnetic Iron Oxide and Contrast Medium.

Blurring comes most obviously from patient motion, but other mechanisms like low resolution sampling also lead to image blurring.

A bolus is a rapid infusion of high dose contrast agent. Dynamic and accumulation phase imaging can be performed after bolus injection. Since the transit time of the bolus through the tissue is only a few seconds, high temporal resolution imaging can be required to obtain sequential images during the wash in and wash out of the contrast material and, therefore, resolve the first pass of the tracer.
For the same injected dose of contrast agent the injection rate (and, consequently, the total injected volume) modifies the bolus peak profile. Increasing the injection rate produces a sharpening of the peak (Cmax increase, Tmax decrease, peak length decrease). At a low injection rate, the first pass presents a plateau form. Substantial changes in the gadolinium concentrations during signal acquisition induce artifacts. Furthermore, the haemodynamic parameters (cardiac output, blood pressure) influence the bolus profile. The characteristics of gadolinium agents are favorable in the early bolus phase, whereas the advantages of large complexes (e.g. blood pool agents) and ultrasmall superparamagnetic iron oxide (USPIO) are most evident in the distribution phase.