Radiomics in Brain Tumor: Image Assessment, Quantitative Feature Descriptors, and Machine-Learning Approaches

Radiomics describes a broad set of computational methods that extract quantitative features from radiographic images. The resulting features can be used to inform imaging diagnosis, prognosis, and therapy response in oncology. However, major challenges remain for methodologic developments to optimize feature extraction and provide rapid information flow in clinical settings. Equally important, to be clinically useful, predictive radiomic properties must be clearly linked to meaningful biologic characteristics and qualitative imaging properties familiar to radiologists. Here we use a cross-disciplinary approach to highlight studies in radiomics. We review brain tumor radiologic studies (eg, imaging interpretation) through computational models (eg, computer vision and machine learning) that provide novel clinical insights. We outline current quantitative image feature extraction and prediction strategies with different levels of available clinical classes for supporting clinical decision-making. We further discuss machine-learning challenges and data opportunities to advance radiomic studies.

Clinical significance of increased density in the proximal femoral marrow detected by visual inspection on abdominopelvic postcontrast CT examination

PURPOSE

The purpose of this study was to ascertain the clinical significance of increased density of the proximal femoral diaphyseal marrow when incidentally detected on postcontrast abdominopelvic CT examinations.

METHOD

The proximal femoral marrow of 63 patients was classified as normal or abnormal based on visual inspection by three attending radiologists. Abnormal density was defined as attenuation greater than that of adjacent musculature. The attenuation of the marrow was also measured. All patient medical records were reviewed for pertinent laboratory and clinical data.

RESULTS

Increased marrow density had a low sensitivity for anemia (28%) but a high specificity and positive predictive value (100%) for anemia. Three of these patients had unilaterally increased attenuation associated with local pathology. Visual inspection was adequate for identifying abnormalities in instances of underlying malignancy.

CONCLUSION

Increased density of the proximal femoral diaphysis is a highly specific finding for a marrow replacement process. Anemia was the most common clinical diagnosis in our series of patients with abnormal marrow density. Although the sensitivity for increased bone marrow attenuation is low, the extremely high specificity and positive predictive value of this finding for marrow reconversion and/or replacement suggest that even if detected incidentally, it should not be disregarded and, in the absence of a preexisting causative diagnosis, warrants further evaluation. The specific pattern of marrow abnormality may be helpful in differentiating localized processes from other processes that may affect hematopoietic function in a more widespread or global distribution. In particular, visual inspection of marrow density was more specific for identifying asymmetric marrow density in localized processes than was a quantitative measure of difference between the two femurs (>20 HU).

An unusual presentation of Zenker's diverticulum

Zenker's diverticula are esophageal outpouchings in the region of the cricopharyngeus which typically grow in a posterolateral and inferior direction and can cause esophageal compression if the diverticulum is large enough. We describe a patient in whom a Zenker's diverticulum expanded posteriorly and superiorly so that it was positioned in the posterior pharyngeal space, causing both esophageal and tracheal narrowing.

Altered glucose metabolism and the invasive tumor phenotype

Multiple genetic changes are necessary for carcinogenesis, yet a wide range of different genetic changes may give rise to malignant behavior and no set or sequence of defects is seen in all cancers. The similar pattern of invasive growth in malignancy despite the genotypic and phenotypic heterogeneity of tumor populations suggests that a final cellular state common to all cancers may exist. Such a state must be the sequela of many possible genetic changes, and the cellular properties of the state must promote malignant, invasive growth. It is hypothesized that the common denominator of the transformed state is reversion to primitive phenotype, and its invasive properties stem from alteration of metabolic pathways. Increased use of glycolysis and consequent production of acid have been consistently demonstrated in malignant cells in vitro and are seen in the vast majority of clinical tumors imaged with FDG Positron Emission Tomography (PET) and Magnetic Resonance Spectroscopy (MRS). Application of mathematical models from population ecology and competition theory demonstrates that these metabolic changes will alter the local microenvironment in ways that favor tumor growth but are lethal to normal cells. This phenomenon alone appears to provide a simple but sufficient mechanism for invasive tumor growth. This hypothesis is testable experimentally and suggests significant new approaches to tumor therapy.

CT staging of esophageal carcinoma in patients treated by primary radiation therapy and chemotherapy

Primary radiation therapy with concurrent chemotherapy is under study as definitive and palliative therapy for patients with esophageal carcinoma. To evaluate the correlation between CT staging and outcome, we retrospectively reviewed the CT scans of 48 patients treated with primary radiation therapy and concurrent chemotherapy and correlated CT staging with disease-free survival, overall survival, and site of relapse. Excluding one patient who was understaged and six patients who died of problems unrelated to esophageal carcinoma, mean survival of CT stage I, II, and III patients was 14.7, 21.3, and 5.2 months, respectively. When the CT stage is modified by the presence of nodal involvement on CT, the mean survival of stage IIn and IIIn (nodes greater than 1.5 cm in diameter) and stage IV patients (distant metastases) was 16.4, 19.2, and 10.6 months, respectively. Despite thickening of the esophageal wall greater than 3.0 cm in five patients with stage IIn cancer, mean survival was still 19.2 months. Patients with pericardial effusion had the worst survival of only 4.3 months. Stage II patients had a significantly longer (p less than 0.05) disease-free period than all other groups and the difference between stage II and III patients was highly significant (p less than 0.01). Stage II patients were also more likely to be disease-free at the time of death or last follow-up (p less than 0.05). Computed tomographic staging of esophageal carcinoma is useful in radiation therapy treatment planning and predicting outcome of patients managed with a nonsurgical technique of concurrent radiation and chemotherapy.

CT-guided needle localization for intraoperative biopsy of the head and neck

Needle-localized intraoperative biopsy was first described for the nonpalpable breast mass using mammography for needle placement. This technique can be adapted by substituting CT (or MRI) for mammography. It can be a valuable tool in localizing the nonpalpable areas of concern in the head and neck, especially when the location is obscure or the patient has undergone previous radiation and/or surgical therapy.

Hepatic metastases: liposomal Gd-DTPA-enhanced MR imaging

Liposomal gadolinium diethylenetriaminepentaacetic acid (DTPA) encapsulated within 70- and 400-nm vesicles was tested as a contrast agent for magnetic resonance (MR) imaging of the liver in rats with hepatic metastases. Liposomal Gd-DTPA caused significant improvement in contrast between liver and tumor (P less than .005) on T1-weighted MR images. Smaller 70-nm liposomal Gd-DTPA vesicles caused greater contrast enhancement, reflecting the larger surface-area-to-volume ratio of the smaller vesicles. Liposomal Gd-DTPA-enhanced images permitted significant improvement in metastasis detection by five blinded radiologists (P less than .005). By comparison, free Gd-DTPA without liposomes caused a statistically significant reduction in contrast between tumor and liver and reduced lesion detection (P less than .01). Liposomal Gd-DTPA also resulted in sustained vascular enhancement for 1 hour after administration. The results suggest that paramagnetic liposomes may become a useful MR imaging contrast agent.

Diagnosis of osteomyelitis by MR imaging

Bone scans are highly sensitive for the diagnosis of acute osteomyelitis, but the difficulty of separating bone-marrow processes from soft-tissue disease limits the specificity and accuracy. A diagnostic technique capable of distinguishing bone-marrow processes from soft-tissue disease would improve the diagnostic accuracy of osteomyelitis. To evaluate the use of MR in the diagnosis of osteomyelitis, MR examinations were performed in 35 patients with suspected acute osteomyelitis. Twelve of these were proved to have osteomyelitis either by surgery (nine patients) or by clinical follow-up (three patients). In the other 23, osteomyelitis was excluded by surgery (12 patients) or by the clinical course (11 patients). Evidence of osteomyelitis on MR consisted of abnormalities of the bone marrow with decreased signal intensity on the T1-weighted images and increased signal intensity on the T2-weighted or short-T1 inversion recovery (STIR) images. MR and bone scintigraphy were interpreted by two radiologists who were given no clinical information other than to rule out osteomyelitis. The sensitivities of MR and static bone scan were 100% for bone-marrow abnormality. Because bone-marrow abnormality in osteomyelitis associated with healing fractures was incorrectly diagnosed by MR (one case) and bone scintigraphy (two cases), the sensitivities of MR and scintigraphy for the diagnosis of osteomyelitis were 92% and 82%, respectively. The specificities of MR and scintigraphy were 96% and 65%, respectively (p less than .05). The overall accuracy for the diagnosis of osteomyelitis was 94% for MR and 71% for bone scan (p less than .05). Because of its ability to separate soft-tissue disease from underlying bone marrow, MR may be used to evaluate patients with positive bone scintigraphy to improve the specificity and accuracy of diagnosis for osteomyelitis.

Transluminal angioplasty of the iliac and femoral arteries: follow-up results without anticoagulation

With the advent of the angiographic balloon catheter, transluminal angioplasty has become a more effective procedure for the alleviation of symptoms of peripheral ischemia. In the past two and a half years we have performed this procedure on over 208 iliac and femoral arteries. One hundred twenty iliac arteries were dilated. Of these, 86% remained patent at one year and 83% at two years. Eighty-eight femoral arteries were dilated. Of these, 75% remained patent at one year and 67% at two years. These vessel survival rates are slightly less than those following surgery. However, the morbidity from transluminal angioplasty is very low and the mortality is essentially zero.