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Coils and Patient Preparation

Imaging can be performed with a phased array torso or body coil. The advantage of using a phased array torso coil is that it provides greater

Fig. 1a, b. Pulmonary perfusion study in a normal individual. (a) demonstrates a raw data image with overlying regions of interest for measurement of perfusion values. (b) represents the corresponding parametric map calculated from the perfusion data in which perfusion values are color coded (red=high perfusion, dark blue=low perfusion)

Fig. 1a, b. Pulmonary perfusion study in a normal individual. (a) demonstrates a raw data image with overlying regions of interest for measurement of perfusion values. (b) represents the corresponding parametric map calculated from the perfusion data in which perfusion values are color coded (red=high perfusion, dark blue=low perfusion)

signal-to-noise ratio (SNR) which can be used to acquire images with higher spatial and temporal resolution. Phased array coils also allow the application of parallel imaging to further increase the spatial and temporal resolution of image acquisition. When pulmonary MRA and pulmonary perfusion are performed in the coronal plane, it is important to have the patient's arms placed over their head in order to reduce or eliminate wrap artifacts. This is especially true if using parallel imaging where wrap can cause extreme artifacts.

Contrast Dosage

Today, there is a tendency to perform more than a single contrast enhanced study during each examination. Often we perform a low dose high temporal resolution functional study followed by a higher dose low temporal but high spatial resolution angiographic study. If more than one contrast-enhanced study is performed within a single examination it is important that the low dose study is performed first so that venous contamination can be minimized. For example in our pulmonary hypertension protocol we first perform an LAO MRA through the aorta to rule out a shunt utilizing 0.025 mmol/kg of contrast agent. Thereafter, we perform a coronal high-resolution pulmonary MRA utilizing 0.15 mmol/kg of contrast agent.

Imaging Protocols

Pulmonary Embolism. We perform a time-resolved pulmonary MRA in 3 seconds utilizing 0.2 mmol/kg of contrast agent at an injection rate of 5 ml/second. Imaging is started 4 seconds after contrast agent administration when breath-holding is initiated. Image acquisition is continued for as long as the patient can maintain a breath-hold. This allows us to obtain both pulmonary MRA and pulmonary perfusion information.

Pulmonary arterial hypertension. We perform a dynamic 3D MRA through the aortic arch in the LAO plane utilizing 0.025 mmol/kg of contrast agent at an injection rate of 5 ml/second. The temporal resolution of each dataset is 0.6 seconds allowing for detection of vascular shunts. We next perform a 3D MRA through the lungs utilizing 0.15 mmol/kg of contrast agent at 5 ml/second. The temporal resolution of this dataset is 3 seconds. This allows us to obtain both perfusion and anatomical information.

Pulmonary arterial vascular malformations (PAVM) or anomalous pulmonary circulation. We perform a dynamic 3D MRA through the lungs in the coronal plane with a temporal resolution of 1 second utilizing 0.1 mmol/kg of contrast agent at an injection rate of 5 ml/second. By obtaining multiple pure arterial phases we can identify small PAVM's. We next perform a 3D MRA through the lungs at a temporal resolution of 3 seconds utilizing 0.1 mmol/kg of contrast agent at an injection rate of 5 ml/second. This allows us to obtain higher spatial resolution images.

To facilitate the accurate planning of interven-tional therapy, a high resolution study with an acquisition time of up to 20 seconds can be performed. This permits the identification of small feeding vessels.

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