Chapter Summaries: Merrill’s Atlas of Radiographic Positioning and Procedures

Chapter 10: Thoracic Viscera


There are several projections performed on the chest, pulmonary apices, Trachea and superior mediastinum and Lungs and pleurae in the US and Canada such as PA, AP, Lateral, PA oblique, and AP axial.


A general understanding of the human body or body habitus is important in the performance of projections noted above. The shape, size, and position and movement of the internal organs are determined by the size and shape of the body (Long, Rollins, & Smith, 2015). This is important in the thoracic cavity where organs such as the lungs, the heart, and diaphragm are often in constant movement to facilitate gaseous exchange process.

Thoracic cavity

The thoracic cavity houses the lungs, heart, thymus gland, and lymphatic systems. The thoracic cavity has three chambers; right and left pleural cavities and one pericardial cavity. Serous membranes line the cavities. Mediastinum lies between the two pleural cavities and houses other respiratory structures except for pleurae and the lungs. The system is delicate and is protected in this kind of a cage structure (Long, Rollins, & Smith, 2015).

Respiratory system

The respiratory system contributes to the gaseous exchange process. The system is made up of organs such as the lungs, pharynx, trachea, and bronchi on the inside and other organs such as the nose, and mouth on the outside. Communication between these external and internal organs allows interaction with the external environment and the internal environment.


The mediastinum ion lies within the sternum on the anterior, spine on the posterior and the lungs lying laterally. The mediastinum region is made of several organs; Heart, thymus, nerves, fat, fibrous tissue, esophagus, trachea, great vessels and the lymphatic (Long, Rollins, & Smith, 2015).


Several conditions affect the respiratory system such as aspiration, bronchiectasis, atelectasis, bronchitis, and cystic fibrosis, epiglottitis, emphysema, sarcoidosis, and tuberculosis among others. 


            General Positions Considerations

Heart and lungs

The patient is placed in an upright position to prevent engorgement of the respiratory system and allow the depression of the diaphragm by gravity.

PA, Oblique, and Lateral Criteria

In the performance of the various projections, the positioning of the body, head, and posture is of critical significance for an accurate, clear view of the internal organs. Breathing instruction should be given; the patient should be protected from harmful radiations, and care taken when the physician has to administer substances such as barium for an accurate view. For example, in the conduction of an AP, Oblique and Lateral IR the following general positioning can be considered (Long, Rollins, & Smith, 2015).

PA Criteria

The patient is to sit or stand upright. The head is to be positioned upright facing forward. The shoulders are to be depressed and held in contact with the grid device.


            The patient rotates the hips with the thorax while the feet point directly forward. The shoulders lie in a traverse position.

Lateral Criteria

The side of interest is to be placed against the IR holder. Patient to remain standing with weight equally distributed to the feet with the arms raised and the head raised straightforward. 

However, it is important to note that these instructions may vary slightly depending on the kind of procedure being conducted and the patient whether a male or female. In most cases, additional procedures are often followed to perform Imaging radiations on female patients due to the obstruction caused by the breast (Long, Rollins, & Smith, 2015).


During the evaluation, several factors are often considered. The evidence of normality varies with the test performed. Some general observations should be looked for such as normal collimation and rotation of the various organs and body parts (Long, Rollins, & Smith, 2015).

Chapter 16: Abdomen


Just as in the projections performed in the thoracic cavity, the projections performed on the abdomen include AP and lateral projections. These projections are the standard projections performed in both Canada and the US.

Abdomen’s anatomy

The understanding of the positioning of organs in the abdomen is equally significant to achieving the best view during projections. The abdomen is subdivided into two main parts:

  1. The Superior Portion (Abdominal Cavity)

This region extends from the diaphragm to the superior bony pelvis region. This region contains the stomach, spleen, liver, gallbladder, small and large intestines, kidneys and pancreases. These are the major digestive organs (Long, Rollins, & Smith, 2015).

  • Smaller Inferior Part (Pelvic Cavity)

The pelvic cavity houses the sigmoid and the rectum, reproductive organs and the urinary bladder. This region is contained within a double membrane layer called the peritoneum membrane containing the serous fluid in the membrane cavity. The abdomen cavity is made up of various components including an abdominal cavity, peritoneum, omenta, mesentery, peritoneal cavity, visceral peritoneum, retroperitoneum, parietal peritoneum, pelvic cavity, abdominal cavity, and abdominopelvic cavity (Long, Rollins, & Smith, 2015).


The abdominal region is equally affected by several disorders. Disorders such as Tumor, Pneumoperitoneum, Ileus, Metastasis, Bowel obstruction, Abdominal aortic aneurysm, and Ascites are some of the conditions noted to affect the abdominal region.


Radiography imaging can be conducted for the issuing a reliable diagnosis.

      Exposure Techniques

A calculated effort is required to achieve maximum softness and right kilovolts of radiations at optimum radiation dose to enable a maximum view of the internal organs and adjacent structures. This is important especially when semi-opaque objects such as gallstones are to be viewed. A quality radiogram image should show the kidneys, the lower border of the liver, sharp outlines of the psoas muscles and the ribs (Long, Rollins, & Smith, 2015).


The movements in the abdominal region, whether intentional or unintentional, prevent the quality imaging of the organs. This occurs through proper positioning, explanation of the breathing procedure, and the application of compression in the region. Movements cause the blurring of the image especially in those regions that do not move such as the liver.


Radiographic Projections

The most commonly performed projection is the supine AP projection. This projection is supplemented by other projections such as AP projections in the lateral decubitus position and upright AP abdomen projections. The supine projection displays the images of the bladder, kidney, and the ureters. The dose, exposure time, and the penetration level vary with each of the projections. Lateral and decubitus projections exhibit the greatest penetration of up to 30cm. Although they give a higher penetration, the dosage required for the performance is also high ranging between 5.230-4.170 and 10.48-13.64 mGy (Long, Rollins, & Smith, 2015).


The positioning of the patient should be in such a way that movement is prevented, and there are no gas obstructions. The choice of the positioning will depend on the physician, the method to be performed and the institution’s traditional practices. Care should be taken that there are no obstructions from the arm and any other objects. For male patients, protections should be provided to cover the gonads. Upright positions are often preferred when the kidney is not the primary target of the procedure. The size of the abdomen may necessitate precautions such as the provision of a compensating filter to ensure that the imaging procedure focuses on the necessary parts (Long, Rollins, & Smith, 2015).


The evaluation procedure should take into account factors such as clear imaging, no movements of the diaphragm, no rotation of the patient, signs of proper collimation, and ease of identification. Additional factors may be incorporated depending on the procedure and the nature of the patent under examination (Long, Rollins, & Smith, 2015).


Long, B. W., Rollins, J. H., & Smith B. J. (2015). Chapters 10 “Thoracic Viscera.” In Merrill’s Atlas of Radiographic Positioning and Procedures. New York, NY: Elsevier Health Sciences.

Long, B. W., Rollins, J. H., & Smith B. J. (2015). Chapter 16 “Abdomen.” In Merrill’s Atlas of Radiographic Positioning and Procedures. New York, NY: Elsevier Health Sciences.

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