C# - Map Class To Get The Db's Records With A Custom Method?

I'm developing a website with ASP.NET MVC, NHibernate and Fluent NHibernate and want to know how can I customize my Map to get records using a custom Method.

My entities:

public class ImageGallery {
public virtual int Id { get; set; }
public virtual string Titulo { get; set; }
public virtual IList<Image> Images { get; set; }
ublic virtual bool IsActive { get; set; }
}
public class Image {
public virtual int Id { get; set; }
public virtual ImageGallery ImageGallery { get; set; }
public virtual string Low { get; set; }
public virtual bool IsActive { get; set; }
}


My Fluent NHibernate Maps:

public class ImageGalleryMap:ClassMap<ImageGallery> {
public ImageGalleryMap() {
Id(x => x.Id);
Map(x => x.Titulo);
HasMany(x => x.Images)
.KeyColumn("ImageGalleryID");
Map(x => x.IsActive);
}
}
public class ImageMap:ClassMap<Image> {
public ImageMap() {
Id(x => x.Id);
References(x => x.ImageGallery);
Map(x => x.Low);
Map(x => x.IsActive);
}
}

And, a method on my ImageRepository class:

public IList<Image> ListActive() {
return this.Session.CreateCriteria<Image>()
.Add(Restrictions.Eq("IsActive", true))
.List<Image>();
}

If I create an object this way:

ImageGallery ig = new ImageGallery();

I can access my the Image's list using:

foreach(Image img in ig.Images) {
...
}

However, ig.Images give me access to all images records and I would like to access just active records (or another criteria), using ListActive()'s repository methods.