Testicular microlithiasis: US follow-up.

PURPOSE: To determine in patients with testicular microlithiasis (TM) the short-term natural history of classic TM (CTM) and limited TM (LTM). MATERIALS AND METHODS: In 104 patients, testicular microliths were identified on ultrasonographic (US) images; 39 patients had five or more microliths on at least one US image (criterion for CTM), and 65 patients had fewer than five microliths (criterion for LTM). Attempts were made to have all patients return for follow-up US to assess for change in TM or development of tumor. RESULTS: Seven (18%) of the 39 patients with CTM and one (2%) of the 65 patients with LTM had tumor at presentation (P =.004). Among all 104 patients, follow-up US was performed in 72 patients (31 with CTM, 41 with LTM), with mean follow-up of 45 months (range, 12-90 months). None of these patients had interval development of testicular neoplasm. LTM did not progress to CTM in any patient. Progression in number of microliths was seen in two patients with CTM. CONCLUSION: Patients with LTM have a lower prevalence of associated malignancy than do patients with CTM. The risk of developing malignancy in patients with isolated TM (LTM or CTM) is low at short-term follow-up. These results raise the question of the need for routine US in this patient population.

Renal cysts: is attenuation artifactually increased on contrast-enhanced CT images?

PURPOSE: To determine if the attenuation values of simple renal cysts are artifactually increased on contrast material-enhanced, clinically acquired spiral computed tomographic (CT) images. MATERIALS AND METHODS: Dual-phase renal spiral CT studies (5-mm collimation; pitch, 1.0) were retrospectively analyzed in 24 consecutive patients who had ultrasonographic (US) documentation of simple renal cysts. Forty-eight cysts were identified. The attenuation values of each cyst were measured on nonenhanced, cortical phase, and nephrographic phase images. The size and the location of each cyst in relation to the renal parenchyma were also recorded. RESULTS: The cysts were 0.6-10.8 cm in diameter (mean, 2.6 cm; SD, 2.0). The mean attenuation change in the cysts from nonenhanced to contrast-enhanced images was statistically significant in a comparison of cortical phase and nephrographic phase images (P: <.01): +1.8 HU (SD, 3.8) for cortical phase and +3. 6 HU (SD, 5.6) for nephrographic phase images. Renal cysts 1.0 cm or smaller showed a higher attenuation increase (mean, +4.0 HU for cortical phase and +11.0 HU for nephrographic phase). None of the renal cysts larger than 1.0 cm demonstrated an increase greater than 10 HU (mean, +1.4 HU for cortical phase and +2.3 HU for nephrographic phase). Intraparenchymal cysts showed higher mean attenuation changes than the exophytic cysts. CONCLUSION: Attenuation values in the renal cysts increased artifactually on contrast-enhanced images, but this pseudoenhancement was not substantial and was less than 10 HU when the cyst was larger than 1. 0 cm in diameter.

Interobserver variability in determining enhancement of renal masses on helical CT.

OBJECTIVE: Because enhancing renal masses are often surgically excised, we assessed interobserver variability in determining enhancement of renal masses. SUBJECTS AND METHODS: Forty-nine complicated cysts or solid lesions were imaged with helical CT. Simple cysts (n = 20) were included, for a total of 69 lesions. Three radiologists obtained three region-of-interest measurements for each lesion in the unenhanced and nephrographic phases. Enhancement was defined as an attenuation increase of 15 H or more, provided that partial volume effects were not the cause. Observer concordance was defined as agreement among all three observers on whether a lesion was enhancing or nonenhancing. Measurement-interpretation agreement was defined as an observer's measuring an attenuation increase of less than 15 H and interpreting the lesion as nonenhancing or measuring an increase of 15 H or greater and interpreting the lesion as enhancing. RESULTS: For the 20 simple cysts, observer concordance was 100% and measurement-interpretation agreement was 100%. For the 49 complicated lesions, observer concordance was 90% and measurement-interpretation agreement was 84% (41/49). Of the five discordant lesions, three were 1.1 or 1.0 cm in size and were interpreted as being of high attenuation on the unenhanced scans, with enhancement, versus a high-attenuation mass with increasing attenuation attributed to volume averaging. The remaining two discordant observations were due to differing interpretations of normally enhancing renal parenchyma versus cyst wall or tumor nodularity. CONCLUSION: For most renal lesions, the observers agreed on whether enhancement was present or absent. Observers were prone to disagree about enhancement for small lesions (1.0-1.5 cm). Occasional disagreements on classification of larger lesions were due to differing interpretations of enhancing normal parenchyma versus abnormal tissue. Discrepancies between an observer's opinion on enhancement and the results of region-of-interest measurements suggest the possibility of disagreement among multiple observers.

Laparoscopic ultrasound imaging of adrenal tumors during laparoscopic adrenalectomy.

BACKGROUND: The purpose of this study was to determine the usefulness of laparoscopic ultrasound (LUS) during laparoscopic adrenalectomy (LA) and to define the ultrasound imaging characteristics of various adrenal tumors. METHODS: LUS was utilized in 27 patients who underwent LA (including one bilateral adrenalectomy) from May 1994 to October 1998. Tumor size ranged from 1.0 to 5.5 cm (mean 3.3 cm), and a transabdominal lateral approach to LA was used. RESULTS: LUS localized the adrenal gland and tumor in all 28 adrenalectomies and demonstrated the relationship of the tumor to the kidney and adjacent vascular structures (renal artery/vein and inferior vena cava). The adrenal vein was visualized sonographically in only six cases (21 %). Pheochromocytomas were mild to markedly heterogenous, whereas most aldosteronomas and cortical adenomas were homogenous. LUS provided useful information to the surgeon in 11 of 28 cases (39%) by: 1) localizing the adrenal gland and tumor and/or guiding the dissection; 2) demonstrating that tumors > or =4 cm were confined to the adrenal gland; and 3) investigating suspected pathology in other organs. Mean operating time for LUS was 10.9 min (range 5 to 24 min) and calculated hospital charges were $602. CONCLUSIONS: LUS accurately localizes adrenal tumors, helps define their relationship to adjacent structures, and provides confirmation that larger tumors are amenable to laparoscopic resection. LUS is a useful adjunct to laparoscopic adrenalectomy in selected patients.

MR imaging of renal function.

MR imaging has advantages over both computed tomography and nuclear scintigraphy for assessing renal function, because it combines high spatial resolution with information on perfusion and function. A further advantage is the lack of ionizing radiation. Quantitation of flow rate by phase contrast in the renal arteries and veins has the potential to provide estimation of renal blood flow, which could prove useful in a number of clinical situations, especially for studying renal vascular disorders and the effects of treatment, and for assessing renal transplants. Evaluation of renal perfusion with MR imaging has become feasible with the development of rapid data acquisition techniques, which provide adequate temporal resolution to monitor the rapid signal changes during the first passage of the contrast agents in the kidneys. More recently, magnetically labeling water protons in blood flowing into kidneys has been used to noninvasively quantitate regional measurement of cortical and medullary perfusion. Other techniques being investigated with MR imaging for assessment of renal function include diffusion imaging GFR estimation and blood oxygenation level dependent imaging to evaluate intrarenal oxygenation levels.

Functional MR imaging of the porcine kidney: physiologic changes of prolonged pneumoperitoneum.

BACKGROUND: Increased intraabdominal pressure (IPA) during laparoscopy has been associated with decreased urine output. The purpose of this study was to use a noninvasive MRI technique to measure renal vessel flow velocity and change in differential renal medulla and cortex perfusion during pneumoperitoneum. STUDY DESIGN: Six female farm pigs underwent general endotracheal anesthesia and dynamic imaging following left ventricular (LV) injection of Gd-DTPA, utilizing a dual echo gradient echo sequence. MRI was repeated after three hours of continuous 15 mm Hg pneumoperitoneum in three study pigs and after three hours of monitored general anesthesia without pneumoperitoneum in three control pigs. Renal artery and renal vein flow velocities were calculated using cine phase-contrast technique. Renal perfusion was independently measured by LV injection of radiolabelled microspheres. RESULTS: There was a decrease in mean renal vein flow velocity in the pneumoperitoneum group as compared to the control group. During pneumoperitoneum there was a similar percentage reduction in the perfusion of the cortex (-28%) and medulla (-31%); this corresponded with a decreased urine output. In addition, radiolabelled microspheres corroborated the similar decrease in both cortical and medullary perfusion rates during pneumoperitoneum. CONCLUSIONS: Prolonged IAP is associated with a decrease in renal vein flow velocity and urine output. There is a similar decrease in the renal medulla and cortex perfusion rates during pneumoperitoneum of 15 mm Hg.

Anatomy of the retroperitoneum: observations of the distribution of pathologic fluid collections.

PURPOSE: To correlate anatomic dissections with clinical observations regarding anatomic distribution of retroperitoneal fluid, and to document the existence of planes that lie between classically described retroperitoneal spaces. MATERIALS AND METHODS: Latex was injected in varying amounts into the pancreatic tail in three fresh cadavers to simulate peripancreatic fluid collections. Spiral computed tomography (CT) was performed of the abdomen and pelvis after each latex injection. Two cadavers were subsequently frozen and sectioned in axial planes; limited dissections were performed on these specimens. One was embalmed and underwent extensive anatomic dissection. Five embalmed, unprepared cadavers were also dissected to confirm observations made in the three prepared cadavers. RESULTS: Latex injected into the tail of the pancreas entered a retromesenteric plane that was posterior to the anterior pararenal space and anterior to the anterior renal fascia. The plane continued superiorly, extending to the diaphragm near the esophageal hiatus; inferiorly, extending to the pelvis along the anterolateral surface of the psoas muscle; and laterally, posterior to the descending colon and its mesentery. The plane also communicated with a retrorenal plane lying between the posterior renal fascia and the posterior pararenal space. CONCLUSION: Embryologic development of the dorsal mesenteries suggests the existence of retromesenteric planes, and clinical observations further support their existence. These findings may explain the observed distribution of retroperitoneal fluid collections from diaphragm to pelvis.

MR imaging of the peritoneum and abdominal wall.

Knowledge of the peritoneal cavity and the peritoneal folds that subdivide it is useful in evaluating for the presence and spread of disease processes that affect the peritoneum. Many disease processes of the peritoneum and abdominal wall are well evaluated with MR imaging, especially as MR techniques improve. In some cases, information is obtained that is not available with other imaging techniques.

Interactions of nitroxides with plasma and blood: effect on 1/T1 of water protons.

Nitroxide stable free radicals (nitroxides) have potential utility as MRI contrast-enhancing agents with the additional capability of reflecting redox metabolism. In order to gain a better understanding of their potential interactions in vivo, we have studied the longitudinal NMRD profiles (1/T1 as a function of field strength) and ESR spectra for lipophilic and aqueous-soluble nitroxides in blood, plasma, and plasma components. Typical water-soluble nitroxides do not interact appreciably with blood, plasma, or plasma proteins. Fatty acid nitroxides do interact physically with blood, predominantly by intercalation within red blood cell membranes and binding to albumin. The latter interaction results in significantly enhanced relaxivity for the nitroxide/HSA complex. Relaxation of water protons in this case is dominated by inner sphere processes, ostensibly due to water molecules hydrogen bonded to nitroxide moieties. The rotational reorientation time for the complex, the electronic relaxation time, and the exchange time for the water molecule reversably bound to the nitroxide, all appear significantly to influence the correlation time (approximately 16 ns) for this inner sphere contribution.

Sources of the increased longitudinal relaxation rates observed in melanotic melanoma. An in vitro study of synthetic melanins.

Researchers have suggested that the increased longitudinal relaxation rates (1/T1) of solvent water protons often found in melanoma result either from the paramagnetism of stable free radicals occurring in melanin or from that of methemoglobin in nonacute hemorrhagic regions of the tumor. However, field-cycling relaxometry and model solutions of synthetic melanin produced data which show that free radicals in melanin do not contribute significantly to 1/T1; instead, aggregation of melanin into macromolecular particles and binding of biologically-common paramagnetic metal ions (ie Fe3+, Mn2+, and Cu2+) to melanin effectively do increase 1/T1. These data have been combined with published histochemical data on melanin-containing tissues, while disregarding any additional effect related to hemorrhage. The result indicates that in melanoma the expected contribution of melanin-bound Fe3+ to 1/T1, at typical imaging fields, predominates under estimated in vivo conditions; furthermore, the total contribution from all sources, specifically due to the presence of melanin, is sufficient to account for reported measurements of 1/T1 in melanoma. Comparing the latter results with published data on T1 relaxation in model solutions of methemoglobin suggests that co-existing regions of nonacute microhemorrhage also may contribute significantly to 1/T1 under certain conditions. Finally, the implications for 1/T2 of melanin occurring in vivo within discrete melanosomes is discussed.

Modulation of water proton relaxation rates by liposomes containing paramagnetic materials.

Liposomes containing paramagnetic chemicals have significant potential for enhancing the effectiveness and selectivity of contrast agents in magnetic resonance imaging. We have studied the interactions of water, liposomes, and contrast agents using NMR and ESR. We find that the permeability of liposomes to water is of major importance in determining the effects of these systems on water proton relaxation. Key factors include (1) liposome composition, which determines the phospholipid membrane phase behavior as a function of temperature; (2) liposome structure (unilamellar or multilamellar); (3) location of the contrast agent in the liposome (aqueous space or lipid membrane); and (4) binding of contrast agents by liposomes. By appropriate selection of these factors it is possible to obtain effective proton relaxation enhancement in a manner suitable for particular experimental or clinical needs for contrast in MRI. For maximum relaxivity using lipophilic nitroxides, the optimum system appears to be 5-doxyl stearate in multilamellar vesicles with a membrane composition that gives a phase transition temperature slightly above body temperature.

Modification of relaxation of lipid protons by molecular oxygen and nitroxides.

Measurement of proton 1/T1 in model lipids from 0.00023 to 1.3 Tesla, at 5 degrees C and 37 degrees C, shows that both oxygen and nitroxides effectively enhance the relaxation rates of the protons of lipids. Equilibration with 1 atm of oxygen has a sixfold greater effect on lipid protons than on water protons, primarily because of the high lipid solubility of oxygen. The maximum relative relaxivity of oxygen for lipid protons occurs at 0.12-0.8 Tesla. Lipid soluble nitroxides have a four- to eightfold greater effect on lipid protons than on water protons. This high relaxivity, combined with the high lipid solubility possible with nitroxides, could lead to significant contrast in vivo in lipid environments.

Effects of nitroxides on the magnetic field and temperature dependence of 1/T1 of solvent water protons.

We report a study of the longitudinal NMRD profiles (proton longitudinal relaxation rates as a function of field strength) over a broad range of magnetic field (0.01 to 50 MHz proton Larmor frequency) and temperature (-9.6 to 37 degrees C) for aqueous solutions of (i) a fatty acid-nitroxide/albumin complex and (ii) 10 low molecular weight nitroxides. Analysis of the NMRD profile for the fatty acid-nitroxide/albumin complex provides a lower bound estimate for the rotational correlation time of the complex, which permits the calculation of an upper bound on the inner sphere contribution to relaxation of the uncomplexed nitroxides. Inner sphere processes, ostensibly due to water molecules hydrogen bonded to the nitroxide moiety, dominate the relaxation effects of the slowly rotating macromolecular nitroxide/albumin complex. By extrapolation, the contribution of these inner sphere processes are negligible for rapidly tumbling nitroxides free in solution, which affect solvent proton relaxation almost entirely through outer sphere processes (i.e., translational diffusion). A comparison of the relaxation data for aqueous solutions of the uncomplexed nitroxides with the theory of outer sphere relaxation of J.H. Freed (J. Chem. Phys. 68, 4034 (1978] yields values for the distance of closest approach of the water and nitroxide molecules, as well as for their relative diffusion constants, at five different temperatures. Our results indicate that the rather modest relaxivities of aqueous solutions of nitroxides increase substantially with increased solvent viscosity and with protein binding, supporting the potential utility of nitroxides for enhancement of contrast in nuclear magnetic resonance images.