Pediatric Imaging

Introduction

Excessive crying, unwillingness for examination, and inability to describe complaints make a child, the most difficult patient. However, it is a challenge to the pediatric radiologist to master the art of talking and achieve a successful examination. Posters on the wall, a fish tank in the waiting area, or toys in the sonography room may give the child reassurance of familiar things. When this is coupled with a friendly radiologist, maximal co-operation is possible. Equally important is a clear, legible request form by the requesting clinician as that is responsible for avoiding an inadequate examination. Hence, it becomes important to understand the basics of various radiological modalities. These are:

• Conventional Radiology (Plain Radiographs)
• Fluoroscopy
• Contrast examinations
• Sonography
• CT
• MRI

Plain Radiographs

This is of paramount importance in achieving an early diagnosis of the spectrum of clinical problems, whether it may be an X-ray skull for head trauma or X-ray chest for LRTI; good quality radiographs are the key to the correct interpretation. However, clear-cut indications & communications with the pediatrician are essential. Though fast film/screen combinations and good quality machines may decrease the radiation dose, correct understanding of pathology is the most vital & repeated radiographs with unnecessary radiation can be prevented.

Fluoroscopy

It consists of an overhead X-ray tube with high definition TV monitor. In present era of excellent cross-sectional modalities, fluoroscopy has a limited role. However, it may be of great help in:

• To confirm air trapping by a foreign body in the tracheobronchial tree.

• To look at diaphragmatic movements in a suspected case of eventration.

• To evaluate stridor/chest mass.

• For Pericardial calcifications or motion of calcified valvular leaflets.

Procedures like Barium swallow & Barium Enema are also performed under fluoroscopic guidance. Though easy & fast to perform, due to high radiation & limited diagnostic yield, fluoroscopy is not routinely done.

Contrast Studies

Barium studies for GI Tract: Oral suspension of Barium sulfate is given & double-contrast procedures are performed with serial x-rays or under fluoroscopic guidance. Laxatives are given one day prior to the procedure. Simple enema is given to the patient (to prepare the colon) before Barium enema. Ideally, the patient should have an overnight fast. Except in the suspected cases of perforation, there are no other contra-indications for Barium Studies.

Following procedures may be performed with Barium

Urographic studies for urinary tract:

Newer, low osmotic, non-ionic contrast media are less painful than the older hyperosmolar ionic contrast medium. All contrast media are safe up to a dose of 300 mg/ml of iodine concentration.

Ideally, all examinations that require intravenous contrast demand an empty stomach, yet a hungry, dehydrated child is unhappy & uncooperative. Thus it is recommended that the examination is performed immediately before the next scheduled feed (in babies, it is usually 2- 3 hours after last light feed). This means that child undergoing IVP at 9:00 a.m. should have a light breakfast at 6:30 a.m.

Angiography: This technique comprises of introduction of an arterial catheter & injecting the contrast through the same.

Digital subtraction Angiography (DSA): It is much quicker & requires less contrast. This procedure requires sedation/anesthesia as even slight movement of the patient will hamper the procedure. Major indications for DSA in the pediatric age group include:

• Hypertension: To rule out renal artery stenosis

• Hepatic masses

• CNS vascular malformations

• GI Bleeding

• Preoperatively in Plastic Surgery cases

Ultrasonography (USG)

USG is the most applicable modality in the pediatric age group as it is easily available, fast to perform & it does not require the use of ionizing radiation. It is mainly used to visualize the abdomen & urinary tract. It is also utilized to see the intracranial contents (in infants, when the anterior fontanelle is open). Testis, Thyroid, and also the eye can be evaluated. It is also used for assessment of congenital dislocation of the hip, the examination of the vertebral canal, septic arthritis, etc. It is a simple & rapid method of guiding a wide variety of invasive procedures (both diagnostic & therapeutic) requiring needle puncture. For pelvis examination, ideally, the patient should be starving. The patient should also have a full urinary bladder. Air is a poor conductor for sound & aerophagia may hamper the yield of USG examination. The child may have to be sedated for Doppler as it is a long procedure.

Computed Tomography

The machine consists of a circular array of detectors and the computer output is displayed on a monitor with the image being presented as a matrix of varying degrees of attenuation of the x-ray beam.

The common indications of a CT Scan are:

• CNS (Tumor/Infection/Congenital abnormality/Trauma)

• Chest (Mediastinal mass)

• Abdomen (Tumor)

• Evaluation of musculoskeletal system

Water-soluble, iodine-containing, contrast medium is usually given for CECT. CT scan gives excellent cross-sectional details. However, its disadvantages include high radiation dose & need for sedation/anesthesia.

Magnetic Resonance Imaging (MRI)

Lack of ionizing radiation, multiplanar imaging, and excellent spatial resolution make MRI more advantageous than CT, especially in CNS & spinal pathologies.

It consists of a magnet operating at a fixed strength, which induces a net proton magnetization in the long axis of the patient. Oscillating magnetic field pulses are used to perturb this magnetization following which it relaxes back to its original position & produces an electrical signal in the reservoir coil that surrounds the patient.

Gadolinium is a commonly used constant medium in MRI. It aids in increasing the sensitivity for the diagnosis of some pathologies.

Any metallic implant (prosthetic valve/Aneer clip) is a contraindication to MRI. Claustrophobia with small gantry & high cost is the limiting factor for MRI.

Interventional Radiology

It has made possible non-invasive treatment of various pathologies for e.g.

• Percutaneous Angioplasty in renal artery stenosis

• Embolization of vascular malformations

• Preoperative embolization of hypervascular tumors

Pediatric Imaging - Precautions

Radiation dosage:

Ratio of radiation dose to skin rads is as follows:

Hence, it is important to correctly use each radiographic modality & thus limit the radiation dose.

Thus, an appropriate and timely use of correct modality in the best possible manner would definitely aid in achieving an early diagnosis.