X-Ray, MRI, and Ultrasound Agents Basic Principles
George C. Kagadis, Nancy L. Ford, Dimitrios N. Karnabatidis, George K. Loudos in Handbook of Small Animal Imaging, 2018
The ability of microbubbles to reflect ultrasound waves from objects in vivo known as echogenicity, analogous to the “relaxivity” or MRCA. Under the influence of the US pressure wave, the microbubbles change their radius, expanding and contracting in a pulsatile manner. Fortunately, the resonance frequency of the microbubbles in the range of diameters that can pass through capillaries lies within the clinical US frequency range of 1 to ~10–15 MHz. What is seen in the images is the scattered signal. The equations that describe this phenomenon are complex (Goldberg et al. 1994) (de Jong 1997) and indicate a detected signal dependence of microbubble radius to the fourth to sixth power. Modern US imagers are also now capable of imaging multiple harmonics of the microbubbles signal, making the micobubble physics of echogenicity in use complex to as great or greater degree than the relaxivity of the MRCA. Like the MRCA, each commercial USCA is probably slightly different in this ability, but in practice, also like MRCA and XRCA, the commercial variants are similar. The echogenicity derives from the difference in the speed of sound between the gas in the microbubbles and the soft tissue surroundings of the body, which is immense, and it is responsible for producing contrast in the images. A very small mass in a fraction of a milliliter dose (sub-milligram quantities of actual shell material and microliters of gas), intravenously administered, is all that is generally needed for imaging. The shell thickness of the bubble is also important because it must be thin enough to allow the bubble to flex as it passes through capillaries. US creates a pressure wave that causes the bubble to expand and contract in a pulsatile manner, and therefore thicker shells have poorer echogenicity and can change the frequency-dependent response of the bubble.
Transrectal Ultrasound (TRUS)-Guided Prostate Biopsy
Ayman El-Baz, Gyan Pareek, Jasjit S. Suri in Prostate Cancer Imaging, 2018
Certain parameters of the ultrasound can be manipulated by the provider to optimize image acquisition. Ultrasound frequency is an important parameter, as manipulation of the frequency will alter the tissue penetration of the sound waves (Kossoff 2002). A high frequency results in a higher-resolution image, with greater discrimination between various tissues and possible lesions, but comes at the expense of decreased tissue penetration. The majority of prostate TRUS are performed at a frequency of 6–10 Hz, although recent studies have described high-resolution ultrasound using high frequencies up to 29 MHz (Ghai et al. 2016). A working knowledge of the technical aspects of the imaging modality will allow the practitioner to set optimal parameters for various clinical indications. For example, the posterior central and peripheral zones are optimally imaged with a higher-frequency setting, whereas the anterior prostate may require a lower-frequency for improved tissue penetration. The most common form of ultrasound performed for prostate TRUS is a gray-scale modality. The amplitude of the sound wave determines the brightness of the pixelation on the image, and the image should be calibrated so that the peripheral zone reflects a medium gray color (Kossoff 2002). Terminology describing the echogenicity, or brightness, of the imaging ranges from hyperechoic (bright) to hypoechoic (dark), with the peripheral zone set as the reference. Anechoic is the term used to describe complete absence of echogenicity as is seen with the passage of sound waves through fluid. The echogenicity of tissue is due to the reverberation of the sound wave against the particles of the tissue (Kossoff 2002). Thus, a denser tissue will result in a more echogenic image. Historically, the echogenicity of lesions within the prostate was felt to correlate with malignant lesions. In 1989, Hodge reported that TRUS prostate biopsy of hypoechoic lesions correlated with a palpable abnormality on DRE in 90% of cases, with histological diagnosis of prostate cancer confirmed in 66% of biopsies obtained from correlating lesions (Hodge 1989). Still, prostate cancers may be hypoechoic, hyperechoic, or anechoic (Shinohara et al. 1989). Indeed, 39% of lesions are isoechoic on ultrasound (Shinohara et al. 1989). Nonetheless, although hypoechoic lesions are not pathognomonic of prostate cancer, such abnormalities still provide visual targets for areas of concern at the time of biopsy.
Urinary system
A Stewart Whitley, Jan Dodgeon, Angela Meadows, Jane Cullingworth, Ken Holmes, Marcus Jackson, Graham Hoadley, Randeep Kumar Kulshrestha in Clark’s Procedures in Diagnostic Imaging: A System-Based Approach, 2020
Upper tract obstruction is a reversible problem until the kidneys become damaged by back pressure, so all patients presenting with acute kidney injury of unknown aetiology require an ultrasound scan within 4–6 hours if septic, or within 24 hours if not septic (NIB guidance). In the majority of affected patients, ultrasound can diagnose hydronephrosis and frequently establish its cause [1]. Ultrasound plays an important primary role in assessing renal size and shape as well as demonstrating blood vessels and the internal renal structure, where it is sensitive in showing a minor degree of dilatation of the collecting system and any mass lesions. Endoscopic (transrectal) ultrasound is extensively used in the diagnosis of prostatic disease, including cancer, and for guiding biopsy. Ultrasound is useful in differentiating a simple benign cyst from a more complex cyst or solid tumour, and in many cases can give more detailed information on internal septation. Where ultrasound is inconclusive, and when more detail of calcification, scarring and enhancement patterns may help in full characterisation, CT may be used. It can also be used to screen for and diagnose polycystic kidney disease. In patients with pyelonephritis who continue to have an incomplete response to antimicrobial therapy, ultrasound should be considered. Ultrasound can rule out the presence of obstruction, renal or peri-nephric abscess, or other complications of pyelonephritis. The presence of irreversible kidney disease may also be assessed with ultrasound. Increased echogenicity is a non-specific finding seen with numerous diffuse renal diseases. Doppler ultrasound: renal vascular flow may be evaluated with Doppler ultrasound for a multitude of disorders including renal vein thrombosis, infarction and renal artery stenosis. Using the following formula, the resistive index (RI) may be calculated:A normal resistive index is
Role of intraluminal bowel echogenicity on prenatal ultrasounds to determine the anatomical level of intestinal atresia
Published in The Journal of Maternal-Fetal & Neonatal Medicine, 2017
Ilaria Goruppi, Silvia Arévalo, Romy Gander, José-Andres Molino, Marc Oria, Elena Carreras, José-Luis Peiro
Objective: To evaluate the correlation between different degrees of bowel intraluminal echogenicity showed by prenatal ultrasounds and the anatomic level of intestinal atresia. Methods: We report three cases of intestinal atresia at different intestinal levels verified during the neonatal surgery with specific ultrasonographic prenatal features. Intensity of sonolucency was analyzed using the image-processing program ImageJ for quantitative measurements based on the gray-scale intensity values. Results: A total of three cases are reported, a jejunal, an ileal and a colonic atresia. All cases showed intestinal dilatation. Both, jejunal and ileal atresia, showed two degrees of hypoechoic intestinal content, while colonic atresia showed hyperechogenic content dilated loop at prenatal ultrasound scan. Conclusions: We propose the use of prenatal ultrasounds echogenicity of intestinal dilated loop fluid content to help in determining the level of obstruction in bowel atresia. These are initial results, to be confirmed by a multicentric research with more cases.
Echogenicity changes in the fetal brain, a 6-year follow-up study
Published in The Journal of Maternal-Fetal & Neonatal Medicine, 2013
F. M. F. Rosier-van Dunné, G. van Wezel-Meijler, L. de Groot, J. I. van Zyl, H. J. Odendaal, J. I. P. de Vries
Objective: To asses the relation between echogenicity changes in the fetal brain and neurodevelopmental outcome until 6 years of age. Methods: Fetuses (n = 124) from pregnancies affected by hypertensive disorders (n = 64) or preterm labor (n = 60) at risk for preterm birth (26–34 weeks gestation) were studied. Moderate echogenicity changes (periventricular grade IB, II; intraventricular grade II–III; local basal ganglia/thalami) in the fetal and neonatal brain were related to neurological outcome and Griffiths mental developmental scales quotients at 1, 2 and 6 years. Multiple regression analysis tested the influence of moderate echogenicity changes and perinatal clinical characteristics on composite outcome (death or abnormal neurodevelopment). Results: Moderate echogenicity changes were present in 37/124 (30%) fetuses. Median gestational age and weight at birth were respectively 31 weeks (range 26–43), 1314 g (range 550–4330), mortality was 19%, follow-up loss 10%. Composite outcome was abnormal in 47/124 (38%). Fetal and neonatal moderate intraventricular echodensities were related to cerebral palsy at 6 years (p
Glutathione synthetase deficiency: a novel mutation with femur agenesis
Published in Fetal and Pediatric Pathology, 2020
Ipek Guney Varal, Pelin Dogan, Orhan Gorukmez, Sevil Dorum, Arzu Akdag
Introduction: Glutathione synthetase (GSS) deficiency is an autosomal recessive disorder (frequency < 1/1,000,000) with different varyingly severe clinical manifestations that include metabolic acidosis, hemolytic anemia, hyperbilirubinemia, neurological disorders and sepsis. Case report: This infant was small for gestational age, had hemolytic anemia, metabolic acidosis, bilateral subependymal pseudocysts and increased echogenicity of the basal ganglia. GSS deficiency was confirmed by genetic analysis. The patient also had unilateral right femur agenesis. Conclusion: By using next generation sequencing analysis, we identified a novel homozygous variant c.800G > A, p.Arg267Gln in the GSS gene of this patient. Femur agenesis had not previously been associated with GSS.
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