MRI with diffusion-weighted imaging (DWI) and apparent diffusion coefficient (ADC) assessment in the evaluation of normal and abnormal fetal kidneys: preliminary experience

Troubleshooting Tips for Diagnosing Complex Fetal Genitourinary Malformations

Fetal genitourinary anomalies can present a diagnostic challenge for the radiologist. The absence of a normally located kidney may represent agenesis or be secondary to a fusion or migration abnormality. A dilated renal pelvis should prompt evaluation for a specific cause, including ureteropelvic junction obstruction, reflux, or an obstructed duplicated system. Cystic parenchymal changes are characteristic of a multicystic dysplastic kidney but may also be seen in obstructive cystic dysplasia. There are numerous causes of megacystis including chromosomal (trisomy 18 syndrome), obstruction (posterior urethral valves, urethral atresia), or muscular dysfunction (prune belly syndrome, megacystis microcolon intestinal hypoperistalsis syndrome). Important mimics of a large bladder include hydrocolpos and urogenital sinus or cloacal malformation. Complications of genitourinary malformations are common and include oligohydramnios, urinary ascites, and urinoma. Making an accurate diagnosis often requires additional US views beyond those obtained in the standard fetal survey and occasionally performing fetal MRI. The appropriate use of orthogonal T2-weighted sequences, in conjunction with diffusion-weighted images for evaluation of the kidneys and gradient-recalled-echo sequences for evaluation of T1-hyperintense meconium in the colon, can play an integral role in diagnosis. Accurate diagnosis of fetal genitourinary malformations is vital to direct patient counseling and pregnancy management as outcomes are highly variable. Some conditions can be surgically corrected quite simply, some require multiple complex procedures, and some are lethal. The authors offer troubleshooting tips to narrow the differential diagnosis for four observations: unilateral absent kidney, dilated renal pelvis, cystic renal parenchyma, and megacystis and its mimics. ©RSNA, 2023 Test Your Knowledge questions are available in the Online Learning Center.

A narrative review of the effects of dexamethasone on traumatic brain injury in clinical and animal studies: focusing on inflammation

Traumatic brain injury (TBI) is a type of brain injury resulting from a sudden physical force to the head. TBI can range from mild, such as a concussion, to severe, which might result in long-term complications or even death. The initial impact or primary injury to the brain is followed by neuroinflammation, excitotoxicity, and oxidative stress, which are the hallmarks of the secondary injury phase, that can further damage the brain tissue. Dexamethasone (DXM) has neuroprotective effects. It reduces neuroinflammation, a critical factor in secondary injury-associated neuronal damage. DXM can also suppress the microglia activation and infiltrated macrophages, which are responsible for producing pro-inflammatory cytokines that contribute to neuroinflammation. Considering the outcomes of this research, some of the effects of DXM on TBI include: (1) DXM-loaded hydrogels reduce apoptosis, neuroinflammation, and lesion volume and improves neuronal cell survival and motor performance, (2) DXM treatment elevates the levels of Ndufs2, Gria3, MAOB, and Ndufv2 in the hippocampus following TBI, (3) DXM decreases the quantity of circulating endothelial progenitor cells, (4) DXM reduces the expression of IL1, (5) DXM suppresses the infiltration of RhoA + cells into primary lesions of TBI and (6) DXM treatment led to an increase in fractional anisotropy values and a decrease in apparent diffusion coefficient values, indicating improved white matter integrity. According to the study, the findings show that DXM treatment has neuroprotective effects in TBI. This indicates that DXM is a promising therapeutic approach to treating TBI.

Signal intensity patterns in health and disease: basics of abdominal magnetic resonance imaging in children

Magnetic resonance imaging (MRI) is playing an increasing role in pediatric abdominal imaging, especially in the evaluation of diffuse parenchymal disease where other imaging modalities might be less sensitive. While quantitative imaging is slowly being incorporated into clinical imaging, qualitative assessment of visceral signal intensity should be part of the routine clinical workflow of all radiologists. Based on their T1 and T2 weighting, the liver, spleen, kidneys and pancreas have characteristic signal intensity patterns with respect to one another and to skeletal muscle. It is important to recognize normal signal intensity patterns of viscera and their evolution with patient age to be able to identify age-related variations and accurately identify diffuse parenchymal disease. Knowledge of normal signal intensity patterns can also help identify ectopic locations of normal tissue such as splenic rests and splenosis. In this review, we discuss normal signal intensity patterns of upper abdominal viscera and their variations on commonly used sequences in pediatric abdominal MRI. We also review normal variations in the perinatal period. Knowledge of these patterns can help pediatric radiologists become more astute in their interpretation of diffuse parenchymal disease in the abdomen.

Robust arterial spin labeling MRI measurement of pharmacologically induced perfusion change in rat kidneys

Kidney diseases such as acute kidney injury, diabetic nephropathy and chronic kidney disease (CKD) are related to dysfunctions of the microvasculature in the kidney causing a decrease in renal blood perfusion (RBP). Pharmacological intervention to improve the function of the microvasculature is a viable strategy for the potential treatment of these diseases. The measurement of RBP is a reliable biomarker to evaluate the efficacy of pharmacological agents' actions on the microvasculature, and measurement of RBP responses to different pharmacological agents can also help elucidate the mechanism of hemodynamic regulation in the kidney. Magnetic resonance imaging (MRI) with flow-sensitive alternating inversion recovery (FAIR) arterial spin labeling (ASL) has been used to measure RBP in humans and animals. However, artifacts caused by respiratory and peristaltic motions limit the potential of FAIR ASL in drug discovery and kidney research. In this study, the combined anesthesia protocol of inactin with a low dose of isoflurane was used to fully suppress peristalsis in rats, which were ventilated with an MRI-synchronized ventilator. FAIR ASL data were acquired in eight axial slices using a single-shot, gradient-echo, echo-planar imaging (EPI) sequence. The artifacts in the FAIR ASL RBP measurement due to respiratory and peristaltic motions were substantially eliminated. The RBP responses to fenoldopam and L-NAME were measured, and the increase and decrease in RBP caused by fenoldopam and L-NAME, respectively, were robustly observed. To further validate FAIR ASL, the renal blood flow (RBF) responses to the same agents were measured by an invasive perivascular flow probe method. The pharmacological agent-induced responses in RBP and RBF are similar. This indicates that FAIR ASL has the sensitivity to measure pharmacologically induced changes in RBP. FAIR ASL with multislice EPI can be a valuable tool for supporting drug discovery, and for elucidating the mechanism of hemodynamic regulation in kidneys.

Fetal MRI for dummies: what the fetal medicine specialist should know about acquisitions and sequences

Fetal MRI is an increasingly used tool in the field of prenatal diagnosis. While US remains the first line screening tool, as an adjuvant imaging tool, MRI has been proven to increase diagnostic accuracy and change patient counseling. Further, there are instances when US may not be sufficient for diagnosis. As a multidisciplinary field, it is important that every person involved in the referral, diagnosis, counseling and treatment of the patients is familiar with the basic principles, indications and findings of fetal MRI. The purpose of the current paper is to equip radiologists and non-radiologists with basic MRI principles and essential topics in patient preparation and provide illustrative examples of when fetal MRI may be used. This aims to aid the referring clinician in better selecting and improve patient counseling prior to arrival in the radiology department and, ultimately, patient care.

The use of fetal MRI for renal and urogenital tract anomalies

Fetal anomalies are detected in approximately 2% of all fetuses and, among these, genitourinary tract abnormalities account for 30% to 50% of all structural anomalies present at birth. Although ultrasound remains the first line diagnostic modality, fetal MRI provides important additional structural and functional information, especially with the development of faster sequences and the use of functional sequences. The added value of MRI-based imaging is three-fold: (a) improvement of diagnostic accuracy by adequate morphological examination, (b) detection of additional anomalies, and (c) in addition, MRI has the potential to provide information regarding renal function. In this review, we describe the role of fetal MRI in the anatomical evaluation of renal and urogenital tract anomalies, and we also touch upon the contribution of functional MRI to the diagnostic workup of these conditions.

Apparent Diffusion Coefficient of the Placenta and Fetal Organs in Intrauterine Growth Restriction

PURPOSE

This study aimed to assess apparent diffusion coefficient (ADC) of the placenta and fetal organs in intrauterine growth restriction (IUGR).

MATERIALS AND METHODS

A prospective study of 30 consecutive pregnant women (aged 21-38 years with mean age of 31.5 years and a mean gestational week of 35 ± 2.3) with IUGR and 15 age-matched pregnant women was conducted. All patients and controls underwent diffusion-weighted magnetic resonance imaging. The ADCs of the placenta and fetal brain, kidney, and lung were calculated and correlated with neonates needing intensive care unit (ICU) admission.

RESULTS

There was a significant difference in ADC of the placenta and fetal brain, lung, and kidney (P = 0.001, 0.001, 0.04, and 0.04, respectively) between the patients and the controls. The cutoff ADCs of the placenta and fetal brain, lung, and kidney used to detect IUGR were 1.45, 1.15, 1.80, and 1.40 × 10 mm/s, respectively, with areas under the curve (AUCs) of 0.865, 0.858, 0.812, and 0.650, respectively, and accuracy values of 75%, 72.5%, 72.5%, and 70%, respectively. Combined ADC of the placenta and fetal organs used to detect IUGR revealed an AUC of 1.00 and an accuracy of 100%. There was a significant difference in ADC of the placenta and fetal brain, lung, and kidney between neonates needing admission and those not needing ICU admission (P = 0.001, 0.001, 0.002, and 0.002, respectively). The cutoff ADCs of the placenta and fetal brain, lung, and kidney used to define neonates needing ICU were 1.35, 1.25, 1.95, and 1.15 × 10 mm/s with AUCs of 0.955, 0.880, 0.884, and 0.793, respectively, and accuracy values of 86.7%, 46.7%, 76.7%, and 70%, respectively. Combined placental and fetal brain ADC used to define neonates needing ICU revealed an AUC of 0.968 and an accuracy of 93.3%.

CONCLUSION

Combined ADC of the placenta and fetal organs can detect IUGR, and combined ADC of the placenta and fetal brain can define fetuses needing ICU.

Prenatal diagnosis of renal duplication by magnetic resonance imaging

Purpose: To determine the value of fetal magnetic resonance imaging (MRI) to detect renal duplication.Methods: In this retrospective study, prenatal MRI and ultrasound (US) diagnoses were compared with postnatal imaging and/or surgical data. Twenty-six pregnant women (average age, 32 years; range, 29-36 years) underwent MRI at a mean gestational age of 25 weeks (range, 21-33 weeks). MRI was performed with a 1.5-T unit within 1 week after prenatal ultrasound examination. The steady-state free-precession (SSFP), single-shot turbo spin echo (SSTSE), and T₁-weighted fast imaging sequences were used.Results: Twenty-four cases of fetal renal duplications diagnosed using prenatal MRI were judged to be correct when compared with postnatal imaging and surgical follow-up. In 18 of 26 cases, the diagnoses established using prenatal US were correct when compared with postnatal diagnosis. In 2 of 26 cases, the diagnosis with both prenatal US and MRI were not entirely correct when compared with postnatal diagnosis. In the two cases, magnetic resonance (MR) identified left two pelvicalyceal systems but could not found ipsilateral ectopic ureteral orifice, US only found left hydronephrosis but could not found duplex collection system. In other six cases, MR corrected the US diagnosis by providing a more accurate renal morphology or additional diagnostic information.Conclusions: MRI is an effective method for the diagnosis of fetal duplex kidney deformity and associated ureteral and other abnormalities.

Magnetic resonance imaging for evaluation of foetal multicystic dysplastic kidney

We sought to evaluate the diagnostic value of foetal magnetic resonance imaging (MRI) for multicystic dysplastic kidney (MCDK) disease. We retrospectively identified 55 foetuses with MCDK diagnosed (51 unilateral; 4 bilateral) by foetal MRI. We analysed the anatomical findings by prenatal MRI and compared them with the prenatal ultrasound (US) and postnatal findings. Additional diagnostic information added by MRI was recorded. The gestational age of the 55 foetuses ranged from 22 to 35 weeks (mean, 26.5 ± 3.6 weeks). The age of the pregnant women ranged from 23 to 40 years (mean, 31 ± 4.2 years). All 55 cases were performed at 1.5 T magnetic resonance unit. MRI sequences, including steady-state free precession (SSFP), single-shot fast spin echo (SSFSE), T₁-weighted imaging (T₁WI), and diffusion weighted imaging (DWI) sequences. Follow-up was obtained for 53 cases (2 cases of autopsy, 51 cases of postnatal imaging or surgery confirmed). Among the 51 unilateral cases, 16 cases were associated with other urinary tract anomalies, 3 cases with extra-renal anomalies, and the remaining 32 cases without associated anomalies. 2 of 16 cases with contralateral renal agenesis were with oligohydramnios and pulmonary hypoplasia. 2 of 4 bilateral MCDK presented with oligohydramnios and pulmonary hypoplasia. 52 of 53 cases were correctly diagnosed by MRI compared with the final diagnoses; 40 of 53 (75.5%) cases were correctly diagnosed by prenatal ultrasound. Both prenatal ultrasound and MRI failed to correctly diagnose one case bilateral MCDK, and MRI correctly changed the ultrasound diagnosis in 12 cases. Foetal MRI can add additional diagnostic information to prenatal US in the assessment of MCDK, even change the prenatal counselling and decisions.

Seventeen years of prenatal magnetic resonance imaging at the Institute of Mother and Child in Warsaw

Purpose

The purpose of this paper is to summarise and to present the experience of the main Polish centre for prenatal magnetic resonance imaging (MRI) and to discuss the place and role of MRI in antenatal diagnosis, management, and counselling.

Material and methods

Retrospective analysis of the examinations performed in the years 2001-2017.

Results

In total, 1221 medical records and/or image files were collected. The full documentation of ultrasonography and MRI referrals, reports, and images was not available in every case. During the first three years 98 pregnant women were examined (approximately 33 per year, one study per fortnight). After purchase of own MR scanner, the number of examinations grew constantly, reaching 208 in 2017, which means almost one per day, and the highest number was eight in one day. We examined 45 pairs of twins, including three pairs of conjoined twins.

Conclusions

MRI at our Institute is a practically used second-line foetal imaging tool, necessary to confirm, complete, or correct sonographic diagnoses, with important impact on clinical decisions concerning management of pregnancy and of the neonate, termination of pregnancy, choice of the time, place, and mode of delivery, and neonatal care, as well as on counselling. In experienced hands, MRI is to date the last and the best non-invasive method of diagnosis in utero. It is frequently requested by the interdisciplinary team for foetal diagnosis and therapy and routinely performed in everyday practice.

Intra-voxel incoherent motion MRI of the living human foetus: technique and test-retest repeatability

Background

Our purpose was to test the within-subject (test–retest) reproducibility of the perfusion fraction, diffusion coefficient, and pseudo-diffusion coefficient measurements in various foetus organs and in the placenta based on the intra-voxel incoherent motion (IVIM) principle.

Methods

In utero diffusion-weighted IVIM magnetic resonance imaging (MRI) was performed in 15 pregnant women (pregnancy age 21–36 weeks) on 1.5-T and 3.0-T clinical scanners with b-factors in the range of 0–900 s/mm² in 16 steps. A bi-exponential model was fitted on the volume-averaged diffusion values. Perfusion fraction (f), diffusion coefficient (d), and pseudo-diffusion coefficient (D*) were calculated. Within-subject reproducibility was evaluated as test–retest variability (VAR %) of the IVIM parameters in the foetal frontal cortex, frontal white matter, cerebellum, lungs, kidneys, liver, and in the placenta.

Results

For the foetal lungs, liver and the placenta, test–retest variability was in the range of 14–20% for f, 12–14% for d, and 17–25% for D*. The diffusion coefficients of the investigated brain regions were moderately to highly reproducible (VAR 5–15%). However, f and D* showed inferior reproducibility compared to corresponding measures for the lungs, liver, and placenta. The IVIM parameters of the foetal kidney were revealed to be highly variable across scans.

Conclusions

IVIM MRI potentially provides a novel method for examining microvascular perfusion and diffusion in the developing human foetus. However, reproducibility of perfusion and diffusion parameters depends greatly upon data quality, foetal and maternal movements, and foetal-specific image post-processing.

Highlights on MRI of the fetal body

Fetal MRI is a level III diagnostic tool performed subsequently a level II prenatal ultrasound (US), in cases of inconclusive ultrasonographic diagnosis or when a further investigation is required to confirm or improve the diagnosis, to plan an appropriate pregnancy management. Fetal MRI plays an increasingly important role in the prenatal diagnosis of fetal neck, chest and abdominal malformations, even if its role has been amply demonstrated, especially, in the field of fetal CNS anomalies. Due to its multiparametricity and multiplanarity, MRI provides a detailed evaluation of the whole fetal respiratory, gastrointestinal and genitourinary systems, especially on T2-weighted (W) images, with a good tissue contrast resolution. In the evaluation of the digestive tract, T1-W sequences are very important in relation to the typical hyperintensity of the large intestine, due to the presence of meconium. The objective of this review is to focus on the application of fetal MRI in neck, chest and abdominal diseases.

Lower urinary tract obstruction: fetal intervention based on prenatal staging

The authors present an overview of lower urinary tract obstruction (LUTO) in the fetus with a particular focus on the insult to the developing renal system. Diagnostic criteria along with the challenges in estimating long-term prognosis are reviewed. A proposed prenatal LUTO disease severity classification to guide management decisions with fetal intervention to maintain or salvage in utero and neonatal pulmonary and renal function is also discussed. Stage I LUTO (mild form) is characterized by normal amniotic fluid index after 18 weeks, normal kidney echogenicity, no renal cortical cysts, no evidence of renal dysplasia, and favorable urinary biochemistries when sampled between 18 and 30 weeks; prenatal surveillance is recommended. Stage II LUTO is characterized by oligohydramnios/anhydramnios, hyperechogenic kidneys but absent renal cortical cysts or apparent signs of renal dysplasia and favorable fetal urinary biochemistry; fetal vesicoamniotic shunting (VAS) or fetal cystoscopy is indicated to prevent pulmonary hypoplasia and renal failure. Stage III LUTO is oligohydramnios/anhydramnios, hyperechogenic kidneys with cortical cysts and renal dysplasia and unfavorable fetal urinary biochemistry after serial evaluation; fetal vesicoamniotic shunt may prevent severe pulmonary hypoplasia but not renal failure. Stage IV is characterized by intrauterine fetal renal failure, defined by anhydramnios and ultrasound (US) findings suggestive of severe renal dysplasia, and is associated with death in 24 h of life or end-stage renal disease (ESRD) within the first week of life; fetal vesicoamniotic shunt and fetal cystoscopy are not indicated.

Bi-parametric magnetic resonance imaging applied to obstetrics

Foetal magnetic resonance imaging (MRI) plays an increasingly important role in the diagnosis of foetal abnormalities. Over the years, we have successfully applied bi-parametric MRI (bp-MRI) to the following obstetric conditions: (1) neurologic vascular diseases; (2) assessment of lung parenchyma maturation; (3) renal pathologies, such as polycystic kidney, suspected renal infarction, unilateral or bilateral renal agenesis; (4) placental pathologies, as twin-twin transfusion syndrome or placenta accreta; (5) benignant and malignant congenital tumours or cysts of the liver, such as haemangioendothelioma, hepatoblastoma or metastatic neuroblastoma, of the kidney (e.g. mesoblastic nephroma) and of the retroperitoneum, such as teratoma. The information derived from bp-MRI, and concerned with water motions in different tissues, improved the morphologic details provided by conventional foetal MRI. It has the potential to increase the value of MRI in the assessment of a wide range of foetal pathologies, particularly in renal diseases, allowing an adequate management decision and therapy.

Clinical applications of diffusion-weighted magnetic resonance imaging in diagnosis of renal lesions - a systematic review

Diffusion-weighted magnetic resonance imaging (DW-MRI) is an established technique to detect the changes of the diffusion of water in biological tissues and reflect the pathophysiological process on the molecular level. It is a promising non-invasive imaging modality in detection of microstructural and functional changes in pathologies of kidney. To systematically review the research advancement of the DW-MRI in diagnosis of renal lesions, a systematic literature search was performed up to 8 October 2014 using the MEDLINE/PubMed and Embase databases for articles reporting on DW-MRI in diagnosis of renal lesions. Only articles with full data about DW-MRI application with potential implication in solving usually encountered clinical challenges about renal lesions were finally examined. The clinical application of DW-MRI allows a better understanding of some pathologic conditions of the kidney including renal insufficiency, renal artery stenosis, ureteral obstruction, foetal kidney disease, hydronephrosis and pyonephrosis. In addition, DW-MRI can also provide clinicians with the information of function evaluation of renal allograft and curative effect assessment of renal tumour. In summary, performance of renal DW-MRI, presuming that measurements are high quality, will further boost this modality, particularly for early detection of diffusion renal conditions, as well as more accurate characterization of renal lesions.

Non-central nervous system fetal magnetic resonance imaging

Fetal magnetic resonance imaging (MRI) is currently offered in a limited number of centers but is predominantly used for suspected fetal central nervous system abnormalities. This article concentrates on the role of the different imaging sequences and their value to clinical practice. It also discusses the future of fetal MRI.

Diffusion-weighted perinatal postmortem magnetic resonance imaging as a marker of postmortem interval

Objective

To evaluate perinatal body organ apparent diffusion coefficient (ADC) values at postmortem magnetic resonance imaging (PMMR) in order to evaluate postmortem changes.

Methods

Postmortem diffusion-weighted imaging (DWI) of the thorax and abdomen were performed with diffusion gradient values b = 0, 500, and 1000 s/mm² on 15 foetal and childhood cases (mean 33.3 ± 7.8 weeks gestation) compared to 44 live infants (mean age 75.5 ± 53.4 days). Mean ADC values were calculated from regions of interest (ROIs) for the lungs, liver, spleen and renal cortex, compared to normative live infantile body ADC values of similar gestational age.

Results

Mean ADC values were significantly lower in postmortem cases than in normal controls for liver (0.88 10^-3 mm²/s ± SD 0.39 vs. 1.13 ± 0.13; p < 0.05) and renal cortex (0.85 ± 0.26 vs. 1.19 ± 0.13; p < 0.05) but not spleen or muscle. Mean lung ADC values were significantly higher than normal controls (1.06 ± 0.18 vs. 0 ± 0; p < 0.001), and there was a significant correlation between postmortem interval and lung ADC (R² = 0.55).

Conclusion

Lung PMMR ADC values are related to postmortem interval, making them a potential marker of time since death. Further research is needed to understand the organ-specific changes which occur in the postmortem period.

Key Points

• Liver and spleen PM ADC values were lower than controls.

• Lung ADC changes correlate with PM interval.

• These findings may be useful in medicolegal cases.

[Fetal magnetic resonance imaging of thoracic and abdominal malformations]

CLINICAL/METHODICAL ISSUE

Diagnosis and differential diagnosis of fetal thoracic and abdominal malformations.

STANDARD RADIOLOGICAL METHODS

Ultrasound and magnetic resonance imaging (MRI).

METHODICAL INNOVATIONS

In cases of suspected pathologies based on fetal ultrasound MRI can be used for more detailed examinations and can be of assistance in the differential diagnostic process.

PERFORMANCE

Improved imaging of anatomical structures and of the composition of different tissues by the use of different MRI sequences.

ACHIEVEMENTS

Fetal MRI has become a part of clinical routine in thoracic and abdominal malformations and is the basis for scientific research in this field.

PRACTICAL RECOMMENDATIONS

In cases of thoracic or abdominal malformations fetal MRI provides important information additional to ultrasound to improve diagnostic accuracy, prognostic evaluation and surgical planning.

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.

Diffusion-weighted MR imaging of native and transplanted kidneys

Applications of diffusion-weighted (DW) magnetic resonance (MR) imaging outside the brain have gained increasing importance in recent years. Owing to technical improvements in MR imaging units and faster sequences, the need for noninvasive imaging without contrast medium administration, mainly in patients with renal insufficiency, can be met successfully by applying this technique. DW MR imaging is quantified by the apparent diffusion coefficient (ADC), which provides information on diffusion and perfusion simultaneously. By using a biexponential fitting process of the DW MR imaging data, these two entities can be separated, because this type of fitting process can serve as an estimate of both the perfusion fraction and the true diffusion coefficient. DW MR imaging can be applied for functional evaluation of the kidneys in patients with acute or chronic renal failure. Impairment of renal function is accompanied by a decreased ADC. Acute ureteral obstruction leads to perfusion and diffusion changes in the affected kidney, and renal artery stenosis results in a decreased ADC. In patients with pyelonephritis, diffuse or focal changes in signal intensity are seen on the high-b-value images, with increased signal intensity corresponding to low signal intensity on the ADC map. The feasibility and reproducibility of DW MR imaging in patients with transplanted kidneys have already been demonstrated, and initial results seem to be promising for the assessment of allograft deterioration. Overall, performance of renal DW MR imaging, presuming that measurements are of high quality, will further boost this modality, particularly for early detection of diffuse renal conditions, as well as more accurate characterization of focal renal lesions.

Diffusion-weighted MR imaging of the placenta in fetuses with placental insufficiency

PURPOSE

To evaluate diffusion-weighted magnetic resonance (MR) imaging of the human placenta in fetuses with and fetuses without intrauterine growth restriction (IUGR) who were suspected of having placental insufficiency.

MATERIALS AND METHODS

The study was approved by the local ethics committee, and written informed consent was obtained. The authors retrospectively evaluated 1.5-T fetal MR images from 102 singleton pregnancies (mean gestation ± standard deviation, 29 weeks ± 5; range, 21-41 weeks). Morphologic and diffusion-weighted MR imaging were performed. A region of interest analysis of the apparent diffusion coefficient (ADC) of the placenta was independently performed by two observers who were blinded to clinical data and outcome. Placental insufficiency was diagnosed if flattening of the growth curve was detected at obstetric ultrasonography (US), if the birth weight was in the 10th percentile or less, or if fetal weight estimated with US was below the 10th percentile. Abnormal findings at Doppler US of the umbilical artery and histopathologic examination of specimens from the placenta were recorded. The ADCs in fetuses with placental insufficiency were compared with those in fetuses of the same gestational age without placental insufficiency and tested for normal distribution. The t tests and Pearson correlation coefficients were used to compare these results at 5% levels of significance.

RESULTS

Thirty-three of the 102 pregnancies were ultimately categorized as having an insufficient placenta. MR imaging depicted morphologic changes (eg, infarction or bleeding) in 27 fetuses. Placental dysfunction was suspected in 33 fetuses at diffusion-weighted imaging (mean ADC, 146.4 sec/mm(2) ± 10.63 for fetuses with placental insufficiency vs 177.1 sec/mm(2) ± 18.90 for fetuses without placental insufficiency; P < .01, with one false-positive case). The use of diffusion-weighted imaging in addition to US increased sensitivity for the detection of placental insufficiency from 73% to 100%, increased accuracy from 91% to 99%, and preserved specificity at 99%.

CONCLUSION

Placental dysfunction associated with growth restriction is associated with restricted diffusion and reduced ADC. A decreased ADC used as an early marker of placental damage might be indicative of pregnancy complications such as IUGR.

SUPPLEMENTAL MATERIAL

http://radiology.rsna.org/lookup/suppl/doi:10.1148/radiol.10092283/-/DC1.

Non-invasive fetal lung assessment using diffusion-weighted imaging

OBJECTIVES

The main goal was to develop a reproducible method for estimating the diffusion of water in human fetal lung tissue using diffusion-weighted imaging (DWI). A secondary objective was to determine the relationship of the apparent diffusion coefficients (ADCs) in the fetal lung to menstrual age and total lung volume.

METHODS

Normal pregnant volunteers were scanned on a 1.5-Tesla (T) magnetic resonance imaging (MRI) system. The MRI system was equipped with 40-mT/m gradients (slew rate 200 T/m/s, rise time 0.2 ms). A six-channel body array coil was used for signal reception. Single-shot DWI utilized TE/TR 125/3400 ms, slice thickness 4 mm, field of view 280 mm x 280 mm, interslice gap 0.8 mm and a matrix of 128 x 128. The voxel size was 2.5 mm x 2.5 mm x 4.0 mm. Two b-values (0 and 1000) were chosen along three orthogonal directions. ADC maps were created using assigned b-values. Simple linear regression was performed with Pearson correlation coefficient. Interexaminer and intraexaminer bias, and 95% limits of agreement (LOA) were determined using Bland-Altman plots.

RESULTS

Forty-seven scans were performed at a mean +/- SD of 29.2 +/- 4.5 weeks. The median coefficient of variation for ADC was 5.6% (interquartile range, 4.0-8.1%). No differences in ADC values were found between right and left lungs. Normally distributed ADC measurements were not significantly correlated with either total lung volume (r(2) = 0.0001, P = 0.94) or menstrual age (r(2) = 0.003, P = 0.70). The mean ADC value was 1.75 (95% CI, 1.63-1.86). Mean +/- SD intraexaminer bias was -0.15 +/- 2.3 (95% LOA, -4.7 to + 4.4) and interexaminer bias was 2.2 +/- 3.5 (95% LOA, -4.7 to + 9.1).

CONCLUSIONS

Our findings suggest that ADC measurements of the fetal lung are reproducible between blinded examiners and are independent of menstrual age, as well as lung volume.

Complementary roles of sonography and magnetic resonance imaging in the assessment of fetal urinary tract anomalies

OBJECTIVE

The purpose of our study was to determine whether fetal magnetic resonance imaging (MRI) provides additional information that might affect the obstetric management of pregnancies complicated by sonographically diagnosed fetal urinary tract anomalies.

METHODS

Fetal MRI and sonography were used to study 39 women with suspected fetal urinary tract anomalies in the second and third trimesters of pregnancy.

RESULTS

In 24 of 39 cases (61%), fetal MRI confirmed the sonographic diagnosis. In 14 cases (36%), fetal MRI modified the initial sonographic diagnosis and counseling but did not change obstetric management. In 1 case (3%), the addition of fetal MRI resulted in a substantial change in the management of the pregnancy.

CONCLUSIONS

During the second and third trimesters of pregnancy, fetal MRI showed fetal urinary tract anomalies in excellent anatomic detail. Fetal MRI is a useful complementary tool in the assessment of sonographically diagnosed fetal urinary tract anomalies. In a small percentage of cases, it can have a substantial impact on obstetric management.

Prenatal ultrasound and fetal MRI: the comparative value of each modality in prenatal diagnosis

Fetal MRI is used with increasing frequency as an adjunct to ultrasound (US) in prenatal diagnosis. In this review, we discuss the relative value of both prenatal US and MRI in evaluating fetal and extra-fetal structures for a variety of clinical indications. Advantages and disadvantages of each imaging modality are addressed. In summary, MRI has advantages in demonstrating pathology of the brain, lungs, complex syndromes, and conditions associated with reduction of amniotic fluid. At present, US is the imaging method of choice during the first trimester, and in the diagnosis of cardiovascular abnormalities, as well as for screening. In some conditions, such as late gestational age, increased maternal body mass index, skeletal dysplasia, and metabolic disease, neither imaging method may provide sufficient diagnostic information.