Magnetic Resonance Imaging Subtraction Research Articles

Early Bone Ischemia in Pediatric Acute Hematogenous Osteomyelitis and its Association With Progression to Chronic Osteomyelitis: New Insights From Gadolinium-enhanced Subtraction MRI.

Acute hematogenous osteomyelitis (AHO), the most common osteoarticular infection in children, carries a significant risk for chronic complications. Predicting chronic complications early in the course of disease is challenging. The underlying pathogenesis of complications is not fully understood. Children who presented to Sultan Qaboos University Hospital, Muscat, Oman between January 2015 and April 2022 for AHO were identified by a search of magnetic resonance imaging (MRI) records. Children between 1 month and 18 years of age who did not meet exclusion criteria, and whose MRI also included gadolinium-enhanced subtraction (GES) sequences were included in the analysis. Outcomes were compared between patients who showed early evidence of bone ischemia and those who did not. The analysis included 11 children who had GES MRI sequences from among 18 AHO cases in total. Median age was 5 years (IQR, 4-9), and 82% were males. Median duration of symptoms at presentation was 5 days (IQR, 3-7). GES sequences showed early bone ischemia in 6 of 11 (55%) patients. Patients with early bone ischemia were treated with significantly longer durations of IV antibiotics (median 23 vs. 10 days, P = 0.017) and oral antibiotics (median 134 vs. 29 days, P = 0.004), and required more surgical debridements (median 3 vs. 0 debridements, P = 0.017). Chronic osteomyelitis only developed among patients with early bone ischemia (5/6 vs. 0/5, P = 0.015). In pediatric AHO, GES MRI sequences revealed early bone ischemia in a significant proportion of patients. Early bone ischemia was strongly associated with progression to chronic osteomyelitis.

The usefulness of contrast-enhanced subtraction magnetic resonance imaging for detecting endoleaks after endovascular aortic repair with prophylactic intraoperative sac embolization.

Metallic and hyperdense artifacts and T1-shortening substances in the abdominal aortic aneurysm (AAA) sac generated by embolic materials and lipiodol pose challenges in the identification of endoleaks on follow-up computed tomography (CT) or magnetic resonance imaging (MRI). To evaluate the usefulness of contrast-enhanced subtraction MRI (CES-MRI) for detecting endoleaks after endovascular abdominal aortic aneurysm repair (EVAR) with intraoperative AAA sac embolization compared with CE-CT, this study was conducted. In this study, 28 consecutive patients who underwent EVAR with prophylactic AAA sac embolization were included. All patients underwent CES-MRI and CE-CT to detect endoleaks. The definitive diagnosis of endoleaks was a consensus reading of CE-CT and CES-MRI by two certified radiologists, in addition to angiography or reproducible radiological findings in the observational examination. Analysis was performed to evaluate which examination was better for detecting endoleaks. The sensitivity, specificity, and area under the curve of CE-CT and CES-MRI according to observer 1 were 50%, 100%, and 0.813 (95% confidence interval [CI] = 0.625-1.00) and 100%, 95%, and 0.997 (95% CI = 0.984-1.00), respectively, and those according to observer 2 were 50%, 100%, and 0.750 (95% CI = 0.514-0.986) and 100%, 95%, and 0.969 (95% CI = 0.903-1.00), respectively. Intolerable artifacts were significantly observed on CE-CT. The severity of the artifacts did not depend on the stent graft on CT and MRI. Although no significant difference was observed, CES-MRI tended to have better accuracy for endoleak detection in EVAR with intraoperative AAA sac embolization than CE-CT.

Magnetic resonance imaging subtraction vs. pre- and post-contrast 3D gradient recalled echo fat suppressed imaging for evaluation of the canine and feline brain.

Subtraction magnetic resonance imaging (MRI) has been reported to increase accuracy in the diagnosis of meningeal and inflammatory brain diseases in small animals. 3D T1W gradient recalled echo (GRE) techniques have been proposed as a suitable alternative to conventional spin echo sequences in imaging the canine brain. The aim of this study was to compare subtraction images and paired pre- and post-contrast 3D T1W GRE fat suppressed (FS) images in canine and feline MRI studies using clinical diagnosis as the gold standard. Paired pre- and post-contrast T1W 3D FS GRE images and individual subtraction images of 100 small animal patients were randomized and independently evaluated by 2 blinded observers. Diagnosis categories were "normal," "inflammatory," "neoplastic," and "other." Clinical diagnosis was made in the same categories and served as the gold standard. Image interpretation results were compared to the clinical diagnosis. Interobserver agreement was determined. Clinically, 41 studies were categorized as "normal," 18 as "inflammatory," 28 as "neoplastic," and 13 as "other." The agreement of the pre- and post-contrast GRE images with the gold standard was significantly higher than that of the subtraction images (k = 0.7491 vs. k = 0.5924; p = 0.0075). The largest sources of error were misinterpretation of "other" as "normal" and "normal" as "inflammatory." There was no significant difference between the two observers (p = 0.8820). Based on this study, subtraction images do not provide an advantage to paired pre- and post-contrast FS GRE images when evaluating the canine and feline brain.

Development of a deep-learning model for classification of LI-RADS major features by using subtraction images of MRI: a preliminary study.

Liver Imaging Reporting and Data System (LI-RADS) is limited by interreader variability. Thus, our study aimed to develop a deep-learning model for classifying LI-RADS major features using subtraction images using magnetic resonance imaging (MRI). This single-center retrospective study included 222 consecutive patients who underwent resection for hepatocellular carcinoma (HCC) between January, 2015 and December, 2017. Subtraction arterial, portal venous, and transitional phase images of preoperative gadoxetic acid-enhanced MRI were used to train and test the deep-learning models. Initially, a three-dimensional (3D) nnU-Net-based deep-learning model was developed for HCC segmentation. Subsequently, a 3D U-Net-based deep-learning model was developed to assess three LI-RADS major features (nonrim arterial phase hyperenhancement [APHE], nonperipheral washout, and enhancing capsule [EC]), utilizing the results determined by board-certified radiologists as reference standards. The HCC segmentation performance was assessed using the Dice similarity coefficient (DSC), sensitivity, and precision. The sensitivity, specificity, and accuracy of the deep-learning model for classifying LI-RADS major features were calculated. The average DSC, sensitivity, and precision of our model for HCC segmentation were 0.884, 0.891, and 0.887, respectively, across all the phases. Our model demonstrated a sensitivity, specificity, and accuracy of 96.6% (28/29), 66.7% (4/6), and 91.4% (32/35), respectively, for nonrim APHE; 95.0% (19/20), 50.0% (4/8), and 82.1% (23/28), respectively, for nonperipheral washout; and 86.7% (26/30), 54.2% (13/24), and 72.2% (39/54) for EC, respectively. We developed an end-to-end deep-learning model that classifies the LI-RADS major features using subtraction MRI images. Our model exhibited satisfactory performance in classifying LI-RADS major features.

Usefulness of subtraction images for accurate diagnosis of pituitary microadenomas in dynamic contrast-enhanced magnetic resonance imaging.

Dynamic contrast-enhanced magnetic resonance imaging (MRI) is the modality of choice for the diagnosis of pituitary microadenomas; however, it may be associated with a relatively high false-negative rate, especially in small lesions. To evaluate the usefulness of subtraction images for enhancing the visual detection of pituitary microadenomas. In total, 50 patients with clinically established diagnosis hyperprolactinemia, acromegaly, and Cushing's disease were enrolled. Ten patients referred for brain MRI for reasons other than pituitary abnormality were selected as control group. Routine dynamic MRI of the pituitary gland and obtained subtraction MRI scans were scrutinized separately on different sessions by an experienced radiologist blinded to the study design and patient's data. The investigator's opinion on the presence or absence of a lesion and lesion size were collected. In patients with pituitary microadenoma, dynamic MRI images were reported positive in 42 (84%) patients and negative in 8 (16%). Subtraction images were described as positive in all patients (100%)-including all patients with negative dynamic MRI-and the difference was statistically significant (P=0.016). Undetected lesions on dynamic MRI had a mean size of 2.84 ± 1.79 mm (median= 2.20 mm, interquartile range=1.62-4.62 mm) and a significant inverse correlation was noted between lesion size and negative report of dynamic MRI (P=0.018). Brain MRI scans in the control group were reported negative for pituitary microadenoma in both dynamic contrast-enhanced and subtraction images. Subtraction images can successfully identify all lesions detectable with conventional dynamic MRI as well as improving visualization of lesions undetected on dynamic MRI, especially in small lesions.

Novel MR-Visible, Biodegradable Microspheres for Transcatheter Arterial Embolization: Experimental Study in a Rabbit Renal Model.

To assess feasibility, embolization success, biodegradability, reperfusion, biocompatibility and in vivo visibility of novel temporary microspheres (MS) for transcatheter arterial embolization. In 9 New Zealand white rabbits unilateral superselective embolization of the lower kidney pole was performed with biodegradable MS made of polydioxanone (PDO) (size range 90-300 and 200-500µm) impregnated with super-paramagnetic iron oxide (SPIO). Magnetic resonance imaging (MRI) was performed post-interventionally to assess in vivo visibility. Embolization success was assessed on digital subtraction angiography, MRI and gross pathology. One animal was killed immediately after embolization to assess original particle appearance. 8 animals were randomly assigned to different observation periods (1, 4, 8, 12 and 16weeks), after which control angiography and MRI were obtained to determine recanalization. Histopathological analysis was performed to determine biodegradability and biocompatibility by using dedicated quantitative assessment analysis. Ease of injection was moderate. Embolization was technically successful in 7 of 8 animals, one rabbit received non-selective embolization of the whole kidney and abdominal off-target embolization. Arterial occlusion was achieved in all kidneys, infarct areas in macro- and microscopic analysis confirmed embolization success. Control angiograms showed evidence of partial reperfusion. The microspheres showed extensive degradation over the course of time along with increasing inflammatory response and giant cell formation. SPIO-loaded MS were visible on MRI at all time points. SPIO-impregnated biodegradable PDO-MS achieved effective embolization with in vivo visibility on MRI and increasing biodegradation over time while demonstrating good biocompatibility, i.e., a physiologically immune response without transformation into chronic inflammation. Further studies are needed to provide clinical applicability.

Abstract P6-10-12: Texture heterogeneity of breast tumour in magnetic resonance imaging can be explained by differentially regulated genes

Abstract Background: Magnetic resonance imaging (MRI) and molecular profiling of tumour tissues have become standard techniques to study breast cancer in recent years. However, despite the myriad imaging and genetic subtypes that have been identified, the underlying biological mechanisms of MRI features are seldom explained, and differentially regulated genes are rarely linked to the phenotypic appearance of tumours. In this study, we propose to fill this gap in knowledge by investigating the unbiased correlations between MRI phenotypes and differential gene expressions in breast cancer. Methods: Patients diagnosed during 2002-15 with invasive breast cancer who went through surgery were retrospectively reviewed for magnetic resonance imaging (MRI) and genomics analysis. In total, we collected dynamic contrast-enhanced subtraction MRI and RNA sequencing results of surgical specimens from a cohort of 56 patients. Of these, 31 patients (aged 33 to 72 years) met our inclusion criteria. Tumour lesion segmentation was performed by a radiologist who has 10 years of experience. We extracted features that quantitatively describe tumour appearance from the segmented lesions using pyradiomics (v2.0.0). We then grouped the tumours into two imaging subtypes using an unsupervised clustering approach (SIMLR, v1.10.0). To probe the underlying biological mechanisms behind the difference in tumour appearance, we performed differential expression analysis (edgeR, v3.26.5) and pathway enrichment analysis (g:profiler) between the two imaging subtypes. Multiple testing correction was conducted with Benjamini-Hochberg correction using a false discovery rate of 0.05. Results: We classified the breast tumours from our cohort into two imaging subtypes that have distinct levels of heterogeneity in texture (p=0.004). We found a list of genes that were significantly differentially expressed between the heterogenous (n=20) and homogenous (n=11) subtypes (Table 1), and their associated biological pathways. We found that the pathways controlling cell growth (p=0.022), cell migration and invasion (p=0.023), estrogen regulation (p=0.022) and DNA damage repair (p=0.015) mechanisms may have contributed to increased heterogeneity in tumour presentation when imaged with MRI. Conclusion: The underlying biological mechanisms affecting breast MRI texture can be investigated by linking tumour appearance to gene expression profiling. Our results suggest that texture heterogeneity in breast MRI could be linked to a number of differentially expressed genes that may be further investigated as a biomarker of cancer risk assessment or recurrence. Further studies with a larger cohort will be conducted to validate and extend these results. Table 1. Differentially expressed genes between heterogenous and homogenous imaging subtypes.Genes upregulated in heterogeneous imaging subtypeLog fold changeAdjusted p valueABCC138.760.0022PROL17.760.0331TDRD127.100.0204SLC12A22.030.0204IGFBP3-1.500.0331UBASH3B-1.740.0331LYZ-2.120.0291CCL5-2.120.0204PDCD1LG2-2.180.0359SLC7A11-2.480.0363GNLY-3.090.0022GZMB-3.100.0204PTHLH-3.270.0246GSTM5-3.370.0325GNAO1-3.430.0363MYOZ1-3.580.0269CLEC4C-3.640.0246AJAP1-3.760.0325IL28B-3.930.0415CCL25-4.770.0325PI15-5.491.48e-7 Citation Format: Jianan Chen, Yutaka Amemiya, Gregory Kuling, Homa Fashandi, Yulia Yerofeyeva, Heba Hussein, Elzbieta Slodkowska, Fiona Ginty, Arun Seth, Martin Yaffe, Anne L. Martel. Texture heterogeneity of breast tumour in magnetic resonance imaging can be explained by differentially regulated genes [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P6-10-12.

The Role of Diffusion Weighted Magnetic Resonance Imaging and Subtraction Magnetic Resonance imaging in Assessing Treatment Response of Hepatocellular Carcinoma After Transarterial Chemoembolization

Background: Hepatocellular carcinoma (HCC) is one of the most common cancers worldwide, and has a poor prognosis unless treated. Ablative therapies are promising treatment options for patients who are not eligible for surgery. Monitoring tumor response after transarterial chemoemolization (TACE) procedure is an important task in oncologic imaging. Early favorable response indicates effectiveness of therapy, while early treatment failure identification is also critical in patient management. In such cases further re-treatment will be mandatory. Aim of work: The aim of this study is to evaluate the efficiency of both diffusion weighted images and subtracted dynamic MRI technique in the detection of residual/ recurrent disease after TACE ablation of non resectable hepatocellular carcinoma (HCC) lesions. Accurate judgment of tumor viability will help diagnose the need for further treatment sessions. Patients and Methods: This study included 32 patients having 54 HCC lesions that underwent transarterial chemoembolization procedure over a period of 6 months (2017- 2018) were followed up 1-1.5 months by dynamic MRI. 12 patients of which underwent a second follow up within 3-4 months. Patients’ ages ranged between 59 to 73 years (mean age 53.1); 26 patients were males and 6 were females. All patients had liver cirrhosis related to chronic viral hepatitis. Results: In 1ry response and follow up findings post TACE, where good response was defied as disappearance of any intra tumoral arterial enhancement in treated lesions, residual disease was defined as at least 30% reduction in the sum of diameters of the viable enhancing lesion in the arterial phase, no response was less than 30% reduction in the enhancing lesion diameters. Progressive disease was defined as 20% increase in the sum of diameters of the enhancing lesions in comparison to the target lesion diameter at the start of treatment. Conclusion: MRI is a powerful tool in detection of residual tumor viability, quantifying tumor necrosis and detecting complications after TACE. Imaging protocol should include dynamic study combined with post processing subtraction images for better tissue characterization.

Identification of Arterial Hyperenhancement in CT and MRI in Patients with Hepatocellular Carcinoma: Value of Unenhanced Images.

ObjectiveAccording to the current guidelines, arterial hyperenhancement for diagnosis of hepatocellular carcinoma (HCC) is determined using the arterial phase only. We investigated the optimal definition of arterial hyperenhancement in patients with HCC using computed tomography (CT) and magnetic resonance imaging (MRI).Materials and MethodsThe Institutional Review Board approved this retrospective study. The requirement for informed consent was waived. Between January 2011 and September 2013, 147 consecutive patients with surgically proven HCCs with both pre-operative CT and MRI were included. Identification rates of arterial hyperenhancement on CT and magnetic resonance (MR) images using arterial phase only, dual phase (unenhanced and arterial phases), and also subtraction MR images were assessed qualitatively.ResultsThe identification rates for arterial hyperenhancement on CT were significantly different between arterial phase and dual phase (72.8% vs. 90.5%; p < 0.001), whereas the rates were similar on MRI (91.8% vs. 93.9%; p = 0.257). The identification rate of arterial hyperenhancement in MRI increased to 98.6% using subtraction MR images.ConclusionVisual comparison of arterial and unenhanced phases could be recommended instead of conventional qualitative arterial phase alone assessment to determine arterial hyperenhancement of HCCs, especially when using CT.

Breast Cancer Heterogeneity: MR Imaging Texture Analysis and Survival Outcomes.

Purpose To determine the relationship between tumor heterogeneity assessed by means of magnetic resonance (MR) imaging texture analysis and survival outcomes in patients with primary breast cancer. Materials and Methods Between January and August 2010, texture analysis of the entire primary breast tumor in 203 patients was performed with T2-weighted and contrast material-enhanced T1-weighted subtraction MR imaging for preoperative staging. Histogram-based uniformity and entropy were calculated. To dichotomize texture parameters for survival analysis, the 10-fold cross-validation method was used to determine cutoff points in the receiver operating characteristic curve analysis. The Cox proportional hazards model and Kaplan-Meier analysis were used to determine the association of texture parameters and morphologic or volumetric information obtained at MR imaging or clinical-pathologic variables with recurrence-free survival (RFS). Results There were 26 events, including 22 recurrences (10 local-regional and 12 distant) and four deaths, with a mean follow-up time of 56.2 months. In multivariate analysis, a higher N stage (RFS hazard ratio, 11.15 [N3 stage]; P = .002, Bonferroni-adjusted α = .0167), triple-negative subtype (RFS hazard ratio, 16.91; P < .001, Bonferroni-adjusted α = .0167), high risk of T1 entropy (less than the cutoff values [mean, 5.057; range, 5.022-5.167], RFS hazard ratio, 4.55; P = .018), and T2 entropy (equal to or higher than the cutoff values [mean, 6.013; range, 6.004-6.035], RFS hazard ratio = 9.84; P = .001) were associated with worse outcomes. Conclusion Patients with breast cancers that appeared more heterogeneous on T2-weighted images (higher entropy) and those that appeared less heterogeneous on contrast-enhanced T1-weighted subtraction images (lower entropy) exhibited poorer RFS. © RSNA, 2016 Online supplemental material is available for this article.

Predictors of Morbidity and Cleavage Plane in Surgical Resection of Pure Convexity Meningiomas Using Cerebrospinal Fluid Sensitive Image Subtraction Magnetic Resonance Imaging.

Meningiomas are the most common primary intracranial tumors. Since the adhesions in the plane of dissection are of interest in surgical planning, we suggest that digital image subtraction of FLAIR data from the T2 sequence of MRI may represent better the CSF spaces in the brain–tumor interface and may be a predictor of the intraoperative cleavage plane. From 2006 to 2016, 83 convexity meningiomas were resected in the Department of Neurosurgery of the University Hospital Complex of Vigo, an analysis of preoperative MRI was performed to assess peritumoral edema (PTE), tumor volume, among others; a digital subtraction of T2-FLAIR sequences was performed and analyzed in relationship to the cleavage plane described in the intraoperative report and postoperative neurological deficits. Simpson grade 1 resection was achieved in 85.54%, the overall 5-year PFS was 93.75%. Our rate of permanent new neurological deficit was 4.82% and the overall complication rate of 14.46%. The grade of PTE was proportional to tumor volume, 20 ± 2.8, 30 ± 5.3, and 34 ± 4.3 cm3 for grades 1, 2, and 3, respectively, positive cleft sign on image subtraction was predictive of good intraoperative cleavage plane and low grade cleavage plane (P = 0.04), and was a protective factor for postoperative neurological deficit (P = 0.02). Positive cleft sign in T2-FLAIR digital subtraction image is an independent predictor of good intraoperative cleavage plane, PTE is an independent predictor of the bad cleavage plane. Negative cleft sign in the image subtraction and a bad intraoperative cleavage plane are predictors of postoperative neurological deficit.

Prophylactic Intraoperative Embolization of Abdominal Aortic Aneurysm Sacs Using N-Butyl Cyanoacrylate/Lipiodol/Ethanol Mixture with Proximal Neck Aortic Balloon Occlusion during Endovascular Abdominal Aortic Repair

PurposeTo determine the feasibility of prophylactic intraoperative abdominal aortic aneurysm (AAA) sac embolization using a mixture of N-butyl cyanoacrylate/Lipiodol/ethanol (NLE) with proximal neck aortic balloon occlusion during endovascular aneurysm repair (EVAR) to prevent the occurrence of endoleak and aneurysm sac expansion. Materials and MethodsProphylactic intraoperative AAA sac embolization was performed in 24 patients with an infrarenal neck angulation > 60° (n = 16) or AAA sac diameter > 60 mm (n = 17). AAA sac pressure was continuously measured with a 3-F catheter inserted into the AAA sac. The systolic sac pressure index (SPI) was calculated as the ratio of systolic AAA sac pressure to the simultaneously measured systolic aortic pressure, and was measured with and without proximal neck aortic balloon occlusion. The aneurysm sac was embolized with NLE during proximal neck aortic balloon occlusion immediately after EVAR. Endoleak and AAA sac diameter were evaluated by enhanced computed tomography and subtraction magnetic resonance imaging at 6 months and yearly after EVAR. ResultsMean SPIs after EVAR with and without proximal neck aortic balloon occlusion were 0.36 and 0.57, respectively. There were no adverse events related to intraoperative sac embolization. Follow-up imaging (mean, 12.1 mo) revealed three minor endoleaks (12.5%) and no aneurysm sac expansion. ConclusionsProphylactic intraoperative sac embolization with NLE during proximal neck aortic balloon occlusion was safe and feasible and may reduce endoleaks and prevent sac expansion after EVAR in patients with unfavorable anatomic factors.

Use of Caval Subtraction 2D Phase-Contrast MR Imaging to Measure Total Liver and Hepatic Arterial Blood Flow: Preclinical Validation and Initial Clinical Translation.

Purpose To validate caval subtraction two-dimensional (2D) phase-contrast magnetic resonance (MR) imaging measurements of total liver blood flow (TLBF) and hepatic arterial fraction in an animal model and evaluate consistency and reproducibility in humans. Materials and Methods Approval from the institutional ethical committee for animal care and research ethics was obtained. Fifteen Sprague-Dawley rats underwent 2D phase-contrast MR imaging of the portal vein (PV) and infrahepatic and suprahepatic inferior vena cava (IVC). TLBF and hepatic arterial flow were estimated by subtracting infrahepatic from suprahepatic IVC flow and PV flow from estimated TLBF, respectively. Direct PV transit-time ultrasonography (US) and fluorescent microsphere measurements of hepatic arterial fraction were the standards of reference. Thereafter, consistency of caval subtraction phase-contrast MR imaging-derived TLBF and hepatic arterial flow was assessed in 13 volunteers (mean age, 28.3 years ± 1.4) against directly measured phase-contrast MR imaging PV and proper hepatic arterial inflow; reproducibility was measured after 7 days. Bland-Altman analysis of agreement and coefficient of variation comparisons were undertaken. Results There was good agreement between PV flow measured with phase-contrast MR imaging and that measured with transit-time US (mean difference, -3.5 mL/min/100 g; 95% limits of agreement [LOA], ±61.3 mL/min/100 g). Hepatic arterial fraction obtained with caval subtraction agreed well with those with fluorescent microspheres (mean difference, 4.2%; 95% LOA, ±20.5%). Good consistency was demonstrated between TLBF in humans measured with caval subtraction and direct inflow phase-contrast MR imaging (mean difference, -1.3 mL/min/100 g; 95% LOA, ±23.1 mL/min/100 g). TLBF reproducibility at 7 days was similar between the two methods (95% LOA, ±31.6 mL/min/100 g vs ±29.6 mL/min/100 g). Conclusion Caval subtraction phase-contrast MR imaging is a simple and clinically viable method for measuring TLBF and hepatic arterial flow. Online supplemental material is available for this article.

MAGNETIC RESONANCE IMAGING OF INTRACRANIAL INFLAMMATORY CONDITIONS IN DOGS: SENSITIVITY OF SUBTRACTION IMAGES VERSUS PRE- AND POST-GADOLINIUM T1-WEIGHTED IMAGE PAIRS.

Ante mortem diagnosis of canine meningoencephalitis is usually based on the results of neurologic examination, cerebrospinal fluid analysis and magnetic resonance (MR) imaging. It has been hypothesized that subtraction MR imaging may increase the sensitivity of MR for intracranial inflammatory lesions compared to conventional post-gadolinium T1-weighted imaging. Sensitivity of pre- and post-gadolinium (C-/C+) image pairs and dynamic subtraction (DS) images was compared in a retrospective diagnostic accuracy study of 52 dogs with inflammatory cerebrospinal fluid and 67 dogs with idiopathic epilepsy. Series of transverse C-/C+ and DS images were reviewed independently for signs of abnormal enhancement affecting the pachymeninges, leptomeninges or intra-axial structures. Sensitivity of C-/C+ image pairs and DS images was 48% (95% CI: 35-61%) and 65% (95% CI: 52-77%), respectively (P = 0.01). Intra-axial lesions were observed more frequently than meningeal lesions in both C-/C+ (43% vs. 31%) and DS images (61% vs. 22%). The difference in sensitivities of C-/C+ and DS series was entirely due to increased sensitivity of DS images for intra-axial lesions. Eight (12%) dogs with epilepsy had evidence of intra-axial gadolinium accumulation affecting the cerebral cortex in DS images. This finding may represent a false-positive result or a true sign of pathology, possibly associated with a leaky blood-brain barrier in areas of the brain affected by neovascularization secondary to repeated seizures. Results suggest that DS imaging has higher sensitivity than comparison of pre- and post-gadolinium image pairs for inflammatory intra-axial lesions.

Is contrast-enhanced MRI efficient in testicular infarction mimicking testicular tumor on scrotal ultrasound?

A 4-year-old boy was admitted to emergency department of our institution with left testicular swelling and pain started 48 h ago. Physical examination revealed left sided erythema and tenderness in scrotum which was refractory to testicular elevation. The parents did not describe undescended testis, trauma or recent mumps history that may explain acute swelling of left scrotum. Immediately after the physical examination, a scrotal Doppler ultrasonography was performed using a high frequency linear transducer. Ultrasonographic evaluation showed heterogeneously enlarged left testis and edema in the left scrotum. Blood supply was decreased in left testis in comparison to the right, however, arterial waveforms were still preserved in the left epididymis. In addition to Doppler and gray scale ultrasonography features, a smooth contoured demarcation line in the left testis was also observed which simulated mass lesion in the left testis. Based on the ultrasonography findings a concurrent testicular neoplasia could not be ruled out completely and the patient was referred to contrast-enhanced magnetic resonance imaging (MRI) promptly after ultrasound examination. MRI revealed left testicular enlargement, scrotal edema, and heterogeneous hypointense areas in T2-weighted images, but there was no solid or cystic mass lesion within the left testis. The affected testis was observed to be prominently hypointense on T1-weighted images compared to right. At post-contrast and subtraction MRI sequences avid contrast enhancement was detected in left paratesticular tissue however, left testis was completely avascular at post-contrast MRI sequences (Fig. 1). Based on the MRI findings, the diagnosis of testicular torsion was made confidently. Emergency surgical exploration confirmed intravaginal testicular torsion but, unfortunately detorsion operation could not have been performed and left sided orchiectomy was required because left testis was observed to be totally necrotic during surgical intervention (Fig. 2). Fig. 1 Post-contrast subtraction axial MRI image reveals left testicular enlargement and left paratesticular enhancement. Note that the affected left testis is hypointense and no contrast enhancement is observed diagnostic for testicular torsion (arrows). However, ... Fig. 2 Photographic view of the left testis during operation shows left testicular necrosis. Intravaginal torsion accounts for most cases of testicular torsion. Most cases are spontaneous but, rarely intravaginal testicular torsion may result from testicular trauma.1 Since irreversible damage may occur within 4–6 h of symptom onset, early diagnosis and urgent surgical intervention are critical.2 In the early stage of torsion, the echogenicity and size of the affected testis may be normal. Later findings include testicular enlargement and increased parenchymal echogenicity. If left untreated, the torsion will eventually progress into infarction which is seen as decreased or absent blood flow in color Doppler ultrasonography.1 The latter is sometimes diagnostic challenge in ultrasonography since, demarcation line of the infarcted testis tissue may simulate tumor particularly in late testicular torsion.3 In the current case, as reported in the literature,4 a testicular tumor was accurately ruled out via emergency contrast-enhanced MRI. In conclusion, late testicular torsion may mimic testicular mass lesion in ultrasonography which may cause a diagnostic challenge in Emergency Medicine. Contrast-enhanced MRI is helpful in the diagnosis as well as in the differential diagnosis in such complex cases.

Angioarchitecture and Posttreatment Magnetic Resonance Imaging Characteristics of Brain Arteriovenous Malformations and Long-Term Seizure Control After Radiosurgery

To corroborate which pretreatment angioarchitectural characteristics and posttreatment magnetic resonance imaging (MRI) features were associated with better seizure and antiepileptic drug outcomes in patients with brain arteriovenous malformations (AVMs) treated by Gamma Knife radiosurgery. During the period 2007-2010, 220 patients with intracranial AVMs undergoing radiosurgery at our hospital were evaluated. Imaging features on digital subtraction angiography and follow-up MRI, medical records, and direct patient interview were retrospectively assessed. Seizure outcome was assessed using the Engel classification and the status of antiepileptic drug use. At the last follow-up, 21 of 31 patients (68%) who met the recruitment criteria had AVM obliteration on digital subtraction angiography or MRI. Seizure-free status (Engel class 1) was achieved in 20 patients (65%), and 13 of 20 (65%) seizure-free patients were medication-free. The presence of total obliteration at last imaging follow-up (P = 0.013), absent retrograde cortical veins on digital subtraction angiography before GKRS (P = 0.013), nidus <3.7 cm (P = 0.006), and lower modified radiosurgery-based AVM score (P = 0.026) were significant predictors of seizure-free outcome. The strongest independent predictor of seizure-free status was absence of retrograde veins (odds ratio = 9.9). No angioarchitectural feature, postradiosurgery imaging finding on MRI, or radiosurgical treatment parameter was a significant predictor of seizure control or cessation of medication in seizure-free patients. This study suggests that radiosurgery provides favorable outcomes in patients with AVM-related epilepsy. Patients with intracranial AVMs can benefit from seizure control after GKRS before undergoing AVM obliteration. Absence of retrograde veins is associated with better seizure-free outcomes, regardless of the parenchymal changes after radiosurgery.

Cavernous hemangioma in the floor of oral cavity masquerading as a ranula

A painless, bluish, submucosal swelling on one side of the floor of the mouth usually indicates the presence of a ranula. Rarely, such a swelling may be caused by an inflammatory disease process in a salivary gland, a neoplasm in the sublingual salivary gland, hemangiomas, a lymphatic nodular swelling, amyloidosis, or embryologic cysts/dermoid cyst. We report a 35-year-old female patient with swelling in the floor of her mouth that was clinically diagnosed as a ranula due to negative diascopy, the site of swelling, and the age of patient. Because of a strong clinical suspicion of a ranula, diagnostic methods such as angiography and magnetic resonance imaging (MRI) were not used in our case. A preoperative diagnosis was not truly established. We report a case of hemangioma in the floor of the mouth masquerading as a ranula. Although a rarity, vascular malformations should always be ruled out by using digital subtraction angiography and MRI studies before going for surgical intervention.

Appearance of the canine meninges in subtraction magnetic resonance images.

The canine meninges are not visible as discrete structures in noncontrast magnetic resonance (MR) images, and are incompletely visualized in T1-weighted, postgadolinium images, reportedly appearing as short, thin curvilinear segments with minimal enhancement. Subtraction imaging facilitates detection of enhancement of tissues, hence may increase the conspicuity of meninges. The aim of the present study was to describe qualitatively the appearance of canine meninges in subtraction MR images obtained using a dynamic technique. Images were reviewed of 10 consecutive dogs that had dynamic pre- and postgadolinium T1W imaging of the brain that was interpreted as normal, and had normal cerebrospinal fluid. Image-anatomic correlation was facilitated by dissection and histologic examination of two canine cadavers. Meningeal enhancement was relatively inconspicuous in postgadolinium T1-weighted images, but was clearly visible in subtraction images of all dogs. Enhancement was visible as faint, small-rounded foci compatible with vessels seen end on within the sulci, a series of larger rounded foci compatible with vessels of variable caliber on the dorsal aspect of the cerebral cortex, and a continuous thin zone of moderate enhancement around the brain. Superimposition of color-encoded subtraction images on pregadolinium T1- and T2-weighted images facilitated localization of the origin of enhancement, which appeared to be predominantly dural, with relatively few leptomeningeal structures visible. Dynamic subtraction MR imaging should be considered for inclusion in clinical brain MR protocols because of the possibility that its use may increase sensitivity for lesions affecting the meninges.

MR Perfusion Index as a Quantitative Method of Evaluating Epiphyseal Perfusion in Legg-Calve-Perthes Disease and Correlation With Short-term Radiographic Outcome

Current radiographic prognosticators of the outcome of Perthes disease can only be applied after femoral head deformity has occurred. Quantification of femoral head perfusion using the gadolinium-enhanced subtraction magnetic resonance imaging (MRI) technique may serve as an early prognosticator of outcome. The purposes of this study were 2-fold: (1) to develop a reliable method to quantify femoral head perfusion using this MRI technique; and (2) to determine whether the perfusion at early stages of Perthes disease correlates with radiographic deformity after a 2-year follow-up. A total of 20 patients meeting the following inclusion criteria were studied: radiographs and MRI obtained of femoral heads predeformity, age between 5 and 13 years, and unilateral disease. MR perfusion index, a measure of perfusion in the epiphysis, was obtained using digital image analysis of subtraction gadolinium-enhanced MRI. Intraobserver and interobserver agreement of this index was assessed by 2 independent observers. MR perfusion index was correlated with a radiographic deformity index (a measure of femoral head deformity) obtained after a minimum of 2 years. The intraobserver agreement assessed by the intraclass correlation coefficient was 0.96 for observer 1 and 0.97 for observer 2. The interobserver agreement of the MR perfusion index was 0.90 for trials 1 and 2. MR perfusion index in the early stages of Perthes disease was highly variable, ranging from 0 to 0.70. After a minimum of 2 years following MRI acquisition, radiographs were obtained and evaluated using the deformity index, a continuous measure of femoral head deformity, by 2 blinded observers. Deformity index at 2-year follow-up showed moderate correlation with predeformity MR perfusion index (r=-0.56, P=0.01, R=0.31). In those patients who were treated nonoperatively, the correlation was stronger (r=-0.79, P=0.006, R=0.63). MR perfusion index obtained from gadolinium-enhanced subtraction MR images showed a high interobserver agreement. MR perfusion index is highly variable at early stages of Perthes disease, and a lower MR perfusion index correlated with greater radiographic deformity at the 2-year follow-up. This pilot study shows the promise of predeformity MR perfusion index as a possible early prognosticator of outcome in Perthes disease. Prognostic level II.

Preoperative State-of-the-Art Magnetic Resonance Imaging of Hip

Hip pain is a frequent complaint of pediatric patients and advanced radiologic imaging is often helpful in elucidating an accurate diagnosis. Magnetic resonance imaging (MRI) is widely implemented for evaluating pediatric hip conditions because it does not use ionizing radiation. This article describes newer MRI techniques that aid in the diagnosis and preoperative evaluation of Perthes disease and labral pathology. These include dynamic gadolinium-enhanced subtraction MRI, diffusion-weighted MRI, and new radial sequence in MRI hip arthrogram . MRI is a proven means to provide diagnostic and prognostic information without the use of ionizing radiation. Early detection of subtle changes in pediatric hip conditions is tremendously aided by newer MRI techniques that can temporally stage pathology and assist in the management of the disease.