Following acceptance of the regional creature care panel, eight domestic pigs which have a weight (BW) out-of 42–forty-two kilogram have been looked at. The latest animals were surgically instrumented such that synchronous catheter-based IPM were you can from the MPA as well as in the fresh new iliac artery (IA). Which have catheters for the situ and you may intubated not ventilated, the latest animals was indeed put on the newest desk of your MR scanner regarding the supine status. In all animals, normocapnia are monitored by repeated arterial bloodstream gas study into the entire sedation.
Pulmonary Hypertension (PAH)
Several experimental designs with various invasiveness have been published to evaluate PAH: open chest models with constriction of the MPA ( 19 ), implanted balloon catheters in the left atrium ( 20 ), injection of microspheres ( 21 ), surgical creation of arteriovenous (av)-fistulas ( 22 ), variations in circulating blood volume inducing an elevation of the pulmonary pressure ( 23 ), and injections of serotonin ( 24 , 25 ). In this study, PAH was generated experimentally by continuous intravenous application of thromboxane A2 (TxA2, C20Hthirty twoO5), a prostaglandin with a half-life in the range of seconds. TxA2 is known to induce a transient, but intense, constriction of the pulmonary arteries with negligible constrictive effects on the systemic circulation. To examine different degrees of severity of PAH, TxA2 was applied at dosages of 0.075, 0.1, and 0.125 ?g/kg BW/minute. In each pig, five IPM and five MR velocity-encoded measurements were obtained at different pulmonary pressure levels. First, basic values without TxA2 were acquired. Second, three different stages of PAH induced by TxA2 were measured. Third, after devolution of TxA2 and recovery of stable pressure levels in the MPA as measured with IPM, a final measurement was performed. Accordingly, seven ? five synchronously acquired MR velocity encoded and IPM data sets were generated.
This new catheter-based studies acquisition was done with Berman angiographic catheters (Arrow Globally Inc., Understanding, PA, USA) having IPM connected to a great MR-compatible overseeing tool (OmniTrak 7000, In Vivo Research, Inc., Orlando, Florida, USA). Zero alignment are over till the proportions. IPM try filed continuously and you will integrated the acquisition of your systolic together with mean stress from the MPA plus in the IA paralleling the five MR specifications.
MR Velocity-Encrypted Measurements
The MR flow measurement technique has been validated and utilized before in a pediatric study on normal values in the pulmonary circulation ( 26 ). Velocity-encoded MR measurements were performed in a 1.5 Tesla system (Magnetom Sonata, Siemens Medical Solutions, Erlangen, Germany) using a phase-contrast fast low angle shot (FLASH)-sequence. Former publications using Doppler ultrasonography to quantify pulmonary hypertension ( 17 ) pointed to the importance of an accurate registration of the AT. Therefore, a high temporal resolution should also be achieved with the MR velocity-encoded measurements. Maximum gradient settings (gradient strength = 40 mT/m, slew rate = 200 T/m/second, rise time = 200 ?s) combined with a bandwidth of 1395 Hertz/pixel resulted in a minimum TE and TR of 2.4 msec and 9.5 msec, respectively. With the selected sequence, TR equaled the temporal resolution. The MPA was centered in the B0 field as far as possible to minimize phase shift errors due to eddy currents ( 27 ) and Maxwell term correction was applied. Three measurements were averaged to increase the signal-to-noise ratio, requiring a heart frequency–dependent acquisition time of approximately seven to 10 minutes. Measurements were performed during free breathing to include the effects of respiration on cardiac output and pulmonary flow ( 18 ). The application of long-term averaging compensated for respiratory motion. The spatial resolution using a matrix size of 256 was 1.1 mm ? 1.4 mm, and the slice thickness was 5 mm. Using multiple scout images, the MR velocity-encoded imaging plane was measured perpendicularly to the MPA (Fig. 1). IPM and MR velocity-encoded measurements were simultaneously acquired before, during, and after experimentally induced pulmonary hypertension. MR flow measurement sequences allow to generate: 1) phase images (containing the direction-encoded quantitative velocity information); 2) magnitude images (containing the not quantitative information about the localization of any flow); and 3) rephased, i.e., anatomical images (with a similar appearance as T1-weighted gradient echo images). MR data sets were analyzed using commercially available flow quantification software (ARGUS®; Siemens Medical Solutions, Erlangen, Germany) to derive the morphological and flow related parameters from the MPA listed in Table 1.