Contrast-enhanced dynamic MR nephrography using the TurboFLASH navigator-gating technique in children

Contrast-enhanced MRI for simultaneous evaluation of renal morphology and split renal function in living kidney donor candidates

PURPOSE

The evaluation process of potential living kidney donors focusses on renal anatomy and split renal function. This study aimed to evaluate a magnetic resonance imaging (MRI)-based approach for simultaneous evaluation of both and its impact on clinical decision making.

METHOD

Over a 3-year period, 65 potential living kidney donors were consecutively enrolled. The MRI protocol was extended by MR-nephrography to measure split renal function. Standard DTPA-scintigraphy was used for functional comparison.

RESULTS

Split renal function showed no systematic bias between the two methods (mean difference 0.3%, p = 0.08). Both methods would have yielded the same clinical decision for donor nephrectomy in 75% of the patients. In 25 % of the patients, one method indicated a relevant side difference while the other did not, and a different clinical decision could have been made based on split renal function alone.

CONCLUSIONS

MRI proved eligible for comprehensive living kidney donor evaluation and non-inferior to scintigraphy for determining split renal function. In clinical decision making, these two methods would have resulted in the same side for donor nephrectomy in a large proportion of potential donors. Whether MRN will be implemented in clinical practice depends on transplant centre infrastructure and policy.

Evaluation of a free-breathing respiratory-triggered (Navigator) 3-D T1-weighted (T1W) gradient recalled echo sequence (LAVA) for detection of enhancement in cystic and solid renal masses

OBJECTIVES

To evaluate free-breathing Navigator-triggered 3-D T1-weighted MRI (NAV-LAVA) compared to breath-hold (BH)-LAVA among cystic and solid renal masses.

MATERIALS AND METHODS

With an IRB waiver, 44 patients with 105 renal masses (71 non-enhancing cysts and 14 cystic and 20 solid renal masses) underwent MRI between 2016 and 2017 where BH-LAVA and NAV-LAVA were performed. Subtraction images were generated for BH-LAVA and NAV-LAVA using pre- and 3-min post-gadolinium-enhanced images and were evaluated by two blinded radiologists for overall image quality, image sharpness, motion artifact, and quality of subtraction (using 5-point Likert scales) and presence/absence of enhancement. Percentage signal intensity change (Δ%SI) = ([SI.post-gadolinium-SI.pre-gadolinium]/SI.pre-gadolinium)*100, was measured on BH-LAVA and NAV-LAVA. Likert scores were compared using Wilcoxon's sign-rank test and accuracy for detection of enhancement compared using receiver operator characteristic (ROC) analysis.

RESULTS

Overall image quality (p = 0.002-0.141), image sharpness (p = 0.002-0.031), and motion artifact were better (p = 0.002) comparing BH-LAVA to NAV-LAVA for both radiologists; however, quality of image subtraction did not differ between groups (p = 0.09-0.14). Sensitivity/specificity/area under ROC curve for enhancement in cystic and solid renal masses using subtraction and %SIΔ were (1) BH-LAVA: 64.7%/98.6%/0.82 (radiologist 1), 61.8%/95.8%/0.79 (radiologist 2), and 70.6%/81.7%/0.76 (%SIΔ) versus 2) NAV-LAVA: 58.8%/95.8%/0.79 (radiologist 1, p = 0.16), 58.8%/88.7%/0.73 (radiologist 2, p = 0.37), and 73.5%/76.1%/0.75 (%SIΔ, p = 0.74).

CONCLUSIONS

NAV-LAVA showed similar quality of subtraction and ability to detect enhancement compared to BH-LAVA in renal masses albeit with lower image quality, image sharpness, and increased motion artifact. NAV-LAVA may be considered in renal MRI for patients where BH is suboptimal.

KEY POINTS

• Free-breathing Navigator (NAV) 3-D subtraction MRI is comparable to breath-hold (BH) images. • Accuracy for subjective and quantitative diagnosis of enhancement in renal masses on NAV 3-D T1W is comparable to BH MRI. • NAV 3-D T1W renal MRI is useful in patients who may not be able to adequately BH.

Fusion and subtraction post-processing in body MRI

Interpreting complex paediatric body MRI studies requires the integration of information from multiple sequences. Image processing software, some freely available, allows the radiologist to use simple and rapid post-processing techniques that may aid diagnosis. We demonstrate the use of fusion and subtraction post-processing techniques with examples from four areas of application: enterography, oncological imaging, musculoskeletal imaging and MR fistulography.

Dynamic MR urography in children with uropathic disease with a combined 2D and 3D acquisition protocol--comparison with MAG3 scintigraphy

OBJECTIVE

The aim of this study was to evaluate combined two-dimensional (2D) and three-dimensional (3D) dynamic MR urography with respiratory compensation in children with anomalies of the genitourinary tract, allowing for computation of split renal function and assessment of urinary tract obstruction.

METHODS

Dynamic MR urography was performed in 53 children (3 months-16 years of age) with anomalies of the urinary tract. A protocol for dynamic MR urography and nephrography was implemented at 1.5 T using a navigator-triggered 2D TurboFLASH sequence. Split renal function and contrast-medium excretion were assessed after the bolus injection of 0.05 mmol kg(-1) body weight of gadolinium dimeglumine. In the excretory phase, a 3D gradient-echo data set with high spatial resolution was acquired. In all patients, mercaptoacetyltriglycine (MAG3) scintigraphy was obtained as a reference standard.

RESULTS

In all children, dynamic MR nephrography and urography could be performed with excellent compensation of breathing artefacts providing region of interest analysis in nearly identical kidney positions. The assessment of contrast-medium excretion into the ureter allowed for discrimination of functional from non-functional stenosis. Split renal function assessed by MRI showed an excellent agreement with the MAG3 reference standard with a correlation coefficient r = 0.95. Additionally recorded 3D data sets offered good depiction of anatomical anomalies in all patients.

CONCLUSION

The proposed protocol provides a robust technique for assessment of ureteral obstruction and split renal function with compensation of breathing artefacts, short post-processing time and excellent 3D spatial resolution.

ADVANCES IN KNOWLEDGE

The combined protocol of 2D and 3D MR urography is an efficient technique for assessment of renal morphology and function.

Comparison of magnetic resonance imaging with radionuclide methods of evaluating the kidney

Nuclear medicine and MRI provide information about renal perfusion, function (glomerular filtration rate), and drainage. Some tracers that are used in nuclear medicine (technetium-diethylene triamine pentaacetic acid ([(99m)Tc-DTPA] and (51)chromium-EDTA) and some contrast media (CM) that are used for MRI (gadolinium-DTPA for instance) share the same pharmacokinetic properties, though, detection techniques are different (low-spatial resolution 2-dimensional projection with a good concentration-to-signal linearity for nuclear medicine and high-resolution 3-dimensional localization with nonlinear behavior for MRI). Thus, though based on the same principles, the methods are not the same and they provide somewhat different information. Many MRI perfusion studies have been conducted; some of them were compared with nuclear medicine with no good agreement. Phase contrast can reliably assess global renal blood flow but not perfusion at a tissular level. Arterial spin labeling has not proven to be a reliable tool to measure renal perfusion. Techniques using CM theoretically can assess perfusion at the tissular level, but they have not proven to be precise. To assess renal function, many models have been proposed. Some MRI techniques using CM, both semiquantitative (Patlak) and quantitative, have shown ability to roughly assess relative function. Some quantitative methods (Annet's and Lee's methods) have even showed that they could roughly estimate absolute renal function, with better results than estimated glomerular filtration rate. Quantification of drainage has not been much studied using MRI.

Single-stage surgical approach in complicated paediatric ureteral duplication: surgical and functional outcome

PURPOSE

Surgical approach to children with complicated ureteral duplication is discussed controversially. Our aim was to determine the outcome of children with complicated renal duplication undergoing a single-stage surgical approach with laparoscopic partial nephrectomy and open bladder reconstruction.

METHODS

Data of patients from 2004 to 2008 were investigated retrospectively. Outcome was analyzed in terms of postoperative course, renal function, urinary tract infection and functional voiding.

RESULTS

Thirteen patients were treated with laparoscopic partial nephrectomy and reconstruction of the lower urinary tract in a single-stage approach. Median age at operation was 15 months (2-63 m). One girl had a renal triplication. 7/13 patients presented with an ectopic ureterocele, two with an ectopic ureter, severe vesicoureteral reflux occurred in 6 patients. All patients had non-functioning renal moieties. Mean operative time was 239 min (129-309; SD 50). One re-operation was necessary 4 years after primary surgery due to a pole remnant. All patients had uneventful recoveries without evidence of recurrent UTI. Postoperative 99mTc-MAG3 scans showed no significant reduction of partial renal function (p = 0.4), and no signs of obstruction (p = 0.188). During a median follow-up of 60 months (49-86), dysfunctional voiding occurred in one patient.

CONCLUSIONS

In children with complicated ureteral duplication a definitive single-stage procedure is feasible and shows excellent functional results.

Magnetic resonance and computed tomography in pediatric urology: an imaging overview for current and future daily practice

The main imaging modality of the urinary tract in children is ultrasound. When further cross-sectional morphologic examination and/or functional evaluation is required, magnetic resonance (MR) imaging is the logical and optimal second step, particularly in pediatric patients. There are two main exceptions to this. The first one is when after an ultrasound, additional diagnostic imaging for urolithiasis is needed. The second one involves severe polytrauma, including blunt abdominal trauma. In this review, an overview of the MR imaging and computed tomography examinations important for current and future daily pediatric uroradiologic practice is presented.

Diffusion-weighted MRI in the assessment of split renal function: comparison of navigator-triggered prospective acquisition correction and breath-hold acquisition

OBJECTIVE

The purpose of this study was to ascertain whether prospective acquisition correction (PACE) diffusion-weighted MRI (DWI) is superior to conventional breath-hold DWI in assessment of split renal function.

SUBJECTS AND METHODS

Fifty-four subjects underwent coronal breath-hold DWI and PACE DWI with the b value set at 0 and 800 s/mm(2). Isotope renographic glomerular filtration rate (GFR) was used as the reference standard for assessing split renal function. A GFR of 40 mL/min or greater indicated normal and a GFR less than 40 mL/min indicated reduced split renal function. Reduced split renal function was further divided into a mild reduction group (GFR ≥ 20 mL/min) and a moderate-to-severe reduction group (GFR < 20 mL/min). Various comparisons between the imaging methods were conducted.

RESULTS

The signal-to-noise and contrast-to-noise ratios of the PACE DW images were greater than those of the breath-hold DW images (p < 0.001). The correlation between the apparent diffusion coefficient (ADC) value and GFR was stronger when the ADC was measured with PACE DWI than with breath-hold DWI (p = 0.033). Area under the receiver operator curve (AUC) analysis revealed that PACE DWI (AUC, 0.790 ± 0.045; p < 0.001) but not breath-hold DWI (AUC, 0.616 ± 0.060; p = 0.053) had diagnostic value in predicting a reduction in split renal function. ADC value assessed with PACE DWI was lower in the groups with mild and moderate-to-severe reduction in split renal function than in the group with normal function (p < 0.01).

CONCLUSION

Preliminary results imply that PACE DWI is superior to breath-hold DWI in the assessment of split renal function.

MRI to assess renal structure and function

PURPOSE OF REVIEW

In addition to excellent anatomical depiction, MRI techniques have expanded to study functional aspects of renal physiology, such as renal perfusion, glomerular filtration rate (GFR) or tissue oxygenation. This review will focus on current developments with an emphasis on clinical applicability.

RECENT FINDINGS

The method of GFR determination is largely heterogeneous and still has weaknesses. However, the technique of employing liver disappearance curves has been shown to be accurate in healthy persons and patients with chronic kidney disease. In potential kidney donors, complete evaluation of kidney anatomy and function can be accomplished in a single-stop investigation. Techniques without contrast media can be utilized to measure renal tissue oxygenation (blood oxygen level-dependent MRI) or perfusion (arterial spin labeling) and could aid in the diagnosis and treatment of ischemic renal diseases, such as renal artery stenosis. Diffusion imaging techniques may provide information on spatially restricted water diffusion and tumor cellularity.

SUMMARY

Functional MRI opens new horizons in studying renal physiology and pathophysiology in vivo. Although extensively utilized in research, labor-intensive postprocessing and lack of standardization currently limit the clinical applicability of functional MRI. Further studies are necessary to evaluate the clinical value of functional magnetic resonance techniques for early discovery and characterization of kidney disease.

MR imaging of the abdomen and pelvis in infants, children, and adolescents

Recent developments in magnetic resonance (MR) imaging have profoundly changed the investigation of abdominal and pelvic disease in pediatrics. Motion reduction techniques, such periodically rotated overlapping parallel lines with enhanced reconstruction, or PROPELLER, have resulted in reliable imaging with quiet breathing. Faster imaging sequences minimize artifact and allow for more efficient studies. Diffusion-weighted imaging has become increasingly important in the evaluation of neoplastic disease, depicting disease with increased cellularity and helping to differentiate benign from malignant masses. MR enterography helps visualize intra- and extraluminal bowel pathologic conditions. MR cholangiopancreatography can depict congenital and acquired causes of pancreatic and biliary abnormalities. MR urography is an effective technique for a one-stop-shop evaluation of structural urinary tract abnormality and renal function. Three-dimensional acquisitions allow volumetric display of structures from multiple angles. Specialized techniques allow quantification of iron and fat in the viscera in children with hemolytic anemia and obesity, respectively. This article covers current techniques and strategies to perform and optimize MR imaging of the abdomen and pelvis in infants, children, and adolescents and describes important practical applications.

Pediatric uroradiology: state of the art

Recent years have witnessed major strides in imaging modalities, including US and contrast-enhanced voiding urosonography, fluoroscopy, CT and MRI, and these have significantly impacted paediatric uroradiology. The trend is towards reduced or no radiation exposure and combined morphological and functional imaging. This review presents the currently available and recommended modalities in modern paediatric uroradiology practice.

Magnetic resonance nephrography for planning of laparoscopic partial nephrectomy in a pediatric case of ureteral triplication

We present the case of ureteral triplication with vesicoureteral reflux into the lowest and middle pole in a 5-year-old girl. Magnetic resonance (MR) nephrography depicted loss of function of the lowest pole, which could not be assessed through MAG3 renal scan. Morphologic analyses revealed organ structure and vascular anatomy in superior quality. A laparoscopic partial nephroureterectomy of the lower pole was performed. Intraoperative findings correlated exactly with morphologic data obtained through MR nephrography. Dynamic MR nephrography should be considered as diagnostic tool of choice for selected kidney anomalies before surgery.

Contrast-enhanced dynamic magnetic resonance nephrography in healthy dogs

Twenty-three healthy mixed-breed male adult dogs were examined using serial magnetic resonance (MR) renograms. The images were obtained using a dynamic gradient-echo, fast SPGR, T1-weighted sequence and low doses of gadolinium chelates (0.025 mmol/kg). Time-intensity curves were obtained to assess typical urinary excretion parameters, namely, time to vascular peak (TVP), time to vascular drop (TVD), time to glomerular peak (TGP), parenchymal phase length (PPL), gradient of parenchymal phase (GPP) and pattern of excretory segment. The mean TVP, TVD, TGP and PPL were 31.6±11.8, 43.4±11.2, 154.0±36.2 and 115.2±37.7s, respectively. The GPP was 24.1±8.6% of signal intensity per min. The excretory segment was concave in all cases, and at the end of the examination, 87.1% of kidneys had shown a reduction in signal intensity of 50%. This MR nephrography protocol can provide adequate time-intensity curve parameters for the urinary system of dogs, offers excellent anatomical detail, and represents an alternative to radionuclide nephrography.

Functional analysis in MR urography - made simple

MR urography (MRU) has proved to be a most advantageous imaging modality of the urinary tract in children, providing one-stop comprehensive morphological and functional information, without the utilization of ionizing radiation. The functional analysis of the MRU scan still requires external post-processing using relatively complex software. This has proved to be a limiting factor in widespread routine implementation of MRU functional analysis and use of MRU functional parameters similar to nuclear medicine. We present software, developed in a pediatric radiology department, that not only enables comprehensive automated functional analysis, but is also very user-friendly, fast, easily operated by the average radiologist or MR technician and freely downloadable at www.chop-fmru.com . A copy of IDL Virtual Machine is required for the installation, which is obtained at no charge at www.ittvis.com . The analysis software, known as "CHOP-fMRU," has the potential to help overcome the obstacles to widespread use of functional MRU in children.

Dynamic Magnetic Resonance Nephrography

PURPOSE

In this volunteer study, 2 navigator-gated strongly T1-weighted saturation-recovery (SR) sequences, a turbo fast low angle shot (TurboFLASH) and a new true fast imaging in steady precession (TrueFISP) readout technique, were compared for suitability in dynamic magnetic resonance nephrography.

MATERIALS AND METHODS

Ten healthy volunteers (mean age 26.1 +/- 3.6) were equally divided into 2 subgroups. After bolus-injection of 3.75 mL of gadobutrol (approximately 0.05 mmol/kg body weight), slightly obliqued coronal single-slice images of the kidneys were recorded every 4-5 seconds during free breathing using 1 of the 2 sequences. Time-intensity curves were determined from manually drawn regions-of-interest over the kidney parenchyma. Both sequences were subsequently evaluated with regard to linearity of signal, signal to noise ratio (SNR), and time-dependent behavior of signal intensity curves.

RESULTS

: The TurboFLASH readout showed better linearity of the signal behavior as compared with the TrueFISP technique (TurboFLASH: no deviation from linearity down to T1 = 400 milliseconds; TrueFISP at T1 = 700 milliseconds: 12% deviation, at T1 = 400 milliseconds: 19%). The time-intensity curves of the TrueFISP sequence exhibited distinctly lower variability than the TurboFLASH approach. The SNR increased with TrueFISP by 3.4 +/- 0.5-fold for native renal parenchyma and by 3.3 +/- 0.9 for contrast-enhanced renal parenchyma. For split renal function evaluation, the linear regression to the signal increase in the first minutes after the first pass could be performed with higher reliability using the TrueFISP technique (increase of correlation coefficient by 17.1%).

CONCLUSION

A SR navigator-gated TrueFISP sequence seems most favorable for dynamic magnetic resonance nephrography due to the high signal yield and low curve variability.