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Nuclear magnetic resonance (NMR) images of live rats with sterile and pyogenic abscesses, hematomas, and various implanted and spontaneous neoplasms demonstrated good contrast differentiation between pathologic and surrounding normal tissues. This differentiation was maximal when both the T1 and T2 tissue relaxation times were used as criteria. Neoplasms have a broad range of T1 and T2 values and may be confused with abscesses or hematomas. Tissue rate constants (1/T1 and 1/T2) are mainly dependent on total water content, the exception being fat, which has a 1/T2 value much shorter than that expected on the basis of water content alone.

Advances in imaging technique have improved the efficiency of clinical nuclear magnetic resonance (NMR) imaging, and will allow total patient examination time that equals or is more favorable than that of x-ray computed tomography (CT). The whole head can be examined with NMR in a 6.5-minute imaging time with a spatial resolution of 1.7 mm. Fifteen sections in the body can be similarly imaged. Quantitative T2 ("spin-spin" relaxation time) information, as well as estimates of T1 ("spin-lattice" relaxation time) can be obtained in this time. Quantitative T1 information requires an additional procedure.

Two dilute oral iron solutions, made from commonly available nonprescription dietary supplements, were found to enhance the gastrointestinal tract in nuclear magnetic resonance imaging of live rats and one human volunteer. The paramagnetic and pharmacologic properties of ferric ammonium citrate were more favorable than those of ferrous sulfate heptahydrate. The paramagnetic iron solutions shorten T1 and T2 relaxation times of water protons in the contrast media-filled gastrointestinal tract, producing easily observable change in NMR intensity. Because these iron solutions are available commercially and are known to be well tolerated, the clinical use of iron-containing NMR contrast agents for the gastrointestinal tract is feasible.

Thirty healthy subjects and 15 patients with a variety of musculoskeletal disorders were examined by conventional radiography, computed tomography (CT), and nuclear magnetic resonance (NMR). NMR proved capable of demonstrating important anatomic structures in the region of the lumbosacral spine. Lumbar disk protrusion was demonstrated in three patients with CT evidence of the disease. NMR appeared to differentiate annulus fibrosus from nucleus pulposus in intervertebral disk material. Avascular necrosis of the femoral head was demonstrated in two patients. The cruciate ligaments of the knee were well defined by NMR. Muscles, tendons and ligaments, and blood vessels could be reliably differentiated, and the excellent soft-tissue contrast of NMR proved useful in the evaluation of bony and soft-tissue tumors. NMR holds promise in the evaluation of musculoskeletal disorders.

Encoding the Precession phase angle of proton nuclei for Fourier analysis has produced accurate measurement of fluid velocity vector components by MRI. A Pair of identical gradient pulses separated in time by exactly ½ TE, are used to linearly encode the phase of flow velocity vector components without changing the phase of stationary nuclei, Two-dimensional Fourier transformation of signals gave velocity density images of laminar flow in angled tubes which were in agreement with the laws of vector addition. These Velocity profile images provide a quantitative method for the investigation of fluid dynamics and hemodynamics.© 1985 Academic Press,Inc.

Although cross-sectional magnetic resonance examination of the head and body is useful for screening large regions of tissue, subsectional regions of the head and body often need to be examined. Orthogonally directed, selectively irradiated planes with different flip angles produce a spatially limited signal region from which two- or three-dimensional volume images can be reconstructed. Images with limited fields-of-view can be acquired in reduced imaging time. We present a general description of this technique. These subsectional or "inner volume" images eliminate respiratory motion artifacts by excluding moving tissues from the imaged volume. A result of this technique is a high signal from rapid pulsatile blood flow, produced without cardiac gating the pulse sequence.

To determine whether hydrogen magnetic resonance imaging at 0.7 T provides added clinical value over imaging at 0.35 T, images of the heads of patients with various intracranial disorders were obtained at these field strengths. Measurements of tissue contrast (C), signal-to-noise (S/N) ratio, and T1 and T2 relaxation times were determined. For a given spin-echo sequence with equal imaging time, resolution, and data sampling window, the product C X S/N was somewhat lower for the lower field strength. Under conditions of imaging with equal chemical shift artifact, C X S/N at 0.35 T was equal to or greater than that measured at 0.7 T. With an increase in field strength, T1 of pathologic areas and surrounding normal tissues increased, resulting in a corresponding loss of absolute signal level and decrease in contrast. Lesions were equally well seen at both 0.35 T and 0.7 T. The increased T1 and decreased C X S/N for higher magnetic fields--when measured with a fixed imaging time, resolution, chemical shift, and sequence--suggest that such field strengths may not improve tissue contrast, diagnostic ability, or clinical throughput when compared with lower field strength systems.

Theoretical analysis predicts that performing magnetic resonance (MR) imaging with partial (less than 90 degrees) flip angles can reduce imaging times two- to fourfold when lesions with elevated T1 values are being examined. This time savings occurs because repetition time (TR) is reduced when imaging is performed with partial flips. Partial flip MR imaging can also improve signal-to-noise ratio (S/N) in fast body imaging. For this study, analytical tools were used to predict image contrast and S/N for short TR, partial flip sequences. Experimental implementation of the short TR, partial flip sequences that analytical work had predicted would be optimal supported the analytical predictions and demonstrated their validity. Partial flip MR imaging is applicable to reducing imaging time only when the ratio of signal differences to noise exceeds threshold values in conventional MR images. Partial flip sequences can be used to advantage in MR imaging of both the head and the body, and the observed effects are predictable through theoretical analysis.

Fibrosarcoma tumor cells were implanted in the hind legs of 25 rats and studied from the first to the sixth week postimplantation. Nuclear magnetic resonance imaging detected all tumors and did not yield any false-positives in five control rats. The T1 relaxation values of tumors overlapped those of muscle, and the T2 values overlapped those of fat, but the combination of the two values allowed discrimination of each of the three tissues with no overlap. The difference in relaxation time between tumor and muscle could be accounted for on the basis of water content, which was approximately 14% higher in the tumors. This study confirms data from previous studies suggesting that nuclear magnetic resonance imaging is a highly sensitive modality, but that T1 and T2 values are not specific for individual pathologic conditions.

The appearance of intraluminal signal in the cardiac chambers, the descending aorta, and blood vessels was studied in healthy subjects and patients with myocardial disease on first and second spin-echo gated magnetic resonance images. Signal was present in the cardiac chambers and the aorta at various phases of the cardiac cycle when physiological or pathological slow flow conditions are expected in healthy subjects and in patients. Healthy individuals tended to show signal in the ventricles and aorta during end-diastole, and signal was less likely to be present at higher heart rates and in systolic images. In patients with regional or global left ventricular dysfunction, intraventricular signal tended to persist into systole. Surprisingly, intraventricular signal was not present with increased frequency adjacent to infarcted regions of the myocardial wall. Thus, the mere presence of intracavitary signal cannot be used as an indicator of either regional or global cardiac contraction abnormalities. In the left atrium, signal was often present during systole. Physical factors determining the appearance of signal of flowing blood are discussed in an Appendix.

Ten patients with definite multiple sclerosis underwent hydrogen nuclear magnetic resonance imaging with a 3.5 kilogauss superconducting magnet, using the inversion recovery and spin-echo techniques of signal acquisition. Results were compared with high-resolution x-ray computed tomography. Spin-echo images demonstrated abnormal regions as areas of variably increased signal intensity. The contrast between abnormal and normal white matter improved as the intervals between sequential radiofrequency pulses and between pulse administration and signal sampling were increased. Inversion recovery images demonstrated abnormal areas as regions of decreased signal intensity but did not visualize lesions as well as spin-echo imaging. Spin-echo and inversion recovery imaging each demonstrated more extensive abnormalities than did computed tomography.

Eleven Sprague-Dawley rats with experimentally produced infarction of the lower extremities were imaged by nuclear magnetic resonance (NMR) immediately after infarction, and 6 and 24 hours later. Contrast between the infarcted and control muscles was noted immediately and continued to increase through 24 hours. These changes corresponded to a significant increase in the water content of the infarcted extremity at 24 hours. These results suggest promise for NMR imaging in the identification of myocardial infarction and should encourage further investigation in this area.

A technique is described for obtaining tomographic images of hydrogen distribution in animals using nuclear magnetic resonance (NMR). Resonant frequency is proportional to magnetic field strength, so that spatial resolution is achieved by frequency selection and magnetic field shaping. The results of scanning a phantom and two rats are presented.

The normal urinary bladder and several benign entities of the bladder were examined in 50 patients by magnetic resonance (MR) imaging. Specific features assessed included appearance of the bladder wall, optimal repetition (TR) and echo delay (TE) parameters for bladder-wall demonstration, and differentiation among various benign abnormalities, including bladder-wall hypertrophy, inflammation, and mucosal congestion, on MR images. The bladder wall in the 30 healthy subjects was best displayed using a TR = 2 sec, TE = 56 msec image, which gave 60% contrast between the bladder wall and urine and 48% contrast between the bladder wall and fat. Demonstration of bladder-wall hypertrophy required similar imaging; bladder distention was necessary to demonstrate the thickness of the bladder wall. Congestion and inflammation were best demonstrated on TR = 2 sec, TE = 56 msec images, which gave 45% contrast. Normal and/or hypertrophic bladder wall were distinguished from inflammation and congestion on the basis of signal intensity variations and/or T1 and T2 relaxation parameters.

Gated magnetic resonance (MR) imaging was used to evaluate central cardiovascular anatomy in 172 subjects, 31 of whom were healthy volunteers. Using the spin-echo technique, images of diagnostic quality were obtained in 93% of cases with TE = 28 msec and in 65% of cases with TE = 56 msec. Transverse multisection sequences encompassing most of the left ventricle required approximately 6-8 minutes. Corroborative studies were available in 134 of 141 patients who had cardiovascular disease; two dimensional echocardiograms and angiography in 133 and 100 patients, respectively. Gated MR demonstrated the wall thinning and complications caused by prior myocardial infarctions and high signal intensity of the myocardium at the site of acute myocardial infarctions. MR accurately demonstrated anatomic abnormalities owing to hypertrophic and congestive cardiomyopathies, congenital abnormalities of the heart and great vessels, rheumatic heart disease, pulmonary hypertension, and cardiac and paracardiac masses. Depiction of cardiovascular anatomy and pathoanatomy was attained without the use of any contrast media. Consequently, gated MR is an effective technique for cardiac diagnosis. The short time required for tomographic examination of the entire heart using the multisection technique renders this a practical cardiac imaging modality.

This retrospective study of 144 patients was made to (a) assess the potential of magnetic resonance (MR) for demonstrating lymph nodes using spin-echo technique, (b) compare the MR results with those of CT, and (c) determine the optimal pulse-sequence interval (TR) and echo-delay time (TE) for imaging lymph nodes. The reported CT findings on normal lymph nodes were compared with MR findings in 60 patients who underwent MR imaging of the neck (20 patients), chest (20 patients), abdomen (10 patients), and pelvis (10 patients) for conditions other than lymph node disease. The results showed that CT is presently better than MR for imaging neck and abdominal lymph nodes less than 13 mm in diameter. The ability of MR to demonstrate normal-size (less than 10 mm) lymph nodes in the chest was comparable to that of CT. In addition, MR scans of 84 patients with proven abnormal lymph nodes (8 neck, 49 chest, and 27 abdomen and pelvis) were assessed: in 72 patients, these nodes had also been imaged by CT. MR and CT gave similar results with abnormal lymph nodes (greater than 13 or 15 mm), but MR displayed these nodes better because of its excellent soft-tissue contrast resolution. MR can clearly differentiate abnormal lymph nodes from normal fat, muscle, vessels, adult thymus, thyroid, and diaphragmatic crura, as well as from primary tumor and lymphoceles. Optimal demonstration of lymph nodes with MR required two sequences: one with a short TR and one with a long TR and long TE. Preliminary results indicate that MR holds great promise for the demonstration of lymph nodes in every part of the body.

To test if changing magnetic fields and radiofrequency fields used in nuclear magnetic resonance imagers could induce electrical currents capable of causing localized tissue heating in metal surgical clips and prostheses, steel surgical clips, copper wire clips, and hip prostheses were exposed to fields greater than those used in the nuclear magnetic resonance imager. Observations indicated that no significant heating should be expected from implanted surgical clips during exposure. The heating of larger metallic implants should be further investigated.

Whole body nuclear magnetic resonance (NMR) imaging of the cardiovascular system was carried out in early clinical trials in 244 volunteers and patients using a 3.5 KGauss (0.35 T) unit. The spin echo technique with multiple imaging parameters was used. Blood vessels were clearly discriminated from solid organs and lesions because little or no intraluminal signal is seen with laminar blood flow at normal velocities, whereas a more intense image is generated by solid organs. Characteristic flow signals were observed in normal patients and were accentuated by varying the imaging parameters. Cardiac chambers were well delineated in some patients on nongated images. In one case, internal topography of the ventricles was exquisitely displayed on a gated image. Intraluminal pathology, such as dissection of the aorta, aneurysms of the aorta and left ventricle, and aortic atheroma, was clearly demonstrated. Patency of coronary arterial bypass grafts was shown. Abnormal flow patterns due to slow or turbulent flow were accentuated on images using the second spin echo. This preliminary experience indicates the considerable potential of NMR imaging in the evaluation of cardiovascular diseases.

A programme was written to detect flow in a sequence of MR images and to construct 3-D vessel maps from the detected flow regions. Reduction in first echo intensity and prolongation of calculated T2 value were used as flow-detection criteria. The programme was used to image the aorta in 6 patients with abdominal aortic aneurysm and 5 patients with aortic dissection. Results were compared with contrast angiography in 9 cases and X-ray CT in 2. The images obtained by the two techniques were comparable in 9 cases. In 2 cases of aortic dissection, where flow in the false lumen was slow, the false lumen could not be demonstrated by angiography, but was clearly seen in the reconstructed MR images.

The potential clinical importance of T1 and T2 relaxation times in distinguishing normal and pathologic tissue with magnetic resonance (MR) is discussed and clinical examples of cerebral abnormalities are given. T1 and T2 values may be used in three ways: (a) Relative values, obtained by an analysis of intensity images with varying dependence on T1 and T2, may be used if absolute values for T1 and T2 are not required for diagnosis. (b) If an absolute value is desired, the numerical values for the relaxation times may be generated using a region of interest on the intensity images. (c) In cases in which both T1 and T2 change may require a calculated image to indicate the contribution of each to the signal intensity, the numerical value may be used to generate analogue images of T1 or T2 calculations. Five patients with cerebral infarction, 15 with multiple sclerosis, two with Wilson disease, and four with tumors were imaged. Hemorrhagic and ischemic cerebrovascular accidents were distinguished using the spin echo technique. In the patients with multiple sclerosis, lesions had prolonged T1 and T2 times, but the definition of plaque was limited by spatial resolution. No abnormalities in signal intensity were seen in the patient with Wilson disease who was no longer severely disabled; abnormal increased signal intensity in the basal ganglia was found in the second patient with Wilson disease. Four tumors produced abnormal T1 and T2 relaxation times but these values alone were not sufficient for tumor characterization.

In multisection magnetic resonance imaging, gradient strength and earliest desired echo time (TE) set a limit to the thinnest section achievable. Offset radio-frequency irradiation techniques and phase encoding within a thick section make possible the production of thin sections of clinically useful quality in practical imaging times.

To determine the efficacy of proton nuclear magnetic resonance (NMR) imaging in documenting acute ischemic infarction and to characterize the changes in these images during the first 24 hours following the ischemic insult, serial NMR imaging was performed in gerbils that had undergone unilateral carotid artery ligation. No significant changes in the signal intensity, T1 or T2 relaxation times were noted for either asymptomatic animals or the control hemisphere of symptomatic gerbils. There was a significant increase in T1 and especially T2 relaxation times and in both the relative signal intensity and Hf(v) for the ischemic hemisphere of symptomatic gerbils. These parameters appeared to increase linearly over 24 hours. The ischemic lesion first could be detected by NMR as early as 3 hours after carotid artery ligation, our earliest time point. The physiologic significance of these changes is discussed. These data suggest that NMR imaging may have significant diagnostic importance for acute cerebral ischemia and infarction in man.

N UCLEAR magnetic resonance (NMR), the exciting new imaging modality, promises to combine the advantages of CT and ultrasound by offering excellent resolution of its tomographic image, the use of nonionizing radiation, and the capability of imaging in any desired plane. Like nuclear medicine, it is expected to supply information about. metabolic processes and about the physiologic status of tissues and organs. It does not appear to have any biologic risks in the imaging energy range.’

Magnetic resonance (MR) imaging was performed in two groups of patients to determine its usefulness in evaluating fluid-containing renal masses deemed complex with computed tomography (CT). Twenty-two patients in group 1 had indeterminate renal masses by CT, five of which were also indeterminate by ultrasound (US). The results in this group were compared with histologic findings. Group 2 consisted of 20 patients with simple renal cysts diagnosed according to rigid CT criteria. On MR imaging, 11 of the 23 masses in group 1 and 19 of the 20 in group 2 were diagnosed as benign cysts. Fluid within the cyst had long T1 and T2, resulting in a low signal intensity on T1-weighted images. In the 12 remaining lesions in group 1 and in one lesion in group 2, the fluid content was indeterminate and MR did not permit differentiation of cystic renal carcinoma from old hemorrhage or adenoma. When fluid within the cystic mass did not have the MR characteristics of simple fluid, MR was not helpful in characterizing the mass, but when the fluid intensity was similar to normal urine, the cyst was benign.

The role of nuclear magnetic resonance (NMR) imaging of the kidney was analyzed in 18 persons (6 normal volunteers, 3 patients with pelvocaliectasis, 2 with peripelvic cysts, 1 with renal sinus lipomatosis, 3 with renal failure, 1 with glycogen storage disease, and 2 with polycystic kidney disease). Ultrasound and/or computed tomography (CT) studies were available for comparison in every case. In the normal kidney distinct anatomical structures were clearly differentiated by NMR. The best anatomical detail was obtained with spin echo (SE) imaging, using a pulse sequence interval of 1,000 msec and an echo delay time of 28 msec. However, in the evaluation of normal and pathological conditions, all four intensity images (SE 500/28, SE 500/56, SE 1,000/28, and SE 1,000/56) have to be analyzed. No definite advantage was found in using SE imaging with a pulse sequence interval of 1,500 msec. Inversion recovery imaging enhanced the differences between the cortex and medulla, but it had a low signal-to-noise level and, therefore, a suboptimal overall resolution. The advantages of NMR compared with CT and ultrasound are discussed, and it is concluded that NMR imaging will prove to be a useful modality in the evaluation of renal disease.

Sagittal or coronal thoracic magnetic resonance (MR) images were obtained in 7 individuals - 4 normal subjects and 3 patients with thoracic masses. In 2 of the abnormal cases, sagittal or coronal MR provided significant anatomic information that was either less evident or invisible on transaxial MR or computed tomographic (CT) images or CT reformations. In the third abnormal patient, a pretracheal lymph node was more clearly seen on transaxial images than on coronal images.

Seventy consecutive patients were examined with magnetic resonance (MR) and computed tomography (CT) of the brain. Each study was independently reviewed. Focal abnormalities were detected by one or both modalities in 51 patients. Neoplastic, infectious, vascular, demyelinating, metabolic, and congenital disorders of the brain were included. The MR pulse sequence that best detected these abnormalities was a spin-echo multisection technique that used a long interval between RF excitations (TR = 1500 or 2000 msec). Forty-eight of 51 patients showed focal lesions with this technique. A supplementary MR pulse sequence with a short TR (500 msec) was useful in helping to characterize certain lesions with a long T1 relaxation component, but in 10 of 26 positive cases in which this sequence was added it would have missed the abnormality had it been the sole sequence used. MR missed focal lesions in 3 of 51 patients. These were lesions that required thin-section (1.5 mm) CT techniques. Two were intrasellar, and one was an intracanalicular neurinoma. In 17 of 48 patients, CT missed the focal lesion seen with MR. Based on this experience, it is concluded that the long TR multisection spin-echo sequence is the optimal MR screening technique for detection of most brain abnormalities, and is more sensitive than CT. Currently, CT remains the screening modality of choice when high-resolution, thin-section studies in the pituitary, inner ear, and orbital regions are indicated.

Nuclear magnetic resonance (NMR) is used to generate cross-sectional images of the human body that show excellent anatomic and functional definition. The NMR imaging process involves interactions between electromagnetic fields and the hydrogen nuclei being imaged. These interactions occur on time scales of milliseconds to seconds. Consequently, the motion of these nuclei, for instance, when carried by blood, produces distinct signatures that are used to assess flow in major vessels. Myocardial dyskinesis also produces visible effects. Because of these effects, NMR imaging may be a safe and effective tool in the diagnosis and assessment of cardiovascular disease.

Twenty-five patients with known or suspected evidence of venous disease based on results of computed tomography, angiography, or ultrasound were imaged with magnetic resonance (MR) to determine the MR characterization of venous abnormalities. MR findings were proved by laparotomy or autopsy in 18 of 25 cases. In seven of 25 patients in whom only biopsy was performed, the MR findings were correlated with findings from other radiologic tests. On MR, the inferior vena cava (IVC), portal vein, and their major tributaries were seen in all but two cases. In those two, identification of collaterals led to the correct diagnosis of splenic vein thrombosis in one case and left renal vein thrombosis in another. MR imaging helped identify intraluminal thrombi in the IVC (12 of 12 cases), portal vein (two of two cases), renal veins (seven of seven cases), superior mesenteric vein (one case), and iliac veins (seven of seven cases). Intraluminal signal intensity secondary to slow blood flow seen in five patients was always differentiated from the thrombus. MR imaging helped identify correctly the nature of the thrombus in 11 of 16 patients. In five patients, the differentiation between tumor thrombus and blood clot thrombus was not possible. Involvement of the IVC wall by tumor was seen in four cases. MR imaging also accurately depicted slow flow in obstructed or constricted veins; encasement, compression, or displacement of veins without intraluminal occlusions; and the presence of venous collaterals. The MR imaging evaluation of venous abnormalities is accurate, easily performed, and will probably become an important application.

Albumin is a macromolecule that remains largely confined to the vascular space after intravenous administration. Human serum albumin was paramagnetically labeled by covalently binding from nine to 18 gadolinium-DTPA (diethylenetriaminepentaacetic acid) chelates per protein molecule. This conjugate was tested in varying doses for in vivo biodistribution and effectiveness in tissue relaxation. After intravenous injection of the agent in rats, T1 relaxation times were significantly reduced in samples of the blood and in lung, heart, spleen, kidney, and brain tissue. These effects persisted at a relatively constant level for the next 30 minutes. In vivo magnetic resonance imaging of the heart and lungs of rats and rabbits confirmed the prolonged contrast-enhancing effect of the labeled albumin. These preliminary studies indicate that paramagnetically labeled macromolecules that distribute in the intravascular space may be effective for MR imaging evaluation of tissue blood volume.

ofmaterialsthathavethepropertyofsuperconduc-tivityatrelativelyhightemperatures. Theprospectthatsuchmaterials willreduceoreliminate theneedforcryogeniccoolingofsuperconducting magnetsposesanumberofques-tionsforthemedicalMRcommunity: ShouldIpostponepurchaseofmyMRsystemuntilanewmagnetdesignisavailable? WillthemoneyIsaveoncryogens payforareplacement magnet?Willanewdesigngivememoreorlessfieldstrength? ShouldIsellmyniobiumminingstockandreinvestinacompanyproducingthenewmaterials?Theworkreportedisatanearlystage.Theresearchershaveconcentrated oninvestigation ofthesuperconductingpropertiesofthematerials.Wemustknowanumberofotherproperties andprocessing aspectstodetermine theirsuita-bilityforuseinmagnets.Itisalsoachallengetotheoreticianstoexplainwhythematerialswork.

Nuclear magnetic resonance (NMR) imaging can be of value in distinguishing vascular and nonvascular lesions in the lung and mediastinum, in that rapidly flowing blood results in little or no NMR signal. We wish to report a patient having a pulmonary arteriovenous fistula evaluated using physiological studies, dynamic computed tomography, and spin-echo NMR. On the NMR images, the fistula was invisible because of rapid flow through its lumen.

The authors describe a new method for magnetic resonance (MR) imaging of flowing protons which can illustrate relative blood velocity in the arteries supplying the brain. The magnetic gradient pulse sequence was synchronized to the cardiac cycle at 100-msec. increments to track pulsatile blood flow perpendicular to the image plane. The magnitude of the signal increased with the velocity of blood in major arteries flowing in the direction of the spatially offset refocusing plane. The blood velocity in the vertebral and internal carotid arteries varied as a function of the phase of the cardiac cycle, and the velocity profiles across the vascular lumina were compatible with laminar flow.

Nuclear magnetic resonance (NMR) imaging characteristics of the normal and abnormal adrenal gland were evaluated and compared with findings on computed tomography (CT). Forty-two patients were examined: 36 had normal adrenal glands and 6 had adrenal disease (3 metastatic lesions, 1 pheochromocytoma, and 2 cortical hyperplasia). NMR clearly showed all 42 left adrenals (100%) and 36 right adrenals (86%). In some patients, it appeared to differentiate the adrenal cortex from the medulla. The ability of NMR to detect adrenal disease was similar to that of CT in 6 cases examined. CT demonstrated superior spatial resolution in most cases, but NMR provided superior soft-tissue contrast. Since NMR does not involve ionizing radiation and provides excellent soft-tissue differentiation without contrast material, it has advantages over CT and appears to be a promising modality for imaging of the adrenal gland.

Twenty normal subjects and ten patients with pericardial abnormalities underwent ECG-gated magnetic resonance (MR) imaging of the thorax using a 0.35-tesla superconducting system. The patients with pericardial abnormalities were also evaluated with serial chest radiographs, ultrasound, computed tomography, and/or angiography. ECG gating was necessary to identify the normal pericardium, which was visualized as a 1- to 2-mm-wide curvilinear structure of low signal intensity. Pericardial thickening in constrictive pericarditis was clearly delineated on gated MR images. Pericardial inflammation caused a marked increase in signal intensity as well as thickening of the pericardium. Pericardial effusions and pericardial adhesions were also demonstrated. A simple pericardial cyst and a complex pericardial mass were identified and differentiated from pericardial fat and diaphragmatic eventration. MR appears to be an important modality for the evaluation of pericardial disease.

Differences in magnetic resonance (MR) imaging signal-to-noise (S/N) performance between saddle-shaped and solenoidal coils have been postulated. Each coil shape is tied to a particular magnetic field configuration, so that they are not typically interchangeable except in special situations. The solenoidal coil is predicted to have a two- to three-fold advantage over the saddle-shaped coil. Simple basic arguments raise a dispute with this assertion. Experiments show that both coils produce essentially equivalent S/N levels.

A preliminary study of the relation between food intake and intensity of gallbladder bile on nuclear magnetic resonance (NMR) images was made. Twelve subjects (seven volunteers, five patients) were imaged following a minimum of 14 hours of fasting. Six of seven volunteers were reimaged one hour after stimulation by either a fatty meal or an alcoholic beverage. An additional seven patients were imaged two hours after a hospital breakfast. It was found that concentrated bile emits a high-intensity spin echo signal (SE), while hepatic bile in the gallbladder produces a low-intensity SE signal. Following ingestion of cholecystogogue, dilute hepatic bile settles on top of the concentrated bile, each emitting SE signals of different intensity. The average T1 value of concentrated bile was 594 msec, while the T1 value of dilute hepatic bile was 2,646 msec. The average T2 values were 104 msec for concentrated bile and 126 msec for dilute bile. The most likely cause for the different SE intensities of bile is the higher water content, and therefore longer T1 and T2 relaxation times, of hepatic bile. It is suggested that NMR imaging has the ability to provide physiological information about the gallbladder and that it may prove to be a simple and safe clinical test of gallbladder function.

Magnetic resonance images of the head, abdomen, and pelvis of normal adult men were obtained using varying magnetic field strength, and measurements of T1 and T2 relaxations and of signal-to-noise (SN) ratios were determined. The T1 relaxation of gray matter, white matter, and muscle increases and T2 decreases with field strength, while T1 of fat remains relatively constant and T2 increases. As a consequence, for any one spin echo sequence, gray/white matter contrast decreases and muscle/fat contrast increases with field. SN levels rise rapidly up to 3.0 kgauss and then change more slowly, actually dropping for muscle. The optimum field for magnetic resonance imaging depends on tissue type, body part, and imaging sequence, so that it does not have a unique value. Magnetic resonance systems that operate in the 3.0-5.0 kgauss range achieve most or all of the gains that can be achieved by higher magnetic fields.

Given a suitable trigger signal, cardiac synchronized magnetic resonance (MR) imaging is simple to implement; however, single section techniques are not efficacious, especially when the heart rate sets the repetition interval. We demonstrate multi-section, double, and single-echo imaging, any of which rapidly covers the cardiac volume; 3-D modes capable of achieving very thin sections; and cycled multi-section imaging capable of efficaciously providing dynamic data on heart motion. These modes form a complementary, powerful set of options for clinical work.

The response of different magnetic resonance (MR) techniques to tissue parameters - T1, T2, and N(H) - is a determinant of clinical efficacy. The large possible number of imaging techniques and range of variable parameters for each make it difficult to perform exhaustive evaluations in a single patient or even in animal models. In addition, changes in operating magnetic field strength change the relaxation times sufficiently so that the efficacy of a technique at a given field does not imply similar results at another field value. Tools are demonstrated that permit the evaluation of the efficacy of any model of response to tissue parameters, and also allow the investigation of the effects of changing magnetic field. Global maps of signal difference between tissues as well as calculated images are obtainable from a minimally sufficient data set. These tools serve as an important adjunct to experimental work.

The feasibility of magnetic resonance imaging for defining anatomy of internal cardiac structures and major blood vessels was assessed in 14 normal subjects. Both electrocardiogram-gated and standard spin-echo images were obtained. The R-R interval determined the pulse repetition times in gated sequences. Gated images provided better visualization of internal cardiac morphology and of upper mediastinal vessels than did nongated images. Trabecular detail and components of the mitral valve could be resolved. All segments of the left ventricular wall could be evaluated by combining axial, coronal, and sagittal images. Gated acquisition of magnetic resonance images did not increase imaging time; five transverse slices of the left ventricle were obtained in 6.0-8.5 min. The good image quality, ease of gated acquisition, large field of view, capability of direct imaging in multiple planes, and noninvasiveness of the technique suggest that it will be an important imaging method in cardiovascular disease.

The hope that MRI relaxation time signatures would identify tissues, specifically, malignancies, has not been realized. This is due much less to measurement inaccuracies than to a large intrinsic variability and overlaps between malignancies and many benign pathologies. Neither has there been success in predicting relaxation times from basic tissue compositions. Nevertheless, MRI provides a qualitative measure of tissue hydration, and of flow, on the basis of relaxation times. Furthermore, pixel-by-pixel maps of relaxation times have proven useful in understanding the MRI process, in predicting the efficacy of untried techniques, and replace, in many circumstances, the need for acquisition of images with diverse sequencing parameters.

Measurements of T1 and T2 relaxation values and spin density of the lumbar vertebral bone marrow were performed in 212 patients, and the results were correlated with the patients' age and sex. T1 and T2 relaxation times for bone marrow in the lumbar vertebral bodies showed a progressive decrease with age for both sexes (except for the T2 relaxation values in female patients). The replacement of hematopoietic marrow by fatty marrow could explain the decrease in T1 and T2. The T1 and T2 values were in the same range for the first two age groups (age 1-10 years and age 21-40 years) and became slightly greater for the older female patients (age 51 years and older) than for the older males. This could be due to the loss of bone and mineral content, which is more rapid and significant for women. These normal T1 and T2 values may provide a baseline for future evaluation of diseases involving the lumbar spine.

Nuclear magnetic resonance imaging has emerged in the past few years as a completely noninvasive method for medical imaging of internal organs. Because of the loss of signal intensity by motional nuclei (hydrogen) using most proton imaging techniques, flowing blood within the cardiovascular system generates little or no signal and consequently there is high natural contrast between blood and the walls of blood vessels or cardiac chambers. However, motion during imaging also complicates cardiac imaging because signal is lost from the nuclei in the moving cardiac structures. Consequently electrocardiographic gating of data acquisition is required for nuclear magnetic resonance imaging of the heart. Distinct advantages of nuclear magnetic resonance imaging in relation to other imaging modalities are good contrast between soft tissues and the capability for characterization of specific tissues by estimation of magnetic relaxation times. Early in vitro studies measuring relaxation times of myocardial tissue samples of excised hearts indicate that nuclear magnetic resonance imaging will be capable of discriminating infarcted from normal myocardium. Recent studies using electrocardiographically gated nuclear magnetic resonance imaging of dogs with acute infarction showed the infarct as a region of high intensity on spin-echo images. Initial clinical experience with electrocardiographically gated nuclear magnetic resonance imaging (0.35 tesla) in patients has clearly defined internal cardiac anatomy without the use of contrast media. This technique has demonstrated the consequence of previous myocardial infarction such as regional wall thinning, aneurysm, thrombus and contractile dysfunction, a number of pericardial abnormalities and the morphology of hypertrophic and congestive cardiomyopathies.

Nuclear magnetic resonance (NMR) imaging of intraabdominal vascular anatomy and the effect of various lesions on retroperitoneal and splanchnic vessels was assessed in 67 patients and volunteers using a superconducting magnet (0.35 tesla) and the spin-echo imaging techniques. Because of the low signal generated by flowing blood in most images, blood vessels, including intraparenchymal vessels, were well demonstrated. Clear delineation of the splenic vein facilitated visualization of the normal pancreas and pancreatic masses. Variation in the size and shape of the inferior vena cava and portal venous system reflected constricting and mass lesions. Preliminary observations from this initial experience suggest conspicuity of splanchnic vessels out of proportion to the current spatial resolution of NMR imaging due to the marked natural contrast between flowing blood and solid organs.

Longitudinal vascular structures are difficult to observe on the standard abdominal transaxial magnetic resonance (MR) image sections. To display the information in a three-dimensional reconstruction, an algorithm was written to identify blood flow in a series of transaxial MR sections and was applied to reconstructing images of the aorta and iliac arteries in 12 patients with aortic aneurysm, dissection, or aortoiliac atherosclerosis. Results were validated by angiography. In all patients, the outline of the flow channel in the reconstructed image followed closely the outline of the lumen on angiograms. In aortic dissection, the MR images showed the two lumens more completely than did the angiograms, and in atherosclerosis, sites of vascular stenosis were correctly identified on MR images. The technique is valuable in providing anatomic information as well as functional information on cross-sectional areas and relative flow velocities.

In magnetic resonance (MR) imaging manipulating spatial resolution, contrast resolution, and imaging time separately results in improvement in some parameters without degradation of others. The authors have found that MR imaging of the head with a repetition time TR = 2.0 seconds produces images with high signal-to-noise levels and excellent sensitivity to demyelinating disease and brain water content. In the body, a long TR yields large signal levels that permit delineation of low-intensity structures such as patent vessels and bone. The long TR technique can be used in a high-resolution mode (256 X 256 data acquisition elements, each 0.8 X 0.8 mm) while maintaining image times of 50 or 100 sec/section. For normal resolution (1.7 X 1.7 mm), imaging time is 25 or 50 sec/section. It is concluded that the combination of slow-imaging techniques with simultaneous multisection imaging will prove practical for clinical MR.