Low field (0.02 T) magnetic resonance imaging of bone and soft tissue tumors

Extremely low field magnetic resonance imaging (MRI) was evaluated in 16 patients with bone and soft tissue tumors, both benign and malignant. Twelve of the lesions were located in the lower extremity, 2 in the gluteal and 2 in the shoulder region. The findings were compared to the results of computed tomography (CT). Low signal-to-noise ratio and poor spatial resolution result in an image quality which is inferior to that obtained with MR imaging at higher field strengths. In spite of this, the diagnostic information seems to be at least comparable to that obtained from CT.     

Low field magnetic resonance imaging of focal hepatic masses at 0.02 T

The diagnostic utility of extremely low field magnetic resonance (MR) imaging was evaluated in 25 patients with focal hepatic masses, including 17 with primary (n = 7) or secondary (n = 10) malignant neoplasms and 8 with benign lesions (6 hemangiomas). The findings were compared with the results of computed tomography (CT). Out of 16 patients with malignant tumors demonstrated by both modalities, the diagnostic information from MR imaging was equal to or better than that from CT in 6 patients and inferior to CT in 10. Shortcomings of MR were mainly due to low signal-to-noise ratio and poor spatial resolution, resulting in an image quality inferior to that obtained at higher field strengths. Considering these facts, together with the long imaging times required, low field MR cannot be recommended for general use in the evaluation of hepatic masses. On the other hand, our results indicate that this technique may be useful in establishing the diagnosis of hepatic hemangioma.     

Magnetic resonance imaging of hematomas in a 0.02 T magnetic field

One intramuscular calf hematoma, 2 ankle hematomas and 4 cephalhematomas were imaged at various ages in a low magnetic field (0.02 T). At least one spin echo (SE) multislice image and a series of inversion recovery images (IR) were made varying the inversion time for estimation of the relaxation time T1. T1 tended to shorten and T2 to stay unchanged. With an unsuitable pulse sequence the hematomas were not visible. They were best seen with short TIs. The images of one of the ankle hematomas and the calf hematoma were compared with sonographic findings. The appearances of the hematomas varied during aging with both imaging modalities. The hematomas were easier to detect with magnetic resonance imaging than with ultrasound, also when aging.     

Low field (0.02 T) MR imaging of the whole body

The diagnostic utility of extremely low field magnetic resonance (MR) (0.02 T) was evaluated in various parts of the body outside the head. The areas investigated included the spine (104 patients), kidneys (19 patients), female pelvis (21 patients), and hips (15 patients). The results were compared with those of other imaging modalities, e.g., ultrasound, CT, and scintigraphy. Available pulse sequences and typical examination times for different types of studies are reported. Poor spatial resolution and long imaging times limit the application of this technique to the whole body. Due to poor signal-to-noise ratio, image quality is not comparable with that obtained at higher field strengths. In spite of these restrictions it was possible to demonstrate lumbar disk herniations, to differentiate renal and ovarian cysts from tumors, and to detect early avascular necrosis of the femoral head. Extremely low field MR imaging may eventually be used in screening spinal pathology and in the diagnosis of early avascular necrosis of the femoral head. At present, this technique can not replace ultrasound or CT in abdominal examinations.     

Visualization of brain infarction with nuclear magnetic resonance imaging

Summary Nine patients with cerebral or cerebellar hemispheric infarction and two patients with brain stem lesions were studied with NMR imaging in order to examine the lesion with different weightings on the various NMR parameters. The time interval between examination and the acute onset of the stroke varied from one day to six months. The lesions were clearly detected by the T₁ weighted inversion recovery sequence but the tissue contrast was better using the spin echo sequence with a long repetition rate and a long echo delay (SE_2000/100). In two patients the brain stem lesions were invisible with CT, but were easily depicted with NMR. In one of them the further progress of the lesion was also confirmed and visualized with the follow-up NMR study.     

Low field magnetic resonance imaging of femoral neck fractures

Fourteen patients with cervical hip fractures were treated with internal fixation using titanium screws. The femoral head vitality was evaluated with 99Tcm-MDP scintigraphy and scintimetry within 2 weeks postoperatively and by serial low field magnetic resonance imaging (MR). Two patients with reduced radionuclide uptake (femoral head ratio less than 1.0) developed radiographic signs of femoral head necrosis. MR disclosed the definite area of the necrosis at 2 and 12 months after fracture, respectively. In three of the patients with a high scintimetric uptake (femoral head ratio greater than or equal to 1.0), MR revealed a focal decrease of the signal intensity in the femoral head or neck at 2, 3 and 7 months after fracture, respectively. The radiographs in one of these patients were normal at 7 months after fracture. The second one showed signs of necrosis at 16 months and the last one developed delayed/non-union. With a non-ferromagnetic osteosynthesis the healing course after femoral neck fracture can be studied with low field MR equipment without disturbing artifacts. The time period between ischaemia and definite abnormalities on MR may embrace several months.     

低场强MR在妇科盆腔疾病诊断中的临床应用

目的探讨低场强MR在妇科盆腔疾病诊断中的临床应用价值。方法对16例患者行MR及超声检查,并与病理相对照,分析妇科盆腔疾病MRI表现,并与超声对照分析其影像特点。结果所有患者行MR及超声检查,盆腔MRI正确诊断的14例,2例与病理结果有差异,诊断符合率87%。结论 MRI由于具有优越的软组织分辨力和多方位成像的特点,当超声检查不能明确诊断时,可作为另一种首选检查方法,女性盆腔疾病在MRI上表现有一定的特异性,结合临床可以对女性盆腔疾病作出诊断及鉴别诊断。     

Tomographic imaging with nuclear magnetic resonance

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.     

Coronal nuclear magnetic resonance (NMR) imaging of the abdomen at 0.5 tesla

Coronal nuclear magnetic resonance (NMR) abdominal imaging was performed on a normal volunteer. The scan technique and anatomic features are described. Coronal abdominal scanning optimizes vascular imaging in the abdomen and is helpful in defining the anatomic relationships of a variety of structures.     

Clinical nuclear magnetic resonance imaging of the body

NMR promises great advances in diagnosis and has delivered so much already that it is expected that in the future it will replace many applications of the currently used imaging modalities. Although x-ray computed tomography is continuing to advance in speed of scanning and resolving power, NMR will most likely soon eliminate its use in many studies of the central nervous system and also in many other areas of the body. The promise of combining topical spectroscopy with imaging is also exciting and should provide further information about metabolic processes of various organs. Progress in NMR is so rapid and the future is so bright that one of the great problems will be to develop a new breed of radiologists who are versatile in biochemistry, mathematics, and computers, as well as competent in morphologic anatomy and pathologic physiology. As time goes on, advances in NMR will be achieved only by teams of clinical and basic scientists encompassing multiple disciplines.     

T2 FLAIR artifacts at 3-T brain magnetic resonance imaging

The purpose of this retrospective clinical study was to identify and evaluate the presence and frequency of T2 FLAIR artifacts on brain MRI studies performed at 3 T.We reviewed axial T2 FLAIR images in 200 consecutive unremarkable brain MRI studies performed at 3 T. All studies were reviewed for the presence of artifacts caused by pulsatile CSF flow, magnetic susceptibility and no nulling of the CSF signal.T2 FLAIR images introduce several artifacts that may degrade image quality and mimic pathology. Knowledge of these artifacts and increased severity and frequency at 3 T is of particular importance in avoiding a misdiagnosis.     

Sodium-23 magnetic resonance brain imaging

Summary This is a review of recent work in²³Na MR imaging. The main emphasis of recent papers has been pulse sequences that, with appropriate postprocessing, give images of the fast, slow, and intermediate components of T2 decay. The assignment of compartmental designation to the T2 component remains a problem except for homogeneous structures easily identifiable anatomically (ventricles, superior sagittal sinus, globe of the eye). Compartmental distribution of sodium is described. The predominance of the interstitial and plasma compartment, the invisibility of part of the intracellular sodium, and the difficulty in imaging the very fast T2 component of visible intracellular sodium make the usual Na spin-echo image essentially an image of the interstitial and plasma space. Use of super paramagnetic iron oxide coupled to dextran as a contrast medium may help to identify the plasma compartment. Because the usual Na MR images are essentially interstitial and plasma images, our own interest is in observing functional changes in these compartments. Another proposed application is the detection of the very fast T2 component in brain tumors to aid in defining tumor grade and extent.Supported in part by the Department of Veterans Affairs Medical Research Service     

Urinary tract imaging by nuclear magnetic resonance

Nuclear magnetic resonance scanning has already found application in the urinary tract in man. It is a method of producing diagnostic images from the radiofrequency signals which can be elicited from hydrogen nuclei when the abdomen is placed in a strong magnetic field and subjected to pulses of RF energy. Computer-generated images depict the distribution of signal-emitting nuclei, modified by their relaxation times and macroscopic motion. The images are tomographic and have great potential flexibility in plane orientation. Normal anatomy, space-occupying lesions and lesions characterized by local edema have been visualized to date, and as clinical experience is accumulated, a much greater range of pathology promises to be detectable by this technique.     

Site planning for nuclear magnetic resonance imaging

The unique factors to be considered in selection of a site for a magnetic resonance imaging installation are addressed, with emphasis on the interaction of the magnet with its environment. The effect of ferrous objects on the magnet and the influence of the magnet on its surroundings are discussed. Design issues for magnetic shields are given.     

Urinary tract imaging by nuclear magnetic resonance

Nuclear magnetic resonance scanning has already found application in the urinary tract in man. It is a method of producing diagnostic images from the radiofrequency signals which can be elicited from hydrogen nuclei when the abdomen is placed in a strong magnetic field and subjected to pulses of RF energy. Computer-generated images depict the distribution of signal-emitting nuclei, modified by their relaxation times and macroscopic motion. The images are tomographic and have great potential flexibility in plane orientation. Normal anatomy, space-occupying lesions and lesions characterized by local edema have been visualized to date, and as clinical experience is accumulated, a much greater range of pathology promises to be detectable by this technique.     

Improvements in snap-shot nuclear magnetic resonance imaging

New variants of the ultra-high-speed echo-planar imaging technique have been used to obtain snap-shot images of adult patients and volunteers at 0.1 T. Modified pulsed-gradient sequences together with non-linear signal sampling and activity screened gradients have greatly improved the image quality obtainable by single-shot methods. A particular variant, modulus blipped echo-planar single-pulse technique (MBEST), although slightly slower than the blipped echo-planar single-pulse technique (BEST), is experimentally more robust and incorporates intrinsic T2 weighting. An account of these improvements together with some experimental results is presented.