[show abstract][hide abstract] ABSTRACT: Task-induced deactivation (TID) potentially reflects the interactions between the default mode and task specific networks, which are assumed to be age dependent. The study of the age association of such interactions provides insight about the maturation of neural networks, and lays out the groundwork for evaluating abnormal development of neural networks in neurological disorders. The current study analyzed the deactivations induced by language tasks in 45 right-handed normal controls aging from 6 to 22years of age. Converging results from GLM, dual regression and ROI analyses showed a gradual reduction in both the spatial extent and the strength of the TID in the DMN cortices as the brain matured from kindergarten to early adulthood in the absence of any significant change in task performance. The results may be ascribed to maturation leading to either improved multi-tasking (i.e. reduced deactivation) or reduced cognitive demands due to greater experience (affects both control and active tasks but leads to reduced overall difference). However, other effects, such as changes in the DMN connectivity that were not included in this study may also have influenced the results. In light of this, researchers should be cautious when investigating the maturation of DMN using TID. With a GLM analysis using the concatenated fMRI data from several paradigms, this study additionally identified an age associated increase of TID in the STG (bilateral), possibly reflecting the role of this area in speech perception and phonological processing.
[show abstract][hide abstract] ABSTRACT: Identifying drop metastases to the spine from pediatric brain tumors is crucial to treatment and prognosis. MRI is currently the gold standard for identifying drop metastases, more sensitive than CSF cytology, but imaging is not uncommonly inconclusive. Although diffusion-weighted imaging (DWI) of the brain is very useful in the evaluation of hypercellular tumors, DWI of the spine has not been clinically useful in children because of susceptibility artifacts and lack of spatial resolution. A new technique, readout-segmented echo planar imaging (EPI), has improved these images, allowing for identification of hypercellular drop metastases. We report a case that illustrates the utility of spine DWI in the detection of metastatic disease in children with primary central nervous system (CNS) tumors. This case suggests that DWI of the spine with readout-segmented EPI should be included in the evaluation for drop metastases.
[show abstract][hide abstract] ABSTRACT: Kidney disease represents a leading cause of morbidity, with high healthcare costs. The existing methods used to evaluate renal function include measures of glomerular filtration rate (GFR), yet the clinical methods are generally inaccurate and poorly reproducible. A method that improves measures of renal function as part of a comprehensive examination that also evaluates renal structure represents an important unmet clinical need. Use of dynamic contrast-enhanced magnetic resonance imaging (MRI) for the evaluation of renal function has been undergoing development by several groups. The methodology has been referred to as MR Urography (MRU) or MR Nephro-urography (MRNU). MRU/MRNU shows promise for providing new insights into the evaluation of renal structure and function in relation to important disease processes, including urinary obstruction and in relation to renal transplantation. MRU/MRNU generally requires consideration of imaging acquisition technique, image postprocessing strategies, and subsequent kinetic mathematical modeling of the data in reference to specific physiological renal processes, such as renal blood flow and GFR. Here we review the specifics of proposed methods in light of the overall strengths and limitations of each of these strategies. The overall objective is to provide a roadmap for future developments in this evolving field of novel MRI applications.
Journal of Magnetic Resonance Imaging 06/2011; 33(6):1270-83. · 2.57 Impact Factor
[show abstract][hide abstract] ABSTRACT: We report a case of bilateral congenital midureteric strictures diagnosed using MR urography. The severity of obstruction differed in the two ureters, resulting in a multicystic dysplastic kidney (MCDK) with an atretic ureter on one side and hydronephrosis that worsened over time due to progressive stenosis on the other. Although midureteric strictures are usually misdiagnosed as ureteropelvic junction (UPJ) or ureterovesical junction (UVJ) obstruction on conventional imaging, MR urography was able to clearly demonstrate both the anatomical and functional abnormalities. Additionally, because of the excellent anatomical resolution, similarities in the underlying pathological lesions could be contrasted with the severity of the pathophysiological impact upon each kidney.
[show abstract][hide abstract] ABSTRACT: Magnetic resonance imaging (MRI) has been well described as a modality for evaluation of a failed anorectal pull-through procedure for imperforate anus. To the authors' knowledge, intraoperative MRI has not been previously used to guide a laparoscopic-assisted anorectoplasty (LAARP). We propose that such a procedure would assure anatomically correct placement of the pulled-through rectum.
Three male patients with imperforate anus and a prostatic urethral fistula underwent an MRI-guided LAARP in an operative MRI suite. The patients' ages ranged from 5 to 6 months at the time of their pull-through procedure. Preoperative MRIs with mineral oil within the distal colostomy were performed on all patients to document the anatomy of the rectourethral fistula and its relationship to the parasagittal and vertical muscle complex. The perineum was pierced with an MRI compatible needle at the central portion of the parasagittal muscle complex as determined by a direct muscle stimulator. Further incremental advancement of the needle within the muscle complex was guided by serial MRIs in axial, coronal, and sagittal planes until the levator floor was penetrated, and the peritoneal cavity was entered. LAARP was then completed.
Completion MRI demonstrated placement of the pulled-through segment in a central location through the length of the muscle complex. Serial MRIs performed intraoperatively during advancement of the localization needle demonstrated a curved path of the vertical fibers. Attempts to nonincrementally advance the needle in a straight plane resulted in a breach of the vertical muscle complex or eccentric placement of the needle.
Magnetic resonance imaging-guided LAARP results in anatomically correct placement of the rectum within the vertical muscle complex. Straight needle advancement techniques in LAARP could result in a deviation of the pulled-through rectum from the central muscular path. Further follow-up will be required to demonstrate functional advantage.
Journal of Pediatric Surgery 01/2010; 45(1):220-3. · 1.38 Impact Factor
[show abstract][hide abstract] ABSTRACT: MR urography has the potential to revolutionize imaging of the urinary tract in both adults and children, because of its ability to provide an unprecedented level of anatomic information and quantitative functional evaluation of each kidney. MR urography can now provide useful assessment of obstructive uropathy and may provide predictive information about which children will benefit from surgery. It has the potential to identify parameters that indicate a significant obstruction as opposed to self-limited hydronephrosis. Further technical developments in the field will produce greater insights into the pathophysiology of not only urologic disorders but also disorders of the kidney itself.
Magnetic Resonance Imaging Clinics of North America 12/2008; 16(4):643-60, viii-ix. · 1.34 Impact Factor
[show abstract][hide abstract] ABSTRACT: Sickle cell disease (SCD) is a chronic disease with a significant rate of neurological complications in the first decade of life. In this retrospective study, cortical thickness was examined in children with SCD who had no detectable abnormalities on conventional magnetic resonance imaging/magnetic resonance angiography. Regional differences in cortical thickness from SCD were explored using age-matched healthy controls as comparison. A comparison analysis was done for SCD (n = 28) and controls (n = 29) based on age (5-11; 12-21 years), due to the age-dependent variation in cortex maturation. Distinct regions of thinning were found in SCD patients in both age groups. The number, spatial extent, and significance (P < 0.001) of these areas of thinning were increased in the older SCD group. Regions of interest (ROIs) were defined on the areas of highly significant thinning in the older group and then mapped onto the younger cohort; a multiparametric linear regression analysis of the ROI data demonstrated significant (P < 0.001) cortical thinning in SCD subjects, with the largest regions of thinning in the precuneus and the posterior cingulate. The regionally specific differences suggest that cortical thickness may serve as a marker for silent insults in SCD and hence may be a useful tool for identifying SCD patients at risk for neurological sequelae.
[show abstract][hide abstract] ABSTRACT: Magnetic resonance (MR) urography is a powerful tool that fuses anatomic information with functional data in a single test without the use of ionizing radiation. This article provides an overview of the technical aspects of MR urography and common clinical applications, such as the evaluation of hydronephrosis, reflux nephropathy, and renal dysplasia.
Magnetic Resonance Imaging Clinics of North America 09/2008; 16(3):515-31, vi. · 1.34 Impact Factor
[show abstract][hide abstract] ABSTRACT: The study design was HIPAA-compliant and approved by the Institutional Review Board, with all participants providing signed informed consent prior to the study. The purpose of this study was to prospectively evaluate the feasibility of determining renal blood flow (RBF) by using a technique based on intravenous administration of gadolinium chelate and evaluation of first-pass gadolinium chelate perfusion by using highly accelerated three-dimensional (3D) gradient-echo magnetic resonance (MR) imaging of the kidney in freely breathing subjects. Flow is determined with Kety-Schmidt formalism by modeling the uptake of gadolinium chelate in the kidney prior to its leaving through the venous system. Validation of the gadolinium chelate perfusion technique is based on comparison of values determined for participants with phase-contrast gradient-echo imaging. The model fit to the measured data is excellent over the first 7-8 seconds of gadolinium chelate uptake and diverges after its appearance in the renal vein. The perfusion data analysis technique showed less than 10% interobserver variation. The average difference between phase-contrast and gadolinium chelate perfusion measurements was 0.08 mL/sec (95% confidence interval: -3.73, 3.58) for left and right kidneys. This study demonstrates feasibility of the gadolinium chelate perfusion method for RBF measurement and discusses potential applications. Supplemental material: http://radiology.rsnajnls.org/cgi/content/full/246/1/241/DC1.
[show abstract][hide abstract] ABSTRACT: MR urography has the potential to significantly improve our understanding of the relationship between reflux nephropathy, pyelonephritis, vesicoureteric reflux and renal dysplasia. MR urography utilizes multiple parameters to assess both renal anatomy and function and provides a more complete characterization of acquired and congenital disease. Pyelonephritis and renal scarring can be distinguished by assessing the parenchymal contours and signal intensity. Characteristic imaging features of renal dysplasia include small size, subcortical cysts, disorganized architecture, decreased and patchy contrast enhancement as well as a dysmorphic pelvicalyceal system. Because of its ability to subdivide and categorize this heterogeneous group of disorders, it seems inevitable that MR urography will replace DMSA renal scintigraphy as the gold standard for assessment of pyelonephritis and renal scarring. MR urography will contribute to our understanding of renal dysplasia and its relationship to reflux nephropathy.
[show abstract][hide abstract] ABSTRACT: Hydronephrosis and the evaluation of obstructive uropathy are the most common indications for MR urography in our practice. Typically our patients fall into one of two groups: infants with antenatal hydronephrosis and older children who present with abdominal pain, hematuria or urinary tract infection. Obstruction in children is usually chronic and partial. Intermittent episodes of increased pressure occur when the urine production exceeds the capacity for drainage. MR urography uses a fluid and diuretic challenge to assess the hydronephrotic kidney. High-quality anatomic images provide a morphologic assessment of the hydronephrotic system. Although it is relatively straightforward to determine if a system is not obstructed on the basis of the renal transit time (RTT), no single parameter is adequate to fully characterize obstruction. By evaluating the changes in signal intensity in the renal parenchyma following contrast administration, the hydronephrotic systems are classified as compensated or decompensated. Delayed RTT and the presence of urine-contrast levels indicate stasis. Calyceal transit time and the difference between the volumetric and the Patlak differential renal function (vDRF-pDRF) are measures of the physiologic changes within the kidney. Additionally, MR urography provides prognostic information by assessing the quality of the renal parenchyma and identifying uropathy preoperatively. MR urography combines both anatomic and functional information in a single test and is capable of providing a comprehensive evaluation of obstructive uropathy that could ultimately help select those patients most likely to benefit from surgical intervention.
[show abstract][hide abstract] ABSTRACT: Dynamic magnetic resonance urography (MRU) scans acquired in conjunction with an injection of a contrast agent can be used to estimate a number of parameters that reflect renal function. This article discusses the methodologies and assumptions used in the estimation of these parameters, with special attention to the problem of deriving the concentration of the contrast agent from the change in the MR signal. The estimates of split renal function derived from MRU are in good agreement with those obtained using nuclear medicine studies. The time-intensity curves show subtle differences from those measured using nuclear medicine but still allow the transit of the contrast agent through the kidney to be assessed. Quantitative estimates of renal function (GFR) can be derived from MRU but have yet to be validated in a pediatric population.
[show abstract][hide abstract] ABSTRACT: This article builds on the previous article in this symposium and shows how MR urography contributes to the postoperative evaluation of children with UPJ obstruction. By analyzing the postoperative results, we derived new insights into their preoperative evaluation. With MR urography we combine simultaneous physiological and anatomic evaluation that enables us to identify changes in renal pathophysiology that occur in association with impaired drainage and obstruction. We studied 35 children before and after pyeloplasty. The pyeloplasty was considered successful in 30 and unsuccessful in 5. Both anatomic and functional criteria were used. The anatomic parameters included the degree of hydronephrosis, the appearance of the renal parenchyma, the quality of the nephrogram and the presence of crossing vessels. The functional criteria included the renal transit time, the calyceal transit time, the volumetric differential function, the Patlak differential function, the difference between the volumetric and Patlak differential function and the Patlak number per milliliter of renal tissue. No single parameter was sufficient to fully characterize UPJ obstruction, but by synthesizing all the information we were able to subdivide UPJ obstruction into compensated, decompensated and uropathic kidneys. Decompensated systems had the most significant improvement following successful pyeloplasty. Compensated systems showed little improvement in renal function, and uropathic kidneys were associated with a poor prognosis. It is clear that not all UPJ obstructions are the same, and it seems logical that treatment should be individually tailored rather than using a standard approach for all cases. Because MR urography can identify pathophysiological differences in children with UPJ obstruction that are occult to renal scintigraphy, it has an important potential role in identifying those who will benefit most from pyeloplasty and those who are probably best observed.
[show abstract][hide abstract] ABSTRACT: In this article we introduce the topic of MR urography in children, focusing on the details required to obtain consistently high-quality scans. Much of the information presented is based on our experience during the last 7 years. We have performed almost 1,000 MR urograms in children, and the technique has evolved considerably during this time. We have learned through trial and error and have improved our protocols to the point that our approach is now standardized and reliably generates high-quality studies. From this standardized protocol, further refinements in technique can be readily implemented. It is important to remember that this clinical application is in its infancy and will improve significantly with further technical development. This paper provides an overview of the practical issues associated with obtaining high-quality scans as well as an introduction into the interpretation of MR urograms.
[show abstract][hide abstract] ABSTRACT: MR urography represents the next step in the evolution of uroradiology in children by combining superb anatomic imaging with quantitative functional evaluation in a single examination that does not use ionizing radiation. MR imaging has inherently greater soft-tissue contrast than other imaging techniques. When used in conjunction with dynamic scanning after administration of a contrast agent, it provides non-invasive analysis of the perfusion, concentration and excretion of each kidney. The purpose of this review is to outline our experience with more than 500 MR urograms in children. We outline our technique in detail, showing how we calculate differential renal function and how we assess concentration and excretion in the different regions of the kidney. We show that the dynamic contrast-enhanced data can be processed to yield quantitative measures of individual kidney GFR. In the clinical section we show how MR urography adds unique aspects to the anatomic evaluation of the urinary tract, and by combining the anatomic information with functional information, how we assess hydronephrosis and obstructive uropathy, congenital malformations, pyelonephritis and renal scarring.
[show abstract][hide abstract] ABSTRACT: We report the role of magnetic resonance urography in children with ureteropelvic junction obstruction. Differential renal function, the single kidney glomerular filtration rate index, renal transit time, renal length and renal pelvis anteroposterior diameter were compared before and after pyeloplasty.
Magnetic resonance urography was performed before and after pyeloplasty in 24 patients with a mean age of 1.9 years (range 3 months to 10 years). Renal length, renal transit time and renal pelvis anteroposterior diameter were determined by the radiologist. The volume of functioning renal tissue and descending aorta were segmented and the ratio of the volumes of functioning kidney tissue was used to calculate differential renal function. Rutland-Patlak plots were used to calculate single kidney glomerular filtration rate index, that is the Patlak score.
Mean renal pelvis renal pelvis anteroposterior diameter was 3.3 cm preoperatively and 2.5 cm postoperatively (p = 0.0003). There was no difference in average renal length (p = 0.22). Of the 24 cases 22 (92%) showed stable or improved differential renal function. Improvement in renal transit time was seen in 20 of 23 cases (87%). Of 15 patients with complete Patlak scores 14 (93%) showed postoperative improvement. Mean preoperative and postoperative differential renal function, renal transit time and Patlak score were 36% and 41% (p = 0.003), 16.2 and 8.6 minutes (p = 0.0005), and 6.6 and 11.9 ml per minute (p = 0.01), respectively.
Magnetic resonance urography provides superior anatomical and unprecedented functional information to fully define the preoperatively and postoperative status of corrected ureteropelvic junction obstruction. Magnetic resonance urography has the potential to become the imaging study of choice for evaluating pediatric hydronephrosis and obstructive uropathy.
The Journal of Urology 11/2006; 176(4 Pt 2):1755-61. · 3.70 Impact Factor
[show abstract][hide abstract] ABSTRACT: We present our experience with dynamic contrast enhanced magnetic resonance urography for evaluation and treatment in infants born with prenatally recognized hydronephrosis. We determined the characteristics of renal dysgenesis in this population.
We reviewed magnetic resonance urography images done within the first 6 months of life in 67 infants born with prenatally recognized hydronephrosis. High resolution imaging was used to establish a morphological diagnosis. Functional evaluation was used to assess obstruction and individual renal function. Voiding cystourethrography was performed in 62 patients.
Our study included 67 infants (87 renal units). There were 54 boys and 13 girls with a mean age of 2.8 months (range 0.9 to 4.6). Of these 87 renal units 30 (35%) had ureteropelvic junction obstruction, 18 (21%) had primary megaureters, 10 (11%) had nondilating vesicoureteral reflux, 10 (11%) had fetal folds, 8 (9%) had posterior urethral valves, 6 (7%) had ectopic ureters, 4 (5%) had multicystic dysplastic kidneys and 1 (1%) had a normal study. Magnetic resonance urography revealed renal dysgenesis in 24 renal units (28%), consisting of loss of corticomedullary differentiation, renal cystic changes distinct from multicystic dysplastic kidneys, solid renal dysplasia, hypoplasia and dysmorphic calyces.
Magnetic resonance urography is an excellent addition to our armamentarium for evaluating neonatal hydronephrosis and renal dysgenesis. Due to its comprehensiveness magnetic resonance urography has the potential to become the study of choice for evaluating infants with significant prenatally recognized hydronephrosis. However, further prospective, comparative studies in larger patient populations are needed to justify the cost and the need for sedation in infants.
The Journal of Urology 11/2006; 176(4 Pt 2):1786-92. · 3.70 Impact Factor
[show abstract][hide abstract] ABSTRACT: The purpose of our study was to retrospectively review our experience using MR urography in the diagnosis of ureteropelvic junction (UPJ) obstruction in children.
Sixty-one studies were performed in 50 children with hydronephrosis but without hydroureter. Anatomic criteria assessed included degree of hydronephrosis, morphology of the renal pelvis, atrophy of medulla, swirling contrast material, fluid levels, and the presence of fetal folds and crossing vessels. Functional criteria included renal transit time, differential renal function, and time-intensity curves when available.
Thirty-one kidneys were classified as obstructed, 15 as equivocal, and 15 as nonobstructed. Obstructed systems had more marked hydronephrosis, more extensive medullary atrophy, more fluid levels, and more swirling contrast material. Fetal folds were seen in only the equivocal and nonobstructed groups. Crossing vessels were seen in all groups. Obstructed systems also showed greater functional derangement, decreased split renal function, and abnormal time-intensity curves.
MR urography provides both excellent anatomic and functional information in children with UPJ obstruction in a single test that does not use ionizing radiation. MR urography may lead to greater understanding of the pathophysiology of UPJ obstruction.
American Journal of Roentgenology 01/2006; 185(6):1608-14. · 2.90 Impact Factor
[show abstract][hide abstract] ABSTRACT: The purpose of our study was to derive time-intensity curves for the renal cortex and medulla from 3D dynamic MR urography and to assess whether these curves are predictive of obstruction.
Fifty-nine examinations were performed in 53 pediatric patients and the degree of obstruction assessed using the renal transit time. The cortex and medulla were segmented using a semiautomatic method, and mean time-intensity curves were derived for the segmented volumes. The basic parameters of the curves (amplitude, washout) were assessed, as was the presence of certain characteristic features of the curves.
The images allowed clear visualization of three phases of the uptake of contrast material in the cortex, the medulla, and the collecting system. Both the amplitude of the curves and the washout of the contrast material were predictive of obstruction. The distal tubular peak was reliably detected in the cortex of nonobstructed kidneys.
Combining signal-intensity-versus-time-curve analysis with the other parameters that can be derived from the same MR urography data set provides a powerful tool for the diagnosis of obstruction.
American Journal of Roentgenology 01/2006; 185(6):1598-607. · 2.90 Impact Factor
[show abstract][hide abstract] ABSTRACT: To prospectively evaluate use of dynamic contrast material-enhanced magnetic resonance (MR) urography for measurement of renal transit time (RTT) of a contrast agent through the kidney and collecting system so as to identify obstructive uropathy in children.
One hundred twenty-six children suspected of having hydronephrosis were hydrated prior to undergoing both conventional and dynamic contrast-enhanced MR urography of the kidneys and urinary tract. A three-dimensional sequence was used to track passage of contrast agent through the kidneys. Time between the appearance of contrast material in the kidney and its appearance in the ureter at or below the level of the lower pole of the kidney was defined as RTT. Bland-Altman plots were used to quantify intra- and interobserver performance. In 30 children, a nuclear medicine renogram was also obtained, and the half-life of renal signal decay after furosemide administration was derived and compared with the MR imaging RTT by using receiver operating characteristic curves.
On the basis of RTT, kidneys were classified as normal (RTT </= 245 seconds), equivocal (245 seconds > RTT </= 490 seconds), or obstructed (RTT > 490 seconds). Inter- and intraobserver agreement indicated that the technique is both robust and reproducible. Receiver operating characteristic analysis for comparison of results of MR imaging and diuretic renal scintigraphy showed good agreement between the modalities, with a mean area under the curve of 0.90.
When used in conjunction with morphologic images obtained in the same examination, RTT generally allowed normal kidneys to be differentiated from obstructed and partially obstructed kidneys.