Five rhesus macaques monkeys surgically prepared with Thiry small intestinal (jejunum) loops and implanted brain electrodes were restrained in primate chairs and kept on 23-hr deprivation-feeding cycle. After being trained to press a lever for sugar pills on an FR 25 schedule of reinforcement, a discrimination training procedure was established. Lever presses were reinforced during the S(D)-a non-aversive mechanical stimulus applied to the internal walls of the Thiry loop by rhythmic inflation-deflation of a small latex balloon by air at the rate of one cycle per sec at 100 mm Hg pressure. The S(Delta) was the absence of the visceral stimulation. The monkeys successfully discriminated between presence and absence of the internal stimulus. A discrimination reversal was attempted and completed on one monkey. The results clearly show operant discrimination based on an interoceptive stimulus. Cortical and subcortical EEG records reflected the onset but not termination of the visceral stimulation.

Animals↗

PubMedDate not supplied

Experimental hyaline cartilage lesions: two-dimensional spin-echo versus three-dimensional gradient-echo MR imaging.

The value of magnetic resonance (MR) imaging, with two-dimensional (2D) spin-echo and FISP (fast imaging with steady-state precession) and FLASH (fast low-angle shot) three-dimensional (3D) gradient-echo sequences, for the detection of hyaline cartilage defects of the femoral condyle and the tibial plateau, was investigated in an animal model. In eight dogs, the anterior cruciate ligament was transected in one knee joint, resulting in rapid development of osteoarthritis with degeneration of the hyaline cartilage. At autopsy, 24 cartilage lesions were found, which were classified into four grades. The overall detection of cartilage lesions with MR imaging was poor. Only five of the 24 lesions were visible on 2D spin-echo images, while 11 of 24 were visible on 3D FISP images and 15 of 24 were seen on 3D FLASH images. The best results were obtained in advanced stages of cartilage degeneration, involving ulceration and complete abrasion of the cartilage layer. Signal loss or signal intensity increase in the cartilage layer was seen inconsistently in grades 3 and 4 degeneration. In this animal model, 2D spin-echo imaging was inadequate for the diagnosis of hyaline cartilage lesions, while 3D gradient-echo imaging permitted satisfactory diagnosis in only grade 4 cartilage disease.

Animals↗

PubMedDate not supplied

Gadolinium-enhanced T1-weighted versus T2-weighted imaging of scrotal disorders: is there an indication for MR imaging?

To evaluate the use of gadopentetate dimeglumine in magnetic resonance (MR) imaging of scrotal disorders, the clinical, ultrasound, and MR imaging data of 29 patients (age range, 19-75 years) with various intra- and extratesticular disorders were retrospectively analyzed. T1- and T2-weighted spin-echo images (T1-T2 group) were compared with T1-weighted spin-echo images before and after intravenous administration of gadopentetate dimeglumine (T1-Gd group). A receiver operating characteristic (ROC) analysis of the findings was undertaken. Better contrast between tumor and parenchyma and a clearer demonstration of the tunica albuginea were noted in the T1-T2 group (although not of diagnostic relevance). ROC analysis revealed no differences between the two imaging groups in the diagnosis of tumor, trauma, hydrocele, or hemorrhage; however, epididymitis was diagnosed more easily with contrast enhancement (0.8834 vs 0.7759, P = .04) and the diagnosis of orchitis was expressed more strongly (0.8221 vs 0.7184, P = .17). Four of the five observers were more confident in making the diagnosis with contrast enhancement. With MR imaging, the diagnosis was correctly suggested in three patients in whom clinical and ultrasound data were inconclusive. Gadolinium-enhanced MR imaging gives additional information in scrotal disorders and facilitates diagnosis. It may be helpful when findings at physical examination and ultrasound differ and when plain T1- and T2-weighted images are equivocal.

Adult↗

PubMedDate not supplied

Gd-DTPA-cascade-polymer: potential blood pool contrast agent for MR imaging.

Gadolinium-DTPA (diethylenetriaminepentaacetic acid)-cascade-polymer, a potential new blood pool contrast agent for magnetic resonance (MR) imaging, was compared with a known blood pool agent, Gd-DTPA-polylysine, in an animal model. The relative signal intensities of liver, renal cortex, pancreas, and trunk muscle were assessed in 12 pigs between 4 seconds and 120 minutes after injection of a 20 mumol/kg dose of each contrast agent, by using a FLASH (fast low-angle shot) sequence. Except for muscle, all tissues showed visible enhancement after injection of either contrast agent. After injection of Gd-DTPA-polymer, enhancement patterns in the liver, renal cortex, and pancreas were similar to those seen after injection of Gd-DTPA-polylysine. No statistically significant differences in enhancement between the two contrast agents were found at any time point. The authors conclude that the contrast kinetics of Gd-DTPA-cascade-polymer are similar to those of Gd-DTPA-polylysine and that this agent may also be used as a blood pool contrast agent for MR imaging.

Animals↗

PubMedDate not supplied

Dynamic MRI of a hypovascularized liver tumor model: comparison of a new blood pool contrast agent (24-gadolinium-DTPA-cascade-polymer) with gadopentetate dimeglumine.

We evaluated the enhancement properties of a new blood pool contrast agent (24-gadolinium-diethylenetriamine pentaacetic acid [Gd-DTPA]-cascade-polymer) in comparison with gadopentetate dimeglumine in 24 rabbits with an experimentally induced VX-2 liver tumor. Dynamic MRI of the liver was performed before, immediately after, and within 15 seconds to 30 minutes after contrast agent administration. Relative signal intensities and contrast-to-noise ratios (CNRs) of both agents were evaluated. After blood pool agent administration a significantly higher CNR between liver and tumor was observed within 2 to 30 minutes after injection as compared with the CNR after gadopentetate dimeglumine. Within 4 to 30 minutes after injection of gadopentetate dimeglumine, the relative signal intensities of tumor were significantly higher than after administration of the blood pool agent. In conclusion, the new blood pool contrast agent demonstrated a significantly better CNR of the experimental hypovascularized liver tumor than gadopentetate dimeglumine.

Animals↗

PubMedDate not supplied

MRI-guided biopsy of bone in a hybrid system.

This is a report of our experience with percutaneous, MRI-guided biopsies in 25 patients with skeletal lesions using a 1.5-T MR hybrid system. Twenty-five consecutive patients with skeletal lesions were referred for MRI-guided biopsy. Biopsies were performed with a 1.5-T Philips Gyroscan (Philips Medical Systems, Best, The Netherlands) combined with a c-arm fluoroscopy. Specimens were obtained percutaneously either with a 14- or 18-gauge "side-slit" type of biopsy needle (n = 10 skeletal lesions that had penetrated through the cortex), or using a prototype coaxial drill system powered either by hand or an optional motor (n = 15 skeletal lesions still covered with cortical bone). All but two biopsies could be completed within the MR unit. For one patient, who required a transpedicular approach to a lumbar vertebra, and for one child, who required general anesthesia, we decided to switch to CT guidance. In 19 of the 25 cases (17 of the 23 cases performed in MR), the sample was sufficient and the histopathologic diagnosis was confirmed. Three patients had an inadequate sample, and three others had adequate samples but inaccurate results. No procedural complications occurred. Percutaneous biopsy of skeletal lesions performed under MRI-guidance was found to be safe and reasonably accurate. There were no procedural complications in our small series. MRI may be used as an alternative to CT, but its role vis-à-vis CT has yet to be ascertained.

Biopsy, Needle↗

PubMedDate not supplied

Visualization of MR-compatible catheters by electrically induced local field inhomogeneities: evaluation in vivo.

The purpose of this study was to assess the feasibility of a newly developed field inhomogeneity catheter for interventional MRI in vivo. Different prototypes of a field inhomogeneity catheter (pigtail and multipurpose configuration, balloon catheters) were investigated in pigs. The catheters were introduced in Seldinger technique via the femoral vessels over a guidewire on an interventional MR system (Philips Gyroscan NT combined with a C-arm fluoroscopy unit [Philips BV 212]). Catheters were placed in veins and arteries. The catheter position was controlled by a fast gradient-echo sequence (turbo field echo [TFE]). Catheters were introduced over a guidewire without complications in all cases. Using the field inhomogeneity concept, catheters were easily visualized in the inferior vena cava and the aorta by the fast gradient-echo technique on MR in all cases. Although aortic branches were successful cannulated, the catheters were not well displayed by the TFE technique due to the complex and tortuous anatomy. All animals survived the experiments without complications. MR-guided visualization of a field inhomogeneity catheter is a simple concept that can be realized on each MR scanner and may allow intravascular MR-guided interventions in future.

Animals↗

PubMedDate not supplied

MR-guided biopsy using a T2-weighted single-shot zoom imaging sequence (Local Look technique).

The purpose of this study was to demonstrate the utility of a T2-weighted single shot turbo spin-echo technique--the so-called "Local Look" (LoLo) and more recently renamed "Zoom Imaging" technique--for MR-guided percutaneous interventions. We performed 28 procedures on 22 patients using a 1.5-T system for MR guidance. All procedures were controlled with the LoLo technique, which acquires T2-weighted images in 600 msec. This is achieved by using a small field of view (250 x 125 mm) along with a maximum echo train length, the so-called "single shot method." To prevent backfolding artifacts, the 90 degrees and 180 degrees pulses were oriented orthogonally to each other. Because signal is created only in the region in which the pulses overlap, no backfolding can occur from outside this area. Half of the biopsies were additionally monitored using a fast gradient-echo sequence, which was compared with the LoLo technique. All of the procedures were technically successful, and there were no procedural complications. The LoLo technique produced images that had good contrast between the lesion and the needle artifact, and the artifact size was smaller than that produced by the gradient-echo technique. Subjective judgment of the ability to accurately delineate the needle tip indicated that the LoLo technique was either superior to (73%) or equal to (27%) the gradient-echo sequence in all cases. The LoLo technique is an accurate and effective method for MR guidance of percutaneous procedures, because it shows good lesion contrast and small needle artifacts. The additional use of a gradient-echo sequence during the procedure planning stage is advisable in more difficult cases, particularly when adjacent blood vessels are a concern. Monitoring of the needle tip is best performed with the LoLo technique.

Artifacts↗