Diagnostic imaging: CT and X-ray

Digital radiography and tomosynthesis

Modern diagnostic radiology departments have completely transitioned from film-based systems to direct digital radiography using flat-panel detectors (flat-panel detector).

Advantages of the technology:

• High energy-to-signal conversion efficiency.
• Wide dynamic range: bone and soft-tissue structures are displayed with high quality on a single image without repeat exposure.
• Convenient storage and instant access to archives.

However, the digital environment carries a serious risk — undetected overexposure. Due to hardware brightness adjustment, excessive radiation dose does not degrade the image quality, and the operator may not realize the patient has received an unnecessary radiation burden. This is especially critical in pediatrics, where equipment designed for adults must be adapted for radiosensitive children.

An alternative is digital tomosynthesis. The tube moves over a stationary detector, taking a series of images at different angles. The method produces clear slices at the required depth while blurring background structures. The radiation dose is 3 times higher than a standard chest X-ray, but significantly lower than CT. The main drawback is that scanning takes about 10 seconds, which leads to motion artifacts from breathing and makes the method unsuitable for young children.

Visualization in acute abdomen

The choice of diagnostic method for acute abdominal pain depends on the patient's body habitus, clinical presentation, and equipment availability.

1. Acute appendicitis. Contrast-enhanced CT is considered the standard. The scans show a thickened appendix with a strongly contrast-enhancing wall and inflamed periappendiceal fat. Targeted imaging of the abdominopelvic transition delivers a dose of about 3 mSv, and a full scan 10 mSv. CT outperforms ultrasound in visualizing a normal appendix and identifies an alternative cause of pain in nearly 89% of cases (e.g., mesenteric adenitis, Meckel's diverticulitis). Ultrasound remains the method of choice for children and asthenic patients.
2. Acute diverticulitis. For pain in the left lower quadrant, CT is the first-choice method. It excellently demonstrates extracolonic complications (abscesses, fistulae, perforations).
3. Acute cholecystitis. Ultrasound leads here due to its high sensitivity for gallstones and the ability to assess the sonographic Murphy's sign.

Diagnostic radiology of renal diseases

Non-contrast CT is the primary diagnostic method for urolithiasis. Stone sizes can also be assessed on plain radiographs, but CT allows for precise localization of the calculus and detection of complications, such as hydronephrosis. Stones under 5 mm typically pass spontaneously, while those over 10 mm require intervention.

Types of calculi:

• Calcium stones (oxalates/phosphates) — the most frequent (75–80%), radiopaque.
• Struvite stones — form in the presence of infections, growing rapidly into staghorn configurations.
• Uric acid stones — associated with gout and low diuresis, can dissolve with urine alkalinization.
• Cystine stones — characteristic of genetic disorders, suspected in children.

Numerous cystic renal lesions are also classified using imaging methods. They range from autosomal dominant polycystic kidney disease to acquired cysts in end-stage renal disease or during long-term lithium therapy.

Rare tumors and new technologies

Diagnosis of bone pathologies requires a high index of suspicion. For instance, adamantinoma is a rare malignant tumor of the tibial cortex. Radiography reveals a destructive lesion in the diaphysis. T2-weighted MRI with fat suppression confirms cortical destruction and demonstrates a soft-tissue component. However, adamantinoma cannot be distinguished from osteofibrous dysplasia based on imaging alone — a biopsy is mandatory for a definitive diagnosis.

In complex diagnostic cases, dual-energy CT (Dual-Energy CT) comes to the rescue. Its principle is based on the fact that the linear X-ray attenuation coefficient depends on photon energy. In standard CT, different materials may have the same density (Hounsfield units). Scanning at two different energies makes it possible to differentiate tissue composition because their attenuation characteristics change non-linearly.

Class and exam questions

What else to study on this topic

• Clinical and MRI criteria for differentiating benign enchondromas from chondrosarcomas.
• Evaluating the response of bone metastases (e.g., in breast cancer) to systemic therapy.
• Atypical femoral fractures associated with intravenous bisphosphonate therapy.
• Differential diagnosis of cystic renal lesions (Bosniak classification).

Other topics in the section "Diagnostic Radiology of the Abdominal Organs"

Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.