Magnetic resonance imaging and histopathology of hydronephrosis in the rat

Magnetic resonance imaging revealed conspicuously hyperintense regions in the papillary area of kidneys of three untreated rats. When the kidneys were examined histologically, a hydronephrosis associated with the presence of bacteria was found. This study relates magnetic resonance images of an early stage of hydronephrosis to its histological picture.     

Magnetic resonance imaging (MRI) studies of knee joint under mechanical loading: Review

Osteoarthritis (OA) is a very common disease that affects the human knee joint, particularly the articular cartilage and meniscus components which are regularly under compressive mechanical loads. Early-stage OA diagnosis is essential as it allows for timely intervention. The primary non-invasive approaches currently available for OA diagnosis include magnetic resonance imaging (MRI), which provides excellent soft tissue contrast at high spatial resolution. MRI-based knee investigation is usually performed on joints at rest or in a non-weight-bearing condition that does not mimic the actual physiological condition of the joint. This discrepancy may lead to missed detections of early-stage OA or of minor lesions. The mechanical properties of degenerated musculoskeletal (MSK) tissues may vary markedly before any significant morphological or structural changes detectable by MRI. Recognizing distinct deformation characteristics of these tissues under known mechanical loads may reveal crucial joint lesions or mechanical malfunctions which result from early-stage OA. This review article summarizes the large number of MRI-based investigations on knee joints under mechanical loading which have been reported in the literature including the corresponding MRI measures, the MRI-compatible devices employed, and potential challenges due to the limitations of clinical MRI sequences.     

Magnetic resonance imaging with stepped B(0) fields

This paper introduces the concept of imaging with stepped magnetic fields within the main B(0) field. The resonance frequency within each step is separated from the next by an amount greater than the imaging bandwidth. Each step thus gives rise to a separate imaging region enabling simultaneous imaging over multiple slices without aliasing. The auxiliary magnetic field regions are produced by coil inserts. The principle is illustrated using simple coil designs which introduce up to two steps into the main B(0) field. Phantoms placed in each uniform region were successfully imaged simultaneously with no aliasing.     

Clinical significance of magnetic resonance imaging (MRI) for focal chondral lesions.

To evaluate the diagnostic potential of magnetic resonance imaging (MRI) and define its role, focal chondral lesions of the femoral surface of the tibiofemoral joint were examined. Full-thickness defects were well detected prospectively (93%) with conventional MRIs initially administered for observation reference of ligaments and menisci. Optimized MRIs, which included right-angled planes to the lesion surface and magnetization transfer contrast (MTC) sequences, delineated the size of lesions (R2 = 0.648,p < 0.0001) and the difference between full-and partial-thickness defects (88% in accuracy). A forward-tilt of 30 degrees to the femoral shaft was the average plane angle that afforded optimal visualization of the chondral lesions. Our findings advocate that routine MRIs are sufficient in detecting severe chondral lesions that require further examination, and the optimized images are highly useful in facilitating the recently developed therapeutic approaches and follow-up studies for articular cartilage defects.     

Magnetic resonance imaging of burn injury in rats.

In-vivo magnetic resonance imaging (MRI) studies have been performed to follow pathological changes induced by 3-sec and 10-second burns on eleven rat tails. T1-weighted, T2-weighted, density-weighted, and water-suppressed images were acquired immediately after and four days following thermal injury. MRI results were correlated with histology. For 3-sec burns, both edema and lipids contributed significantly to the hyperintensity seen on MRI at the site of injury. For 10-sec burns, edema was the major contributor to hyperintensity. Quantitative comparisons indicated the intensity and spatial extent of the edema signal to be most indicative of the degree of injury. MRI also demonstrated potential in determining coagulation necrosis and lipid accumulation at burn sites. These studies indicate the potential of MRI in diagnosing and monitoring burn injuries and therapies.     

Magnetic resonance imaging of the uterus at an ultra low (0.02 T) magnetic field.

In vivo pelvic imaging of 39 women and in vitro relaxation time measurements of four uterine specimens were performed using an ultra low field (0.02 T) MRI unit. Average T1 times measured in vitro at 37 degrees C for the myometrium and endometrium were 206 ms (SD 47 ms) and 389 ms (SD 21 ms), respectively. Corresponding T2 times were 95 ms (SD 20 ms) and 167 ms (SD 13 ms). The proton relaxation of almost all myometrial specimens proved to be biexponential, but of all endometrial specimens was monoexponential. Contrast measurements between endometrium versus myometrium and myometrium versus the junctional zone were performed after imaging 18 volunteer women using different pulse sequence parameters. Normal uterine structures were optimally demonstrated by SE 700/70. Relatively short repetition times could be used, because spin-lattice relaxation times were short at the low magnetic field. Consequently, the short repetition times allowed averaging of four excitations to create adequate images within an acceptable scanning time. In addition to T2-weighted images a T1-weighted inversion recovery sequence with a short inversion time of 50 ms (IR 1000/50/40) adequately differentiated the three uterine zones. Although pathologic lesions of the uterus including leiomyomas, anomalies and carcinomas were well demonstrated, especially with the T2-weighted spin echo pulse sequence, further investigations are needed to evaluate the optimal technique for ultra low field MR imaging of uterine tumors.     

Magnetic resonance arthrography (MRA) in the postoperative shoulder.

To evaluate changes in capsular mechanisms and the labroligamentous complex with magnetic resonance arthrography (MRA) after shoulder surgery and to establish possible criteria for the expected post-operative appearance of the shoulder. MRA of the shoulder was performed in 16 patients, before and 6 months after undergoing arthroscopic surgery for recurrent unidirectional dislocation. MR studies were performed after application of a constant amount of contrast solution (2 mmol Gd-DTPA). Axial and coronal oblique T1-weighted images were obtained with and without fat suppression techniques. Anterior (a) and posterior (p) capsular distances were measured, and the p/a ratio was established. Capsule thickness, capsular leaking, estimation of the volume of the axillary recess, appearance of the glenohumeral ligaments, and evidence of labral lesions were compared on pre- and postoperative images. Mean anterior capsular distance (a) decreased from 9.73 +/- 1.03 mm preoperatively to 5.27 +/- 2.49 mm postoperatively, whereas dorsal capsular distance (p) increased from 6.13 +/- 2.36 to 8.93 +/- 2.37. The p/a ratio increased from 0.64 +/- 0.25 to 2.36 +/- 2.54 (p = 0.007). Capsular leaking was suspected preoperatively in seven patients, but was not evident postoperatively. Capsular thickness and the estimated volume in the axillary recess did not change significantly. Contrast extension into pre-existent labral tears (nine patients) decreased or were not evident postoperatively. Changes in the appearance of the glenohumeral ligaments were found in six patients. Changes in capsular distances might be indicative of a decreased capsular laxity and could be a valuable criterion in the evaluation of the postoperative shoulder. Postoperative follow-up of labral tears is demonstrated by a decrease in contrast extension into or under a tear. Reactive capsular thickening or scar tissue formation can be reactive or preexistent. Changes in ligaments might be secondary to surgery. MRA may be helpful in the reevaluation of patients with suspected recurrent instability.     

Magnetic resonance imaging in obstetrics and gynecology

Magnetic resonance imaging of the female pelvis permits visualization of soft tissue structure previously unseen with other radiological techniques. The internal architecture of the corpus uterus, cervix and vagina are directly visualized in any plane. Furthermore, the hormonal environment of the female can be indirectly determined via assessment of the MR appearance of the uterus. Similarly, the complex changes which occur during pregnancy, such as cervical effacement and the relationship of internal os, fetal part and placenta, are easily documented. MR pelvimetry enables fast, safe depiction of the birth canal. Finally, the demonstrated fetal anatomy may prove particularly useful in the evaluation of intrauterine growth retardation and anomalies indeterminate by ultrasound.     

Magnetic resonance imaging of the brain in children

Differences between MRI of the brain in children and adults are discussed. These include the need for sedation, greater difficulties in obtaining normal controls and substantial differences in pulse sequences due to changes in T1 and T2 with age. The common features in the major pathological entities are presented and the need to relate them to physiological changes is emphasized.     

Characterisation of magnetic resonance imaging (MRI) contrast agents using NMR relaxometry

ABSTRACT

This contribution describes the use of Fast Field-cycling relaxometry (FFC-NMR) for the characterisation of Gd(III)- and Mn(II)-based contrast agents for MRI. Through a series of selected examples, we analyse the role of different structural and dynamic parameters on ¹H relaxivity and on the shape of the ¹H Nuclear Magnetic Relaxation Dispersion (NMRD) profiles. The amplitude and shape of the profiles is affected by the number of water molecules coordinated to the metal ion, the water exchange rate, the rotational correlation time of the complex and the relaxation of the electron spin. As a result, ¹H NMRD profiles represent a powerful tool for the understanding of the properties of MRI contrast agent candidates at the molecular level.     

Magnetic resonance imaging features in melanoma

T1 and T2 relaxation time shortening secondary to paramagnetic compounds has been described in melanoma. The purpose of this paper is to evaluate the signal behavior of melanoma involved in various body areas using short TR, TE and long TR, TE sequences. Twenty-seven sites of melanoma were evaluated with MR using T1 weighted and T2-weighted techniques. Using fat and muscle signal intensities as references tissues, lesions were graded into high, low or intermediate intensity categories for each of the sequences. Four signal patterns emerged. The typical pattern characterized by high signal on T1-weighted images and low signal on T2-weighted images reflected T1 and T2 shortening. The other pattern categories comprised of lesions demonstrating low signal T1-weighted images and high signal on T2-weighted images, high signal on both T1- and T2-weighted images and lesions showing intermediate signal on either T1- or T2-weighted images. We observed a tendency away from the typical signal pattern in extraocular melanoma cases with only one of 14 demonstrating this pattern. Moreover, only seven of thirteen ocular melanomas exhibited such behavior. Possible explanations for this findings as well as the existence of a variety of MR appearances to melanoma are offered. We conclude that while signal patterns showing T1 and T2 shortening are typical of melanoma, the absence of these does not exclude the diagnosis.     

Magnetic resonance imaging of the menstrual cycle

This study examines the ability of magnetic resonance imaging (MRI) to monitor follicular and endometrial development during the menstrual cycle. MR scans, sonograms and hormonal levels of estradiol (E₂) and progesterone (P) obtained from five ovulatory volunteers were evaluated on approximately days 4, 8, 12, 16, 20 and 24 of the cycle. MRI reliably demonstrated folliculogenesis in all of the volunteers. Changes depicted in the endometrial and junctional zones of the uterus reflected physiologic events occurring during the normal cycle. Important implications exist for infertile women undergoing stimulated cycles and/or in-vitro fertilization.