Short name: Gd-HP-DO3A, generic name: Gadoteridol injection, chemical compound: Gd-1,4,7-tris(carbonylmethyl)-10-(2'-hydroxypropyl)-1,4,7,10-tetraazacyclododecane
(ProHance®) A nonionic MRI contrast agent with a low molecular weight complex of gadolinium (macrocyclic chelate, which tightly binds the Gd atom).
Gadoteridol does not cross the blood brain barrier. If the barrier is damaged, gadoteridol will penetrate into lesions such as tumors. It also highlights areas of increased vascularity so it has been used to improve the delimitation of lesions elsewhere in the body.
Apart from its paramagnetic effects, gadoteridol has no pharmacological activity in the body. After intravenous injection, most of the dose is excreted unchanged in the urine within 24 hours.

See also Contrast Agents and ProHance®.

Rectal staging is necessary for the preoperative assessment of intra- and extramural tumor infiltration or the decision for adjuvant radio-chemotherapy. One indication of MRI with luminal contrast enhancement is small bowel enteroclysis after duodenal intubation for visualization of inflammatory bowel wall thickening and other complications.
"Double contrast" enhancement of the bowel lumen is the administration of plain water or water with methylcellulose along with heavily T2 weighted sequences or contrast enhanced T1 weighted sequences.
Several oral contrast agents have been used for small bowel MRI: Mannitol, metamucil, locust bean gum, and PEG. All provide sufficient bowel distension and homogeneity, but suffer from side effects such as diarrhea. The volume of PEG or mannitol administered must be not too large in order to achieve the best compromise between distension and acceptance by the patient.
MR colonography with positive bowel lumen enhancement requires higher concentrations of paramagnetic agents compared to the available dedicated enteral contrast agents, IV compounds are used to dope water enemas for this purpose.
Some investigators advocate negative bowel enhancement with Contrast Agents to suppress high signal bowel content in MRCP ( Magnetic resonance cholangiopancreaticography ). The use of a mixture of metamucil and 20 ml of gadolinium chelate provides good homogeneity and good tolerance without diarrhea.

Paramagnetic substances, for example Gd-DTPA solutions, are used as MRI oral contrast agents in gastrointestinal imaging to depict the lumen of the digestive organs. Different Gd-DTPA solutions or zeolites containing gadolinium can be used e.g., for diagnosis of delayed gastric emptying, diagnosis of Crohn's disease etc.
Low concentrations of gastrointestinal paramagnetic contrast agents cause a reduction in T1 relaxation time; consequently, these agents act on T1 weighted images by increasing the signal intensity of the bowel lumen. High concentrations cause T2 shortening by decreasing the signal, similar to superparamagnetic iron oxide. Gd-DTPA chelates are unstable at the low pH in the stomach, therefore buffering is necessary for oral use.

See also Gadopentetate Gastrointestinal, Gadolinium Zeolite, Negative Oral Contrast Agents, Gastrointestinal Superparamagnetic Contrast Agents, and Ferric ammonium citrate.

(Hb) Haemoglobin is the major endogenous oxygen-binding molecule, responsible for binding oxygen in the lung and transporting it to the tissues by means of the circulation. Haemoglobin is contained in very high concentration in the red blood cells.
Haemoglobin is an Fe chelate tightly binding one Fe ion in its II oxidation state where it carries the charge 2+ (ferrous iron). If an oxygen molecule is bound to Hb, Hb is called oxyhaemoglobin, if no oxygen molecule is bound it is called deoxyhaemoglobin. When haemoglobin is oxidized (i.e. in a haematoma), Fe2+ is transformed into Fe3+. The resulting haemoglobin is then called metoxyhaemoglobin (Hb Fe3+).
Deoxyhaemoglobin and metoxyhaemoglobin act as paramagnetic contrast agents in MR, while oxyhaemoglobin is diamagnetic. This partly explains the special appearance of an aging haematoma in MR imaging and is also the basic of the blood oxygenation level dependent contrast (BOLD) used in functional magnetic resonance imaging of the brain (fMRI).

The characteristics of a hepatobiliary contrast agent are specific liver uptake and excretion via the biliary system. The paramagnetic substance (e.g. manganese, gadolinium) is taken up by normal hepatocytes. Diseased liver tissue did not include hepatocytes or their function is disturbed. Therefore, the signal of healthy liver tissue increases on T1 weighted sequences, but not in the liver lesions.
Another type of liver imaging contrast agent is superparamagnetic iron oxide. These particles accumulate in the reticuloendothelial system (RES) of the liver, and darken the healthy liver tissue in T2 weighted images. RES cells (including Kupffer cells) are existing in healthy liver tissue, in altered tissue with reduced RES activity or without RES cells the contrast agent concentration is also low or not existing, which improves the liver to lesion contrast.
Benefits of hepatobiliary contrast agents:
Differences of a hepatobiliary contrast agent compared with a targeted contrast agent for Kupffer cells:
See also Superparamagnetic Contrast Agents, Hepatobiliary Chelates, Liver Imaging, Endoremâ„¢, Primovistâ„¢, and Classifications, Characteristics, etc.

See also the related poll result: 'The development of contrast agents in MRI is'