Localization of pheochromocytoma: MIBG [correction of MIGB], CT, and MRI correlation.

Nineteen patients (8 M, 11F) ranging in age from 15 - 67 yr old (mean = 39 yr) with clinically diagnosed pheochromocytomas were prospectively evaluated with 131I metaiodobenzyl-guanidine (MIBG) scintigraphy (n = 19), computed tomography (CT) (n = 19), and magnetic resonance imaging (MRI) (n = 17) in order to determine their relative diagnostic efficacy. Pathologic confirmation was obtained in all 19 patients: 13 intraadrenal and six extraadrenal with metastases in five (Table 1). All three imaging modalities were in agreement in 11 of 14 completed examinations (79%). MIBG and CT agreed in 16 of the 19 patients in whom both were performed (84%). MIBG/MR and CT/MR results were concordant in 12 of 14 (86%) and 13 of 14 (93%) jointly completed examinations, respectively. There was one false-negative (FN) MIBG scan, two FN CT scans, and one FN MR scan. MIBG, CT, and MRI are complementary procedures with MIBG providing more specific functional information and the latter two superior anatomic detail. MIBG scintigraphy is recommended as the initial localizing study of choice (especially for the detection of extraadrenal disease and postoperative recurrence), as a guide for CT and/or MR and specific functional confirmation of their findings. Although MRI is capable of imaging in multiple planes (without exposure to ionizing radiation or the need for i.v. contrast material) with superior contrast compared to CT, it is expensive and has poor patient cooperation. However, it may be capable of differentiating pheochromocytomas from other adrenal masses on the basis of signal characterization.

The complementary role of gallium citrate imaging and computed tomography in the evaluation of suspected abdominal infection.

Fifteen patients with a suspected abdominal abscess were examined by both gallium-67 and computed tomographic scanning. The Ga-67 scan was a useful screening examination, correctly identifying all eight cases of infection, whereas the CT scan missed one case of a pericecal phlegmon. Misdiagnosis of infection by Ga-67 scan occurred in 2/8 cases without infection but the CT scan correctly identified all noninfected patients. While this series is too small to decide whether there is significant difference in the ability of the two procedures to suggest the correct diagnosis, it is felt that Ga-67 and subsequent CT scans may be complementary in that a Ga-67 scan can initially locate the abnormality and thus direct the CT scan, which can confirm the diagnosis or avoid a misinterpretation of the Ga-67 scan. Computed tomography also provides more anatomical detail, better location of the lesion, and demonsrates lesions noninfectious in nature.

Thermographic assessment of intestinal viability following ischemic damage.

Reactive hyperemia has been shown to be a characteristic of viable ischemic tissue that has been revascularized. A segment of small bowel was made ischemic by arterial occlusion and the ischemia maintained for 2 1/2 hrs (ischemic, viable bowel) or 8 hrs (ischemic, nonviable bowel) before circulation was restored. Thermograms and surface temperature measurements of exposed ischemic and non-ischemic bowel segments were obtained before and every five minutes after revascularization. Thermograms of segments revascularized after 2 1/2 hrs of ischemia demonstrated reactive hyperemia and a one to four degree increase in surface temperature compared to normal surrounding bowel. No hyperemic response was seen in bowel segments that were ischemic for 8 hrs. Our results indicate that thermograms can document reactive hyperemia of an exposed ischemic bowel that has been successfully revascularized and may be an important aid in assessing bowel viability during surgery.

Use of thermography to predict intestinal viability and survival after ischemic injury: a blind experimental study.

Reactive hyperemia is a characteristic of viable ischemic tissue that has been revascularized. In 14 normal dogs, segments of bowel were made ischemic for periods of 2--8 hours. Thermograms and surface temperature measurements of exposed ischemic and nonischemic segments were obtained before and every 5 minutes for 30 minutes after revascularization. Thermograms demonstrated uniform reactive hyperemia throughout the segments ischemic for 2--3 hours; hyperemia with some nonuniform, patchy areas in segments ischemic for 3--7 hours; and no hyperemic response in segments ischemic for 8 hours. All five dogs demonstrating uniform hyperemia survived and the bowels were found to be histologically normal. Four of the six dogs showing hyperemia with some nonuniform areas survived, but all six showed areas of transmural damage with fibrosis and scarring histopathologically. The three dogs with no hyperemic response died of pathologically proved bowel infarction. Our results indicate that thermograms can document the degree and extent of reactive hyperemia. Thermograms, therefore, may be an important aid in assessing bowel viability during surgery.

Radionuclide imaging of bowel infarction complicating small bowel intussusception in dogs.

Technetium-99m (99mTc)-pyrophosphate was investigated for use as an indicator of intestinal infarction in intussuscepted bowel. Irreducible intussusceptions were created in eight adult mongrel dogs. Technetium-99m-pyrophosphate was then injected intravenously 24 and 48 hrs later for external scanning. In six of the dogs, infarction developed in the intussusception, and each demonstrated increased uptake of 99mTc-pyrophosphate on in vivo scintiscans. The two dogs without infarction showed no increase uptake of the radionuclide. Well-counting and specimen scanning confirmed increased radionuclide in the infarcted intussusceptions. These observations suggest that 99mTc-pyrophosphate is a reliable indicator of the vascular compromise that sometimes occurs with intestinal intussusception.

Variability of myocardial signal on magnetic resonance images.

The diagnosis of myocardial disease by magnetic resonance (MR) imaging depends on accurate measurement of myocardial signal intensity. The authors performed 15 experiments in four rabbits at 1.9 T with spin-echo MR imaging to study the variability of myocardial signal intensity throughout the cardiac cycle and to measure myocardial T2 values. Variability in signal from the myocardium throughout the cardiac cycle was observed in all experiments. During systole, a significant increase in myocardial signal was noted, when data acquisition was performed with electrocardiogram (ECG)-gating and controlled ventilation (P = .02). An inverse relationship between myocardial signal and phase noise was found, indicating the motion-related nature of the variation of myocardial signal. A similar inverse relationship was observed in images obtained from a normal human volunteer. Ex vivo myocardial T2 values of rabbit myocardial tissue were significantly higher than the in vivo values (P = .003), reflecting residual motion despite cardiac gating and controlled ventilation.

Magnetic resonance angiography of the pelvis and lower extremities. Works in progress.

Two-dimensional time-of-flight (TOF) magnetic resonance angiography (MRA) of the lower extremities has recently been rediscovered as a technique that can be used to find small vessels in the foot and leg for surgical revascularization in patients with severe peripheral vascular disease. The purpose of this article is to acquaint the reader with some of the common problems that may be encountered in this imaging technique and to show their derivations and solutions were applicable. In addition, the authors show receiver operator curve analysis of one radiologist's ability to determine the location and patency of arteries using this technique to be outstanding (AZ, 0.9737). This represents a promising new technique for imaging the arterial system in patients with severe peripheral vascular disease.

Magnetic resonance imaging of abscesses using lipid-coated iron oxide particles.

RATIONALE AND OBJECTIVES: The authors investigated whether iron oxide particles can be used as a magnetic resonance imaging (MRI) contrast agent to image abscesses in a two-stage experimental design. METHODS: Human buffy coat was incubated with iron oxide particles of different sizes and coatings. Smears of the incubation mixture were made on a glass slide and stained for iron. The percentage of iron oxide uptake was determined by counting 100 neutrophils and monocytes and scoring the number of cells that contain iron. Subcutaneous abscesses were created in the flanks of 18 Sprague-Dawley rats by injecting them with 0.1 mL of turpentine. Iron oxide was given intravenously, and the animals were imaged by MRI (1.5 T) 12 to 24 hours later. Different iron oxide coatings and doses were compared. RESULTS: The four different types of coating (constant fragment [Fc] of IgG, bovine serum albumin [BSA], lipid [Ferrosome], and dextran) had an uptake of 72% +/- 5.3%, 61% +/- 6.2%, 30.5% +/- 6.8%, and 5% +/- 2.5%, respectively. Comparison of two particle sizes (mean, 90 versus 35 nm) showed the large particles to have higher uptake (61% +/- 6.2%) compared with the small particles (6% +/- 1.8%) (P less than .001). Post-contrast imaging of the rats showed a hypointense ring around the abscess only in the animals injected with the lipid-coated agent. The effect was discernible within 12 hours after contrast injection and at a dose of 25 mumols iron/kg. Histologic sections showed phagocytic cells with iron granules in the periphery of the abscess. No hypointense ring on MRI or iron granules on histologic sections was seen around the abscess of the control animals or those injected with BSA-iron oxide or Fc-iron oxide. CONCLUSIONS: Lipid-coated iron oxide particles can be used to image abscesses by virtue of their phagocytosis into surrounding inflammatory cells. Positive uptake of these particles by human phagocytes in vitro suggests that similar results may be applicable in humans.

Magnetic resonance imaging and magnetic resonance spectroscopy of bone tumors and bone marrow disease.

The authors have made use of an integrated magnetic resonance imaging/spectroscopy (MRI/MRS) examination to study seven patients with a variety of bone tumors. The spatial localization method used in the 31P portion of the examination was surface coil localization and a one-dimensional chemical shift imaging method (3 cases). The authors found that the precision of spatial localization was critical in many of these cases, since most of these bone tumors were surrounded by muscle tissue that contained high concentrations of phosphocreatine (PCr). For this reason, they suggest that the metabolite ratios should be referenced to the adenosine triphosphate (beta-NTP) resonance rather than PCr. The phosphate monoester (PME) to beta-NTP ratio was elevated as compared with normal muscle in all of the bone tumors studied. The authors found that all of these tumors exhibited pHs between 7.0 and 7.2, which are similar to the values found for normal muscle. They also show the feasibility of using a line-selective proton chemical shift imaging sequence with high spatial resolution for investigating changes in the fatty composition of bone marrow. This method is illustrated in an example of a patient with advanced avascular necrosis in the femoral heads.

An experience with a LeVeen ascites shunt.

A patient with intractable ascites was treated by placement of the LeVeen peritoneovenous shunt. Shunt failure was caused by malpositioning of the venous limb in the inferior vena cava. This was demonstrated by injection of water-soluble contrast material into the venous limb. Revision of the shunt led to diuresis, weight loss, and reduction of ascites. The physiologic process of the LeVeen shunt is reviewed and we suggest placement of a radiopaque marker into the tubing.

Magnetic resonance imaging of the genitourinary tract.

Magnetic resonance imaging, in general, is in a state of evolution. This article demonstrates its potential use in the diagnosis of genitourinary pathology. Controlled studies will be required, however, in order to determine the place of this imaging modality in the vast array of imaging options currently available to the radiologist and urologic surgeon. It is expected that, in the not too distant future, the indications for magnetic resonance imaging in the diagnosis of genitourinary disorders will become clear.

Human exposure to 4.0-Tesla magnetic fields in a whole-body scanner.

Details are given for the design, construction, properties, and performance of a large, highly homogeneous magnet designed to permit whole-body magnetic resonance imaging and spectroscopy at 4 T. The magnet has an inductance of 1289 H and a stored energy of 33.4 MJ at rated field. The health of a group of 11 volunteers who had varying degrees of exposure to this field was followed over a 12-month period and no change that could be associated with this exposure was detected. A mild level of sensory experiences, apparently associated with motion within the field of the magnet, was reported by some of the volunteers during some of their exposures. A questionnaire regarding sensory effects associated with magnetic resonance scanners and possibly caused by the static magnetic field of these instruments, was given to nine respondents who had experience within both 1.5-T scanners and this 4-T scanner and to another group of 24 respondents who had experience only within 1.5-T scanners. For the sensations of vertigo, nausea, and metallic taste there was statistically significant (p less than 0.05) evidence for a field-dependent effect that was greater at 4 T. In addition, there was evidence for motion-induced magnetophosphenes caused by motion of the eyes within the static field. These results indicate the practicality of experimental whole-body body scanners operating at 4 T and the possibility of mild sensory effects in humans associated with motion within a static magnetic field. The results also indicate the likelihood of a wide margin of safety for the exposure of noncompromised patients to the static fields of conventional magnetic resonance scanners operated at 1.5 to 2 T and below.

Strategies for magnetic resonance imaging of focal liver disease.

Strategies for the successful application of MRI to the liver are reviewed. Technical improvements in scanner performance have resulted in marked improvements in image quality in the upper abdomen and liver. In addition, increased experience has demonstrated that a number of lesions can be characterized on MRI through the use and analysis of signal intensity patterns and morphology. These include cavernous hemangiomas, cysts, focal nodular hyperplasia, encapsulated hepatomas, and hematomas in the liver. While the sensitivity of MR in the detection of focal liver disease is quite high and comparable to that of CT, deficiencies in the detection of the extrahepatic manifestations of malignant disease suggest that it is still not the primary screening modality. At present, MR appears to be a problem-solving modality in the evaluation of focal liver disease. It is useful in characterizing solitary lesions and defining the segmental extent of a detected abnormality, and as an adjunctive study when there is a discrepancy in the results of two imaging studies.

Evaluation of gynecologic malignancy by magnetic resonance imaging.

Currently, MR imaging has demonstrated the greatest accuracy and has potentially the greatest clinical utility for the staging of cervical carcinoma. Endometrial carcinoma also can be staged by MR imaging with reasonable accuracy, although the clinical indications for preoperative endometrial carcinoma staging are less clear. MR imaging has unparalleled capacity for the tissue characterization of adnexal disease and has demonstrated utility for diagnosis of common adnexal masses such as pedunculated leiomyoma, endometrioma, and ovarian dermoid. Its use in the evaluation or staging of ovarian, vaginal, and vulvar carcinoma has not been evaluated fully. MR imaging can demonstrate complications of radiation therapy and surgery and can distinguish most recurrent carcinomas from postradiation fibrosis. New techniques such as arrayed use of surface coils, endoluminal surface coils, fast spin-echo acquisitions, and contrast agents show promise for contributing to the already rapid pace of technologic advancement in the field of MR imaging of the female pelvis.

Principles of performance and interpretation of double-contrast gastrointestinal studies.

Successful use of double-contrast techniques requires skill both in performing and interpreting the examination. To perform the examination properly, great care must be taken in evaluating the coating of the mucosal surface. An appropriate barium suspension designed for double-contrast radiography must be used. The necessity of varying the degree of gaseous distention for demonstrating certain types of lesions must also be appreciated. To interpret these examinations, the radiologist must understand the factors contributing to the radiographic image--the dependent and nondependent surfaces and the pool of barium. A firm understanding of both the uses and drawbacks of the pool of barium not only is helpful in the performance of the examination but also is essential for accurate interpretation. A knowledge of the differing appearances of structures on the dependent and nondependent surfaces is of the most utmost importance because this knowledge can be used to obtain a three-dimensional view of both elevated and depressed lesions. An accurate correlation of this picture with the gross pathologic appearance of a lesion is the aim of the double-contrast technique.

The potential role of NMR imaging in thoracic disease.

The technical details of producing an NMR image are briefly explained, followed by a discussion of what relaxation times mean and how tissue properties affect the NMR image. The rest of the article is devoted to the NMR imaging of the thorax.

Strategies for musculoskeletal magnetic resonance imaging.

There is a broad range of clinical applications for MRI in the diagnosis of musculoskeletal disease, and the emphasis in this article is on the evaluation of the joints and extremities. A discussion of basic principles, including radiofrequency coils, positioning, pulsing sequences, imaging planes, and technical parameters is followed by discussions of tailored approaches to the evaluation of mass lesions and joint pathology for specific regions of the musculoskeletal system. In the final section, consideration is given to the overall role of MRI in the diagnosis of musculoskeletal disorders with respect to other established imaging modalities.

The use of magnetic resonance imaging in the evaluation of bone and soft-tissue tumors.

We believe that MR imaging should follow plain films in the imaging analysis of soft-tissue tumors and bone tumors suspected of malignancy. MR imaging is primarily useful in tumor staging, although it may aid in diagnosis and the detection of recurrent or residual disease. Gd-DTPA and MR spectroscopy are currently being evaluated in many medical centers; their utility in the work-up and management of tumors of bone and soft tissue has yet to be determined.

Controversies in the radiologic diagnosis of pelvic malignancies.

Although vast differences exist among the many pelvic malignancies, several unifying concepts emerge from this discussion. First, there is a different role for diagnostic imaging for each type of pelvic malignancy. The radiologist should be aware that although the radiographic findings may be similar, the clinical impact varies greatly with a particular tumor. Second, although clinical staging is notoriously inaccurate, nevertheless diagnostic imaging techniques only improve upon but do not replace it because of false-positive and false-negative results. Third, because of the high false-negative rates of most of the modalities in use, negative studies do not in fact rule out the presence of disease. A surgical procedure may still be needed. Finally, several new techniques, including MRI and transrectal or transurethral ultrasound, may improve the accuracy rates. These developments will probably further enliven the controversies surrounding the radiologic evaluation of pelvic malignancies.