H D Sostman

Magnetic resonance imaging of blood flow with a phase subtraction technique: In vitro and in vivo validation

RATIONALE AND OBJECTIVES.One promising approach to flow quantification uses the velocity-dependent phase change of moving protons. A velocity-encoding phase subtraction technique was used to measure the velocity and flow rate of fluid flow in a phantom and blood flow in volunteers. METHODS.In a model, the authors measured constant flow velocities from 0.1 to 270.0 cm/second with an accuracy (95% confidence intervals) of ±12.5 cm/second. There was a linear relationship between the magnetic resonance imaging (MRI) measurement and the actual value (r2 = .99; P = .0001). RESULTS.Measuring mean pulsatile flow from 125 to 1,900 mL/minute, the accuracy of the MRI pulsatile flow measurements (95% confidence intervals) was ±70 mL/minute. There was a linear relationship between the MRI pulsatile flow measurement and the actual value (r2 =.99;P = .0001). In 10 normal volunteers, the authors tested the technique in vivo, quantitating flow rates in the pulmonary artery and the aorta. The average difference between the two measurements was 5%. In vivo carotid flow waveforms obtained with MRI agreed well with the shape of corresponding ultrasound Doppler waveforms. CONCLUSIONS.Velocity-encoding phase subtraction MRI bears potential clinical use for the evaluation of blood flow. Potential applications would be in the determination of arterial blood flow to parenchymal organs, the detection and quantification of intra- and extra-cardiac shunts, and the rapid determination of cardiac output and stroke volume.

RENAL MAGNETIC RESONANCE ANGIOGRAPHY IN THE PREOPERATIVE DETECTION OF SUPERNUMERARY RENAL ARTERIES IN POTENTIAL KIDNEY DONORS

RATIONALE AND OBJECTIVES.Careful evaluation of the renovascular anatomy in potential living-related kidney donors is essential regarding the presence of accessory renal arteries. Conventional arteriography remains the standard of evidence for delineating the renal arterial supply. We assessed the utility of two-dimensional phase contrast (PC) magnetic resonance angiography (MRA) in the workup of potential living-related renal donors. METHODS.Thirty-nine patients were examined with conventional arteriography and MRA, which was performed on a 1.5-T system using a two-dimensional PC technique in both coronal and axial planes (repetition time[TR]/echo time [TE] = 39/8.5 msec; flip 60°; matrix 256 × 128; field of view, 28 cm2; 2 excitations; first-order gradient-moment nulling; 7-mm section with 2-mm overlap). The number of hilar and polar supernumerary renal arteries was determined. Hilar supernumerary arteries were classified as co-dominant if they were similar in size to the ipsilateral main renal artery. RESULTS.Conventional arteriography identified 78 dominant and 13 supernumerary (3 co-dominant, 10 accessory) renal arteries. Magnetic resonance angiography identified the proximal 35 mm of all 78 dominant and the 3 co-dominant renal arteries. Of the remaining ten (7 polar and 3 hilar) accessory vessels, only four were correctly identified with MRA. CONCLUSION.The high error rate (60%) suggests that two dimensional PC MRA, as implemented, should not be used in the preoperative evaluation of potential renal donors.

Magnetic resonance imaging--cardiac ejection fraction measurements. Phantom study comparing four different methods.

The accuracy of cardiac ejection fraction (EF) measurements with thin, contiguous cine-magnetic resonance imaging (MR) sections is well established. Still, faster imaging and measurement techniques would be desirable. The authors evaluated the accuracy of four different MR EF measurements methods in a biventricular, anthropomorphic, foam-latex rubber phantom which was connected via noncompliant fluid-filled tubing to a pulsatile flow pump. Nine contiguous 10 mm cine-MR sections (TR/TE, 25/13; flip angle, 45 degrees) were obtained through the heart in long and short cardiac axes at 16 frames per cardiac cycle at a pump rate of 60 beats/minute. EF measurements were based on either the multi-slice summation technique (nine contiguous 10-mm sections versus four 10-mm sections spaced 10 mm apart) or the area-length method (single largest long section versus combination of largest long- and short-axis section). Three replications were performed for each of the tested EFs (40.8%, 29.4%, and 13.4%), which were compared with actual EFs. EF measurements based on contiguous 1-cm sections correlated best with the actual EFs. Average relative errors ranged from 3.2% to 6.0%. EF measurements based on every other section were less accurate; average relative errors were between 5.2% and 10.2%. Single and biplane area-length algorithm EF measurements were significantly less accurate; average relative errors were as high as 59%. EF measurements based on multi-slice summation are more accurate than those based on the area-length algorithm. Contiguous 1-cm section acquisitions are most accurate and most time consuming. With slight decrease of accuracy, acquisition and processing times can be halved by skipping every other slice.

Quantification of Myocardial Perfusion with MRI and Exogenous Contrast Agents

This review discusses the applications of MRI to quantification of the myocardial perfusion. The first step of the measurement is to obtain a concentration-time curve from a signal intensity-time (SI) curve. Factors which influence the correlation between SI and the concentration are discussed for relaxivity and susceptibility agents. The second stage of measurement is to extract parameters of myocardial perfusion from the concentration-time curve. Two methods are considered, one for an intravascular agent and the other for an extravascular agent. Key points are illustrated with experimental data.

Thoracic metastases from cervical carcinoma: Current status

Thoracic metastases from squamous carcinoma and adenocarcinoma of the cervix were studied by reviewing 245 consecutive cases to describe comparative incidence, natural history, and radiographic patterns. The incidence of chest metastases was higher for adenocarcinoma (20%) than for squamous carcinoma (4%). Few patients diagnosed in the early stages of squamous carcinoma developed metastases; for adenocarcinoma, chest metastases occurred regardless of the stage at diagnosis. For both histologies, parenchymal (often cavitary) nodules only were seen; lymphangitic pattern was not observed. Both adenopathy and malignant effusion are common (44% of metastases) in thoracic metastasis from squamous carcinoma. Adenopathy but not effusion was common in adenocarcinoma.

Mri of Absent Left Pulmonary Artery

Unilateral absence of a pulmonary artery, more accurately referred to as unilateral proximal interruption of a pulmonary artery, is a rare congenital anomaly that may occur as an isolated lesion or in association with other congenital cardiovascular abnormalities. Diagnosis of associated lesions is imperative as early detection and intervention may significantly improve the patients prognosis. We present the case of an adult patient who had come to our attention after suffering neurological decompression illness related to scuba diving. The patients cardiopulmonary anatomy was evaluated using MRI gated spin echo, cine, and breath-held fast spoiled recalled echo sequences.

Magnetic resonance imaging of the thorax: techniques, current applications, and future directions

Magnetic resonance imaging (MRI) has been used extensively to evaluate the central nervous and musculoskeletal systems. MRI provides excellent contrast between normal and pathologic tissues, identifies vascular structures without the need of intravenous contrast, and is able to image in multiple planes. Until recently, physiologic motion produced artifacts that markedly limited the use of MRI in the thorax. However, with the advent of cardiac gating and respiratory motion compensation, diagnostic images can now be readily acquired. The ability to distinguish between flowing blood and adjacent tissue allows for the detection of aortic aneurysms and dissections. Prominent vessels may be differentiated from hilar adenopathy without the use of contrast agents. Preliminary experience suggests MRI may be useful in assessing central pulmonary emboli and mediastinal venous obstruction. The ready identification of flow combined with the multiplanar capability of MRI provide a means of assessing congenital abnormalities and other anatomic information. Fast scan techniques provide a dynamic means of assessing cardiac function and are sensitive to valvular stenosis and insufficiency. Combined with spin-echo techniques, areas of myocardial infarction and focal wall motion abnormalities can be detected. Currently, MRI has little application in the assessment of pulmonary nodules, bronchogenic cancer, and diffuse parenchymal disease. Sagittal MR images may more clearly show tumor extension into the axilla, brachial plexus, and spinal canal in patients with superior sulcus neoplasms. Future applications may include faster imaging techniques, blood flow measurement, detection of thrombus using phase sensitive techniques, regional perfusion, and assessment of cellular energy metabolism.

1982 George Simon Memorial Fellowship Award. Experimental studies with 111indium-labeled platelets in pulmonary embolism.

The effects of several potential modifiers on the detection of experimental pulmonary emboli by indium-111-labeled autologous platelets were studied. Contrast material did not affect embolus visualization; heparin prevented it, but its effect was not irreversible. The addition of exogenous thrombin to the experimental thrombus was not necessary for successful detection of the resulting emboli. Indium-111-oxine detected a small number of emboli without in vitro platelet labeling. Acutely embolized thrombi up to 72 hours old were readily identified by labeled platelets, but emboli older than 24 hours were almost impossible to detect. There was evidence suggesting propagation of emboli within the pulmonary arteries.

Platelet kinetics and biodistribution in canine endotoxemia.

Kinetics and magnitudes of changes in Indium-labeled platelet biodistribution were studied in dogs given E. coli endotoxin. Marked, reversible, dose-dependent shifts of platelets from blood to lung and apparently irreversible shifts to liver were demonstrated. These were contemporaneous with alterations in blood gases and in pulmonary and systemic hemodynamics. Morphologic studies revealed atelectasis, sequestration of leukocytes and platelets in the lungs, and mild interstitial pulmonary edema. This study provides in vivo quantification of labeled platelet response to a specific stimulus, and illustrates a method that could be applied to more extensive study of blood element participation in acute lung injury.

Radiolabeled fibronectin for the scintigraphic detection of pulmonary emboli in dogs.

Plasma fibronectin, a glycoprotein that is a component of blood thrombi, was evaluated for the in vivo scintigraphic detection of pulmonary emboli in dogs. Fibronectin (canine or human) was labeled with either 131I or with 111In and diethylenetriaminepenta-acetic acid (DTPA) as the bifunctional chelating agent using a modification of the mixed anhydride method. The radiolabeled proteins were administered intravenously 20 to 30 minutes after the embolization of a 99mTc-labeled thrombus. The uptake of radioactivity by the embolus was monitored scintigraphically up to 24 hours. At the end of each experiment, the animal was killed and in vitro tissue counting of radioactivity was performed. Comparative study of the 131I- and 111In-labeled agent is presented with particular reference to their pharmacokinetics. The in vivo uptake of radioactivity by the emboli was limited, indicating that radiolabeled fibronectin is not a good scintigraphic agent for the detection of pulmonary emboli.